, 刘敏, 杨波, 张子荷, 罗亲普, 翟占伟, 潘琰北京师范大学地表过程与资源生态国家重点实验室, 北京师范大学地理科学学部资源学院, 北京 100875
Advances in the effect of nitrogen deposition on grassland litter decomposition
YANGLi-Li, GONGJi-Rui, LIUMin, YANGBo, ZHANGZi-He, LUOQin-Pu, ZHAIZhan-Wei, PANYan通讯作者:
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在过去一个世纪里, 化石燃料燃烧、施肥等人类活动使全球大气氮(N)沉降量迅速增加。人类活动造成的N沉降量由1860年的31.6 Tg·a-1增加到20世纪90年代的103 Tg·a-1, 预计到2050年, 可能会增至195 Tg·a-1 (Galloway et al., 2004; IPCC, 2007)。随着工农业的发展, 我国平均N沉降速率从20世纪80年代的13.2 kg·hm-2增加到21世纪初的21.1 kg·hm-2, 成为继欧美之后第三大N沉降区。N是生物地球化学循环和能量流动的基础, N沉降的增加造成土壤酸化、生物多样性和植物生长状况改变, 打破了生态系统碳(C)输入和损失的平衡, 显著影响了生态系统C循环过程(Liu et al., 2013; Sun et al., 2015)。全世界草地约占陆地总面积的1/3, 草地C储量占陆地总C储量的25%-30%, 是人类活动和全球气候变化的直接承受者, 其功能的正常发挥对维持全球及区域性生态平衡有重要的作用(胡中民等, 2005; Piao et al., 2007)。N是草地生态系统生产力的主要限制因子, 因此草地生态系统的C源、汇对N沉降的变化较其他生态系统更为敏感(陈佐忠和汪诗平, 2000; Xia et al., 2009)。研究N沉降背景下草地生态系统C循环对深入理解全球C循环具有极其重要的意义。
草地凋落物是由植物地上和地下部分产生并归还到土壤的所有有机质的总称, 是土壤C库的主要来源和维持土壤肥力的基础。凋落物分解是陆地生态系统养分循环的关键过程, 陆地生态系统中约90%的净初级生产量以凋落物的形式归还给土 壤, 其养分再循环供给植物的生长发育(Berg & McClaugherty, 2003)。凋落物分解过程包括淋溶、机械破碎、有机物转化和土壤动物、微生物的消化作用等, 并受许多因子, 如气候因子、凋落物质量和生物因子等的影响(Meentemeyer, 1978; Gartner & Cardon, 2004; Smith et al., 2014)。N沉降增加引起草地生态系统土壤N有效性和植被群落结构发生变化, 导致凋落物产量、质量, 土壤微生物和酶活性等发生改变, 进而影响了草地凋落物分解(Gough et al., 2000)。在N沉降背景下, 对草地凋落物的分解过程和驱动因素的研究是草地生态系统动态机理研究和全球变化生态学研究的重要内容。
目前, 国内外已有很多研究关注N沉降对凋落物分解过程产生的影响, 也有****对N沉降影响森林生态系统凋落物分解的研究结果进行汇总整理(Knorr et al., 2008; 卢广超等, 2014; Zhu et al., 2015)。但有关N沉降对草地生态系统凋落物分解影响的系统梳理还十分缺乏。为此, 本文对国内外研究进展进行了全面梳理和系统分析, 具体目标如下: (1)综述N沉降对草地凋落物分解过程的影响及其机理; (2)探讨整合目前N沉降影响草地凋落物分解的主要研究内容、方向和方法, 为深入研究N沉降对草地生态系统C循环的影响提供一定的思路; (3)分析研究中存在的主要问题与不足, 并对未来的重点研究方向进行展望, 以期为深入研究草地生态系统C循环过程与N沉降之间的相互作用与反馈机制提供参考。
1 影响凋落物分解的因子
凋落物分解是一个复杂的物理、化学、生物过程, 包括淋溶, 机械破碎, 有机物转化, 以及土壤动物、微生物的消化作用等。调控凋落物分解的关键因素有环境因子、凋落物质量和生物因子, 且各因子之间存在复杂的相互关系(图1)(Meentemeyer, 1978; Zhou et al., 2008; Smith et al., 2014)。影响凋落物分解的环境因子包括温度和降水。温度是调控生态系统生化过程和物质能量周转的关键因子, 对凋落物分解起主导作用(Aerts, 2006)。短期内温度变化影响土壤微生物和分解酶活性, 改变凋落物分解过程中的生物化学反应速率; 长期气温波动影响凋落物质量、植物群落组成, 从根本上改变凋落物的可分解性和分解环境, 影响凋落物分解(Bontti et al., 2009; 宋飘等, 2014)。降水是干旱半干旱地区凋落物分解的重要驱动因素, 短期降水增多可加快表层凋落物的碎裂和水溶性物质的淋溶, 加速凋落物质量损失, 促进分解(Dirks et al., 2010; 王新源等, 2013)。降水的季节和年际变化通过影响凋落物产量及物种组成来改变凋落物分解速率(Weatherly et al., 2003)。土壤水分增加能提高半干旱草地生态系统的地上净初级生产力, 微生物分解者活动频繁, 促进分解(Liu et al., 2010)。
凋落物质量, 即凋落物的相对可分解性。衡量凋落物质量的指标主要有C含量、N含量、磷(P)含量、木质素含量、纤维素含量, 以及它们之间的比值(Aerts, 1997; Cornwell et al., 2008)。凋落物所含水溶性物质、蛋白质和N、P浓度越高, 木质素、纤维素含量越低, 相应的C:N和木质素:N越小, 凋落物质量越好, 分解越快(Valenzuela-Solano & Crohn, 2006)。影响凋落物分解的化学组成中, 除凋落物化学元素、木质素和纤维素外, 植物次生代谢产物也会影响凋落物分解, 近年来引起****的广泛关注。植物次生代谢产物主要包括生物碱、酚类(如黄酮类、单宁等)和萜类物质, 它们通过淋溶、根系分泌和凋落物分解3条途径从植物体释放到土壤中, 影响土壤有机体的生命活动和凋落物分解过程(Rice, 1984; Chomel et al., 2014)。大多数次生代谢产物限制微生物的生长和活性, 或对其产生毒害作用, 其中酚类物质是决定腐生真菌在凋落物定殖的首要因子(H?ttenschwiler & Vitousek, 2000; Chomel et al., 2014)。凋落物中次生代谢产物与土壤有机体的相互作用的机理尚不明确, 这也将是研究凋落物分解过程和土壤有机体之间关系的关键环节(Chomel et al., 2016)。
显示原图|下载原图ZIP|生成PPT图1影响凋落物分解的因子及其相互关系。
-->Fig. 1Factors controlling litter decomposition and their interactions.
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凋落物分解是一个连续的生物降解过程, 影响凋落物分解的生物因子包括土壤动物、微生物及其产生的分解酶(刘强和彭少麟, 2010)。土壤动物是土壤生态系统中的重要部分, 其踩踏、粉碎、摄食等过程可影响凋落物分解, 加速凋落物中营养元素的循环(Carrillo et al., 2011; Gergócs & Hufnagel, 2016)。土壤微生物是凋落物的主要分解者, 包括细菌、放线菌、真菌、原生动物等, 其种类和数量随土壤环境及土层深度的不同而变化, 参与土壤中氧化、硝化、氨化、固氮等过程, 促进土壤有机质的分解和养分的转化, 直接参与凋落物的分解过程(Esperschütz et al., 2011)。凋落物为微生物供给食物, 促进微生物生长和代谢; 反过来, 微生物群落结构和活性的变化也会影响凋落物分解环境和分解过程(Gessner et al., 2010)。凋落物的微生物分解实质是凋落物在分解酶作用下的生物化学过程。土壤酶是土壤中微生物活动和动植物残体腐解过程中产生的具有催化能力的生物活性物质(Waring, 2013)。根据凋落物底物营养成分的不同, 凋落物分解酶可分为纤维素分解酶类、木质素分解酶类、蛋白水解酶类和磷酸酶类4大类(Arai et al., 2007)。分解酶系的活性也同凋落物的分解密切相关, 体现出特定微生物群落对凋落物分解进程的响应(Fioretto et al., 2000)。
2 氮沉降对草地凋落物分解的影响及机理
N是草地生态系统关键的养分因子, 对植物的生长起十分重要的作用(Elser et al., 2007)。N沉降提高了草地生态系统的土壤N有效性, 影响其生产力和C循环过程, 并造成影响凋落物分解的因子发生改变, 进而影响草地凋落物分解(图2) (Gough et al., 2000; Frey et al., 2004)。近年来, 国内外****对N添加条件下的草地凋落物分解进行了研究, 但结果存在较大的不一致性, 如促进效应(Henry & Moise, 2015; Schuster, 2015; 李英滨等, 2016)、抑制效应(?gren et al., 2001; Peng et al., 2014; Freedman et al., 2016)或没有影响(Zhang et al., 2013)。不同N添加剂量对草地凋落物分解的影响不同, 高N (> 120 kg?hm-2·a-1)和中N (61-120 kg?hm-2·a-1)水平的N添加抑制凋落物分解, 而低N (< 60 kg?hm-2·a-1)促进凋落物分解(Chen et al., 2015b)。另外, N添加对凋落物不同分解阶段的影响不同, 前期表现为促进效应, 后期表现为抑制效应, 这可能与分解者活性和凋落物质量的变化有关(Berg & Staaf, 1980; Johansson et al., 2012)。总之, N沉降对凋落物分解的影响取决于样地情况、分解时间、凋落物质量及N沉降水平等(Liu et al., 2011)。表1总结了近年来国内外****对N添加影响草地凋落物分解的主要研究区域及研究内容, 以供研究者参考借鉴。
显示原图|下载原图ZIP|生成PPT图2氮(N)沉降对凋落物分解影响。
-->Fig. 2Effects of nitrogen (N) deposition on litter decomposition.
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Table 1
表1
表1氮添加对草地凋落物分解研究的区域和研究内容
Table 1Current researches on litter decomposition under different nitrogen (N) addition treatments in grassland ecosystems
| 研究区域 Study area | 氮添加浓度 N addition concentration | 影响分解的因子 Factors that affect decomposition | 参考文献 Reference |
|---|---|---|---|
| 新疆阜康荒漠生态站 Fukang Desert Ecological Station of Xinjiang | 21 g?m-2?a-1 | 凋落物质量 Litter quality | Zhao et al., 2015a |
| 青藏高原 Qinghai-Xizang Plateau | 10 g?m-2?a-1 | 凋落物质量 Litter quality | Zhu et al., 2016a |
| 内蒙古温带草原 Nei Mongol temperate grassland | 0-15 g?m-2?a-1 | 凋落物质量 Litter quality | Li et al., 2016 |
| 中国南方种植园 China Southern Plantation | 0-10 g?m-2?a-1 | 凋落物化学计量、养分释放 Litter stoichiometry and nutrient release | Zhu et al., 2016b |
| 呼伦贝尔草甸草原 Hulunbeier meadow steppe | 0-2 g?m-2?a-1 | 凋落物质量 Litter quality | Zhang et al., 2013 |
| 英国Silwood公园 British Silwood Park | 5.5-330 mg?L-1 | 凋落物质量、土壤生物 Litter quality and soil biology | Smith & Bradford, 2003 |
| 澳大利亚落基山脉 Australia Rocky Mountains | 113-225 mg?L-1 | 微生物呼吸、土壤化学计量 Microbial respiration and soil stoichiometry | Finn et al., 2015 |
| 加拿大荒废草地 Canadian wasteland | 6 g?m-2?a-1 | 温度、凋落物质量 Temperature and litter quality | Henry & Moise, 2015 |
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2.1 氮沉降对凋落物产量和质量的影响
2.1.1 氮沉降对土壤氮素有效性和凋落物产量的 影响N是草地生态系统的主要限制因子, N沉降使植物可有效利用的N增加, 减弱草地N限制, 促进植物生长, 凋落物产量和土壤C输入随之增多(LeBauer & Treseder, 2008; Bai et al., 2010)。但有时N沉降对地上生物量的影响并不显著, 一方面是因为在干旱、半干旱草地生态系统中, 水分和N都是植物生长的限制因子, 水分的匮乏限制了N沉降对地上生物量的促进作用; 另一方面, 施加N肥的总量可能超过本地区植物N饱和的阈值, 植物生长对N沉降的敏感性降低(Sala et al., 2012; Hedwall et al., 2013; Xu et al., 2015)。
根系的生产和储存是生态系统生产力的重要组成部分, 其分解对草地生态系统养分循环具有重要的意义, 但目前针对根系凋落物的研究很少(Solly et al., 2014)。在半干旱草地生态系统中, 10-20 g?m-2的N添加可改变根系生长模式, 导致浅层的地下凋落物产量显著增加(Zeng et al., 2010)。但也有研究表明, N添加条件下草地生态系统的根系生物量与地上生物量和N添加浓度都无关, 而与土壤水分可利用性有关(Ladwig et al., 2012)。在受光照限制的草地生态系统中, N添加后植物根冠比降低, 植物体分配更多的资源给地上部分以最大程度地利用光能, 地下凋落物产量减少(Hautier et al., 2009; Xu et al., 2016)。与地上凋落物相比, 根系凋落物的养分含量低、木质素含量高, 分解速率慢, 其分解主要受凋落物C:N的影响(Wang et al., 2015)。对根系的不同分级而言, N添加促进一级和二级侧根的伸长和分解, 而对第三级、第四级等更细的侧根无影响(Guo & Fan, 2007; Wang et al., 2017)。
2.1.2 氮沉降对凋落物组成的影响
植物群落组成的改变包括物种的演替、优势种的定居和稀有物种的消失。N沉降会减弱物种丰富度, 改变草地植物群落组成, 使凋落物质量发生改变, 从而影响分解(Cleland & Harpole, 2010; 于雯超等, 2013)。在内蒙古典型草原、高寒草甸草原等地区的研究均表明: N添加后植物物种多样性减少, 主要表现为一年生物种优势度的增加和多年生物种优势度的降低(Bai et al., 2010; Ren et al., 2010; He et al., 2016)。且在酸性草地上, N沉降每增加0.25 g?m-2?a-1, 在4 m2的样方中就会减少一个物种(Stevens et al., 2012)。另外, N添加使草地物种组成的改变通常朝着凋落物质量好的物种变化(Chapin et al., 1986; Suding et al., 2005)。N添加改变C3植物(如羊草Leymus chinensis)和C4植物(禾本科植物)的生产力和竞争力, 羊草的种群密度、高度、地上生物量、地下生物量和总生物量显著增加; 而禾本科植物对N添加响应更敏感, 在N添加条件下容易消失(Pan et al., 2005; Niu et al., 2008; Xia & Wan, 2008)。总之, N添加引起草地群落组成和植物功能群发生转变, 从而影响凋落物质量和分解速率, 并对草地生态系统的养分循环产生长期影响。
2.1.3 氮沉降对凋落物质量的影响
N沉降加快营养元素循环, 促进凋落物形成过程中的营养元素再分配, 使凋落物中N、P含量增加(Lü et al., 2013)。但凋落物质量对不同N添加的敏感程度不同, 这与实验区N可利用性和N添加水平有关, 通常在土壤N有效性低的实验中, 凋落物质量的变化更为显著, N添加对凋落物分解的影响也更大(Knorr et al., 2008; Valera-Burgos et al., 2013)。N沉降对凋落物质量和分解过程的影响具有阶段性。分解前期, 土壤N有效性增加可增加植物的N含量, 凋落物N含量升高, 凋落物C:N降低, 促进分解。N添加也促进分解前期纤维素和可溶性物质的分解(Berg & Matzner, 1997; Smith & Bradford, 2003; 于雯超等, 2013)。分解后期, 木质素对纤维素等物质产生物理保护, 使微生物难以进入, 阻碍后期凋落物分解(Deforest et al., 2004)。另外, 凋落物中的多酚、多糖等化合物与植物组织中的N进一步形成难分解物质, N添加条件下难分解物质增多, 阻碍凋落物的后期分解(Knicker et al., 1997; Hobbie et al., 2012)。
凋落物质量是导致N添加对凋落物分解影响不一致性的主要原因(Zhang et al., 2016)。近年来, 有两种完全相反的假说解释N添加影响凋落物分解的过程中凋落物质量所起的作用。一种假说认为N添加影响凋落物分解主要是通过改变凋落物化学计量比, 即N添加使凋落物C:N降低, 达到微生物与凋落物之间的化学计量平衡, 促进凋落物分解。另一种假说的依据是能量分配原理, 即微生物通过分解易分解C源获得能量, 进而分解木质素等难分解有机物, 以此来获得N源。如果外界的N已经满足了微生物需要, 微生物用来分解难分解物质的投资就会降低。因此, N添加会阻碍凋落物分解。其中, 第一种假说适用于N限制的生态系统中, 用来解释N添加促进质量差(高C:N)的凋落物分解; 第二种假说适用于N饱和的生态系统中, 用来解释N添加抑制质量好(低C:N)的凋落物分解(廖利平等, 2000; Moorhead & Sinsabaugh, 2006; Hobbie, 2008)。另外, N添加也会引起凋落物中一些微量元素(Mn、Ca、Mg)含量的变化, 它们也是预测分解速率的重要指标, 今后应受到关注(Güsewell & Gessner, 2009; Kai et al., 2016)。
2.2 氮沉降对凋落物分解环境、土壤微生物和酶活性的影响
土壤酸度是调控陆地生态系统生物多样性和生物地球化学循环的重要因子。人类活动产生的氮氧化合物(NOX)使草地生态系统土壤酸化现象越来越严重(Yang et al., 2012)。N沉降使土壤中NH4+和NO3-含量增加, 促进土壤溶液的硝化作用, 释放出大量的H+, 导致土壤pH值降低(Gandois et al., 2011; Chen et al., 2013b)。不同土壤微生物适宜生长的pH值不同, 细菌生长的pH值范围是6.5-7.5, 放线菌为7.5-8.0, 真菌为5.0-6.0 (Abbasi & Adams, 2000)。N沉降使草地土壤pH值显著下降, 微生物群落结构和酶活性发生改变, 影响草地凋落物分解(Turner & Henry, 2009; Chen et al., 2015a)。细菌和真菌是分解者, 在凋落物分解的各阶段中作用不同: 在前期, 真菌起主要作用; 在后期, 细菌起主要作用(Wardle et al., 2004)。真菌是凋落物最主要的分解者, 它利用菌丝软化凋落物, 改变凋落物的物理性质和组成成分, 方便土壤动物和其他微生物分解, 其中担子菌门的真菌对纤维素分解贡献最大, 褐腐真菌、白腐真菌主要分解木质素。N添加条件下, 不同微生物对养分的竞争能力不同。菌根真菌因其共生关系, 生长旺盛; 细菌因其表面积大, 容易移动, 也较易生存和繁衍; 而分解木质素的腐生真菌则竞争力较弱, 得不到养分, 木质素分解易受到抑制(Clemmensen et al., 2013)。放线菌与凋落物中几丁质和木质素的分解密切相关, 有研究对土壤中微生物进行功能基因分析, 发现N添加减弱这类放线菌的多样性和丰富度, 阻碍凋落物分解(Eisenlord et al., 2013)。真菌/细菌是评估微生物群落对环境变化响应的重要指标, 近年来被广泛使用(Strickland & Rousk, 2010)。N沉降促进土壤中真菌(尤其是子囊菌门)生长, 导致土壤真菌/细菌升高, 凋落物分解加快(Allison et al., 2010; Xu et al., 2016)。但也有研究得出相反的结果, N沉降也会使植物地下部分的生物量减少, 导致真菌与植物共生的菌根真菌减少, 凋落物分解减慢(Hogberg et al., 2010; Rousk et al., 2011)。N沉降不仅会改变微生物的群落组成, 还会使微生物C:N化学计量比降低, 进而减弱微生物对C源的需求, 凋落物分解减慢(?gren et al., 2001; Compton et al., 2004)。
分解凋落物中木质素的酶类主要是多酚氧化酶, 在质量较差(木质素含量高)的凋落物中, N添加抑制多酚氧化酶活性, 阻碍了难分解物质的分解, 这是N添加抑制凋落物分解的重要机制(Carreiro et al., 2000)。另外, 木质素分解酶只能由担子菌门和子囊菌门的白腐真菌产生, N添加条件下白腐真菌的竞争能力下降, 木质素分解酶的合成降低, 影响凋落物中木质素的分解(Deforest et al., 2004)。N沉降使纤维素分解酶的活性升高, 促进纤维素分解(Keeler et al., 2009)。总之, N沉降的环境中有利于高纤维素、低木质素含量的凋落物分解(Knorr et al., 2008)。
3 氮沉降影响草地凋落物分解的研究内容及研究方向
近几十年来, 草地凋落物分解对N沉降的响应引起国内外****的广泛关注。在研究初期, 人们大多仅仅关注不同水平N添加对凋落物产量、质量和分解速率的影响。随着人们对草地凋落物分解影响机制的深入了解, 加上同位素示踪、基因分析等各种生物化学技术的进步, 越来越多的研究开始深入探讨N添加影响草地凋落物分解过程中生物和非生物学机制, 研究内容更加全面和具体, 现对目前主要的研究内容和方向进行总结, 以期为深入研究N沉降对草地生态系统C循环的影响提供一定的思路。3.1 影响凋落物分解的关键因子的研究
调控凋落物分解的关键因子主要有环境因子、凋落物质量和生物因子等, 它们起作用的顺序通常为: 气候>凋落物质量>土壤生物(Swift et al., 1979; Aerts, 2006)。目前, 对影响凋落物分解的关键因子的确定是凋落物分解的主要研究方向。在早些阶段, 环境因子被认为是全球和区域尺度上决定凋落物分解的关键因子, 只有当环境因子影响不显著时, 凋落物质量才被认为是影响分解的主要因子。但越来越多的研究发现环境因子与凋落物质量之间存在交互作用——环境因子通过改变群落优势种的组成来改变凋落物质量, 进而影响凋落物分解。过去的实验过度夸大了环境因子对分解的影响, 而掩盖了局部小尺度上影响分解的重要因子。因此, ****们对传统的“环境因子为中心”的凋落物分解理论进行了修改(Wall et al., 2008; Zhang et al., 2008)。目前比较一致的结论是, 在大尺度上, 环境因子和凋落物质量是决定凋落物分解的关键因子, 并且这些因子之间存在很强的相互作用; 分解者不直接影响分解, 它只受环境因子和凋落物质量的影响, 进而影响凋落物分解; 而在很小尺度上, 分解者才是直接影响分解的关键因子。但是各个因子在不同生态系统中和在不同分解阶段的重要程度和所起的作用还需进一步研究(Gracia-Palacios et al., 2013)。由此可见, 土壤过程和分解者对凋落物分解的影响是今后凋落物分解研究的重点。不同生态系统类型、不同凋落物分解阶段中影响分解的主导因子不同, 也可能存在一定的阈值, 使得主导凋落物分解的因子从一个转向另一个。因此, 重视小区域尺度上凋落物分解过程的研究、确定凋落物分解主导因子发生改变的原因和阈值是今后凋落物分解因子研究的关键(Prescott 2010; Bradford et al., 2016)。
3.2 植物-凋落物-土壤连续体的C:N:P化学计量比及养分转移的研究
过去关于凋落物分解的研究集中在某一时间段内的静态研究, 而对凋落物分解整个过程中养分元素的转移路径、转移速率及其在植物、凋落物、土壤中的剩余情况等了解不足。生态化学计量学是生态学的一个新兴领域, 主要研究生物体与其所处环境之间的养分元素关系, 是分析生态系统养分循环过程的工具(王绍强和于贵瑞, 2008)。植物和土壤微生物之间以土壤为平台, 以凋落物分解过程为媒介, 通过动态交换维持相对平衡的C:N:P化学计量比, 形成植物-凋落物-土壤连续体(Fan et al., 2016; Pan et al., 2016)。N沉降改善草地生态系统的N状况, 导致N饱和和P限制(Vitousek et al., 2010)。因此, N沉降导致草地生态系统中C:N:P化学计量比发生改变, 这种变化对凋落物分解过程产生的影响也受到广泛关注(Finn et al., 2015; Zhu et al., 2016b)。N添加可增加土壤和凋落物中的N含量, 改变土壤和凋落物的C:N:P化学计量比并影响分解环境的pH值, 调控和影响凋落物分解过程(Hessen et al., 2004; 王晶苑等, 2013)。植物和凋落物C:N:P之间的差异反映了叶片衰老时养分的再吸收效率, 这是植物在养分供应有限的环境中保持养分的策略。植物、凋落物和土壤C:N:P化学计量比的差异, 代表了微生物和生产者为维持生态系统平衡面临的养分竞争。土壤微生物在分解过程中, 既需要C作为能量, 也需要N来构成其身体。在凋落物C:N较高时, 微生物需要从外界吸收N来满足它的生长; 在C:N较低时, 超过微生物生长所需的N就会通过分解释放到土壤中。因此, 有机物C:N越高, 分解速度越慢, 微生物得不到足够的N来构成其躯体, 从而影响其繁殖速度(贺金生和韩兴国, 2010; 周正虎和王传宽, 2016)。研究表明, 当凋落物C:N低于5-15时或C:P低于200-480时, 凋落物N、P元素出现净释放。当凋落物中N、P不足时, 微生物通常从周围环境中固定N、P以维持自身的化学计量平衡(Manzoni et al., 2010)。
在N沉降背景下, 探究植物吸收的N在植物-凋落物-土壤-大气中分解、释放、转移的方式和路径对深入研究N沉降对生态系统C循环的影响具有十分重要的意义。但是, N添加条件下植物、凋落物和土壤C:N:P化学计量比对凋落物分解的影响及其微生物学和酶学机制研究不足(Zhu et al., 2016b)。以往对生态化学计量比的研究大多针对植物、土壤、凋落物单独进行, 迫切需要开展生态化学计量学和土壤微生物生态学相结合的研究, 综合探究N添加条件下植物-凋落物-土壤连续体中C:N:P化学计量比的相互转化及其内在机制。因此, 结合新技术手段对凋落物分解中养分元素的动态观测是今后凋落物分解研究的新亮点。
3.3 氮沉降对混合凋落物分解的影响
草地凋落物分解的研究对象分为单种凋落物和混合凋落物。单种凋落物分解的研究集中在草地优势种。优势种是草地群落的重要组成部分, 在一定程度上决定草地生态系统的属性, 草地优势种的研究是不同尺度凋落物分解研究的基础。因此, 研究草地优势种凋落物分解对N沉降的响应是理解N沉降影响凋落物分解的关键(Makhnev & Makhneva, 2010)。但是, 草地生态系统是多种植物的复合系统, 自然界中植物凋落物主要以混合状态存在, 在分解过程中化学组成和物理结构不同的凋落物发生相互作用, 仅依据单种凋落物预测N沉降对草地凋落物分解的研究具有局限性(熊勇等, 2012)。混合凋落物可以更加准确地预测自然生态系统的凋落物分解, 对生物地球化学循环起到非常重要的作用。近年来, 越来越多的研究关注N沉降对混合凋落物分解及养分释放的影响。混合凋落物的实际分解速率偏离于期望分解速率时则称为混合凋落物的非加和性效应, 混合凋落物复杂的化学成分和丰富的空间异质性是影响混合凋落物分解时非加性效应产生的重要原因(Barantal et al., 2011)。各组分化学性质差异大的混合凋落物, 其观测分解速率高于期望分解速率(基于组分凋落物分解速率的算术平均值), 产生促进的非加性效应(Quested et al., 2002)。N沉降使混合凋落物中组分凋落物的化学组成差异变大, 使混合凋落物产生促进的非加性效应, 促进混合凋落物分解(Valera-Burgos et al., 2013)。另外, N添加能调节混合凋落物中组分凋落物之间的相互作用, 使凋落物纤维素、半纤维素、木质素含量降低, N、P含量增加, 转变混合凋落物的中性作用为非加性效应, 促进混合凋落物分解(Vivanco & Austin, 2011; Li et al., 2016; 李英滨等, 2016)。但是也有研究认为N添加对混合凋落物的重量损失没有明显的作用(张彩虹, 2013)。另外, 高N含量的混合凋落物与N添加相互作用促进难分解物质的产生, 产生抑制效应, 阻碍混合凋落物分解(?gren et al., 2001; Flury & Gessner, 2011)。不同的研究结果可能是因为两个研究针对的研究区环境和初始凋落物质量不同。
总之, 全球气候变化引起陆地生态系统多样性丧失, 凋落物作为影响陆地生态系统生物多样性的一个重要因子又受到物种多样性的调控, 对全球变化背景下对混合凋落物和单一凋落物分解的对比研究, 对预测全球变化背景下生态系统物质循环和能量流动的规律有重要意义。N添加可以改变混合凋落物在分解过程中的相互作用和凋落物的分解环境, 对分解产生影响, 但其内在机制还需进一步研究。
3.4 氮沉降与其他全球变化和草地管理方式的交互作用
自然生态系统中, 各种全球变化的现象(如全球变暖, 降水变化, N、P沉降, 以及紫外辐射等)时有发生, 且它们的交互作用无处不在。因此单独研究N沉降对凋落物分解过程的影响, 无法准确、全面地评估生态系统C循环和养分循环对未来全球变化响应的真实情况, 需要将其综合分析(Chartzoulakis & Psarras, 2005; 张乃莉等, 2007)。并且, 人们对草地生态系统的利用方式多种多样, 不同的草地管理方式与N沉降发生交互作用, 共同影响凋落物分解(Apolinário et al., 2014; Song et al., 2017)。近年来, 越来越多的研究关注N沉降与其他全球变化及草地管理方式的交互作用对草地凋落物分解的影响, 并取得一定的成果, 对准确预测未来全球气候变化对凋落物分解的影响具有重要意义。水分和N是干旱和半干旱草地生态系统的限制因子。随着地表温度的升高, 降水特征发生变化, 长期干旱和强降雨天气频繁发生(Stocker et al., 2014)。降水是影响凋落物分解的重要环境因子, 通过影响土壤水分状况和分解者活性影响凋落物分解。水、N添加可以影响植物养分的综合状况, 使凋落物质量发生变化, 影响凋落物分解。水分有效性可以调节凋落物养分和化学计量特征对N添加的响应。水分增加条件下, N添加引起的凋落物N浓度增加会被水分添加所稀释, 导致凋落物C:P降低, 但C:N和N:P没有显著变化(Lü et al., 2012)。环境中的水分可利用性影响凋落物分解对N添加的响应。在干旱条件下, 土壤N的流动性减弱, 植物可获取的N减少, N沉降对植物和微生物的影响取决于土壤湿度, 因此N添加后凋落物质量和分解速率的变化不大。相反, 在水分充足或强降雨条件下, N添加对凋落物分解的影响才更有效(Everard et al., 2010)。水和N的交互作用除了影响凋落物质量和分解环境外, 还改变植物群落组成影响凋落物质量, 进而影响凋落物分解(Henry et al., 2005; 卢广超等, 2014)。
P是植物生长的重要限制因子, 控制着生态系统的关键过程。N添加后, 许多草地生态系统由N限制转向N饱和, 且N在生态系统中的归还速率高于P, 因此生态系统过程受到P限制。探究草地凋落物分解对N、P添加耦合效应的响应可为深入分析N、P添加对生态系统物质循环和能量流动产生的影响提供理论依据(Jacobson et al., 2010)。凋落物和土壤环境中N、P的平衡是影响凋落物分解和养分释放的关键因素。N沉降增加会降低凋落物中P的养分释放速率, 降低土壤P的有效性, 加剧生态系统P限制。N、P同时添加,可以缓解N沉降造成的生态系统P限制, 对凋落物分解产生促进效应, 且N、P同时添加对凋落物分解的影响作用比单独添加更强烈(Qualls & Richardson, 2000; Chen et al., 2013a)。
放牧和围封是人类管理和利用草地资源最普遍的方式, 是影响草地生态系统碳库和养分循环的重要人为因素。牲畜的啃食、排泄和踩踏作用可以改变地表植被特征、土壤环境(如温度、含水量等)及其养分含量, 影响凋落物分解(Raich & Tufekciogiu, 2000)。在一定范围内, 放牧能促进植物的补偿性生长, 改善凋落物质量(C:N降低), 加快凋落物分解; 但放牧强度的增加也导致土壤容重增加, 土壤生物多样性降低, 阻碍凋落物分解(Giese et al., 2009; Wang et al., 2015; 杨丽丽等, 2016)。围封是退化草地恢复与重建的重要措施, 围封后排除人为和牲畜干扰, 植被盖度、生物量均有显著增加, 草地土壤有机质输入显著提高, 凋落物质量和土壤条件也得到改善, 进一步促进了凋落物的分解(Tessier et al., 2003; Haynes et al., 2014; Wang et al., 2015)。目前, 随着N沉降的加剧, 一些****开始关注N沉降与草地管理方式交互作用对凋落物分解的影响。有研究表明, N添加可以促进放牧草地的凋落物分解, 对退化草地的修复起到积极作用, 与放牧管理相比, N添加对凋落物分解的促进作用更强(Liu et al., 2011; Apolinário et al., 2014)。也有研究表明, 草地管理方式会促进N添加对凋落物分解的影响(Song et al., 2017)。N沉降和草地管理方式的交互作用对凋落物分解影响的研究还存在不足, 今后的研究应与生产实际相结合, 根据未来的大气N沉降量制定适合草地生态系统能量流动和养分循环的草地管理方式。
4 氮沉降对草地凋落物分解影响的研究方法
4.1 氮添加实验的布设方法
欧美国家由于工农业较发达, N沉降研究起步早, 手段和技术相对成熟, 目前已经建立了系统而全面的跨地区大型监测网络。但对于N添加的研究一直只局限于森林生态系统, 直到20世纪90年代才有欧洲和北美的一些国家和地区对草地生态系统的响应进行研究(Fagerli & Aas, 2008)。近几十年来, 由于工农业发展迅速, 中国已经成为继欧美之后的第三大N沉降区域。我国草地N添加的研究区域主要集中在内蒙古温带典型草原(齐玉春等, 2015; Long et al., 2016)和青藏高原高寒草甸(Gao et al., 2015)。N添加形式包括硝酸铵、尿素和其他形式(NaNO3和混合肥等)。大气湿沉降主要是NO3-、NH4+及少量可溶性有机氮经降水下降到地表, 采用硝酸铵的施肥方式能最大程度地模拟大气N沉降, 且硝酸铵含N量高达34%, 施肥后NH4+和NO3-都能被植物和土壤吸收, 因此施用硝酸铵是模拟N沉降实验中最常见和最有效的施肥方式(Aber et al., 2003)。N沉降的模拟方法有野外施肥和室内微环境培养, 施肥方式包括植物表层喷洒和土壤施肥等, 而且一次性施加N肥和分次少量施肥对生态系统产生的影响也不同(Ning et al., 2015; Zhang et al., 2015a, 2015b)。植物表层喷洒的方法操作简单, 并且植物可截留或通过质流快速吸收表层喷洒的N, 促进植物生长, 但喷洒施肥过程会受到风或太阳辐射的影响, 造成N的大量损失。特别是在干旱、半干旱草原等降水少的地区, 植物表层喷洒会加速挥发损失, 影响实验结果(Wilson, 1992; 张彩虹, 2013)。土壤施肥会大大减少N的挥发损失, 但忽略了植物和凋落物层对N的截留和吸收过程, 可能会高估微生物群落和凋落物分解对N添加的响应(Zhu et al., 2013; 刘双娥等, 2015)。
N添加的浓度范围和梯度的设置是造成诸多实验结果存在差异的主要原因, 其设置的合理性也是影响实验结果的重要指标。通过总结, N添加实验的浓度范围在10-640 kg·hm-2·a-1, 很多研究只是单纯设置高、中、低3个N添加梯度, 缺乏一定的理论依据(Chen et al., 2015b)。有研究者按每年的N沉降速率设置N添加梯度, 模拟未来几十年甚至上百年的N沉降情况对草地生态系统C循环的影响(Liu et al., 2013; Luo et al., 2016)。因此, 今后研究中N沉降梯度的设置应该具有一定的理论依据, 并在方法部分准确描述。大多数N添加实验持续时间不超过两年, 但在草地生态系统中, 两年的时间还不足以揭示凋落物分解后期的动态(Knorr et al., 2008; Prescott, 2010)。因此, 有****进行长期N添加实验, 发现N添加在凋落物分解前期和后期所起到的作用不同, 并且N添加效应深受凋落物质量的影响: 凋落物分解前期, N添加促进分解; 在木质素分解起主导作用的分解后期, N添加会抑制凋落物分解(Hobbie et al., 2012; Sun et al., 2016)。
综上所述, N添加的方法、施肥浓度和施肥年限等都是影响草地凋落物分解的重要因素, 也是造成实验结果不同的主要原因。研究者应结合当地的N沉降量和N沉降速率, 综合分析各种方法, 根据研究区特点和拟解决的问题选择合适的N添加方式。
4.2 凋落物分解的研究方法
草地凋落物分解的研究方法有凋落物网袋法、现量估算法、室内分解培养法等, 随着分子生物学技术的迅速发展, 同位素示踪、磷脂脂肪酸分析(PLFA)、DNA/RNA等方法为凋落物分解和土壤微生物研究提供了新手段, 有利于凋落物分解的微生物学和酶学机制研究。未来生态学研究的一个发展趋势是将传统生态学研究与这些新技术手段相结合(表2)(Yoccoz, 2012)。凋落物网袋法是现在凋落物分解研究最常用的方法, 其原理是在不可降解的尼龙网袋中(袋的大小为15-600 cm2, 孔径为2-10 mm)装入一定量的凋落物, 然后将网袋直接接触地表或埋置在深度为5-10 cm的土壤中(Silver & Miya, 2001)。在探究不同土壤动物类群对凋落物分解影响时, 可采用不同孔径大小的凋落物网袋控制参与分解的土壤动物(Smith & Bradford, 2003)。该方法最大程度地模拟了自然分解状态, 操作简便, 结果真实可信。但是由于网袋的隔离作用及其形成的小环境改变了土壤生物的活动, 因此具有一定的局限性。目前有研究发现双面袋(上孔径>下孔径)更能反映凋落物分解的真实情况, 可应用于今后的实验布设中(张艳博等, 2012)。
Table 2
表2
表2凋落物分解的研究方法及特点
Table 2Study methods of litter decomposition and their characteristics
| 研究方法 Method | 应用原理 Principle of application | 特点 Characteristics | 参考文献 Reference |
|---|---|---|---|
| 凋落物网袋法 Litterbag method | 将凋落物装入尼龙网袋并放置于地表土壤中, 测定质量损失 The litter was loaded into a nylon mesh bag and placed in the surface soil to measure the mass loss | 最大程度模拟自然分解, 但隔离了部分土壤生物的作用 The maximum degree of simulation of natural decomposition, but with the isolation of some soil organisms | Smith & Bradford, 2003 |
| 室内培养法 Indoor culture method | 人为控制各因子梯度 Controlling the factor gradient artificially | 用于控制实验, 但不能真实反映分解状态 Manipulation experiments, but not relecting real conditions | Jiang et al., 2014 |
| 同位素示踪法 Isotope method | 用15N、13C同位素进行标记并追踪其转移情况 Litter is labeled with 15N, 13C isotopes to trace the transfer of these elements | 观察各养分元素的转移方向和转移速率 To study the direction and transfer rate of an element | Liu et al., 2013 |
| 红外光谱分析 Infrared spectroscopy | 利用近红外光光谱吸收特征来表示凋落物元素和化合物含量 The near infrared spectroscopy absorption characteristics are used to study elements and compound in decomposed litter | 同时测定凋落物中的多种元素和化合物含量 Determination of a variety of elements and compounds in the litter simultaneously | Fortunel et al., 2009 |
| 代谢组学 Metabolomics | 与核磁共振、气象色谱等结合, 测定代谢组分 Application of nuclear magnetic resonance and gas chromatography to study metabolic components | 探讨小分子物质随着环境因子的微小变化 Exploration of the changes of small molecules with tiny changes of environmental factors | Wallenstein et al., 2013 |
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室内分解培养法是指在实验室内模拟凋落物自然分解状态, 此方法多用于控制实验, 研究光照、水分、温度等因子的变化对凋落物分解过程的影响(Jiang et al., 2014)。应用室内培养法尽管能人为地控制各因子的变化范围, 但其结果不能真实地反映凋落物分解的实际情况(Sall et al., 2003)。室内模拟实验和野外实验各有利弊, 因此将室内和室外实验相结合的凋落物分解研究有利于更加全面地分析各因子对凋落物分解的影响。
同位素示踪法是指在实验室或野外条件下用15N、13C同位素进行跟踪, 并与PLFA、PCR等生物化学技术结合, 研究凋落物分解过程中C、N元素在凋落物-微生物-土壤连续体中的转移方向、转移速率等。有研究采用同位素标记技术与PLFA相结合, 将用13C标记的凋落物置于土壤中分解, 测定凋落物分解产生的13CO2、土壤和微生物中的13C以及土壤微生物群落组成, 可对不同种类凋落物分解过程中C的转移路径和微生物对不同C源的利用情况进行动态监测(Pan et al., 2016; Xu et al., 2017)。采用13C标记植物根系, 可精确地观察可分解底物在根系和土壤中的流转和剩余情况。也可利用13C和15N同位素对混合凋落物中各物种进行标记, 观察各养分元素在混合凋落物各物种之间的转移情况, 有研究得出混合凋落物之间N的转移方向是由高N凋落物转向低N凋落物, 并发现N是以氨基酸的形式通过真菌菌丝转移的(Tiunov, 2009; Lummer et al., 2012)。大气N沉降的形式主要有NH4+和NO3-, 它们在陆地生态系统中的转移路径及转移速率是否相同对于理解N沉降影响凋落物分解至关重要。近年来, 大气N沉降中NO3-所占的比例逐渐上升, 到2010年, NH4+与NO3-的比值已经降至2 (Liu et al., 2013)。利用15N同位素示踪技术, 可以探究不同N沉降形式在草地生态系统凋落物-土壤中的转移路径, 客观准确地把握N沉降对草地生态系统的影响(Liu et al., 2016)。
凋落物质量(N、木质素、纤维素、单宁等)的分析测定常采用化学分析法, 测定前都需要经过复杂的研磨、提取过程, 耗费时间长且存在较大的误差。目前, 有研究利用红外光谱分析(near-infrared spectrometry, NIRS)和代谢组学等新技术测定凋落物中的化合物含量。与化学分析法相比, 红外光谱分析技术免除了研磨、提取等复杂的步骤, 且可以同时测量凋落物中的多种化合物含量, 具有很强的整合性(Fortunel et al., 2009)。应用代谢组学技术, 可以监测环境变化条件下凋落物分解过程中其化学成分的微小变化(Wallenstein et al., 2013)。另外, Real- Time PCR、PCR-DGGE等分子生物学技术可用来研究N添加对土壤N素转化相关的功能基因以及微生物群落结构的影响, 它们都将成为深入研究凋落物分解和土壤微生物的不可缺少的技术手段(Ning et al., 2015)。
综上所述, 凋落物分解是一个复杂的降解过程, 很难得出确切的分解速率, 我们计算得出的分解速率只是在特定条件下凋落物分解状况的反映。凋落物分解的研究方法也需要根据研究目的、尺度范围和实验精度的不同而异。选择研究方法时应综合考虑各方法的优缺点, 综合运用各种技术手段, 从更加微观的角度探讨凋落物分解的机制。
4.3 凋落物分解的研究尺度的变化
过去大多数的凋落物分解研究多为短期的原位观测, 近年来, 凋落物分解研究的时空尺度发生了变化。越来越多的研究将原位观测的凋落物分解实验进行整合, 通过对比不同生态系统类型、不同气候区凋落物分解的差异, 来研究大尺度上影响凋落物分解的因子(Adair et al., 2008; Kang et al., 2010)。也有研究借助纬度或海拔形成的气候梯度, 采用时空互代法, 进行跨气候带的大尺度凋落物分解研究, 模拟未来凋落物分解的情况。这种方法可克服小尺度或实验室的实验结果外推至大尺度自然状态时尺度转换的困难, 是十分有效的预测研究方法(刘强等, 2004)。Adair等(2008)通过整合分析凋落物分解研究, 根据凋落物分解所需时间和分解的难易程度建立了凋落物三库模型, 描述凋落物分解的完整过程, 即易分解库、中期分解库和难分解库(Adair et al., 2008)。Moorhead和Sinsabaugh (2006)的分解模型根据主导分解过程的微生物不同将分解过程分为3个阶段: 第一阶段是利用凋落物中可溶性化合物的微生物起作用, 此阶段分解速率最快; 第二阶段, 专门分解全纤维素和小分子物质的微生物分解起作用, 分解速率有所降低; 第三阶段, 专门分解高分子化合物(木质素、单宁等)的微生物起作用, 此阶段分解速率最低(Moorhead & Sinsabaugh, 2006)。除了大时空尺度的凋落物分解研究外, 也有****关注更小的时空尺度, 研究一天内主导凋落物分解的因子, 结果表明主导白天和夜晚凋落物分解的因子不同——白天以非生物降解(光降解和热降解)为主, 而夜晚以微生物降解为主(Gliksman et al., 2016)。综上所述, 为更准确地预测凋落物分解和生态系统碳平衡, 未来的研究应当更加注重地上、根系凋落物分解的整合与对比, 综合各种影响分解的因子, 并且在分解模型中加入更多的因子(如可溶性有机碳的淋溶过程、土壤生物因子)并赋予它们代表不同权重的系数, 最终期望得出一个能对凋落物分解的长期动态做出准确预测的综合模型(Campbell et al., 2016; Schilling et al., 2016)。
5 研究不足与展望
凋落物分解是一个非常复杂的生物、物理、化学过程, 深受非生物因子(环境因子、土壤理化性质)、凋落物基质质量和生物因子(土壤微生物和酶活性)的影响, 且各因子间存在复杂的交互作用, 共同影响凋落物的形成和分解。N添加可通过改变土壤养分有效性、凋落物产量和质量、土壤生物及凋落物分解环境影响凋落物分解(Gough et al., 2000; Frey et al., 2004; Manning et al., 2008; 施瑶, 2014)。到目前为止, 关于N沉降对草地凋落物分解的影响已展开了深入的研究, 但还有一些问题值得进一步关注和继续完善。5.1 氮添加研究时间过短
大多数N添加研究持续时间太短, 其中85.5%的N添加研究持续时间不超过4年, 加上高的空间差异性, 我们无法准确地评估凋落物分解对N添加的响应(Chapin III et al., 2002)。部分实验布设的凋落物网袋埋于土层内部, N添加后大量N无法立刻深入土层, 大多被表层有机质固定, 在分解初期对凋落物分解无显著影响(Sun et al., 2015)。因此建议应尽可能延长实验时间, 关注N沉降对草地N沉降的长期效应。另外, 在草地生态系统凋落物分解实验中, 基于单一的取样间隔实验来研究凋落物质量损失对全球气候变化的响应会忽略C周转随时间的变化以及影响分解的因素在各阶段所起的作用。因此, 应该重视凋落物分解的分阶段研究, 增加取样次数。在应用凋落物分解模型时, 注意N沉降对凋落物分解各阶段的效应不同, 各阶段影响分解的主导因素也有差异, 应当选择适当的分解模型进行估算(Henry & Moise, 2015; Sun et al., 2015)。5.2 根系分解研究不足
细根是生态系统的重要组成部分, 它的死亡和分解对全球C收支和土壤养分循环有着重要的意义。与森林生态系统相比, 草地生态系统地下生产力高、根系周转速率快, 其根系分解的研究更应该受到研究者的重视(Silver & Miya, 2001)。根系凋落物的C输入是地上部分的3倍以上, 但是过去仅有2%的植物凋落物研究关注于地下凋落物(Solly et al., 2014; Wang et al., 2015; 杨丽丽等, 2016)。另外, 根系凋落物的分解环境与地上凋落物存在很大差异, 用N添加影响地上凋落物分解的规律来分析地下凋落物分解会造成对生态系统C循环和养分循环的错误估计(Freschet et al., 2013; Xia et al., 2015)。因此, N添加影响根系分解的研究成为凋落物分解研究的新亮点, 需要引起研究者的关注。土壤动物、微生物、分解酶和植物根系等构成了地下生物群落, 比起地上凋落物的分解, 根系分解与土壤物理、化学和生物特性的联系更加密切, 弄清影响根系分解的关键因子是研究地下生态系统C循环和养分循环的关键。5.3 非生长季分解研究不足
干旱和半干旱草原的非生长季漫长, 植被覆盖率低, 地表温湿度变化剧烈。大多数研究认为, 非生长季的低温使微生物休眠或者死亡, 非生长季的凋落物分解几乎停滞, 很少有研究关注非生长季的凋落物分解(夏磊等, 2012)。但是近年来, 对非生长季土壤微生物研究的结果表明, 积雪能防止土壤冻结, 一些抗低温的微生物在非生长季仍能维持较高的活性。并且雪被形成期频繁的冻融循环利于凋落物的破碎, 为土壤生物留下更多可利用的有机物。更有研究表明, 在冬季严酷的环境下凋落物分解过程中仍有明显的土壤动物和微生物活动, 并表现出密切联系, 但均受到低温和环境剧烈变化等因素的影响(王娓等, 2007; Zhao et al., 2015b)。全球变暖加剧造成冬季增温和雪被覆盖的减少, 非生长季的土壤微生物活性和凋落物分解过程不容忽视, 对非生长季凋落物分解的研究是全球变化背景下全球C循环研究的重要环节。5.4 氮添加效应的研究不全面
N沉降除提高土壤N有效性外, 还会造成土壤酸化, 土壤中H+和Al3+的浓度上升, 矿质阳离子(Ca2+、Mg2+、Na+等)浓度下降, 土壤质量变差, 阻碍植被和地下微生物群落的生长(Bowman et al., 2008; Rousk et al., 2010)。之前的大多数研究仅仅关注N添加后土壤N有效性增多对凋落物分解带来的效应(尤其是积极效应), 而忽视了N添加引起的土壤酸化对土壤微生物、酶活性和凋落物分解所起的作用(Chen et al., 2015a)。因此在今后的N添加影响草地生态系统C碳循环的研究中, N添加引起的土壤酸化应当引起重视, 以便我们更加客观全面地预测N添加对草地生态系统C循环的影响。The authors have declared that no competing interests exist.
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| [1] | Gaseous emission of N from soil is essentially related to microbial activity, which includes nitrification and denitrification. In grassland soils subjected to high annual rainfall and intensive grazing, aerobic and anaerobic zones can develop in close proximity in the upper few centimeters of the soil, hence nitrification and denitrification can occur concurrently and adjacently. The objective of this study was to demonstrate the occurrence of simultaneous nitrification and denitrification following the addition of NO 3 61 and NH 4 + fertilizers to a grassland soil under field conditions. After applying 100 kg NO 3 61 –N ha 611 , ca. 25–75 kg ha 611 of the added N disappeared from the mineral N pool in 7 days. Emission of N 2 O and total denitrification was substantial, and 5–22 kg ha 611 of the added N was evolved as gaseous N. In the soil where NH 4 + –N was added, almost 50% of the N that disappeared from the mineral pool could not be accounted for. A substantial proportion of the applied N (7 kg ha 611 ) was evolved as gaseous N. The rate and amount of N loss and fluxes of N 2 O from both NO 3 61 and NH 4 + sources were greater in soils at 84% water-filled pore space (WFPS) compared with 71% and 63% WFPS. Emission of N 2 O from soil following NO 3 61 addition can therefore be attributed to denitrification. In the soils to which NH 4 + was added, accumulation of NO 3 61 –N was greatest at low moisture content (63% WFPS), while the gaseous emissions were greatest at the highest WFPS. The study demonstrated that nitrification and denitrification occur simultaneously in compacted silty grassland soils at moisture conditions close to field capacity. |
| [2] | In situ, on-farm conservation is an important complement to ex situ conservation of traditional crop varieties. In Yunnan Province, China, management for crop diversity by mixed planting (intercropping) of traditional and hybrid rice varieties provides a possible means for sustainable on-farm conservation of traditional rice varieties. Since the adoption of this form of crop diversity management in 1997, the number of traditional rice varieties in cultivation has increased dramatically and now includes some varieties that were formerly locally extinct. The cultivated area of traditional varieties has also been greatly expanded. This form of management is easy to implement and links farmers' economic concerns with conservation. Management for crop diversity can promote on-farm conservation of rice, and potentially other crops too, in a feasible and sustainable way. [References: 13] |
| [3] | Abstract As atmospheric CO 2 increases, ecosystem carbon sequestration will largely depend on how global changes in climate will alter the balance between net primary production and decomposition. The response of primary production to climatic change has been examined using well-validated mechanistic models, but the same is not true for decomposition, a primary source of atmospheric CO 2 . We used the Long-term Intersite Decomposition Experiment Team (LIDET) dataset and model-selection techniques to choose and parameterize a model that describes global patterns of litter decomposition. Mass loss was best represented by a three-pool negative exponential model, with a rapidly decomposing labile pool, an intermediate pool representing cellulose, and a recalcitrant pool. The initial litter lignin/nitrogen ratio defined the size of labile and intermediate pools. Lignin content determined the size of the recalcitrant pool. The decomposition rate of all pools was modified by climate, but the intermediate pool's decomposition rate was also controlled by relative amounts of litter cellulose and lignin (indicative of lignin-encrusted cellulose). The effect of climate on decomposition was best represented by a composite variable that multiplied a water-stress function by the Lloyd and Taylor variable Q 10 temperature function. Although our model explained nearly 70% of the variation in LIDET data, we observed systematic deviations from model predictions. Below- and aboveground material decomposed at notably different rates, depending on the decomposition stage. Decomposition in certain ecosystem-specific environmental conditions was not well represented by our model; this included roots in very wet and cold soils, and aboveground litter in N-rich and arid sites. Despite these limitations, our model may still be extremely useful for global modeling efforts, because it accurately ( R 2 =0.6804) described general patterns of long-term global decomposition for a wide array of litter types, using relatively minimal climatic and litter quality data. |
| [4] | Litter decomposition is an important component of the global carbon budget. Due to the strong climatic control of litter decomposition, climate change may significantly affect this pathway. This review quantifies the climatic influences on litter decomposition rates, both directly and indirectly through effects on litter chemistry. To this end, I analysed first-year leaf litter decomposition data from 44 locations, ranging from cool temperate sites to humid tropical sites. Actual evapotranspiration (AET) was used as an index for the climatic control on decomposition. As litter chemistry parameters I included N and P concentrations, C/N and C/P ratios, lignin concentrations, and lignin/N and lignin/P ratios. At a global scale, climate (expressed as AET) is the best predictor for the decomposition constants (ic-values) of the litter, whereas litter chemistry parameters have much lower predictive values. Path analysis showed that the control of AET on litter decomposability is partly mediated through an indirect effect of AET on litter chemistry. Thus, the relation between climate, leaf litter chemistry and leaf litter decomposition is a triangular relationship. Mean AET in the humid tropical region is three times as high as in both the temperate and the Mediterranean region and this results in a more than six-fold increase in mean k-values. However, due to the large variability in k-values within each region there is a considerable overlap in k-values between the tropics and the other climatic regions. Within a particular climatic region litter chemistry parameters are the best predictors of k-values, especially in the tropics, whereas the percentage of variance in k-values explained by AET is low or absent. In general, litters from the tropical sites have higher N concentrations and lower lignin/N ratios than litters from other climatic regions. In both the tropics and in the Mediterranean region, the lignin/N ratio is the best chemical predictor of litter decomposab |
| [5] | Summary Top of page Summary Introduction Direct effects of temperature Indirect temperature effects on litter chemistry Indirect effects on detritivore and decomposer communities How to proceed? Acknowledgements References 1 Decomposition of plant litter, a key component of the global carbon budget, is hierarchically controlled by the triad: climate > litter quality > soil organisms. Given the sensitivity of decomposition to temperature, especially in cold biomes, it has been hypothesized that global warming will lead to increased litter decomposition rates, both through direct temperature effects and through indirect effects on litter quality and soil organisms. 2 A meta-analysis of experimental warming studies in cold biomes (34 site-species combinations) showed that warming resulted in slightly increased decomposition rates. However, this response was strongly dependent on the method used: open top chambers reduced decomposition rates, whereas heating lamps stimulated decomposition rates. The low responsiveness was mainly due to moisture-limited decomposition rates in the warming treatments, especially at mesic and xeric sites. This control of litter decomposition by both temperature and moisture was corroborated by natural gradient studies. 3 Interspecific differences in litter quality and decomposability are substantially larger than warming-induced phenotypic responses. Thus, the changes in the species composition and structure of plant communities that have been observed in medium-term warming studies in cold biomes will have a considerably greater impact on ecosystem litter decomposition than phenotypic responses. 4 Soil fauna communities in cold biomes are responsive to climate warming. Moreover, temperature-driven migration of the, hitherto absent, large comminuters to high-latitude sites may significantly increase decomposition rates. However, we do not know how far-reaching the consequences of changes in the species composition and structure of the soil community are for litter decomposition, as there is a lack of data on functional species redundancy and the species鈥 dispersal ability. 5 Global warming will lead to increased litter decomposition rates only if there is sufficient soil moisture. Hence, climate scenario and experimental studies should focus more on both factors and their interaction. As interspecific differences in potential decomposability and litter chemistry are substantially larger than phenotypic responses to warming, the focus of future research should be on the former. In addition, more light should be shed on the below-ground 鈥榙arkness鈥 to evaluate the ecological significance of warming-induced soil fauna community changes for litter decomposition processes in cold biomes. |
| [6] | . It has been long recognised that mineral elements, and nitrogen in particular, play an important role in determining the rate at which organic matter is decomposed. The magnitude and even the sign of the effects are, however, not universal and the underlying mechanisms are not well understood. In this paper, an explanation for the observed decreases in decomposition/CO 2 evolution rates when inorganic nitrogen increases is proposed by combining a theoretical approach with the results of a 6-year litter decomposition-forest nitrogen fertilisation experiment. Our results show that the major causes of observed changes in decomposition rate after nitrogen fertilisation are increases in decomposer efficiency, more rapid formation of recalcitrant material, and, although less pronounced, decreased growth rate of decomposers. This gives a more precise description of how inorganic nitrogen modifies decomposition rates than the previously loosely used "decrease in microbial activity". The long-term consequences for soil carbon storage differ widely depending on which factor is changed; stores are much more sensitive to changes in decomposer efficiency and/or rate of formation of recalcitrant material than to changes in decomposer growth rate. |
| [7] | Boreal forests are an important source of wood products, and fertilizers could be used to improve forest yields, especially in nutrient poor regions of the boreal zone. With climate change, fire frequencies may increase, resulting in a larger fraction of the boreal landscape present in early-successional stages. Since most fertilization studies have focused on mature boreal forests, the response of burned boreal ecosystems to increased nutrient availability is unclear. Therefore, we used a nitrogen (N) fertilization experiment to test how C cycling in a recently-burned boreal ecosystem would respond to increased N availability. We hypothesized that fertilization would increase rates of decomposition, soil respiration, and the activity of extracellular enzymes involved in C cycling, thereby reducing soil C stocks. In line with our hypothesis, litter mass loss increased significantly and activities of cellulose- and chitin-degrading enzymes increased by 45–61% with N addition. We also observed a significant decline in C concentrations in the organic soil horizon from 19.5±0.7% to 13.5±0.6%, and there was a trend toward lower total soil C stocks in the fertilized plots. Contrary to our hypothesis, mean soil respiration over three growing seasons declined by 31% from 78.3±6.5mg CO 2 –C m 612 h 611 to 54.4±4.1mg CO 2 –C m 612 h 611 . These changes occurred despite a 2.5-fold increase in aboveground net primary productivity with N, and were accompanied by significant shifts in the structure of the fungal community, which was dominated by Ascomycota. Our results show that the C cycle in early-successional boreal ecosystems is highly responsive to N addition. Fertilization results in an initial loss of soil C followed by depletion of soil C substrates and development of a distinct and active fungal community. Total microbial biomass declines and respiration rates do not keep pace with plant inputs. These patterns suggest that N fertilization could transiently reduce but then increase ecosystem C storage in boreal regions experiencing more frequent fires. |
| [8] | ABSTRACT Maintaining a mixture of cool-and warm-season turfgrasses year-round instead of overseeding into a perennial monoculture stand annually in the transition zone may be an effective way to combine the strengths of two species. Four mixtures of tall fescue (Festuca arundinacea L.) (Jaguar 3 and Bonsai) and zoysiagrass (Zoysia japonica Steud.) (Zenith and Cathy) were evaluated under 5- and 7.5-cm mowing heights and N regimes of 400, 200, and 100 kg ha(-1) yr(-1) in Beijing, China, during 2011 and 2012. Turf quality was better at a 5-cm mowing height than a 7.5-cm mowing height in July and October and was equivalent between the two mowing heights for the other months. Visual quality was highest in plots receiving N at 400 kg ha(-1) yr(-1) in May, June, September, October, and November. In August, however, the highest visual turf quality was observed for an N rate of 100 kg ha(-1) yr(-1). Generally, the 5-cm mowing height and low N application produced high shoot density and ground coverage by zoysiagrass, whereas the shoot density of tall fescue showed no difference between the two mowing heights. The higher N rate most often favored greater tall fescue shoot density and ground coverage. Based on the results, we recommend a 5-cm mowing height and an N rate of 400 kg ha(-1) yr(-1), avoiding application in August, for the mixture. |
| [9] | Changes in land use sometimes lead to soil C loss, and a long time may be required for the C stock to recover to initial levels. Thus, it is important to evaluate the mechanisms related to accumulation of newly input C following land use changes. In this study, we sought to determine the signature of newly input C in the soil profile after land use change. We used stable and radioactive C isotopes with soil fractionation methods in a C-3 coniferous plantation converted from C-4 grassland in Japan. The difference in delta C-13 values between the surface litter and the soil organic carbon (SOC) below the litter was 5 parts per thousand or greater; this large isotopic difference was attributed to rapid decomposition in the litter layer and preservation of C derived from the previous C-4 vegetation. Most SOC Delta C-14 values were negative throughout the soil profile, suggesting that most of the SOC in the soil profile was recalcitrant and had been preserved for a long time. Only the surface sand values were slightly positive. These results suggest that most newly input C is consumed at the soil surface. The low ability of these soils to preserve newly input C is one factor in the slow recovery of soil C. |
| [10] | Abstract Nitrogen (N) deposition is widely considered an environmental problem that leads to biodiversity loss and reduced ecosystem resilience; but, N fertilization has also been used as a management tool for enhancing primary production and ground cover, thereby promoting the restoration of degraded lands. However, empirical evaluation of these contrasting impacts is lacking. We tested the dual effects of N enrichment on biodiversity and ecosystem functioning at different organizational levels (i.e., plant species, functional groups, and community) by adding N at 0, 1.75, 5.25, 10.5, 17.5, and 28.0gNm 612 yr 611 for four years in two contrasting field sites in Inner Mongolia: an undisturbed mature grassland and a nearby degraded grassland of the same type. N addition had both quantitatively and qualitatively different effects on the two communities. In the mature community, N addition led to a large reduction in species richness, accompanied by increased dominance of early successional annuals and loss of perennial grasses and forbs at all N input rates. In the degraded community, however, N addition increased the productivity and dominance of perennial rhizomatous grasses, with only a slight reduction in species richness and no significant change in annual abundance. The mature grassland was much more sensitive to N-induced changes in community structure, likely as a result of higher soil moisture accentuating limitation by N alone. Our findings suggest that the critical threshold for N-induced species loss to mature Eurasian grasslands is below 1.75gNm 612 yr 611 , and that changes in aboveground biomass, species richness, and plant functional group composition to both mature and degraded ecosystems saturate at N addition rates of approximately 10.5gNm 612 yr 611 . This work highlights the tradeoffs that exist in assessing the total impact of N deposition on ecosystem function. |
| [11] | Plant litter diversity effects on decomposition rates are frequently reported, but with a strong bias towards temperate ecosystems. Altered decomposition and nutrient recycling with changing litter diversity may be particularly important in tree species-rich tropical rainforests on nutrient-poor soils. Using 28 different mixtures of leaf litter from 16 Amazonian rainforest tree species, we tested the hypothesis that litter mixture effects on decomposition increase with increasing functional litter diversity. Litter mixtures and all single litter species were exposed in the field for 9聽months using custom-made microcosms with soil fauna access. In order to test the hypothesis that the long-term presence of tree species contributing to the litter mixtures increases mixture effects on decomposition, microcosms were installed in a plantation at sites including the respective tree species composition and in a nearby natural forest where these tree species are absent. We found that mixture decomposition deviated from predictions based on single species, with predominantly synergistic effects. Functional litter diversity, defined as either richness, evenness, or divergence based on a wide range of chemical traits, did not explain the observed litter mixture effects. However, synergistic effects in litter mixtures increased with the long-term presence of tree species contributing to these mixtures as the home field advantage hypothesis assumes. Our data suggest that complementarity effects on mixed litter decomposition may emerge through long-term interactions between aboveground and belowground biota. |
| [12] | |
| [13] | , |
| [14] | |
| [15] | Abstract One of the major concerns about global warming is the potential for an increase in decomposition and soil respiration rates, increasing CO 2 emissions and creating a positive feedback between global warming and soil respiration. This is particularly important in ecosystems with large belowground biomass, such as grasslands where over 90% of the carbon is allocated belowground. A better understanding of the relative influence of climate and litter quality on litter decomposition is needed to predict these changes accurately in grasslands. The Long-Term Intersite Decomposition Experiment Team (LIDET) dataset was used to evaluate the influence of climatic variables (temperature, precipitation, actual evapotranspiration, and climate decomposition index), and litter quality (lignin content, carbon:nitrogen, and lignin:nitrogen ratios) on leaf and root decomposition in the US Great Plains. Wooden dowels were used to provide a homogeneous litter quality to evaluate the relative importance of above and belowground environments on decomposition. Contrary to expectations, temperature did not explain variation in root and leaf decomposition, whereas precipitation partially explained variation in root decomposition. Percent lignin was the best predictor of leaf and root decomposition. It also explained most variation in root decomposition in models which combined litter quality and climatic variables. Despite the lack of relationship between temperature and root decomposition, temperature could indirectly affect root decomposition through decreased litter quality and increased water deficits. These results suggest that carbon flux from root decomposition in grasslands would increase, as result of increasing temperature, only if precipitation is not limiting. However, where precipitation is limiting, increased temperature would decrease root decomposition, thus likely increasing carbon storage in grasslands. Under homogeneous litter quality, belowground decomposition was faster than aboveground and was best predicted by mean annual precipitation, which also suggests that the high moisture in soil accelerates decomposition belowground. |
| [16] | Anthropogenic nitrogen deposition over the past half century has had a detrimental impact on temperate ecosystems in Europe and North America, resulting in soil acidification and a reduction in plant biodiversity. During the acidification process, soils release base cations, such as calcium and magnesium, neutralizing the increase in acidity. Once these base cations have been depleted, aluminium is released from the soils, often reaching toxic levels. Here, we present results from a nitrogen deposition experiment that suggests that a long legacy of acid deposition in the Western Tatra Mountains of Slovakia has pushed soils to a new threshold of acidification usually associated with acid mine drainage soils. We show that increases in nitrogen deposition in the region result in a depletion of both base cations and soluble aluminium, and an increase in extractable iron concentrations. In conjunction with this, we observe a nitrogen-deposition-induced reduction in the biomass of vascular plants, associated with a decrease in shoot calcium and magnesium concentrations. We suggest that this site, and potentially others in central Europe, have reached a new and potentially more toxic level of soil acidification in which aluminium release is superseded by iron release into soil water. |
| [17] | Summary Litter decomposition is a biogeochemical process fundamental to element cycling within ecosystems, influencing plant productivity, species composition and carbon storage. Climate has long been considered the primary broad-scale control on litter decomposition rates, yet recent work suggests that plant litter traits may predominate. Both decomposition paradigms, however, rely on inferences from cross-biome litter decomposition studies that analyse site-level means. We re-analyse data from a classical cross-biome study to demonstrate that previous research may falsely inflate the regulatory role of climate on decomposition and mask the influence of unmeasured local-scale factors. Using the re-analysis as a platform, we advocate experimental designs of litter decomposition studies that involve high within-site replication, measurements of regulatory factors and processes at the same local spatial grain, analysis of individual observations and biome-scale gradients. Synthesis . We question the assumption that climate is the predominant regulator of decomposition rates at broad spatial scales. We propose a framework for a new generation of studies focused on factoring local-scale variation into the measurement and analysis of soil processes across broad scales. Such efforts may suggest a revised decomposition paradigm and ultimately improve confidence in the structure, parameter estimates and hence projections of biogeochemical models. |
| [18] | New understanding of the connection between dynamic microbial carbon use efficiency (CUE), litter decomposition products, and pathways of soil organic carbon (SOC) formation have not been fully integrated into current generalizable litter decomposition models. We developed a new approach, the Litter Decomposition and Leaching (LIDEL) model, that: 1) includes leaching and formation of dissolved organic carbon (DOC), important components of vertical C movement and SOC inputs into deeper soil layers, and 2) uses widely available litter chemistry data to drive the simulation of microbial processes that partition litter during decomposition, through affecting rates of CO 2 respiration versus formation of microbial biomass and microbial products. Two ecologically important but poorly understood processes explored in this analysis include 1) the relationship between litter nitrogen (N) availability and rates of microbial decay and assimilation, and 2) the efficiency of DOC generation from the decomposition and leaching of soluble- versus cellulose-dominated plant litter fractions. We tested multiple hypothesis-driven model formulations, and for each estimated initial conditions and parameters using hierarchical Bayesian approaches. We combined data from experimental results and literature review for five types of litter that vary by initial lignin and N content. Our analyses showed the LIDEL model formulations with a logistic N limitation curve gave better predictions than model formulations using a linear N limitation curve. Model formulations with higher DOC generation efficiency from the soluble litter pool yielded more variable predictions and parameter estimations (shown by consistently wider 95% Bayesian credible intervals), but may have better simulated large DOC leaching events in early decomposition. Our analyses highlight a need for targeted studies clarifying measures of soluble litter and the generation of DOC during early litter decomposition, as well as rates of microbial biomass turnover and the flux of soluble versus non-soluble microbial products. Overall, the LIDEL model provides a robust generalizable framework to express and test hypotheses connecting litter chemistry and dynamic microbial CUE with the generation of DOC and microbial products during litter decomposition. |
| [19] | Some natural ecosystems near industrialized and agricultural areas receive atmospheric nitrogen inputs that are an order of magnitude greater than those presumed for preindustrial times. Because nitrogen (N) often limits microbial growth on dead vegetation, increased N input can be expected to affect the ecosystem process of decomposition. We found that extracellular enzyme responses of a forest-floor microbial community to chronically applied aqueous NH4NO3can explain both increased and decreased litter decomposition rates caused by added N. Microbes responded to N by increasing cellulase activity in decaying leaf litter of flowering dogwood, red maple, and red oak, but in high-lignin oak litter, the activity of lignin-degrading phenol oxidase declined substantially. We believe this is the first report of reduced ligninolytic enzyme activity caused by chronic N addition in an ecosystem. This result provides evidence that ligninolytic enzyme suppression can be an important mechanism explaining decreased decay rates of plant matter seen in this and other N-addition experiments. Since lignin and cellulose are the two most abundant organic resources on earth, these altered enzyme responses signal that atmospheric N deposition may be affecting the global carbon cycle by influencing the activities of microbes and their carbon-acquiring enzymes--especially the unique ligninolytic enzymes produced by white-rot fungi--over broad geographic areas. |
| [20] | Plant chemical composition and the soil community are known to influence litter and soil organic matter decomposition. Although these two factors are likely to interact, their mechanisms and outcomes of interaction are not well understood. Studies of their interactive effects are rare and usually focus on carbon dynamics of litter, while nutrient dynamics in the underlying soil have been ignored. A potential mechanism of interaction stems from the role fauna plays in regulating availability of litter-derived materials in the mineral soil. We investigated the role of soil fauna (meso, macro) in determining the effect of surface-litter chemical composition on nitrogen mineralization and on the micro-food web in mineral soils. In a field setting we exposed mineral soil to six types of surface-applied litter spanning wide ranges of multiple quality parameters and restricted the access of larger soil animals to the soils underlying these litters. Over six months we assessed litter mass and nitrogen loss, nitrogen mineralization rates in the mineral soils, and soil microbes and microfauna. We found evidence that the structure of the soil community can alter the effect of surface-litter chemical composition on nitrogen dynamics in the mineral soil. In particular, we found that the presence of members of the meso- and macrofauna can magnify the control of nitrogen mineralization by litter quality and that this effect is time dependent. While fauna were able to affect the size of the micro-food web they did not impact the effect of litter composition on the abundance of the members of the micro-food web. By enhancing the strength of the impact of litter quality on nitrogen dynamics, the larger fauna can alter nitrogen availability and its temporal dynamics which, in turn, can have important implications for ecosystem productivity. These findings contribute to evidence demonstrating that soil fauna shape plant litter effects on ecosystem function. |
| [21] | The concept of nutrient limitation, as developed in agriculture, applies well to wild plants grown under controlled conditions, although plants adapted to infertile soils are less responsive to nutrient addition than are most crop species. There are serious difficulties in transferring the concept of nutrient limitation directly to plant communities, however, because (1) in comparing communities with different dominant species, the species characteristic of nutrient-rich sites are inherently more responsive to nutrient supply and may be more strongly nutrient-limited than species in low-nutrient sites, and (2) ecosystem-level feedback complicates the analysis of experiments involving fertilization. We suggest that nutrient limitation in communities can be best measured by assessing the plants' response to large nutrient additions that are sufficient to saturate chemical and microbial immobilization processes and still meet plant nutrient requirements. The magnitude of community-level nutrient limitation is highly sensitive to the potential growth rate of component species; it may be greatest in sites of intermediate fertility. |
| [22] | , Humans have directly modified half of the ice-free terrestrial surface and use 40% of terrestrial production. We are causing the sixth major extinction event in the history of life on Earth. With the Earth鈥檚 climate, flora, and fauna changing rapidly, there is a pressing need to understand terrestrial ecosystem processes and their sensitivity to environmental and biotic changes. This book offers a framework to do just that. Ecosystem ecology regards living organisms, including people, and the elements of their environment as components of a single integrated system. The comprehensive coverage in this textbook examines the central processes at work in terrestrial ecosystems, including their freshwater components. It traces the flow of energy, water, carbon, and nutrients from their abiotic origins to their cycles through plants, animals, and decomposer organisms. As well as detailing the processes themselves, the book goes further to integrate them at various scales of magnitude鈥攖hose of the ecosystem, the wider landscape and the globe. It synthesizes recent advances in ecology with established and emerging ecosystem theory to offer a wide-ranging survey of ecosystem patterns and processes in our terrestrial environment. Featuring review questions at the end of each chapter, suggestions for further reading, and a glossary of ecological terms, Principles of Terrestrial Ecosystem Ecology is a vitally relevant text suitable for study in all courses in ecosystem ecology. Resource managers and researchers in many fields will welcome its thorough presentation of ecosystem essentials. |
| [23] | Global change will definitely introduce changes in agricultural ecosystems that will affect photosynthesis and plant productivity. However, the effects on plants will be different for each region depending on the pre-existing climatic conditions and the adaptation potential of local cultivated species. In Crete, an island with typical Mediterranean climate, high temperatures and lack of rainfall during summer are the most important factors determining productivity of tree crops. Meteorological data and predictive models of climate change indicate that the annual mean temperature of the island has already increased by 0.3 掳C in the past two decades and will further increase in the future. Moreover, summer precipitation will be lower and the frequency of extreme climatic phenomena, like heat waves, will increase. Consequently, the combination of reduced rainfall and increased temperature will impose higher evapotranspiration losses, increasing the water stress problems of cultivated crops, while the reduction in the availability of irrigation water of good quality will increase the use of saline water and augment the already existing problem of salinity in the island. Therefore, cultivated species in Crete, and the Eastern Mediterranean region in general, will have to grow in a hotter, drier and, in some cases, more saline environment. In this report, the possible effects of increased temperature, UV-B radiation and reduced precipitation on the typical agricultural crops of the area are discussed, based on the current knowledge about the effects of climate change on plant photosynthesis and productivity. Special consideration is accounted to the negative effects that may counterbalance the benefits of higher photosynthetic rates and water use efficiency introduced by the future increase in atmospheric CO 2 concentration. |
| [24] | 61N enrichment increased both above- and belowground plant biomass mainly via N availability.61N enrichment had negative effects on both microbial and nematode communities in semi-arid grassland.61The positive effects of belowground C allocation on belowground communities were outweighed by soil acidification.61N enrichment weakens the linkages between aboveground and belowground components of grassland ecosystems. |
| [25] | The responses of litter decomposition to nitrogen (N) and phosphorus (P) additions were examined in an old-growth tropical forest in southern China to test the following hypotheses: (1) N addition would decrease litter decomposition; (2) P addition would increase litter decomposition, and (3) P addition would mitigate the inhibitive effect of N addition. Two kinds of leaf litter, Schima superba Chardn. & Champ. (S.S.) and Castanopsis chinensis Hance (C.C.), were studied using the litterbag technique. Four treatments were conducted at the following levels: control, N-addition (150 kg N ha611 yr611), P-addition (150 kg P ha611 yr611) and NP-addition (150 kg N ha611 yr611 plus 150 kg P ha611 yr611). While N addition significantly decreased the decomposition of both litters, P addition significantly inhibited decomposition of C.C., but did not affect the decomposition of S.S. The negative effect of N addition on litter decomposition might be related to the high N-saturation in this old-growth tropical forest; however, the negative effect of P addition might be due to the suppression of “microbial P mining”. Significant interaction between N and P addition was found on litter decomposition, which was reflected by the less negative effect in NP-addition plots than those in N-addition plots. Our results suggest that P addition may also have negative effect on litter decomposition and that P addition would mitigate the negative effect of N deposition on litter decomposition in tropical forests. |
| [26] | Nitrogen (N) deposition in China has increased greatly, but the general impact of elevated N deposition on carbon (C) dynamics in Chinese terrestrial ecosystems is not well documented. In this study we used a meta-analysis method to compile 88 studies on the effects of N deposition C cycling on Chinese terrestrial ecosystems. Our results showed that N addition did not change soil C pools but increased above-ground plant C pool. A large decrease in below-ground plant C pool was observed. Our result also showed that the impacts of N addition on ecosystem C dynamics depend on ecosystem type and rate of N addition. Overall, our findings suggest that 1) decreased below-ground plant C pool may limit long-term soil C sequestration; and 2) it is better to treat N-rich and N-limited ecosystems differently in modeling effects of N deposition on ecosystem C cycle. |
| [27] | As the first and rate-limiting step of nitrification, ammonia oxidation can be realized either by ammonia-oxidizing bacteria (AOB) or archaea (AOA). However, the key factors driving the abundance, community structure and activity of ammonia oxidizers are still unclear, and the relative importance of AOA and AOB in ammonia oxidation is unresolved. In the present study, we examined the effects of long-term (6 years) nitrogen (N) addition and simulated precipitation increment on the abundance and community composition of AOA and AOB based on a field trial in a typical temperate steppe of northern China. We used combined approaches of quantitative PCR, terminal-restriction fragment length polymorphism (T-RFLP) and clone library analyses of amoA genes. The study objective was to determine (1) AOA and AOB diversity and activity in response to N addition and increased precipitation and (2) the relative contributions of AOA and AOB to soil ammonia oxidation in the typical temperate steppe. The results showed that the potential nitrification rate (PNR) increased with N addition, but decreased with increased precipitation. Both N addition and increased precipitation significantly increased AOB but not AOA abundance, and a significant correlation was only observed between PNR and AOB amoA gene copies. The T-RFLP analysis showed that both N and precipitation were key factors in shaping the composition of AOB, while AOA were only marginally influenced. Phylogenetic analysis indicated that all AOA clones fell within the soil and sediment lineage while all AOB clones fell within the Nitrosospira. The study suggested that AOA and AOB had distinct physiological characteristics and ecological niches. AOB were shown to be more sensitive to N and precipitation than AOA, and the ammonia oxidation process was therefore supposed to be mainly driven by AOB in this temperate steppe. (C) 2013 Elsevier B.V. All rights reserved. |
| [28] | |
| [29] | Over a century of agricultural abandonment across the Mediterranean region has favoured the installation of the pioneer expansionist species Aleppo pine (Pinus halepensis Miller). This species synthesizes a wide range of secondary metabolites that are partially released during needle decomposition, and which can thus affect the ‘brown food chain’. Litter decomposition is a key process connecting ecosystem structure and function, and involving microbial and faunal components.The goal of this study was to determine the effect of chemical compounds from Aleppo pine needles on the litter decomposition process along a gradient of Mediterranean forest secondary succession. Using in situ litterbags, we compared the dynamics of decomposers, particularly the relative contributions of fungal and mesofauna biomass to litter mass loss (calculations based on the measured decomposer biomass, published fungal growth efficiency and mesofauna feeding rate), against the dynamics of secondary metabolites associated with decomposed needles in three successional stages (early, middle and late, i.e. pinewoods that were aged 10, 30 and over 60 years old).Our first key finding was that fungi accounted for the largest portion of overall litter mass loss (60–79%) and detritivorous mesofauna contributed to 8–12%. In the early stage of succession, fungal biomass after 6 months of decomposition was lower than in middle and late stages, and may be responsible for the delay in litter colonization by mesofauna. We linked this result to a clearly longer residence time for phenolic compounds in young pine forest, leading to an overall slowdown in the decomposition process.Synthesis. Litter phenolic content emerged as a key functional trait for predicting litter decomposition, delaying the colonization of litter by decomposers in Mediterranean forest ecosystems. Another key finding is that the relative contributions of fungi and detritivores to needle mass loss were different between the successional stages. From the food-web perspective, the organic matter available for higher trophic levels thus remains unchanged beyond 30 years after pine colonization. |
| [30] | Summary A broad and diversified group of compounds, secondary metabolites, are known to govern species interactions in ecosystems. Recent studies have shown that secondary metabolites can also play a major role in ecosystem processes, such as plant succession or in the process of litter decomposition, by governing the interplay between plant matter and soil organisms. We reviewed the ecological role of the three main classes of secondary metabolites and the methodological challenges and novel avenues for their study. We highlight emerging general patterns of the impacts of secondary metabolites on decomposer communities and litter decomposition and argue for the consideration of secondary compounds as key drivers of soil functioning and ecosystem functioning. Synthesis . Gaining a greater understanding of plant鈥搒oil organisms relationships and underlying mechanisms, including the role of secondary metabolites, could improve our ability to understand ecosystem processes. We outline some promising directions for future research that would stimulate studies aiming to understand the interactions of secondary metabolites across a range of spatio-temporal scales. Detailed mechanistic knowledge could help us to develop models for the process of litter decomposition and nutrient cycling in ecosystems and help us to predict future impacts of global changes on ecosystem functioning. |
| [31] | Abstract Anthropogenic nitrogen (N) enrichment of many ecosystems throughout the globe has important ramifications for plant communities. Observational and experimental studies frequently find species richness declines with N enrichment, in concert with increasing primary production. Nitrogen enrichment also reorders species composition, including species turnover through gains and losses of species, changes in dominance and rarity, and shifts in the relative abundance of particular functional groups. Nitrogen has traditionally been considered the primary limiting nutrient for plant growth in terrestrial ecosystems, but recent synthetic work suggests that colimitation by phosphorus (P), water, and other resources is widespread, consistent with theoretical predictions. At the same time, disproportionate increases in ecosystem N input are expected to exacerbate limitation by P and other resources. Similarly, synthetic research has pointed out the important role of consumers and pathogens in determining plant community structure, especially with respect to shifting resource availability. We argue here that environmental and biotic contexts, including limitation by multiple resources, herbivores and pathogens, play important roles in our understanding of plant community responses to N enrichment. |
| [32] | Boreal forest soils function as a terrestrial net sink in the global carbon cycle. The prevailing dogma has focused on aboveground plant litter as a principal source of soil organic matter. Using (14)C bomb-carbon modeling, we show that 50 to 70% of stored carbon in a chronosequence of boreal forested islands derives from roots and root-associated microorganisms. Fungal biomarkers indicate impaired degradation and preservation of fungal residues in late successional forests. Furthermore, 454 pyrosequencing of molecular barcodes, in conjunction with stable isotope analyses, highlights root-associated fungi as important regulators of ecosystem carbon dynamics. Our results suggest an alternative mechanism for the accumulation of organic matter in boreal forests during succession in the long-term absence of disturbance. |
| [33] | Soil microbial communities may respond to anthropogenic increases in ecosystem nitrogen (N) availability, and the microbial response may ultimately feed back on ecosystem carbon and N dynamics. We examined the long-term effects of chronic N additions on soil microbes by measuring soil microbial biomass, composition and substrate utilization patterns in pine and hardwood forests at the Harvard Forest Chronic N Amendment Study. Functional and structural genes for important N cycling processes were studied using DNA community profiles. In the O horizon soil of both stands, N additions decreased microbial biomass C as determined by chloroform fumigation-extraction. Utilization of N-containing substrates was lower in N-treated pine soils than in the controls, suggesting that N additions reduced potential microbial activity in the pine stand. Counts of fungi and bacteria as determined by direct microscopy and culture techniques did not show a clear response to N additions. Nitrogen additions, however, strongly influenced microbial community DNA profiles. The ammonia monooxygenase gene ( amoA ) generally was found in high N-treated soils, but not in control soils. The nifH gene for N 2 -fixation was generally found in all soils, but was more difficult to amplify in the pine N-treated soil than the controls, suggesting that the population of N 2 -fixers was altered by N additions. The 16S rDNA gene for Nitrobacter was found in all samples, but distinct differences among DNA profiles were observed in the pine B horizon in the control, low N, and high N-treated plots. Our findings indicate that chronic N additions decreased chloroform microbial carbon and altered microbial community profiles. These changes in microbial community structure may be an important component of the response of terrestrial ecosystems to human-accelerated N supply. |
| [34] | |
| [35] | Human activity has increased the amount of N entering terrestrial ecosystems from atmospheric NO 3 61 deposition. High levels of inorganic N are known to suppress the expression of phenol oxidase, an important lignin-degrading enzyme produced by white-rot fungi. We hypothesized that chronic NO 3 61 additions would decrease the flow of C through the heterotrophic soil food web by inhibiting phenol oxidase and the depolymerization of lignocellulose. This would likely reduce the availability of C from lignocellulose for metabolism by the microbial community. We tested this hypothesis in a mature northern hardwood forest in northern Michigan, which has received experimental atmospheric N deposition (3002kg02NO 3 61 –N02ha 611 02y 611 ) for nine years. In a laboratory study, we amended soils with 13 C-labeled vanillin, a monophenolic product of lignin depolymerization, and 13 C-labeled cellobiose, a disaccharide product of cellulose degradation. We then traced the flow of 13 C through the microbial community and into soil organic carbon (SOC), dissolved organic carbon (DOC), and microbial respiration. We simultaneously measured the activity of enzymes responsible for lignin (phenol oxidase and peroxidase) and cellobiose (β-glucosidase) degradation. Nitrogen deposition reduced phenol oxidase activity by 83% and peroxidase activity by 74% when compared to control soils. In addition, soil C increased by 76%, whereas microbial biomass decreased by 68% in NO 3 61 amended soils. 13 C cellobiose in bacterial or fungal PLFAs was unaffected by NO 3 61 deposition; however, the incorporation of 13 C vanillin in fungal PLFAs extracted from NO 3 61 amended soil was 82% higher than in the control treatment. The recovery of 13 C vanillin and 13 C cellobiose in SOC, DOC, microbial biomass, and respiration was not different between control and NO 3 61 amended treatments. Chronic NO 3 61 deposition has stemmed the flow of C through the heterotrophic soil food web by inhibiting the activity of ligninolytic enzymes, but it increased the assimilation of vanillin into fungal PLFAs. |
| [36] | Abstract Litter production in many drought-affected ecosystems coincides with the beginning of an extended season of no or limited rainfall. Because of lack of moisture litter decomposition during such periods has been largely ignored so far, despite potential importance for the overall decay process in such ecosystems. To determine drivers and extent of litter decay in rainless periods, a litterbag study was conducted in Mediterranean shrublands, dwarf shrublands and grasslands. Heterogeneous local and common straw litter was left to decompose in open and shaded patches of various field sites in two study regions. Fresh local litter lost 4–18% of its initial mass over about 4 months without rainfall, which amounted to 15–50% of total annual decomposition. Lab incubations and changes in chemical composition suggested that litter was degraded by microbial activity, enabled by absorption of water vapor from the atmosphere. High mean relative humidity of 85% was measured during 8–9h of most nights, but the possibility of fog deposition or dew formation at the soil surface was excluded. Over 95% of the variation in mass loss and changes in litter nitrogen were explained by characteristics of water-vapor uptake by litter. Photodegradation induced by the intense solar radiation was an additional mechanism of litter decomposition as indicated by lignin dynamics. Lignin loss from litter increased with exposure to ultraviolet radiation and with initial lignin concentration, together explaining 90%–97% of the variation in lignin mass change. Our results indicate that water vapor, solar radiation and litter quality controlled decomposition and changes in litter chemistry during rainless seasons. Many regions worldwide experience transient periods without rainfall, and more land area is expected to undergo reductions in rainfall as a consequence of climate change. Therefore, absorption of water vapor might play a role in decomposition and nutrient cycling in an increasing number of ecosystems. |
| [37] | Future rates of anthropogenic N deposition can slow the cycling and enhance the storage of C in forest ecosystems. In a northern hardwood forest ecosystem, experimental N deposition has decreased the extent of forest floor decay, leading to increased soil C storage. To better understand the microbial mechanisms mediating this response, we examined the functional genes derived from communities of actinobacteria and fungi present in the forest floor using GeoChip 4.0, a high-throughput functional-gene microarray. The compositions of functional genes derived from actinobacterial and fungal communities was significantly altered by experimental nitrogen deposition, with more heterogeneity detected in both groups. Experimental N deposition significantly decreased the richness and diversity of genes involved in the depolymerization of starch (6512%), hemicellulose (6516%), cellulose (6516%), chitin (6515%), and lignin (6516%). The decrease in richness occurred across all taxonomic groupings detected by the microarray. The compositions of genes encoding oxidoreductases, which plausibly mediate lignin decay, were responsible for much of the observed dissimilarity between actinobacterial communities under ambient and experimental N deposition. This shift in composition and decrease in richness and diversity of genes encoding enzymes that mediate the decay process has occurred in parallel with a reduction in the extent of decay and accumulation of soil organic matter. Our observations indicate that compositional changes in actinobacterial and fungal communities elicited by experimental N deposition have functional implications for the cycling and storage of carbon in forest ecosystems. |
| [38] | |
| [39] | Abstract Initial ecosystems are characterized by a low availability of nutrients and a low soil organic matter content. Interactions of plants and microorganisms in such environments, particularly in relation to litter decomposition, are very important for further ecosystem development. In a litter decomposition study using an initial substrate from a former mining area, we applied the litter of two contrasting pioneer plant species (legume vs. pasture plants), Lotus corniculatus and Calamagrostis epigejos , which are commonly observed in the study area. Litter decomposition was investigated and carbon (C) translocation from litter into soil microorganisms was described by following 13 C from labelled plant litter materials into the fraction of phospholipid fatty acids. Labile C compounds of both plant litter types were easily degraded during the first 4 weeks of litter decomposition. In contrast to climax ecosystems, where the importance of fungi for litter degradation has been shown in many studies, in our experiment, data clearly indicate an outcompetition of fungi by Gram-positive bacteria as soon as available nitrogen is limited in the detritusphere. |
| [40] | |
| [41] | We analyze trends of some nitrogen compounds using long-term measurements and results from the EMEP (co-operative programme for monitoring and evaluation of the long-range transmissions of air pollutants in Europe) chemical transport model at EMEP sites. We find statistically significant declines at the majority of sites for NH(x) (sum of ammonia and ammonium) in air and for nitrate and ammonium in precipitation, but only at a few sites for xNO3 (sum of nitrate and nitric acid) in air. Model calculations and measurements give similar results. We demonstrate that the lack of trends for xNO3 in air at least partly can be attributed to a shift in the equilibrium between nitric acid and ammonium nitrate towards particulate phase, caused by reductions in the sulfur dioxide emissions. |
| [42] | Nitrogen (N) and phosphorus (P) are most commonly the limiting essential elements that affect the functioning of plants and ecosystems. However, their stoichiometry in relation to climatic variables a |
| [43] | 61We investigated decomposition of three plant species in four varying pasture soils.61The respiration of organic carbon in response to nitrogen addition was monitored.61Nitrogen addition increased the loss of carbon from some soils but not others.61The soil carbon to nitrogen ratio determined how decomposition responds to nitrogen. |
| [44] | The decomposition of Cistus incanus leaf litter, a summer deciduous species, was compared to that of Myrtus communis , an evergreen species, during 15 months of incubation in a Mediterranean low shrubland. The litterbags were placed under randomly selected shrubs of Myrtus and Cistus , respectively. Owing to the different microclimatic conditions under deciduous and evergreen shrubs Cistus litter was also incubated under Myrtus shrubs. Microbial activity was evaluated by measuring litter respiration and enzyme activities (cellulase, xylanase, α-amylase, β-amylase, laccase and peroxidase). During the first 8 months of incubation the decomposition rate of both litters was independent of litter quality and incubation conditions. The average decay constant ( k ) ranged between 0.29±0.03 and ja:math Subsequently, it increased only for litters incubated under Myrtus shrubs ( k =0.57±0.15 and ja:math for Cistus and Myrtus litters, respectively). The dry summer affected the decay rate of litters incubated under Myrtus but not under Cistus . Microbial respiration showed seasonal changes (from 25 to 15002μmol CO 2 02g 611 dry wt. 2402h 611 ), with low levels in summer, mainly because of the low litter water content. After samples were placed in the field, α-amylase activity decreased rapidly, dropping to zero in Cistus litter, whereas it remained detectable in Myrtus litter (>0.0202μmol glucose g 611 dry wt. h 611 ). The β-amylase activity was low over the entire period. The activities of cellulase and xylanase ranged from 1 to 3002μmol glucose equivalents (reducing sugar) g 611 dry wt. h 611 . Both litters showed the lowest enzyme activities in summer, when litter respiration was also at the lowest level. Peroxidase activity was detected in the litter of Myrtus (from 0 to 5002μmol o -tolidine oxidised g 611 dry wt. h 611 ) and had a seasonal pattern similar to cellulase and xylanase. It was undetectable in Cistus . In both litters laccase increased significantly going from 10 to 14002μmol o -tolidine oxidised g 611 dry wt. h 611 between eight and nine months when a large increase of fungal biomass occurred (from 0.5 to 2.502mg g 611 dry wt.). The analyses of these enzymes have shown qualitative and quantitative differences depending on the litter type and the microclimatic conditions, suggesting changes in the microbial succession. |
| [45] | Atmospheric warming and increased nitrogen deposition can lead to changes of microbial communities with possible consequences for biogeochemical processes. We used an enclosure facility in a freshwater marsh to assess the effects on microbes associated with decomposing plant litter under conditions of simulated climate warming and pulsed nitrogen supply. Standard batches of litter were placed in coarse-mesh and fine-mesh bags and submerged in a series of heated, nitrogen-enriched, and control enclosures. They were retrieved later and analyzed for a range of microbial parameters. Fingerprinting profiles obtained by denaturing gradient gel electrophoresis (DGGE) indicated that simulated global warming induced a shift in bacterial community structure. In addition, warming reduced fungal biomass, whereas bacterial biomass was unaffected. The mesh size of the litter bags and sampling date also had an influence on bacterial community structure, with the apparent number of dominant genotypes increasing from spring to summer. Microbial respiration was unaffected by any treatment, and nitrogen enrichment had no clear effect on any of the microbial parameters considered. Overall, these results suggest that microbes associated with decomposing plant litter in nutrient-rich freshwater marshes are resistant to extra nitrogen supplies but are likely to respond to temperature increases projected for this century. |
| [46] | Abstract Land use and climate changes induce shifts in plant functional diversity and community structure, thereby modifying ecosystem processes. This is particularly true for litter decomposition, an essential process in the biogeochemical cycles of carbon and nutrients. In this study, we asked whether changes in functional traits of living leaves in response to changes in land use and climate were related to rates of litter potential decomposition, hereafter denoted litter decomposability, across a range of 10 contrasting sites. To disentangle the different control factors on litter decomposition, we conducted a microcosm experiment to determine the decomposability under standard conditions of litters collected in herbaceous communities from Europe and Israel. We tested how environmental factors (disturbance and climate) affected functional traits of living leaves and how these traits then modified litter quality and subsequent litter decomposability. Litter decomposability appeared proximately linked to initial litter quality, with particularly clear negative correlations with lignin-dependent indices (litter lignin concentr tion, lignin:nitrogen ratio, and fiber component). Litter quality was directly related to community-weighted mean traits. Lignin-dependent indices of litter quality were positively correlated with community-weighted mean leaf dry matter content (LDMC), and negatively correlated with community-weighted mean leaf nitrogen concentration (LNC). Consequently, litter decomposability was correlated negatively with community-weighted mean LDMC, and positively with community-weighted mean LNC. Environmental factors (disturbance and climate) influenced community-weighted mean traits. Plant communities experiencing less frequent or less intense disturbance exhibited higher community-weighted mean LDMC, and therefore higher litter lignin content and slower litter decomposability. LDMC therefore appears as a powerful marker of both changes in land use and of the pace of nutrient cycling across 10 contrasting sites. |
| [47] | Litter decomposition is an enzymatically-complex process that is mediated by a diverse assemblage of saprophytic microorganisms. It is a globally important biogeochemical process that can be suppressed by anthropogenic N deposition. In a northern hardwood forest ecosystem located in Michigan, USA, 20 years of experimentally increased atmospheric N deposition has reduced forest floor decay and increased soil C storage. Here, we paired extracellular enzyme assays with shotgun metagenomics to assess if anthropogenic N deposition has altered the functional potential of microbial communities inhabiting decaying forest floor. Experimental N deposition significantly reduced the activity of extracellular enzymes mediating plant cell wall decay, which occurred concurrently with changes in the relative abundance of metagenomic functional gene pathways mediating the metabolism of carbohydrates, aromatic compounds, as well as microbial respiration. Moreover, experimental N deposition increased the relative abundance of 50 of the 60 gene pathways, the majority of which were associated with saprotrophic bacteria. Conversely, the relative abundance and composition of fungal genes mediating the metabolism of plant litter was not affected by experimental N deposition. Future rates of atmospheric N deposition have favored saprotrophic soil bacteria, whereas the metabolic potential of saprotrophic fungi appears resilient to this agent of environmental change. Results presented here provide evidence that changes in the functional capacity of saprotrophic soil microorganisms mediate how anthropogenic N deposition increases C storage in soil. |
| [48] | |
| [49] | We examined how chronic nitrogen (N) enrichment of pine and hardwood forest stands has affected the relative abundance, functional capacity, and activity of soil bacteria and fungi. During Fall 2002 we collected one soil core (5.602cm diameter; organic horizon plus 1002cm of mineral soil) from each of four ja:math 02m subplots within the control, low N (502g02N02m 612 per year), and high N (1502g02N02m 612 per year) plots in both the hardwood and pine stands at the Chronic Nitrogen Amendment Study at Harvard Forest. The samples were analyzed for total and active bacterial and fungal biomass, microbial catabolic response profiles, the activities of cellulolytic and ligninolytic enzymes, and total, labile and microbially derived organic carbon (C). Live, fine roots were also collected from the control and low N pine plots and analyzed for ectomycorrhizal fungal community composition and diversity. Active fungal biomass was 27–61% and 42–69% lower in the fertilized compared to control plots in the hardwood and pine stands, respectively. Active bacterial biomass was not greatly affected by N additions, resulting in significantly lower fungal:bacterial biomass ratios in the N-treated plots. This shift in microbial community composition was accompanied by a significant reduction in the activity of phenol oxidase, a lignin-degrading enzyme produced by white-rot fungi. In the pine stand, ectomycorrhizal fungal community diversity was lower in the low N-treated plot than in the control plot. Differences in ectomycorrhizal community structure were also detected between control and fertilized pine plots, including a reduction in those species with the highest relative frequencies in the control community. Finally, N enrichment altered the pattern of microbial substrate use, with the relative response to the addition of carboxylic acids and carbohydrates being significantly lower in the N-treated plots, even after the data were normalized to account for differences in microbial biomass. These patterns are consistent with lower decomposition rates and altered N cycling observed previously at this site. |
| [50] | |
| [51] | An experimental study was carried out in order to evaluate the impact of nitrogen fertiliser-induced acidification in carbonated soils. Undisturbed soil columns containing different carbonate content were sampled in the field. Fertiliser spreading was simulated by NH 4Cl addition on top of the soil column. Soil solution composition (mainly nitrate and base cations) was studied at the soil column鈥檚 base. Nitrification occurred to a different extent depending on soil type. Higher nitrification rates were observed in calcareous soils. In all the soil types, strong correlations between leached base cation and nitrate concentrations were observed. Regression coefficients between base cations, nitrate and chloride were used to determine the dominant processes occurring following NH 4Cl spreading. In non-carbonated soils, nitrogen nitrification induced base cation leaching and soil acidification. In carbonated soils, no change of soil pH was observed. However, fertilisers induced a huge cation leaching. Carbonate mineral weathering led to the release of base cations, which replenished the soil exchangeable complex. Carbonated mineral weathering buffered acidification. Since direct weathering might have occurred without atmospheric CO 2 consumption, the use of nitrogen fertiliser on carbonated soil induces a change in the cation and carbon budgets. When the results of these experiments are extrapolated on a global scale to the surface of fertilised areas lying on carbonate, carbonated reactions with N fertilisers would imply an additional flux of 5.7 脳 10 12 mol yr 鈭1 of Ca + Mg. The modifications of weathering reactions in cultivated catchments and the ability of nitrogen fertilisers to significantly modify the CO 2 budget should be included in carbon global cycle assessment. |
| [52] | Abstract An incubation experiment was conducted to examine the effects of nitrogen (N) application on microbial respiration in alpine meadow and alpine shrub soils from eastern of Qinghai-Tibetan Plateau. Four different levels of nitrogen fertilization were selected in this study: control (CK, 0 mg N g(-1)), low (LN, 0.04 mg N g(-1)), medium (MN, 0.16 mg N g(-1)), high (HN, 0.4 mg N g(-1)). The results showed that microbial respiration was higher in alpine shrub than in alpine meadow soil, regardless of the rate of N application. Total microbial respiration overthe course of incubation period decreased in both soils with HN and MN treatments relative to control, but no significant differences were observed in soils with LN treatments. There was significantly positive correlation between total microbial respiration and dissolved organic carbon concentration in both soils. The results indicated that DOC may be a useful indicator of microbial respiration rate in alpine soils and the increasing N inputs could drive a negative feedback to global warming effects of carbon dioxide emitted to the atmosphere in alpine soils. |
| [53] | |
| [54] | Many studies have investigated whether microbiota has been adapted to decompose a given litter type but we have limited information about the specific role of microarthropods in litter decaying processes. This experiment studied functional redundancy of microarthropods in a litter decomposition system by interchanging mesofauna among three different litter types. The study hypothesized that total microarthropod densities would be lower in foreign litter type than in original (‘home’) litter; and litter with foreign mesofauna would decompose slower than with native one. Scotch pine ( Pinus sylvestris ), Turkey oak ( Quercus cerris ) and black locust ( Robinia pseudoacacia ) litter were stored in microcosms with original microbiota. Microarthropods from the same (‘home’) or different (‘foreign’) type of litter were inoculated to microcosms. Litter mass loss and total density of collembolans, oribatid and other mites were recorded at the end of incubation (3 and 12 months). Litter quality determined total density of microarthropods irrespective of the origin of animals. Litter mass loss values differed in the three litter types. For pine litter, the origin of microarthropods had significant effects on litter mass loss. In oak litter, mainly microarthropod density influenced decomposition. Neither the origin nor the density of animals influenced the decomposition rate of black locust litter. Litter quality may have determined the different patterns of decaying. Mesofauna may enhance litter decomposition stronger in recalcitrant litter than in high-quality litter. |
| [55] | |
| [56] | Overgrazing increasingly affects large areas of Inner Mongolian semi-arid grasslands. Consequences for ecosystem functions and, in particular, for the decomposition as a key process of ecosystem carbon (C) and nitrogen (N) cycling are still unclear. We studied the effects of grazing on shoot and root decomposition with the litter bag method in a long-term grazing exclosure (UG79), a moderate winter grazed (WG) and a long-term heavily grazed site (HG). We separated the effects of local environmental factors and litter quality as altered by grazing. Growing seasons of average and very low precipitation allowed us to study the effect of inter annual rainfall variability on decomposition. Grazing-induced differences in environmental factors of the three studied grassland sites had no effect on decay rates of shoot and root dry mass. Also differences in litter quality among the grazing sites were not reflected by root decomposition dynamics. The accelerated shoot decay at site HG could not clearly be linked to litter quality parameters. Shoot decay rates were more or less constant, even under very dry conditions. This indicates the possibility of photodegradation (solar UV-B radiation) to control aboveground decomposition in this semi-arid ecosystem. By selecting the best predictors of root decomposition from regression analysis, we found that soil water content was the best parameter explaining the dynamics. Net N immobilization was generally not detected during the decay process of shoot and root. It is likely, when root decomposition is strongly reduced in dry periods, shoot decomposition becomes relatively more important for nutrient cycling. A separate analysis of shoot and root decay dynamics is required in order to describe C and N cycling in this semi-arid grassland. The grazing impact on C and N fluxes through decomposition of plant material likely exhibits a strong interaction with seasonal rainfall pattern. |
| [57] | Abstract The arid and semi-arid drylands of the world are increasingly recognized for their role in the terrestrial net carbon dioxide (CO 2 ) uptake, which depends largely on plant litter decomposition and the subsequent release of CO 2 back to the atmosphere. Observed decomposition rates in drylands are higher than predictions by biogeochemical models, which are traditionally based on microbial (biotic) degradation enabled by precipitation as the main mechanism of litter decomposition. Consequently, recent research in drylands has focused on abiotic mechanisms, mainly photochemical and thermal degradation, but they only partly explain litter decomposition under dry conditions, suggesting the operation of an additional mechanism. Here we show that in the absence of precipitation, absorption of dew and water vapor by litter in the field enables microbial degradation at night. By experimentally manipulating solar irradiance and nighttime air humidity, we estimated that most of the litter CO 2 efflux and decay occurring in the dry season was due to nighttime microbial degradation, with considerable additional contributions from photochemical and thermal degradation during the daytime. In a complementary study, at three sites across the Mediterranean Basin, litter CO 2 efflux was largely explained by litter moisture driving microbial degradation and ultraviolet radiation driving photodegradation. We further observed mutual enhancement of microbial activity and photodegradation at a daily scale. Identifying the interplay of decay mechanisms enhances our understanding of carbon turnover in drylands, which should improve the predictions of the long-term trend of global carbon sequestration. 脗漏 2016 John Wiley & Sons Ltd. |
| [58] | Fertilization experiments in plant communities are often interpreted in the context of a hump-shaped relationship between species richness and productivity. We analyze results of fertilization experiments from seven terrestrial plant communities representing a productivity gradient (arctic and alpine tundra, two old-field habitats, desert, short- and tall-grass prairie) to determine if the response of species richness to experimentally increased productivity is consistent with the hump-shaped curve. In this analysis, we compared ratios of the mean response in nitrogen-fertilized plots to the mean in control plots for aboveground net primary productivity (ANPP) and species density ( D ; number of species per plot of fixed unit area). In general, ANPP increased and plant species density decreased following nitrogen addition, although considerable variation characterized the magnitude of response. We also analyzed a subset of the data limited to the longest running studies at each site (鈮4 yr), and found that adding 9 to 13 g N m 鈭2 yr 鈭1 (the consistent amount used at all sites) increased ANPP in all communities by approximately 50% over control levels and reduced species density by approximately 30%. The magnitude of response of ANPP and species density to fertilization was independent of initial community productivity. There was as much variation in the magnitude of response among communities within sites as among sites, suggesting community-specific mechanisms of response. Based on these results, we argue that even long-term fertilization experiments are not good predictors of the relationship between species richness and productivity because they are relatively small-scale perturbations whereas the pattern of species richness over natural productivity gradients is influenced by long-term ecological and evolutionary processes. |
| [59] | With global changes such as increasing temperature and enhanced N deposition,soil nitrogen(N)availability is predicted to increase substantially,and how fine root dynamics responds to the altered soil N has become one of the key questions in terrestrial ecology.As such,a number of hypotheses have been proposed to explain the relationship between increasing soil N availability and fine root production,mortality,and turnover.This article considered four major hypotheses:with increasing soil N availability,1)both fine root production and turnover rate would increase,2)both fine root production and turnover rate would decrease,3)fine root production would decrease while fine root turnover rate would increase,and 4)fine root production would increase while fine root turnover rate would decrease.Current evidence suggests that the patterns depicted in hypothesis 1)and 2)could both occur in nature and may reflect characteristics of different species.Hypotheses 3)and 4)were thought to characterize only a transient stage of the responses of fine root dynamics to increasing N availability.To better understand the response of root dynamics to increasing soil N,future studies should consider:1)the definition of fine roots and heterogeneity in fine root structure and function;2)methods used in estimating fine root production and turnover rate;3)changes of soil N availability both in space and time.More attention should also be paid to the influences of mycorrhizal infection on root dynamic responses to soil N availability. |
| [60] | Climate and litter quality have been identified as major drivers of litter decomposition at large spatial scales. However, the role played by soil fauna remains largely unknown, despite its importance for litter fragmentation and microbial activity. We synthesised litterbag studies to quantify the effect sizes of soil fauna on litter decomposition rates at the global and biome scales, and to assess how climate, litter quality and soil fauna interact to determine such rates. Soil fauna consistently enhanced litter decomposition at both global and biome scales (average increment ~ 37%). [corrected]. However, climate and litter quality differently modulated the effects of soil fauna on decomposition rates between biomes, from climate-driven biomes to those where climate effects were mediated by changes in litter quality. Our results advocate for the inclusion of biome-specific soil fauna effects on litter decomposition as a mean to reduce the unexplained variation in large-scale decomposition models. |
| [61] | Summary 1 Nitrogen and phosphorus supply influences the rate of litter decomposition and nutrient dynamics during decomposition. Besides the total amount of N and P available to decomposers, their relative supply (N:P ratio) might be important, e.g. through an influence on the composition and activity of microbial communities. 2 We carried out two experiments using laboratory microcosms to test that (i) N:P ratios (in either litter or the environment) determine whether N or P limits the rate of decomposition, (ii) the ‘critical’ N:P ratio between N and P limitation depends on overall nutrient availability, (iii) litter colonization by fungi and bacteria depends on the N:P ratio, and (iv) N:P ratios determine if proportionately more N or P is retained or immobilized by the litter. 3 In one experiment, cellulose as a nutrient-free litter analogue was incubated on sand fertilized with varying N:P supply ratios, whereas in a second experiment, Carex leaf litter with varying N:P ratios was incubated on nutrient-free sand. 4 Results essentially support our hypotheses. Cellulose decomposition was N- or P-limited depending on the N:P supply ratio. The shift from N to P limitation occurred at N:P supply ratios of 1·7–45, depending on overall nutrient supply. Bacteria were most abundant on cellulose at low N:P supply ratios, when decomposition was N-limited, while fungi were relatively more important at high N:P ratios, when decomposition was P-limited. The amounts of mineral N and P immobilized on cellulose and those released from litter, both in absolute terms and relative to supply, depended on the type of nutrient limitation (N vs. P). 5 The N:P ratio of nutrients available to decomposers appears to be an important determinant of plant litter decomposition, the relative importance of fungi and bacteria in litter-associated microbial communities, and litter nutrient dynamics. |
| [62] | Interspecific variation in polyphenol production by plants has been interpreted in terms of defense against herbivores. Several recent lines of evidence suggest that polyphenols also influence the pools and fluxes of inorganic and organic soil nutrients. Such effects could have far-ranging consequences for nutrient competition among and between plants and microbes, and for ecosystem nutrient cycling and retention. The significance of polyphenols for nutrient cycling and plant productivity is still uncertain, but it could provide an alternative or complementary explanation for the variability in polyphenol production by plants. |
| [63] | |
| [64] | Herbivore-driven changes to soil properties can influence the decomposition rate of organic material and therefore soil carbon cycling within grassland ecosystems. We investigated how aboveground fora |
| [65] | |
| [66] | Understanding the response of the plant community to increasing nitrogen (N) deposition is helpful for improving pasture management in semi-arid areas. We implemented a 5-year N addition experiment in aStipa kryloviisteppe of Inner Mongolia, northern China. The aboveground biomass (AGB) and species richness were measured annually. Along with the N addition levels, the species richness declined significantly, and the species composition changed noticeably. However, the total AGB did not exhibit a noticeable increase. We found that compensatory effects of the AGB occurred not only between the grasses and the forbs but also among Gramineae species. The plant responses to N addition, from the community to species level, lessened in dry years compared to wet or normal years. The N addition intensified the reduction of community productivity in dry years. Our study indicated that the compensatory effects of the AGB among the species sustained the stability of grassland productivity. However, biodiversity loss resulting from increasing N deposition might lead the semi-arid grassland ecosystem to be unsustainable, especially in dry years. |
| [67] | Forest floor vegetation is an important component of forest biodiversity, and numerous studies have shown that N input alters the vegetation. In some cases, however, the effects of experimental N addition have been small or absent. Two alternative hypotheses have been suggested: (a) competition from the tree layer confounds the response to N, or (b) N response in areas with high background deposition is limited by N saturation. Neither of these hypotheses has so far been explicitly tested. Here, we compile data on forest floor vegetation from N addition experiments, in which the forest had been clear-cut, along an N deposition gradient ranging from 4 to 16 kg ha(-1) year(-1) in Sweden. We analyzed the effects of N addition and its interaction with N deposition on common species and thereby tested the second hypothesis in an environment without the confounding effects of the tree layer. The results show that the effects of the experimental N addition are significantly influenced by background N deposition: the N addition effects are smaller in areas with high N deposition than in areas with low N deposition, despite the fact that the highest N deposition in this study can be considered moderate from an international perspective. The results are important when assessing the reliability of results from N addition experiments on forest floor vegetation in areas with moderate to high background N deposition. We conclude that the interacting effects of N addition and N deposition need to be included when assessing long-term N sensitivity of plant communities. |
| [68] | Although global changes can alter ecosystem nutrient dynamics indirectly as a result of their effects on plant litter quality, the interactive effects of global changes on plant litter remain largely unexplored in natural communities. We investigated the effects of elevated CO2, N deposition, warming and increased precipitation on the composition of organic compounds in plant litter in a fully-factorial experiment conducted in a California annual grassland. While lignin increased within functional groups under elevated CO2, this effect was attenuated by warming in grasses and by water additions in forbs. CO2-induced increases in lignin within functional groups also were counteracted by an increase in the relative biomass of forbs, which contained less lignin than grasses. Consequently, there was no net change in the overall lignin content of senesced tissue at the plot level under elevated CO2. Nitrate additions increased N in both grass and forb litter, although this effect was attenuated by water additions. Relative to changes in N within functional groups, changes in functional group dominance had a minor effect on overall litter N at the plot level. Nitrate additions had the strongest effect on decomposition, increasing lignin losses from Avena litter and interacting with water additions to increase decomposition of litter of other grasses. Increases in lignin that resulted from elevated CO2 had no effect on decomposition but elevated CO2 increased N losses from Avena litter. Overall, the interactions among elements of global change were as important as single-factor effects in influencing plant litter chemistry. However, with the exception of variation in N, litter quality had little influence on decomposition over the short term. |
| [69] | Aims We explored how climate warming and increased atmospheric nitrogen (N) deposition may influence grass litter decomposition over time, how litter quality versus environmental effects contribute to these responses, and the importance of these responses over winter. Methods We used litter bags to examine decomposition over 2聽years in a warming and N addition field experiment, and examined the contributions of litter quality and environment to these responses by transferring litter reciprocally between the treatment plots and a common garden. Results Warming increased mass loss over the first year for Bromus inermis litter, which was consistent with the litter quality response, but by the second year there was no overall warming effect, and this change coincided with a negative environmental effect of warming. N addition increased mass loss and was more influential than warming in the early stages of Poa pratensis litter decomposition; the N effect appeared to be driven primarily by litter quality. Winter decomposition was not a substantial component of the treatment responses. Conclusions Our results indicate that litter quality and environmental effects play different roles at different time scales in the decomposition responses of grass litter to warming and N addition, and these responses can be species specific. |
| [70] | The fate of carbon (C) in organisms, food webs, and ecosystems is to a major extent regulated by mass-balance principles and the availability of other key nutrient elements. In relative terms, nutrient limitation implies excess C, yet the fate of this C may be quite different in autotrophs and heterotrophs. For autotrophs nutrient limitation means less fixation of inorganic C or excretion of organic C, while for heterotrophs nutrient limitation means that more of ingested C will "go to waste" in the form of egestion or respiration. There is in general a mismatch between autotrophs and decomposers that have flexible but generally high C:element ratios, and consumers that have lower C:element ratios and tighter stoichiometric regulation. Thus, C-use efficiency in food webs may be governed by the element ratios in autotroph biomass and tend to increase when C:element ratios in food approach those of consumers. This tendency has a strong bearing on the sequestration of C in ecosystems, since more C will be diverted to detritus entering soils or sediments when C-use efficiency is low due to stoichiometric imbalance. There will be a strong evolutionary pressure to utilize such excess C for structural and metabolic purposes. This article explores how these basic principles may regulate C sequestration on different scales in aquatic and terrestrial ecosystems. |
| [71] | Abstract The influence of inorganic nitrogen (N) inputs on decomposition is poorly understood. Some prior studies suggest that N may reduce the decomposition of substrates with high concentrations of lignin via inhibitory effects on the activity of lignin-degrading enzymes, although such inhibition has not always been demonstrated. I studied the effects of N addition on decomposition of seven substrates ranging in initial lignin concentrations (from 7.4% to 25.6%) over five years in eight different grassland and forest sites in central Minnesota, USA. I predicted that N would stimulate the decomposition of lignin-poor substrates but retard the decomposition of lignin-rich substrates. Across these sites, N had neutral or negative effects on decomposition rates. However, in contrast to my hypothesis, effects of N on decomposition were independent of substrate initial lignin concentrations, and decomposition of the lignin fraction was unaffected by N fertilization. Rather, substrate-site combinations that exhibited more rapid decomposition rates in the control treatment were affected more negatively by addition of N fertilization. Taken together, these results suggest that decreased decomposition with added N did not result from inhibition of lignin-degrading enzyme activity, but may have resulted from abiotic interactions between N fertilizer and products of microbial degradation or synthesis or from N effects on the decomposer community. Low initial substrate N concentrations and N fertilization both stimulated N immobilization, but the differences among substrates were generally much larger than the effects of fertilization. This study suggests that atmospheric N addition could stimulate ecosystem carbon sequestration in some ecosystems as a result of reduced rates of forest floor decomposition. |
| [72] | Despite the importance of litter decomposition for ecosystem fertility and carbon balance, key uncertainties remain about how this fundamental process is affected by nitrogen (N) availability. Resolving such uncertainties is critical for predicting the ecosystem consequences of increased anthropogenic N deposition. Toward that end, we decomposed green leaves and senesced litter of northern pin oak (Quercus ellipsoidalis) in three forested stands dominated by northern pin oak or white pine (Pinus strobus) to compare effects of substrate N (as it differed between leaves and litter) and externally supplied N (inorganic or organic forms) on decomposition and decomposer community structure and function over four years. Asymptotic decomposition models fit the data equally well as single exponential models and allowed us to compare effects of N on both the initial decomposition rate (k a ) and the level of asymptotic mass remaining (A, proportion of mass remaining at which decomposition approaches zero, i.e., the fraction of slowly decomposing litter). In all sites, both substrate N and externally supplied N (regardless of form) accelerated the initial decomposition rate. Faster initial decomposition rates corresponded to higher activity of polysaccharide-degrading enzymes associated with externally supplied N and greater relative abundances of Gram-negative and Gram-positive bacteria associated with green leaves and externally supplied organic N (assessed using phospholipid fatty acid analysis, PLFA). By contrast, later in decomposition, externally supplied N slowed decomposition, increasing the fraction of slowly decomposing litter (A) and reducing lignin-degrading enzyme activity and relative abundances of Gram-negative and Gram-positive bacteria. Higher-N green leaves, on the other hand, had lower levels of A (a smaller slow fraction) than lower-N litter. Contrasting effects of substrate and externally supplied N during later stages of decomposition likely occurred because higher-N leaves also had considerably lower lignin, causing them to decompose more quickly throughout decomposition. In conclusion, elevated atmospheric N deposition in forest ecosystems may have contrasting effects on the dynamics of different soil carbon pools, decreasing mean residence times of active fractions in fresh litter (which would be further reduced if deposition increased litter N concentrations), while increasing those of more slowly decomposing fractions, including more processed litter. |
| [73] | Abstract SUMMARY: *The flux of carbon from tree photosynthesis through roots to ectomycorrhizal (ECM) fungi and other soil organisms is assumed to vary with season and with edaphic factors such as nitrogen availability, but these effects have not been quantified directly in the field. *To address this deficiency, we conducted high temporal-resolution tracing of (13)C from canopy photosynthesis to different groups of soil organisms in a young boreal Pinus sylvestris forest. *There was a 500% higher below-ground allocation of plant C in the late (August) season compared with the early season (June). Labelled C was primarily found in fungal fatty acid biomarkers (and rarely in bacterial biomarkers), and in Collembola, but not in Acari and Enchytraeidae. The production of sporocarps of ECM fungi was totally dependent on allocation of recent photosynthate in the late season. There was no short-term (2 wk) effect of additions of N to the soil, but after 1 yr, there was a 60% reduction of below-ground C allocation to soil biota. *Thus, organisms in forest soils, and their roles in ecosystem functions, appear highly sensitive to plant physiological responses to two major aspects of global change: changes in seasonal weather patterns and N eutrophication. |
| [74] | . |
| [75] | |
| [76] | Abstract This study investigated changes in diversity of shrub-tree layer, leaf decomposition rates, nutrient release and soil NO fluxes of a Brazilian savanna (cerrado sensu stricto) under N, P and N plus P additions. Simultaneous addition of N and P affected density, dominance, richness and diversity patterns more significantly than addition of N or P separately. Leaf litter decomposition rates increased in P and NP plots but did not differ in N plots in comparison to control plots. N addition increased N mass loss, while the combined addition of N and P resulted in an immobilization of N in leaf litter. Soil NO emissions were also higher when N was applied without P. The results indicate that if the availability of P is not increased proportionally to the availability of N, the losses of N are intensified. Copyright 脗漏 2010 Elsevier Ltd. All rights reserved. |
| [77] | Litter decomposition is an important process of C and N cycling in the soil. Variation in the response of litter decomposition to nitrogen (N) addition (positive, negative or neutral) has been observed in many field studies. However, mechanism about variability in individual fungal species response to N addition has not yet been well demonstrated in the literature. Therefore, the objective of this study was to investigate the effects of N addition and litter chemistry properties on litter decomposition and enzyme activities of individual fungi. Three fungal species ( Penicillium , Aspergillus , and Trichoderma ) were isolated from a subtropical mixed forest soil. An incubation experiment was conducted using the individual fungi with two types of litter (leaf of Pinus massoniana and needle of Cryptocarya chinensis ) and different N addition levels (0, 50 and 100 for N-deficient treatments, and 500 and 1000聽渭g聽N for N-excessive treatments). Cumulative CO 2 -C, enzyme activities, and lignin and cellulose loss were measured during the incubation period of 60 days. Litter decomposition and enzyme activities significantly varied with the fungal species, while the N addition and litter types greatly affected fungal enzyme activities. The N treatments significantly increased lignin-rich needle decomposition by lignocellulose decomposers ( Penicillium and Aspergillus ) but did not affect their leaf decomposition. On the contrary, The N treatments stimulated leaf decomposition by cellulolytic species ( Trichoderma ) but did not affect its needle decomposition. Correlation analysis showed that lignin in the litter was the key component to affect litter decomposition. Activities of N-acetyl-尾-glucosaminidase and phenol oxidase were both positively correlated to litter decomposition. The fungi ( Penicillium and Aspergillus ) with higher production of N-acetyl-尾-glucosaminidase showed higher litter decomposition ability. The low N addition levels stimulated Penicillium and Aspergillus litter decomposition, but they still required more N source (e.g., litter N source) to support decomposition. Depressed fungal litter N uptake (lower N-acetyl-尾-glucosaminidase activities) only occurred at the highest N addition level. Litter decomposition of Trichoderma depended more on external N and its litter decomposition capability was the lowest among the three species. |
| [78] | |
| [79] | Litter decomposition is a biological process fundamental to element cycling and a main nutrient source within forest meta-ecosystems, but few studies have looked into this process simultaneously in individual ecosystems, where environmental factors can vary substantially. A two-year field study conducted in an alpine forest meta-ecosystem with four litter species (i.e., willow: Salix paraplesia , azalea: Rhododendron lapponicum , cypress: Sabina saltuaria , and larch: Larix mastersiana ) that varied widely in chemical traits showed that both litter species and ecosystem type (i.e., forest floor, stream and riparian zone) are important factors affecting litter decomposition, and their effects can be moderated by local-scale environmental factors such as temperature and nutrient availability. Litter decomposed fastest in the streams followed by the riparian zone and forest floor regardless of species. For a given litter species, both the k value and limit value varied significantly among ecosystems, indicating that the litter decomposition rate and extent (i.e., reaching a limit value) can be substantially affected by ecosystem type and the local-scale environmental factors. Apart from litter initial acid unhydrolyzable residue (AUR) concentration and its ratio to nitrogen concentration (i.e., AUR/N ratio), the initial nutrient concentrations of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) were also important litter traits that affected decomposition depending on the ecosystem type. |
| [80] | 61 Forest ecosystems exert an important influence on global biogeochemical cycles. A global dataset of nitrogen (N) and phosphorus (P) concentrations in leaf-litter of woody plants was compiled from th |
| [81] | Long-term nitrogen (N) addition experiments have found positive, negative, and neutral effects of added N on rates of decomposition. A leading explanation for this variation is differential effects of N on the activity of microbially produced extracellular enzymes involved in decomposition. Specifically, it is hypothesized that adding N to N-limited ecosystems increases activity of cellulose degrading enzymes and decreases that of lignin degrading enzymes, and that shifts in enzyme activity in response to added N explain the decomposition response to N fertilization. We measured litter and soil organic matter (SOM) decomposition and microbial enzyme activity in a long-term N fertilization experiment at eight forested and grassland sites in central Minnesota, USA, to determine (1) variation among sites in enzyme activity, (2) variation in the response of enzymes, litter decomposition, and soil respiration to added N, and (3) whether changes in enzyme activity in response to added N explained variability among sites in the effect of N on litter and SOM decomposition. Site differences in pH, moisture, soil carbon, and microbial biomass explained much of the among-site variation in enzyme activity. Added N generally stimulated activities of cellulose degrading and N- and phosphorus-acquiring enzymes in litter and soil, but had no effect on lignin degrading enzyme activity. In contrast, added N generally had negative or neutral effects on litter and SOM decomposition in the same sites, with no correspondence between effects of N on enzyme activity and decomposition across sites. |
| [82] | This study focuses on the processes occurring during incorporation of inorganic nitrogen into humic substances. Therefore rye grass, wheat straw, beech saw dust, sulphonated lignin and organosolve lignin were incubated together with highly 15 N-enriched ammonium sulphate in the laboratory for 600 days. Samples from the incubates were periodically analysed for weight loss, and carbon and nitrogen contents. The samples were also analysed by solid-state 13 C- and 15 N-CPMAS-NMR-spectroscopy to follow the turnover of the materials during incubation. Most of the detectable N-signals was assigned to amide - peptide structures. The remaining intensities could be ascribed to free and alkylated amino groups, and those on the low field side of the broad amide-peptide signal to indole, pyrrole and nucleotide derivatives. Abiotic reactions of ammonia with suitable precursors and the formation of pyridine, pyrazine or phenyloxazone derivatives were not observed. Signals from ammonia and nitrate occurred only at the end of the incubation. |
| [83] | We conducted a meta-analysis of previously published empirical studies that have examined the effects of nitrogen (N) enrichment on litter decomposition. Our objective was to provide a synthesis of existing data that comprehensively and quantitatively evaluates how environmental and experimental factors interact with N additions to influence litter mass loss. Nitrogen enrichment, when averaged across all studies, had no statistically significant effect on litter decay. However, we observed significant effects of fertilization rate, site-specific ambient N-deposition level, and litter quality. Litter decomposition was inhibited by N additions when fertilization rates were 2-20 times the anthropogenic Ndeposition level, when ambient N deposition was 5-10 kg N· ha-1· yr-1, or when litter quality was low (typically high-lignin litters). Decomposition was stimulated at field sites exposed to low ambient N deposition (<5 kg N· ha-1· yr-1) and for high-quality (low-lignin) litters. Fertilizer type, litterbag mesh size, and climate did not influence the litter decay response to N additions. |
| [84] | Increased available soil nitrogen can increase biomass, lower species richness, alter soil chemistry and modify community structure in herbaceous ecosystems worldwide. Although increased nitrogen availability typically increases aboveground production and decreases species richness in mesic systems, the impacts of nitrogen additions on semiarid ecosystems remain unclear. To determine how a semiarid grassland responds to increased nitrogen availability, we examined plant community structure and above- and belowground net primary production in response to long-term nitrogen addition in a desert grassland in central New Mexico, USA. Plots were fertilized annually (10聽g聽N聽m 鈭2 ) since 1995 and NPP measured from 2004 to 2009. Differences in aboveground NPP between fertilized and control treatments occurred in 2004 following a prescribed fire and in 2006 when precipitation was double the long-term average during the summer monsoon. Presumably, nitrogen only became limiting once drought stress was alleviated. Belowground NPP was also related to precipitation, and greatest root growth occurred the year following the wettest summer, decreasing gradually thereafter. Belowground production was unrelated to aboveground production within years and unrelated to nitrogen enrichment. Species richness changed between years in response to seasonal precipitation variability, but was not altered by nitrogen addition. Community structure did respond to nitrogen fertilization primarily through increased abundance of two dominant perennial grasses. These results were contrary to most nitrogen addition studies that find increased biomass and decreased species richness with nitrogen fertilization. Therefore, factors other than nitrogen deposition, such as fire or drought, may play a stronger role in shaping semiarid grassland communities than soil fertility. |
| [85] | Our meta-analysis of 126 nitrogen addition experiments evaluated nitrogen (N) limitation of net primary production (NPP) in terrestrial ecosystems. We tested the hypothesis that N limitation is widespread among biomes and influenced by geography and climate. We used the response ratio (R 鈮 ANPPN/ANPPctrl) of aboveground plant growth in fertilized to control plots and found that most ecosystems are nitrogen limited with an average 29% growth response to nitrogen (i.e., R = 1.29). The response ratio was significant within temperate forests (R = 1.19), tropical forests (R = 1.60), temperate grasslands (R = 1.53), tropical grasslands (R = 1.26), wetlands (R = 1.16), and tundra (R = 1.35), but not deserts. Eight tropical forest studies had been conducted on very young volcanic soils in Hawaii, and this subgroup was strongly N limited (R = 2.13), which resulted in a negative correlation between forest R and latitude. The degree of N limitation in the remainder of the tropical forest studies (R = 1.20) was comparable to that of temperate forests, and when the young Hawaiian subgroup was excluded, forest R did not vary with latitude. Grassland response increased with latitude, but was independent of temperature and precipitation. These results suggest that the global N and C cycles interact strongly and that geography can mediate ecosystem response to N within cerlain biome types. |
| [86] | |
| [87] | |
| [88] | |
| [89] | Abstract Increasing atmospheric reactive nitrogen (N) deposition due to human activities could change N cycling in terrestrial ecosystems. However, the differences between the fates of deposited NH 4 + and NO 3 - are still not fully understood. Here we investigated the fates of deposited NH 4 + and NO 3 - respectively via the application of 15 NH 4 NO 3 and NH 4 15 NO 3 in a temperate forest ecosystem. Results showed that at 410 days after tracer application, most 15 NH 4 + was immobilized in litter layer (50 卤 2%), while a considerable amount of 15 NO 3 - penetrated into 0-5 cm mineral soil (42 卤 2%), indicating that litter layer and 0-5 cm mineral soil were the major N sinks of NH 4 + and NO 3 - , respectively. Broad-leaved trees assimilated more 15 N under NH 4 15 NO 3 treatment compared to under 15 NH 4 NO 3 treatment, indicating their preference for NO 3 - -N. At 410 days after tracer application, 16 卤 4% added 15 N was found in aboveground biomass under 15 NO 3 - treatment, which was twice more than that under 15 NH 4 + treatment (6 卤 1%). At the same time, approximately 80% added 15 N was recovered in soil and plants under both treatments, which suggested that this forest had high potential for retention of deposited N. These results provided evidence that there were great differences between the fates of deposited NH 4 + and NO 3 - , which could help us better understand the mechanisms and capability of forest ecosystems as a sink of reactive nitrogen. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved. |
| [90] | Nitrogen availability is critically important to litter decomposition, especially in arid and semiarid areas where N is limiting. We studied the relative contributions of litter quality and soil N to litter decomposition of two dominant grassland species, Stipa krylovii and Artemisia frigida, in a semiarid typical steppe ecosystem in Inner Mongolia, China. The study had four different rates of N addition (0, 8, 32, and 64 g N m(-2) year(-1)), and litter samples were decomposed under varying site conditions and by litter types. Litter-mixing effects of the two species were also examined. We found that N addition increased litter N concentration and thus enhanced litter decomposition by improving substrate quality. This increase, however, was offset by the negative effect of increased soil N, resulting in a diminished effect of increased soil N availability on in situ litter decomposition. The positive effects of improved litter quality slightly out-performed the negative effects of increased soil N. Our further analysis revealed that the negative effect of increasing soil N on litter decomposition could be partially explained by reduced soil microbial biomass and activity. Decomposition was significantly faster for litters of a two-species mixture than litters of the single species, but the rate of litter decomposition did not differ much between the two species, suggesting that compositional balance, rather than changes in the dominance between Stipa and Artemisia, is more critical for litter decomposition, hence nutrient cycling in this ecosystem. This semiarid steppe ecosystem may become more conservative in nutrient use with switching of dominance from Artemisia to Stipa with increasing soil N, because Stipa has a slower decomposition rate and a higher nutrient retention rate than Artemisia. |
| [91] | |
| [92] | |
| [93] | . |
| [94] | Nitrogen (N) deposition is an important component in the global N cycle that has induced large impacts on the health and services of terrestrial and aquatic ecosystems worldwide. Anthropogenic reactive N (N r ) emissions to the atmosphere have increased dramatically in China due to rapid agricultural, industrial and urban development. Therefore increasing N deposition in China and its ecological impacts are of great concern since the 1980s. This paper synthesizes the data from various published papers to assess the status of the anthropogenic N r emissions and N deposition as well as their impacts on different ecosystems, including empirical critical loads for different ecosystems. Research challenges and policy implications on atmospheric N pollution and deposition are also discussed. China urgently needs to establish national networks for N deposition monitoring and cross-site N addition experiments in grasslands, forests and aquatic ecosystems. Critical loads and modeling tools will be further used in N r regulation. |
| [95] | Abstract China is experiencing intense air pollution caused in large part by anthropogenic emissions of reactive nitrogen. These emissions result in the deposition of atmospheric nitrogen (N) in terrestrial and aquatic ecosystems, with implications for human and ecosystem health, greenhouse gas balances and biological diversity. However, information on the magnitude and environmental impact of N deposition in China is limited. Here we use nationwide data sets on bulk N deposition, plant foliar N and crop N uptake (from long-term unfertilized soils) to evaluate N deposition dynamics and their effect on ecosystems across China between 1980 and 2010. We find that the average annual bulk deposition of N increased by approximately 8090009kilograms of nitrogen per hectare (P090009<0900090.001) between the 1980s (13.2090009kilograms of nitrogen per hectare) and the 2000s (21.1090009kilograms of nitrogen per hectare). Nitrogen deposition rates in the industrialized and agriculturally intensified regions of China are as high as the peak levels of deposition in northwestern Europe in the 1980s, before the introduction of mitigation measures. Nitrogen from ammonium (NH4(+)) is the dominant form of N in bulk deposition, but the rate of increase is largest for deposition of N from nitrate (NO3(-)), in agreement with decreased ratios of NH3 to NOx emissions since 1980. We also find that the impact of N deposition on Chinese ecosystems includes significantly increased plant foliar N concentrations in natural and semi-natural (that is, non-agricultural) ecosystems and increased crop N uptake from long-term-unfertilized croplands. China and other economies are facing a continuing challenge to reduce emissions of reactive nitrogen, N deposition and their negative effects on human health and the environment. |
| [96] | Nitrogen (N) deposition greatly influences ecosystem processes through the alteration of plant nutrition; however, there is limited understanding about the effects of phosphorus (P) inputs, especially |
| [97] | |
| [98] | The effects of global change factors on the stoichiometric composition of green and senesced plant tissues are critical determinants of ecosystem feedbacks to anthropogenic-driven global change. So far, little is known about species stoichiometric responses to these changes. We conducted a manipulative field experiment with nitrogen (N; 17.5 g m(-2) year(-1)) and water addition (180 mm per growing season) in a temperate steppe of northern China that is potentially highly vulnerable to global change. A unique and important outcome of our study is that water availability modulated plant nutritional and stoichiometric responses to increased N availability. N addition significantly reduced C:N ratios and increased N:P ratios but only under ambient water conditions. Under increased water supply, N addition had no effect on C:N ratios in green and senesced leaves and N:P ratios in senesced leaves, and significantly decreased C:P ratios in both green and senesced leaves and N:P ratios in green leaves. Stoichiometric ratios varied greatly among species. Our results suggest that N and water addition and species identity can affect stoichiometric ratios of both green and senesced tissues through direct and interactive means. Our findings highlight the importance of water availability in modulating stoichiometric responses of plants to potentially increased N availability in semi-arid grasslands. |
| [99] | Human activities have significantly altered nitrogen (N) availability in most terrestrial ecosystems, with consequences for community composition and ecosystem functioning. Although studies of how changes in N availability affect biodiversity and community composition are relatively common, much less remains known about the effects of N inputs on the coupled biogeochemical cycling of N and phosphorus (P), and still fewer data exist regarding how increased N inputs affect the internal cycling of these two elements in plants. Nutrient resorption is an important driver of plant nutrient economies and of the quality of litter plants produce. Accordingly, resorption patterns have marked ecological implications for plant population and community fitness, as well as for ecosystem nutrient cycling. In a semiarid grassland in northern China, we studied the effects of a wide range of N inputs on foliar nutrient resorption of two dominant grasses, Leymus chinensis and Stipa grandis. After 4years of treatments, N and P availability in soil and N and P concentrations in green and senesced grass leaves increased with increasing rates of N addition. Foliar N and P resorption significantly decreased along the N addition gradient, implying a resorption-mediated, positive plant-soil feedback induced by N inputs. Furthermore, N:P resorption ratios were negatively correlated with the rates of N addition, indicating the sensitivity of plant N and P stoichiometry to N inputs. Taken together, the results demonstrate that N additions accelerate ecosystem uptake and turnover of both N and P in the temperate steppe and that N and P cycles are coupled in dynamic ways. The convergence of N and P resorption in response to N inputs emphasizes the importance of nutrient resorption as a pathway by which plants and ecosystems adjust in the face of increasing N availability. |
| [100] | Synergistic effects on decomposition in litter mixtures have been suggested to be due to the transfer of nitrogen from N-rich to N-poor species. However, the dominant pathway and the underlying mechanisms remain to be elucidated. We conducted an experiment to investigate and quantify the control mechanisms for nitrogen transfer between two litter species of contrasting nitrogen status (15N labeled and unlabeled Fagus sylvatica and Fraxinus excelsior) in presence and absence of micro-arthropods. We found that 15N was predominantly transferred actively aboveground by saprotrophic fungi, rather than belowground or passively by leaching. However, litter decomposition remained unaffected by N-dynamics and was poorly affected by micro-arthropods, suggesting that synergistic effects in litter mixtures depend on complex environmental interrelationships. Remarkably, more 15N was transferred from N-poor beech than N-rich ash litter. Moreover, the low transfer of 15N from ash litter was insensitive to destination species whereas the transfer of 15N from labeled beech litter to unlabeled beech was significantly greater than the amount of 15N transferred to unlabeled ash suggesting that processes of nitrogen transfer fundamentally differ between litter species of different nitrogen status. Microbial analyses suggest that nitrogen of N-rich litter is entirely controlled by bacteria that hamper nitrogen capture of microbes in the environment supporting the source-theory. In contrast, nitrogen of N-poor fungal dominated litter is less protected and transferable depending on the nitrogen status and the transfer capacity of the microbial community of the co-occurring litter species supporting the gradient-theory. Thus, our results challenge the traditional view regarding the role of N-rich litter in decomposing litter mixtures. We rather suggest that N-rich litter is only a poor nitrogen source, whereas N-poor litter, can act as an important nitrogen source in litter mixtures. Consequently both absolute and relative differences in initial litter C/N ratios of co-occurring litter species need to be considered for understanding nitrogen dynamics in decomposing litter mixtures. |
| [101] | Anthropogenic activities have increased nitrogen (N) inputs to grassland ecosystems. Knowledge of the impact of soil N availability on soil respiration ( R S ) is critical to understand soil carbon balances and their responses to global climate change. A 2-year field experiment was conducted to evaluate the response of R S to soil mineral N in a temperate grassland in northern China. R S , abiotic and biotic factors, and N mineralization were measured in the grassland, at rates of N addition ranging from 0 to 2502g02N02m 61022 02yr 61021 . Annual and dormant-season R S ranged from 241.34 to 283.6402g C m 61022 and from 61.34 to 83.8402g C m 61022 respectively. High N application significantly increased R S , possibly due to increased root biomass and increased microbial biomass. High N treatment significantly increased soil NO 3 –N and inorganic N content compared with the control. The ratio of NO 3 –N to NH 4 –N and the N mineralization rate were significantly positively correlated with R S , but NH 4 –N was not correlated or negatively correlated with R S during the growing season. The temperature sensitivity of R S ( Q 10 ) was not significantly affected by N levels, and ranged from 1.90 to 2.20, but decreased marginally significantly at high N. R S outside the growing season is an important component of annual R S , accounting for 25.0 to 29.6% of the total. High N application indirectly stimulated R S by increasing soil NO 3 –N and net nitrification, thereby eliminating soil N limitations, promoting ecosystem productivity, and increasing soil CO 2 efflux. Our results show the importance of distinguishing between NO 3 –N and NH 4 –N, as their impact on soil CO 2 efflux differed. |
| [102] | The paper gives short characteristics of the main stages of forming the strategy of restoration of the industrially disturbed lands and their monitoring, along with the examples of its successful use. |
| [103] | Elevated nitrogen (N) deposition can affect litter decomposition directly, by raising soil N availability and the quantity and quality of litter inputs, and indirectly by altering plant community composition. We investigated the importance of these controls on litter decomposition using litter bags placed in annual herb based microcosm ecosystems that had been subject to two rates of N deposition (which raised soil inorganic N availability and stimulated litter inputs) and two planting regimes, namely the plant species compositions of low and high N deposition environments. In each microcosm, we harvested litter bags of 10 annual plant species, over an 8-week period, to determine mass loss from decomposition. Our data showed that species differed greatly in their decomposability, but that these differences were unlikely to affect decomposition at the ecosystem level because there was no correlation between a species鈥 decomposability and its response to N deposition (measured as population seed production under high N, relative to low N, deposition). Litter mass loss was 鈭2% greater in high N deposition microcosms. Using a comprehensive set of measurements of the microcosm soil environments, we found that the most statistically likely explanation for this effect was increased soil enzyme activity (cellobiosidase, 尾 -glucosidase and 尾 -xylosidase), which appears to have occurred in response to a combination of raised soil inorganic N availability and stimulated litter inputs. Our data indicate that direct effects of N deposition on litter input and soil N availability significantly affected decomposition but indirect effects did not. We argue that indirect effects of changes to plant species composition could be stronger in natural ecosystems, which often contain a greater diversity of plant functional types than those considered here. |
| [104] | The mineralization of nitrogen and phosphorus from plant residues provides an important input of inorganic nutrients to the soil, which can be taken up by plants. The dynamics of nutrient mineralization or immobilization during decomposition are controlled by different biological and physical factors. Decomposers sequester carbon and nutrients from organic substrates and exchange inorganic nutrients with the environment to maintain their stoichiometric balance. Additionally, physical losses of organic compounds from leaching and other processes may alter the nutrient content of litter. In this work, we extend a stoichiometric model of litter nitrogen mineralization to include (1) phosphorus mineralization, (2) physical losses of organic nutrients, and (3) chemical heterogeneity of litter substrates. The enhanced model provides analytical mineralization curves for nitrogen and phosphorus as well as critical litter carbon: nutrient ratios (the carbon: nutrient ratios below which net nutrient release occurs) as a function of the elemental composition of the decomposers, their carbon-use efficiency, and the rate of physical loss of organic compounds. The model is used to infer the critical litter carbon: nutrient ratios from observed nitrogen and phosphorus dynamics in about 2600 litterbag samplings from 21 decomposition data sets spanning artic to tropical ecosystems. At the beginning of decomposition, nitrogen and phosphorus tend to be immobilized in boreal and temperate climates (i.e., both C:N and C:P critical ratios are lower than the initial ratios), while in tropical areas nitrogen is generally released and phosphorus may be either immobilized or released, regardless of the typically low phosphorus concentrations. The critical carbon: nutrient ratios we observed were found to increase with initial litter carbon: nutrient ratios, indicating that decomposers adapt to low-nutrient conditions by reducing their carbon-use efficiency. This stoichiometric control on nutrient dynamics appears ubiquitous across climatic regions and ecosystems, although other biological and physical processes also play important roles in litter decomposition. In tropical humid conditions, we found high critical C:P ratios likely due to high leaching and low decomposer phosphorus concentrations. In general, the compound effects of stoichiometric constraints and physical losses explain most of the variability in critical carbon: nutrient ratios and dynamics of nutrient immobilization and release at the global scale. |
| [105] | |
| [106] | Despite the central role of microorganisms in the decomposition of dead organic matter, few models have integrated the dynamics of litter chemistry with microbial interactions. Here we propose a functional resolution of the microbial community that parallels the commonly used chemical characterization of plant litter, i.e., a guild of opportunist microorganisms that grows quickly and has high affinity for soluble substrates, a guild of decomposer specialists that grows more slowly and has high affinity for holocellulose substrates, and a guild of miners that grows very slowly and is specialized for degrading lignin. This guild-based decomposition model (GDM) includes the interactions of holocellulose and lignin, manifest as mutual feedback controls on microbial-based activities. It also includes N limitations on early stages of litter decay resulting from nutritional demands of microorganisms and N inhibition on late stages of litter decay resulting from reduced lignin degradation. Competitive interactions between microbial guilds result from different growth rates and substrate affinities, given limits on microbial colonization of litter. Simulations are consistent with commonly reported and proposed patterns of microbial community succession during litter decay, changes in and controls imposed by litter chemistry, and system responses to N availability. Modest impacts of litter chemistry and N effects on patterns of decay can yield substantial impacts on the relative amount of litter remaining through time, the time required to stabilize litter carbon (i.e., as the lignin content approaches similar to 70% of the total litter carbon), the relative contributions of different guilds to decay, and the net amount of microbial production. Moreover, seemingly inconsistent patterns in system responses to N regimes can be explained by interactions between litter chemistry and microbial guilds. A validation exercise demonstrated general correspondence of model behavior to f |
| [107] | Microbial processes driving nitrogen (N) cycling are hot topics in terms of increasing N deposition. Abundances of N-related functional genes (NFG) can be most responsive to N deposition and commonly |
| [108] | Understanding temporal niche separation between C sub(3) and C sub(4) species (e.g. C sub(3) species flourishing in a cool spring and autumn while C sub(4) species being more active in a hot summer) is essential for exploring the mechanism for their co-existence. Two parallel pot experiments were conducted, with one focusing on water and the other on nitrogen (N), to examine growth responses to water or nitrogen (N) seasonality and competition of two co-existing species Leymus chinensis (C sub(3) grass) and Chloris virgata (C sub(4) grass) in a grassland. The two species were planted in either monoculture (two individuals of one species per pot) or a mixture (two individuals including one L. chinensis and one C. virgata per pot) under three different water or N seasonality regimes, i.e. the average model (AM) with water or N evenly distributed over the growing season, the one-peak model (OPM) with more water or N in the summer than in the spring and autumn, and the two-peak model (TPM) with more water or N in the spring and autumn than in the summer. Seasonal water regimes significantly affected biomass in L. chinensis but not in C. virgata, while N seasonality impacted biomass and relative growth rate of both species over the growing season. L. chinensis accumulated more biomass under the AM and TPM than OPM water or N treatments. Final biomass of C. virgata was less impacted by water and N seasonality than that of L. chinensis. Interspecific competition significantly decreased final biomass in L. chinensis but not in C. virgata, suggesting an asymmetric competition between the two species. The magnitude of interspecific competition varied with water and N seasonality. Changes in productivity and competition balance of L. chinensis and C. virgata under shifting seasonal water and N availabilities suggest a contribution of seasonal variability in precipitation and N to the temporal niche separation between C sub(3) and C sub(4) species. |
| [109] | The application of straw and biochar to soil has received great attention because of their potential benefits such as fertility improvement and carbon (C) sequestration. The abiotic effects of these materials on C and nitrogen (N) cycling in the soil ecosystem have been previously investigated, however, the effects of straw or its derived biochar on the soil microbial community structure and function are not well understood. For this purpose, a short-term incubation experiment was conducted using 13 C-labeled rice straw and its derived biochar ( 13 C-labeled biochar) to deepen our understanding about soil microbial community dynamics and function in C sequestration and greenhouse gas emission in the acidic paddy soil amended with these materials. Regarding microbial function, biochar and straw applications increased CO 2 emission in the initial stage of incubation and reached the highest level (0.52 and 3.9602mg02C02kg 61021 02soil02h 61021 ) at 102d and 302d after incubation, respectively. Straw amendment significantly ( p 02<020.01) increased respiration rate, total phospholipid fatty acids (PLFAs) and 13 C-PLFA as compared to biochar amendment and the control. The amount and percent of Gram positive bacteria, fungi and actinomycetes were also significantly ( p 02<020.05) higher in 13 C-labeled straw amended soil than the 13 C-labeled biochar amended soil. According to the 13 C data, 23 different PLFAs were derived from straw amended paddy soil, while only 17 PLFAs were derived from biochar amendments. The profile of 13 C-PLFAs derived from straw amendment was significantly ( p 02<020.01) different from biochar amendment. The PLFAs0218:1ω7c and cy17:0 (indicators of Gram negative bacteria) showed high relative abundances in the biochar amendment, while 10Me18:0, i17:0 and 18:2ω6,9c (indicators of actinomycetes, Gram positive bacteria and fungi, respectively) showed high relative abundance in the straw amendments. Our results suggest that the function, size and structure of the microbial community were strongly influenced by the substrate composition and availability. |
| [110] | Leymus chinensis, a rhizomatous graminoid, is a dominant species in the grasslands of northern China. The characteristics of L. chinensis populations have been well documented in many research papers. Because of overgrazing, grasslands of northern China have become degraded since the 1980s. As a result, the density and biomass of L. chinensis populations have decreased significantly. Fertilization is a common technique for management of pastures in many countries; however, it is not widely used in the grasslands of China. Nitrogen is an important driver of community succession in grassland ecosystems, but the response of L. chinensis populations to nitrogen additions in typical steppe, a semiarid area of northern China, remains unclear. We conducted a sequential nitrogen addition experiment in a lightly degraded grassland plot that was fenced in 1999. Nitrogen (NH 4NO 3) was applied on July 5 for two years at application rates of: 0, 1.75, 5.25, 10.5, 17.5, and 28 g N路m -2 ,respectively. There were 9 replicate 5 m脳5 m plots of each of the six treatments with each plot spaced 1 m apart. A completely randomized design was used for this experiment. Before the experiment, soil samples were collected and dry bulk density, pH, soil nitrogen and soil carbon were analyzed. After two years of nitrogen fertilization, we measured the density, height, aboveground biomass and belowground biomass of L. chinensis in each plot. The results showed that L. chinensis population characteristics were highly responsive to nitrogen additions. With an increase in nitrogen application rates, the density, height, aboveground biomass, belowground biomass and total biomass of L. chinensis increased significantly whereas the ratio of aboveground biomass/belowground biomass decreased. The allocation of biomass among plant parts was significantly affected by nitrogen additions: the proportion of biomass allocated to rhizomes decreased remarkably with increasing nitrogen rates whereas that allocated to leaves and roots increased significantly. The relative biomass and relative density of L. chinensis also increased with increasing nitrogen additions. In summary, adding nitrogen to lightly degraded grassland not only increased the density and biomass of L. chinensis population but changed the resource partitioning among plant parts as well. |
| [111] | |
| [112] | |
| [113] | Key recent developments in litter decomposition research are reviewed. Long-term inter-site experiments indicate that temperature and moisture influence early rates of litter decomposition primarily by determining the plants present, suggesting that climate change effects will be small unless they alter the plant forms present. Thresholds may exist at which single factors control decay rate. Litter decomposes faster where the litter type naturally occurs. Elevated CO 2 concentrations have little effect on litter decomposition rates. Plant tissues are not decay-resistant; it is microbial and biochemical transformations of materials into novel recalcitrant compounds rather than selective preservation of recalcitrant compounds that creates stable organic matter. Altering single characteristics of litter will not substantially alter decomposition rates. Nitrogen addition frequently leads to greater stabilization into humus through a combination of chemical reactions and enzyme inhibition. To sequester more C in soil, we need to consider not how to slow decomposition, but rather how to divert more litter into humus through microbial and chemical reactions rather than allowing it to decompose. The optimal strategy is to have litter transformed into humic substances and then chemically or physically protected in mineral soil. Adding N through fertilization and N-fixing plants is a feasible means of stimulating humification. |
| [114] | ( 2009~2010年,选择内蒙古温带典型草原区2个不同退化程度羊草群落为研究对象,利用小区模拟控制试验,设置0g·(m2·a)-1(CK)、10 g·(m2·a)-1(MN)这2个氮处理水平,模拟研究了大气氮沉降水平变化对植物净初级生产力(NPP),土壤呼吸(Rs)以及整个群落碳收支(NEE)的定量影响,比较了不同退化程度草地群落NEE对等量氮添加的响应差异.结果表明,对于轻度退化羊草草原(样地A),MN处理生长季平均地上生物量(AGB)两年分别比CK增加21.5%及46.8%,而对于中度退化羊草草原(样地B),氮添加在2009年降低了植物AGB及地上NPP(ANPP),在2010年则表现为正效应;两年氮添加均增加了样地A与样地B的根系生物量(BGB)以及样地B的地下NPP(BNPP),但降低了2010年样地A的BNPP;氮输入增加并未明显改变Rs的时间变化规律.与CK处理相比,样地A的MN处理两年土壤微生物呼吸年累积通量较CK分别增加了14.6%与25.7%,而样地B则分别降低了10.4%与11.3%;样地A与样地B两年均表现为大气的碳汇,碳汇强度(以碳计)分别为59.22 g·(m2·a)-1与166.68 g·(m2·a)-1以及83.27 g·(m2·a)-1与117.47 g·(m2·a)-1.相对于CK,样地A两年碳汇增加量分别为15.79 g·(m2·a)-1与82.94 g·(m2·a)-1,样地B分别为74.54 g·(m2·a)-1与101.23 g·(m2·a)-1,单位氮输入量在初始氮水平低的草地群落能获得更大的增汇效应. |
| [115] | Areas of the northern Everglades of Florida, USA, have been influenced by P eutrophication. The objective was to determine if P enrichment of water influences the litter decomposition rate and nutrient immobilization by litter and to determine the quantitative relationship of these responses across a range of P concentrations in surface water. In addition, it was determined whether P additions ... |
| [116] | We investigated the hypothesis that hemiparasites accelerate nutrient cycling in nutrient-poor communities. Hemiparasites concentrate nutrients in their leaves, thus potentially producing high quality litter that releases nutrients that would otherwise remain in host tissues or in slowly decomposing plant litter. This hypothesis was tested using species from a European sub-arctic community where root hemiparasites are abundant. The N content of green leaves, and the N, P and C content of leaf litter were measured in seven species of root hemiparasitic Scrophulariaceae, and nine species of commonly co-occurring dwarf shrubs, graminoids and herbs. Fresh leaves of the hemiparasites had greater N concentrations than leaves of dwarf shrubs, graminoids or herbs. This difference was even more marked in litter, with hemiparasite litter containing 1.8鈥4.1% N, between 1.8 and 8.5聽times as much N as in the litter of commonly co-occurring species. Litter of the hemiparasitic plant Bartsia alpina and of three commonly co-occurring dominant species of dwarf shrub was decomposed alone and in two species mixtures, in a laboratory microcosm experiment. Bartsia litter decomposed faster and lost between 5.4 and 10.8聽times more N than that of the dwarf shrubs over the 240聽days of the experiment. Mixtures of dwarf shrub and hemiparasite litter showed significantly more mass loss and CO 2 release than expected, while nutrient release was the same as or less than expected. It is concluded that hemiparasites have the potential to enhance decomposition and nutrient cycling in nutrient-poor environments. |
| [117] | |
| [118] | [Aims] Theories based on resource additions indicate that plant species richness is mainly determined by the number of limiting resources. However, the individual effects of various limiting resources on species richness and aboveground net primary productivity (ANPP) are less well understood. Here, we analyzed potential linkages between additions of limiting resources, species loss and ANPP increase and further explored the underlying mechanisms. [Methods] Resources (N, P, K and water) were added in a completely randomized block design to alpine meadow plots in the Qinghai-Tibetan Plateau.... |
| [119] | |
| [120] | Soils collected across a long-term liming experiment (pH 4.0-8.3), in which variation in factors other than pH have been minimized, were used to investigate the direct influence of pH on the abundance and composition of the two major soil microbial taxa, fungi and bacteria. We hypothesized that bacterial communities would be more strongly influenced by pH than fungal communities. To determine the relative abundance of bacteria and fungi, we used quantitative PCR (qPCR), and to analyze the composition and diversity of the bacterial and fungal communities, we used a bar-coded pyrosequencing technique. Both the relative abundance and diversity of bacteria were positively related to pH, the latter nearly doubling between pH 4 and 8. In contrast, the relative abundance of fungi was unaffected by pH and fungal diversity was only weakly related with pH. The composition of the bacterial communities was closely defined by soil pH; there was as much variability in bacterial community composition across the 180-m distance of this liming experiment as across soils collected from a wide range of biomes in North and South America, emphasizing the dominance of pH in structuring bacterial communities. The apparent direct influence of pH on bacterial community composition is probably due to the narrow pH ranges for optimal growth of bacteria. Fungal community composition was less strongly affected by pH, which is consistent with pure culture studies, demonstrating that fungi generally exhibit wider pH ranges for optimal growth. |
| [121] | Abstract The effects of nitrogen (N) fertilization (0–15002kg02N02ha61102year611 since 1865) and pH (3.3–7.4) on fungal and bacterial growth, biomass and phospholipid fatty acid (PLFA) composition were investigated in grassland soils from the ‘Park Grass Experiment’, Rothamsted Research, UK. Bacterial growth decreased and fungal growth increased with lower pH, resulting in a 50-fold increase in the relative importance of fungi between pH 7.4 and 3.3. The PLFA-based fungal02:02bacterial biomass ratio was unchanged between pH 4.5 and 7.4, and decreased only below pH 4.5. Respiration and substrate-induced respiration biomass both decreased three- to fourfold with lower pH, but biomass concentrations estimated using PLFAs were unaffected by pH. N fertilization did not affect bacterial growth and marginally affected fungal growth while PLFA biomass marker concentrations were all reduced by higher N additions. Respiration decreased with higher N application, suggesting a reduced quality of the soil organic carbon. The PLFA composition was strongly affected by both pH and N. A comparison with a pH gradient in arable soil allowed us to generalize the pH effect between systems. There are 30–50-fold increases in the relative importance of fungi between high (7.4–8.3) and low (3.3–4.5) pH with concomitant reductions of respiration by 30–70%. |
| [122] | Variability of above-ground net primary production (ANPP) of arid to sub-humid ecosystems displays a closer association with precipitation when considered across space (based on multiyear averages for different locations) than through time (based on year-to-year change at single locations). Here, we propose a theory of controls of ANPP based on four hypotheses about legacies of wet and dry years that explains space versus time differences in ANPP-precipitation relationships. We tested the hypotheses using 16 long-term series of ANPP. We found that legacies revealed by the association of current- versus previous-year conditions through the temporal series occur across all ecosystem types from deserts to mesic grasslands. Therefore, previous-year precipitation and ANPP control a significant fraction of current-year production. We developed unified models for the controls of ANPP through space and time. The relative importance of current-versus previous-year precipitation changes along a gradient of mean annual precipitation with the importance of current-year PPT decreasing, whereas the importance of previous-year PPT remains constant as mean annual precipitation increases. Finally, our results suggest that ANPP will respond to climate-change-driven alterations in water availability and, more importantly, that the magnitude of the response will increase with time. |
| [123] | The comparative decomposition of tropical leaf litters (e.g. Andropogon gayanus , Casuarina equisetifolia , Faidherbia albida ) of different qualities was investigated under laboratory conditions during a 60-day incubation period conducted with a typical oxisol. Total CO 2 -C, soil inorganic N, microbial biomass (fumigation-extraction), 尾-glucosidase and dehydrogenase activities were determined over the incubation to assess how they responded to the addition of inorganic N (+N). Cumulative CO 2 -C evolved from the litter-amended soils was higher than that recorded for the unamended control soil. For the unfertilized treatment (0聽N), correlation coefficients calculated between initial chemical data and CO 2 flux during the first day of incubation were r =0.963 for water soluble-C and 0.869 for soluble carbohydrates ( P <0.05). At the end of the incubation, the amounts of CO 2 -C in the F. albida - and A. gayanus -amended soils were higher than that in the C. equisetifolia -amended treatment. Cumulative net N immobilization increased during the first 30聽days of incubation, the amounts being similar for A. gayanus - and C. equisetifolia -amended soil and higher than that recorded in the F. albida -amended treatment. Soil microbial biomass and enzyme activities increased in the litter-amended soils during the first 15聽days of incubation and decreased (except for the dehydrogenase activity) thereafter. The addition of inorganic N modified the patterns of CO 2 -C respiration and net N immobilization. The magnitude of these modifications varied according to the litter quality. The use of an accurate indicator based on several litter components to predict the amplitude of organic material decomposition is discussed. |
| [124] | Abstract Plant pathogens can have cascading consequences on insect herbivores, though whether they alter competition among resource-sharing insect herbivores is unknown. We experimentally tested whether the infection of a plant pathogen, the parasitic plant dwarf mistletoe (Arceuthobium americanum), on jack pine (Pinus banksiana) altered the competitive interactions among two groups of beetles sharing the same resources: wood-boring beetles (Coleoptera: Cerambycidae) and the invasive mountain pine beetle (Dendroctonus ponderosae) (Coleoptera: Curculionidae). We were particularly interested in identifying potential mechanisms governing the direction of interactions (from competition to facilitation) between the two beetle groups. At the lowest and highest disease severity, wood-boring beetles increased their consumption rate relative to feeding levels at moderate severity. The performance (brood production and feeding) of mountain pine beetle was negatively associated with wood-boring beetle feeding and disease severity when they were reared separately. However, when both wood-boring beetles and high severity of plant pathogen infection occurred together, mountain pine beetle escaped from competition and improved its performance (increased brood production and feeding). Species-specific responses to changes in tree defense compounds and quality of resources (available phloem) were likely mechanisms driving this change of interactions between the two beetle groups. This is the first study demonstrating that a parasitic plant can be an important force in mediating competition among resource-sharing subcortical insect herbivores. |
| [125] | Anthropogenic nitrogen deposition and projected increases in rainfall variability (the frequency of drought and heavy rainfall events) are expected to strongly influence ecosystem processes such as litter decomposition. However, how these two global change factors interact to influence litter decomposition is largely unknown. I examined how increased rainfall variability and nitrogen addition affected mass and nitrogen loss of litter from two tallgrass prairie species, Schizachyrium scoparium and Solidago canadensis, and isolated the effects of each during plant growth and during litter decomposition. I increased rainfall variability by consolidating ambient rainfall into larger events and simulated chronic nitrogen deposition using a slow-release urea fertilizer. S. scoparium litter decay was more strongly regulated by the treatments applied during plant growth than by those applied during decomposition. During plant growth, increased rainfall variability resulted in S. scoparium litter that subsequently decomposed more slowly and immobilized more nitrogen than litter grown under ambient conditions, whereas nitrogen addition during plant growth accelerated subsequent mass loss of S. scoparium litter. In contrast, S. canadensis litter mass and N losses were enhanced under either N addition or increased rainfall variability both during plant growth and during decomposition. These results suggest that ongoing changes in rainfall variability and nitrogen availability are accelerating nutrient cycling in tallgrass prairies through their combined effects on litter quality, environmental conditions, and plant community composition. |
| [126] | . . 全球变化背景下，土壤固碳能力增强有利于减少大气中CO2含量，对缓解全球变暖具有积极意义。近几十年来，氮沉降日益增加，我国已成为继欧美之后的第三大氮沉降区，持续增加的氮沉降使大气向土壤的氮输入显著增加，而过量的氮输入对土壤碳储量的改变可能对全球变暖、草原植被生长及其凋落物分解等产生一定影响，此外，过量的氮输入还可能造成土壤酸化、植物对天然胁迫的抵御能力和生产力下降、生物多样性降低等不利影响。目前，氮沉降对森林和农田生态系统的影响已有较为广泛而深入的研究，而对草原生态系统的氮沉降响应研究还不够全面。内蒙古草原是欧亚大陆草原的重要组成部分，具有欧亚大陆草原众多草原类型的典型特征和天然草原生态系统的自然特征，对持续增加的氮沉降更为敏感。而土壤酶是有机物分解和养分循环过程中具有专一性的高效催化剂，其活性能够表征土壤中微生物活性、有机物分解速率以及微生物和植物吸收养分的有效性，对于揭示微生物功能和生态系统碳、氮、磷循环过程的相互关系具有重要作用。 本论文以内蒙古温带典型草原为研究对象，进行连续6年氮添加试验，研究6个氮添加水平：对照N0（0kg N ha-1.yr-1）、N56（56kg N ha-1.yr-1）、N112（112kg N ha-1.yr-1）、N224（224kg N ha-1.yr-1）、N392（392kg N ha-1.yr-1）、N560（560kg N ha-1.yr-1）对全土和微团聚体中β-1,4-葡萄糖苷酶（βG）、β-1,4-N-乙酰葡糖胺糖苷酶（NAG）、L-亮氨酸氨基肽酶（LAP）、酸性磷酸酶（AP）活性的变化规律，结果表明： 1、随氮添加增加，全土中的βG、NAG、LAP活性呈下降趋势，均以N560水平（560kg N ha-1.yr-1）的活性最低，而各氮添加水平的AP活性无显著变化； 2、随氮添加增加，全土的pH值显著降低，铵态氮含量显著升高，pH与βG、NAG、LAP活性正相关而与AP活性负相关，铵态氮与AP活性正相关而与βG、NAG、LAP活性负相关； 3、随氮添加增加，全土中有机碳含量呈上升趋势，其中氮添加量大于112kg N ha-1.yr-1时的有机碳含量显著高于对照，即适量氮沉降能够增加全土中有机碳含量； 4、随氮添加增加，土壤微团聚体中的βG、NAG、AP活性均无显著变化，而只有LAP活性在氮添加量为392kg N ha-1.yr-1时显著降低； 5、随氮添加增加，土壤微团聚体pH值显著降低，铵态氮含量显著升高，且pH与βG、NAG、LAP、AP活性正相关，而铵态氮与βG、NAG、AP活性正相关，与LAP活性负相关； 6、随氮添加增加，土壤微团聚体中有机碳含量呈下降趋势，氮添加量大于56kg N ha-1.yr-1时的处理，有机碳含量显著低于对照，表明氮沉降具有导致土壤微团聚体中稳定有机碳减少的作用，过量的氮输入对土壤碳储存不利。 |
| [127] | Root decomposition represents a significant C flux in terrestrial ecosystems. Roots are exposed to a different decomposition environment than aboveground tissues, and few general principles exist regarding the factors controlling rates of root decay. We use a global dataset to explore the relative importance of climate, environmental variables, and litter quality in regulating rates of root decomposition. The parameters that explained the largest amount of variability in root decay were root Ca concentrations and C:N ratios, with a smaller proportion explained by latitude, mean annual temperature, mean annual precipitation, and actual evapotranspiration (AET). Root chemistry and decay rates varied by plant life form (conifer, broadleaf, or graminoid). Conifer roots had the lowest levels of Ca and N, the highest C:N and lignin:N ratios, and decomposed at the slowest rates. In a stepwise multiple linear regression, AET, root Ca, and C:N ratio accounted for approximately 90% of the variability in root decay rates. Root chemistry appeared to be the primary controller of root decomposition, while climate and environmental factors played secondary roles, in contrast to previously established leaf litter decomposition models. |
| [128] | Root litter is the dominant soil carbon and nutrient input in many ecosystems, yet few studies have considered how root decomposition is regulated at the landscape scale and how this is mediated by land-use management practices. Large herbivores can potentially influence below-ground decomposition through changes in soil microclimate (temperature and moisture) and changes in plant species composition (root traits). To investigate such herbivore-induced changes, we quantified annual root decomposition of upland grassland species in situ across a landscape-scale livestock grazing experiment, in a common-garden experiment and in laboratory microcosms evaluating the influence of key root traits on decomposition. Livestock grazing increased soil temperatures, but this did not affect root decomposition. Grazing had no effect on soil moisture, but wetter soils retarded root decomposition. Species-specific decomposition rates were similar across all grazing treatments, and species differences were maintained in the common-garden experiment, suggesting an overriding importance of litter type. Supporting this, in microcosms, roots with lower specific root area (m(2) g(-1)) or those with higher phosphorus concentrations decomposed faster. Our results suggest that large herbivores alter below-ground carbon and nitrogen dynamics more through their effects on plant species composition and associated root traits than through effects on the soil microclimate. |
| [129] | The main factors controlling decomposition rate are climate, litter quality and soil organisms. We investigated how decomposition was affected by interactions between litter quality and the composition of the soil community. To do this, we designed an experiment using the litterbag technique and three grass species for which a gradient of four distinct litter qualities (defined as initial nitrogen content) had been generated. We manipulated the soil community composition using different mesh sizes to constrain access of specific soil fauna to the litter on the basis of body size. Litter of a single species and quality was placed into litterbags of each of four different mesh sizes (0.1, 2, 2.8 and 4.7聽mm) and bags were retrieved from the field after 30 and 60 days. Whether litter quality was a significant determinant of litter decomposition rate was dependent on both the soil community composition and length of field exposure. After 30 days there was a significant positive relationship between litter quality and decomposition for the most complex community (coarsest mesh size). The strength of this relationship declined with decreasing mesh size and, for the most restricted community (smallest mesh size), no quality鈥揹ecomposition relationship was apparent. In contrast, after 60 days, decomposition was most strongly related to litter quality in the smallest mesh size bags and the relationship between quality and decomposition in the two coarsest mesh bags was non-significant. The pattern of these interactive effects between litter quality, soil community composition and time was consistent across the three grass species. We hypothesize that the effect of litter quality on mass loss within a specific mesh size was dependent on time because, while soil organisms of all size-classes responded positively to increased litter quality, they did so at a rate dependent upon their mobility. |
| [130] | Fine root decomposition contributes significantly to element cycling in terrestrial ecosystems. However, studies on root decomposition rates and on the factors that potentially influence them are fewe |
| [131] | 凋落物分解作为生态系统核心过程,参与生态系统碳的周转与循环,影响生态系统碳的收支平衡,调控生态系统对全球气候变暖的反馈结果。全球气候变暖通过环境因素、凋落物数量和质量以及分解者3个方面,直接或间接地作用于凋落物分解过程,并进一步影响土壤养分周转和碳库动态。气候变暖可通过升高温度和改变实际蒸散量等环境因素直接作用于凋落物分解。气候变暖可引起植物物种短期内碳、氮和木质素等化学性质的改变以及群落中物种组成的长期变化从而改变凋落物质量。在凋落物分解过程中,土壤分解者亚系统作为主要生命组分(土壤动物和微生物)彼此相互作用、相互协调共同参与调节凋落物的分解过程。凋落物分解可以通过改变土壤微生物量、微生物活动和群落结构来加快微生物养分的固定或矿化,以形成新的养分利用模式来改变土壤有机质从而对气候变化做出响应。未来凋落物分解的研究方向应基于大尺度跨区域分解实验和长期实验,关注多个因子交互影响下,分解过程中碳、氮养分释放、地上/地下凋落物分解生物学过程与联系、分解者亚系统营养级联效应等方面。 |
| [132] | The combined effects of nitrogen (N) deposition and management practices on fine root decomposition remain unknown. The objective of this study was to investigate the effects of the two factors on fin |
| [133] | Large areas of Great Britain currently receive nitrogen (N) deposition at rates which exceed the thresholds above which there is risk of damage to sensitive components of the ecosystem (critical loads for nutrient nitrogen and critical levels for ammonia), and are predicted to continue to do so. Excess N can damage semi-natural ecosystems. Lichens are potentially sensitive to air quality because they directly utilise nutrients deposited from the atmosphere thus may be good indicators of air quality. We used data from the British Lichen Society (BLS) database, which records the presence of all lichen taxa growing in Britain at 10km resolution. The probability of presence of a taxa at a given level of N deposition was analysed together with driver data for climate, change in sulphur deposition, land-use and N deposition using generalised additive models (GAMs). Many taxa showed negative responses to N deposition with reductions in the probability of presence as N deposition increased. In all of the habitats, there were a mix of terricolous taxa which showed negative or no significant relationship with N deposition. Most of the taxa with negative relationships with N deposition started to decline in prevalence at the lowest levels of deposition found in this study. Levels of deposition over which a negative response apparently occurs are lower than those at which critical loads have been set for some habitats. These findings suggest that some terricolous lichen taxa are sensitive to atmospheric N deposition and even low levels of nitrogen deposition could be damaging terricolous lichen communities making then potentially good indicators of N deposition. |
| [134] | |
| [135] | An expectation in soil ecology is that a microbial communities鈥 fungal:bacterial dominance indicates both its response to environmental change and its impact on ecosystem function. We review a selection of the increasing body of literature on this subject and assess the relevance of its expectations by examining the methods used to determine, the impact of environmental factors on, and the expected ecosystem consequences of fungal:bacterial dominance. Considering methods, we observe that fungal:bacterial dominance is contingent on the actual measure used to estimate it. This has not been carefully considered; fungal:bacterial dominance of growth, biomass, and residue indicate different, and not directly relatable aspects, of the microbial community鈥檚 influence on soil functioning. Considering relationships to environmental factors, we found that shifts in fungal:bacterial dominance were not always in line with the general expectation, in many instances even being opposite to them. This is likely because the traits expected to differentiate bacteria from fungi are often not distinct. Considering the impact of fungal:bacterial dominance on ecosystem function, we similarly found that expectations were not always upheld and this too could be due to trait overlap between these two groups. We explore many of the potential reasons why expectations related to fungal:bacterial dominance were not met, highlighting areas where future research, especially furthering a basic understanding of the ecology of bacteria and fungi, is needed. |
| [136] | Human activities have increased N availability dramatically in terrestrial and aquatic ecosystems. Extensive research demonstrates that local plant species diversity generally declines in response to nutrient enrichment, yet the mechanisms for this decline remain unclear. Based on an analysis of >900 species responses from 34 N-fertilization experiments across nine terrestrial ecosystems in North America, we show that both trait-neutral and trait-based mechanisms operate simultaneously to influence diversity loss as production increases. Rare species were often lost because of soil fertilization, randomly with respect to traits. The risk of species loss due to fertilization ranged from >60% for the rarest species to 10% for the most abundant species. Perennials, species with N-fixing symbionts, and those of native origin also experienced increased risk of local extinction after fertilization, regardless of their initial abundance. Whereas abundance was consistently important across all systems, functional mechanisms were often system-dependent. As N availability continues to increase globally, management that focuses on locally susceptible functional groups and generally susceptible rare species will be essential to maintain biodiversity. |
| [137] | ABSTRACT Roots concentrated on the smallest distal branching orders have short life spans and thus dominate root mortality, and may contribute predominately to plant carbon and nutrient transfer into soil. Yet the effects of nitrogen (N) enrichment on decomposition of the finest root branching orders have not yet been examined. Resolving such N effects is critical for predicting the ecosystem consequences of increased anthropogenic N deposition. The first four root orders were separated into two classes: first- and second-order roots; third- and fourth-order roots. We studied the effects of N addition on decomposition of different root order classes in four temperate tree species over 4 years. Asymptotic decay models best fit the decomposition and allowed us to examine effects of N on initial versus later stages of decomposition separately. Very early in decomposition, N fertilization stimulated decomposition rates in higher-order roots, but had no effects on initial rates of decomposition in lower-order roots. In contrast, later in decomposition, N fertilization inhibited decomposition, ultimately resulting in a larger, slowly decomposing fraction in both lower-order and higher-order roots. Inhibitory effects of N addition on lignin-degrading enzyme activity might be an important mechanism explaining the negative effects of N on decomposition here. This study highlights the importance of long-term studies for understanding N effects on decomposition, and suggests that contrasting effects of N on different decomposition processes and carbon pools should be widely considered in biogeochemical models. Furthermore, the inhibitory effects of elevated atmospheric N deposition on decomposition of lower-order roots suggest that these roots may provide a critical mechanism of carbon and nutrient retention in soil because of their rapid input via root mortality. |
| [138] | Resolving the effects of nitrogen (N) on decomposition is ecologically critical for predicting the ecosystem consequences of increased anthropogenic N deposition. Although root litter is the dominant soil carbon (C) and nutrient input in many forest ecosystems, studies have rarely examined how the process of root decomposition is affected by N availability. In a field experiment, we studied the effects of N addition on fine root (<0.5mm diameter) decomposition using five substrates ranging in initial gravimetric lignin concentrations (from 10.8% to 34.1%) over five years, and made a simultaneous characterization of effects of N on the enzymatic activity of the decomposer community in three temperate forests. Across substrates, asymptotic decomposition models best described the decomposition. The effects of N addition shifted over the course of fine root decomposition, regardless of initial lignin concentrations, with N speeding up the initial rate of decomposition, but ultimately resulting in a larger, slowly decomposing litter fraction ( A ). Such contrasting effects of N addition on initial and later stages of decomposition were closely linked to the dynamics of its extracellular enzyme activity. Our results emphasized the need for studies of N effects on litter decomposition that encompass the later stages of decomposition. This study suggested that atmospheric N addition may have contrasting effects on the dynamics of different carbon pools in forest soils, and such contrasting effects of N should be widely considered in biogeochemical models. |
| [139] | A general reference text on decomposition. The first 2 chapters review the processes as a basis for a detailed account of the decomposer organisms and their activities in chapter 3. Chapters 4, 5 and 6 examine the influence of substrate quality, soil chemistry and climate. The final chapter shows how all the biological, chemical and climatic factors interrelate to produce varying rates of decom... |
| [140] | Experiments in exclosures were conducted on a salt marsh in a macrotidal system in western France. The aim of this study was threefold: (1) to compare vegetation dynamics over a period of 8 years in grazed and ungrazed conditions (2) to investigate the response of annual species to grazing duration during seedling establishment (3) to test the effect of an increase in soil nitrogen availability after cessation of grazing on interactions between Suaeda maritima and Puccinellia maritima . In grazed conditions, during all the survey, vegetation was dominated by a short P. maritima sward with the annual Salicornia europaea in the lower and middle marshes. However, after cessation of grazing in 1994, a homogeneous matrix of the forb Halimione portulacoides , quickly replaced P. maritima in the well drained lower marsh. At the middle marsh level, fine sediment and poor drainage maintained P. maritima while the annual S. maritima which tolerates taller and denser vegetation replaced S. europaea. Elymus pungens cover was limited till 2000 but its rising in 2001 let expect its dominance in the future. While P. maritima abundance remained high, spring abundance of annual species such as S. europaea and S. maritima globally decreased with sheep grazing duration on the salt marsh between February and June. Experiments with monocultures of P. maritima and S. maritima demonstrated that nitrogen was a limiting factor on the salt marsh. In a mixed community, a moderate application of nitrogen (15 g N m –2 year –1 as NH 4 -NO 3 ) promoted growth of P. maritima and limited the biomass of S. maritima , but growth of the latter was enhanced by a high application of nitrogen (30 g N m –2 year –1 ). An increase in the abundance of annuals such as S. maritima on the salt marsh is discussed. |
| [141] | Nutrient transfer between decomposing leaves may explain non-additive species diversity effects on decomposition. The influence of the diversity of litter species on decomposition was compared in mixtures composed of large (>200聽mm 2 ) or small (<9聽mm 2 ) litter fragments. The increase in the number of species (aspen, oak, alder and pine, from monocultures to four species in all possible combinations) initially (at day 43) suppressed respiration, but eventually (after 142 days) did not affect the mass loss of the mixtures of small litter fragments. In contrast, the decomposition of litter in large fragments increased with increased diversity, and 93% of all mixtures decomposed faster than would be predicted from monocultures. The results suggest that the active transport of nutrients by fungal hyphae, rather than passive diffusion, drives positive effect of the litter species diversity on decomposition. |
| [142] | |
| [143] | The influence of chemical composition on the decomposition and N release rates from samples of 11 organic mulches enclosed in nylon mesh bags was assessed under field conditions at the University of California, Riverside. Time was adjusted by temperature and the cumulative temperature-adjusted days (tad) were used to model the pattern of the decay and N release. The chemical composition of the mulches significantly affected their decay. In descending order of significance, the concentration of the polar extractable carbon fraction ( C P ) and the acid insoluble fraction ( C AI ) were significantly correlated with decomposition during the year of study. Correlation was positive with C P and N and negative with C AI (mostly lignin). The C P was selected as the best predictor for mulch decomposition during the early and intermediate phases of this process (36 and 195 tad), but C AI was selected as the best variable for predicting the fraction of the initial mulch mass remaining at the end of the study (397 tad). N was immobilized, as indicated by temporary increases in N masses in mulches above initial conditions, in shredded redwood, pine trimmings and in two of three compost mulches. Immobilization was most pronounced during the first 36 tad of the study, with a maximum rate that varied from 6 to 11.5% above the initial N concentrations. At the end of the study N releases ranged from 97% of initial N (grass clippings) to only 8% (one of the composts.) The C P was selected as the best predictor for N remaining in the four sampling dates (397 tad) and explained from 52 to 68% of the variation in N release as a percentage of initial N content. |
| [144] | The effects of nitrogen addition on rates of litter decomposition of plants growing under different competition levels were assessed in a multifactorial glasshouse experiment. We established a two nitrogen-level treatment (control and fertilization) and three competition-level (plants growing alone, intra- and interspecific competition) experiment for Pinus pinea L., Pistacia lentiscus L. and Cistus salvifolius L. during one year. We collected leaves from different combinations at 3, 6 and 12 months and we established a 2-month microcosm experiment. We measured K pot and different leaf and litter traits in order to test the hypothetical relationships between these traits and litter decomposability among the target species. Leaf nitrogen concentration was higher in plants growing under N-supply treatments but this supply only affected decomposition rates in the cases of P. pinea and P. lentiscus when grown alone. For P. pinea and C. salvifolius decay rate was higher in the fertilized treatment when growing alone. Leaf dry matter content was the leaf trait best related to litter decomposability. The results derived from the microcosm experiment provided evidence of the effect of some leaf and litter traits on litter decomposability and how some traits can give information about some important processes in ecosystems, such as decomposition. |
| [145] | |
| [146] | Nitrogen (N) deposition and biodiversity loss are important drivers of global change, with uncertain consequences for carbon (C) and nutrient turnover in terrestrial ecosystems. We evaluated the simultaneous effects of N deposition and plant diversity on litter decomposition within a temperate forest in Patagonia. We identified ‘tree triangles’ created by the intersection of three tree-canopies that directly controlled micro-environmental conditions on the forest floor, and combined it with an N addition treatment. Triangles were composed of one or three Nothofagus species (N. dombeyi, N. obliqua or N. nervosa). We placed litterbags containing litter of each of the Nothofagus species and litterbags containing a mixture of the three species within all triangles and assessed mass loss over 2 years. We used a standard litter type in all triangles to independently evaluate triangle effects on decomposition. N addition had strong and positive effects on decomposition with an average 46% increase in the decomposition constant. Litter species significantly differed in their response to N addition; litter with higher lignin content and lower labile C content had larger increase in decomposition due to fertilization. Also, N addition disrupted two types of species interactions that control decomposition. The affinity relation between litter and decomposers, that enhanced decomposition of home litter (‘home-field advantage’) that was demonstrated to be significant for all three Nothofagus species, disappeared with N addition. Second, N addition modified litter species interactions, transforming neutral effects of litter mixtures to positive, nonadditive effects on mass loss. Finally, N addition stimulated N release from decomposing litter which was modulated by plant species effects. Together, these results suggest that N addition to unpolluted forests increases C loss, contrary to what has been observed for temperate forests in industrialized areas of the world, and that alterations in nutrient pools have effects on species interactions, including the elimination of affinity effects for decomposition. |
| [147] | Climate and litter quality are primary drivers of terrestrial decomposition and, based on evidence from multisite experiments at regional and global scales, are universally factored into global decomposition models. In contrast, soil animals are considered key regulators of decomposition at local scales but their role at larger scales is unresolved. Soil animals are consequently excluded from global models of organic mineralization processes. Incomplete assessment of the roles of soil animals stems from the difficulties of manipulating invertebrate animals experimentally across large geographic gradients. This is compounded by deficient or inconsistent taxonomy. We report a global decomposition experiment to assess the importance of soil animals in C mineralization, in which a common grass litter substrate was exposed to natural decomposition in either control or reduced animal treatments across 30 sites distributed from 43 degree S to 68 degree N on six continents. Animals in the mesofaunal size range were recovered from the litter by Tullgren extraction and identified to common specifications, mostly at the ordinal level. The design of the trials enabled faunal contribution to be evaluated against abiotic parameters between sites. Soil animals increase decomposition rates in temperate and wet tropical climates, but have neutral effects where temperature or moisture constrain biological activity. Our findings highlight that faunal influences on decomposition are dependent on prevailing climatic conditions. We conclude that (1) inclusion of soil animals will improve the predictive capabilities of region- or biome-scale decomposition models, (2) soil animal influences on decomposition are important at the regional scale when attempting to predict global change scenarios, and (3) the statistical relationship between decomposition rates and climate, at the global scale, is robust against changes in soil faunal abundance and diversity. |
| [148] | Recent evidence suggests that soil organic matter (SOM) is largely composed of microbial products rather than plant compounds that resist decomposition. The chemical transformation of leaf litter components during decomposition is critical in controlling SOM formation. Plant leaf litter tends to decompose faster in its native environment than when it is placed under other vegetation types. This home-field advantage (HFA) suggests that decomposer communities are specialized to most efficiently degrade the litter found in their native environment, possibly through the production of specific enzymes that degrade unique compounds within that litter. Could this affect the degree to which leaf litter chemistry is altered during decomposition? We used pyrolysis-molecular beam mass spectrometry (py-MBMS) to analyze whether the chemistry of aspen and lodgepole pine litter was altered to a greater degree when decomposed in its home environment compared to an away environment. We had previously reported a 4% HFA for pine litter decomposition rates in this reciprocal experiment, and attributed that effect to differences in decomposer communities. Our high-resolution analysis revealed that litter chemistry also changed to a greater extent in its home environment. The changes in litter chemistry were more pronounced for the more recalcitrant pine litter, suggesting that decomposer community specialization is more important for recalcitrant litter. The accumulation of microbial products and microbially-transformed plant components resulted in an overall convergence in litter chemistry as decomposition proceeded, but the imprints of both initial litter chemistry and decomposer communities remained evident. The detection of new compounds in decomposed litter and the HFA effect on litter chemistry suggest that decomposer communities affect both the rate at which individual compounds within litter are decomposed, and the chemical nature of compounds that are incorporated into SOM. |
| [149] | Global nitrogen deposition alters grassland ecosystems. Whether added nitrogen changes root production and turnover by root orders is unclear.We compared the root dynamics across four root orders of |
| [150] | 氮沉降持续增加背景下土壤C∶N∶P化学计量比和pH环境等的改变及其可能的土壤微生物学机制已经成为陆地生态系统与全球变化研究的新生长点和科学研究前沿.以生态化学计量学和土壤微生物生态学为理论基础,综述了氮沉降对森林土壤有机质和凋落物分解的影响及其微生物学机制的基本理论、最新进展、研究热点与难点,旨在促进全球变化背景下陆地生态系统地下生态学的研究.氮沉降持续增加会导致森林生态系统磷循环加速,导致磷限制.氮沉降不但改变森林土壤有机质和凋落物的C∶N∶P化学计量比和降低土壤pH值,而且改变土壤微生物生物量碳氮磷、细菌、真菌和放线菌的组成以及影响碳氮磷分解的关键酶活性.氮沉降对森林土壤有机质和凋落物分解的影响表现为促进、抑制和无影响,其影响的差异可能来源于微生物效应的不同.叶片在凋落前有显著的氮磷养分回收,但是根无明显的养分回收,造成土壤有机质和凋落物的C∶N∶P化学计量比存在明显差异.基于DNA/RNA等分子生物学方法为土壤微生物生态学研究提供了强有力的手段,将促进氮沉降对森林土壤有机质和凋落物化学计量比改变的微生物学机制研究. |
| [151] | 生态系统元素平衡是当前全球变化生态学和生物地球化学循环的研究热点和焦点。在系统介绍生态化学计量学与碳氮磷元素循环研究进展的基础上，重点从土壤C：N：P化学计量比的分布特征、指示作用、对碳固定的影响，以及人类活动对C：N：P比的影响等方面探讨了C：N：P比在养分限制、生物地球化学循环、森林演替与退化等领域中的应用等问题，并展望了生态系统碳氮磷平衡的元素化学计量学未来研究的发展方向。通过对生态化学计量学理论和方法的研究，可以深入认识植物-凋落物-土壤相互作用的养分调控因素，对于揭示碳氮磷元素之间的相互作用及平衡制约关系，为减缓温室效应提供新思路和理论依据，具有重要的现实意义。 |
| [152] | |
| [153] | |
| [154] | Land use greatly affects litter production, quality, and decomposition rates, and therefore alters the soil carbon stocks and influences ecosystem carbon cycling. In this study, our aims were to investigate the effects of land use (grazing, mowing, and grazing exclusion), litter types, and precipitation on litter production, decomposition processes, and soil carbon stocks. Litter inputs, quality, and decomposition rates were significantly influenced by land use and differed greatly between 2011 (a dry year) and 2012 (a moist year). Above-ground litter production in 2012 ranged from 165 to 18002g02m 612 , versus from 50 to 7302g02m 612 in 2011; below-ground litter production in 2012 was 1.9 to 6.0 times that in 2011. Decomposition rates of above-ground litter ( k a ) were greater than those of below-ground litter ( k b ). The k a in 2012 was 1.9 to 2.8 times those in 2011 and k b in 2012 was 6.5 to 10.8 times those in 2011. The k a was strongly positively correlated with the N content ( R 2 02 =02 0.713) and strongly negatively correlated with the C/N ratio ( R 2 02=020.585), whereas k b was explained best by the C/N ratio. Precipitation was a main factor that controlled ecosystem C cycling processes, and increased litter decomposition increased soil carbon stocks. Land use therefore played an important role in litter input and decomposition processes and in carbon sequestration, but these processes responded to the initial litter quality and precipitation. |
| [155] | All terrestrial ecosystems consist of aboveground and belowground components that interact to influence community- and ecosystem-level processes and properties. Here we show how these components are closely interlinked at the community level, reinforced by a greater degree of specificity between plants and soil organisms than has been previously supposed. As such, aboveground and belowground communities can be powerful mutual drivers, with both positive and negative feedbacks. A combined aboveground-belowground approach to community and ecosystem ecology is enhancing our understanding of the regulation and functional significance of biodiversity and of the environmental impacts of human-induced global change phenomena. |
| [156] | The theory of ecological stoichiometry predicts that the microbial biomass should regulate production of extracellular enzymes to target the resource in shortest supply. Therefore, microbial communities on decomposing leaf litter should optimize allocation to C-, N-, and P-degrading enzymes according to the stoichiometry of the foliar substrate. Because extracellular enzymes are the proximate agents of leaf litter decay, shifts in microbial enzyme allocation may influence overall rates of litter mass loss. To test these hypotheses, I measured fungal growth and the activities of acid phosphatase (AP), beta-glucosidase (BG), cellobiohydrolase (CB) and glycine aminopeptidase (GAP) on decaying leaf litter of five plant species over the course of a 394-day decomposition experiment. I used regression and correlation analyses to link to interspecific variation in mass loss rates with enzyme activities and foliar nutrient content. Enzymes explained 35% of the variance in foliar decay rates across plant species, yet fungal abundance and enzyme activities were unrelated to foliar concentrations of N, P, K, or 9 other nutrients. Furthermore, relative activities of C-, N-, and P-acquiring enzymes did not vary across litter types despite wide variance in foliar C:N and C:P ratios. This weak relationship between litter stoichiometry and decomposition rates suggests that nutrients are not the primary control on microbial growth or enzyme allocation in this tropical forest. However, substantial interspecific differences in fungal abundance and enzyme activities imply that differences in litter composition strongly influence microbial communities and the ecosystem processes they mediate. (C) 2013 Elsevier Ltd. All rights reserved. |
| [157] | Rising atmospheric CO 2 has been predicted to reduce litter decomposition as a result of CO 2 -induced reductions in litter quality. However, available data have not supported this hypothesis in mesic ecosystems, and no data are available for desert or semi-arid ecosystems, which account for more than 35% of the Earth's land area. The objective of our study was to explore controls on litter decomposition in the Mojave Desert using elevated CO 2 and interannual climate variability as driving environmental factors. In particular, we sought to evaluate the extent to which decomposition is modulated by litter chemistry (C:N) and litter species and tissue composition. Naturally senesced litter was collected from each of nine 25 m diameter experimental plots, with six plots exposed to ambient [CO 2 ] or 367 μL CO 2 L 611 and three plots continuously fumigated with elevated [CO 2 ] (550 μL CO 2 L 611 ) using FACE technology beginning in April 1997. All litter collected in 1998 (a wet, or El Ni09o year; 306 mm precipitation) was pooled as was litter collected in 1999 (a dry year; 94 mm). Samples were allowed to decompose for 4 and 12 months starting in May 2001 in mesh litterbags in the locations from which litter was collected. Decomposition of litter produced under elevated CO 2 and ambient CO 2 did not differ. Litter produced in the wetter year showed more rapid initial decomposition (over the first 4 months) than that produced in the drier year (27±2% yr 611 or 7.8±0.7 g m 612 yr 611 for 1998 litter; 18±3% yr 611 or 2.2±0.4 g m 612 yr 611 for 1999 litter). C:N ratios of litter produced under elevated CO 2 (wet year: 37±0.5; dry year: 42±2.5) were higher than those of litter produced under ambient CO 2 (wet year: 34±1.1; dry year: 35±1.4). Litter production in the wet year (amb. CO 2 : 25.1±1.1 g m 612 yr 611 ; elev. CO 2 : 35.0±1.1 g m 612 yr 611 ) was more than twice as high as that in the dry year (amb. CO 2 : 11.6±1.7 g m 612 , elev. CO 2 : 13.3±3.4 g m 612 ), and contained a greater proportion of Lycium pallidum and a lower proportion of Larrea tridentata than litter produced in the dry year. Decomposition, viewed across all treatments, decreased with increasing C:N ratios, decreased with increasing proportions of Larrea tridentata and increased with increasing proportions of Lycium pallidum and Lycium andersonii . Because litter C:N did not vary by litter production year, and CO 2 did not alter decomposition or litter species/tissue composition, it is likely that the impact of year-to-year variation in precipitation on the proportion of key plant species in the litter may be the most important way in which litter decomposition will be modulated in the Mojave Desert under future rising atmospheric CO 2 . |
| [158] | summary Foliar uptake and release of inorganic nitrogen compounds were studied by immersing current-year shoots of Scots pine ( Pinus sylvestris L.) and Norway spruce [ Pica abies (L.) Karst] in either NH 4 + - or NO 3 61 -rain solutions at different N concentrations. The effects of N form, N concentration and tree species on ion influx and efflux were investigated. Spruce shoots absorbed NH 4 + from the external solution. Uptake apparently occurred by diffusion rather than by H + or base cation exchange as commonly accepted, and increased linearly with NH 4 + concentration in the external solution. In contrast, pine shoots released NH 4 + to the external solution. The different reactions of spruce and pine may reflect species differences in physical and chemical properties or differences in tissue N concentration. If the latter is the case, a tree's N status may determine whether the canopy acts as a source or sink for NH 4 + influencing deposition rates to the needle surface. The results show that where NH 4 + concentration on the needle surface exceeds 4 mg 1 611 , foliar uptake may make a significant contribution to N status. In the absence of NH 4 + -base cation exchange, atmospheric inputs of NH 4 + to the canopy appear unlikely to be directly-responsible for the nutrient deficiencies typical of Dutch forest decline. Neither spruce or pine shoots were able to utilize NO 3 61 in the external solution and generally released NO 3 61 . Adverse effects resulting from foliar accumulation of wet-deposited NO 3 61 appear unlikely. However, higher NO 3 61 concentrations and longer residence times than simulated in this experiment may result in foliar uptake of NO 3 61 in the field. |
| [159] | |
| [160] | A large remaining source of uncertainty in global model predictions of future climate is how ecosystem carbon (C) cycle feedbacks to climate change. We conducted a field manipulative experiment of warming and nitrogen (N) addition in a temperate steppe in northern China during two contrasting hydrological growing seasons in 2006 [wet with total precipitation 11.2% above the long-term mean (348 mm)] and 2007 (dry with total precipitation 46.7% below the long-term mean). Irrespective of strong intra- and interannual variations in ecosystem C fluxes, responses of ecosystem C fluxes to warming and N addition did not change between the two growing seasons, suggesting independence of warming and N responses of net ecosystem C exchange (NEE) upon hydrological variations in the temperate steppe. Warming had no effect on NEE or its two components, gross ecosystem productivity (GEP) and ecosystem respiration (ER), whereas N addition stimulated GEP but did not affect ER, leading to positive responses of NEE. Similar responses of NEE between the two growing seasons were due to changes in both biotic and abiotic factors and their impacts on ER and GEP. In the wet growing season, NEE was positively correlated with soil moisture and forb biomass. Negative effects of warming-induced water depletion could be ameliorated by higher forb biomass in the warmed plots. N addition increased forb biomass but did not affect soil moisture, leading to positive effect on NEE. In the dry growing season, NEE showed positive dependence on grass biomass but negative dependence on forb biomass. No changes in NEE in response to warming could result from water limitation on both GEP and ER as well as little responses of either grass or forb biomass. N addition stimulated grass biomass but reduced forb biomass, leading to the increase in NEE. Our findings highlight the importance of changes in abiotic (soil moisture, N availability) and biotic (growth of different plant functional types) in mediating the responses of NEE to climatic warming and N enrichment in the semiarid temperate steppe in northern China. |
| [161] | 2010年10月26日-2011年4月18日在川西亚高山地区季节性冻融期间,选择典型的红桦-岷江冷杉林,采用凋落物分解袋法调查了不同网孔(0.02、0.125、1和3 mm)凋落物分解袋内的凋落物质量损失,分析微型、中型和大型土壤动物对红桦凋落叶分解的贡献.结果表明:在季节性冻融期间,0.02、0.125、1和3 mm分解袋内的红桦凋落叶质量损失率分别为11.8％、13.2％、15.4％和19.5％,不同体径土壤动物对红桦凋落叶质量损失的贡献率为39.5％；不同孔径凋落物袋内土壤动物的类群和个体相对密度与凋落叶的质量损失率的变化趋势相对一致.在季节性冻融的初期、深冻期和融化期,不同土壤动物对红桦凋落叶质量损失的贡献率为大型土壤动物(22.7％)＞中型土壤动物(11.9％)＞微型土壤动物(7.9％).季节性冻融期间土壤动物活动是影响川西亚高山森林凋落物分解的重要因素之一. |
| [162] | Most studies of forest litter dynamics examine the biochemical characteristics and decomposition of leaf litter, but fine roots are also a large source of litter in forests. We quantified the concentrations of eight biochemical fractions and nitrogen (N) in leaf litter and fine roots at four sugar maple (Acer saccharum)-dominated hardwood forests in the north-central United States. We combined these results with litter production data to estimate ecosystem biochemical fluxes to soil. We also compared how leaf litter and fine root biochemistry responded to long-term simulated N deposition. Compared with leaf litter, fine roots contained 2.9-fold higher acid-insoluble fraction (AIF) and 2.3-fold more condensed tannins; both are relatively difficult to decompose. Comparatively, leaf litter had greater quantities of more labile components: nonstructural carbohydrates, cellulose and soluble phenolics. At an ecosystem scale, fine roots contributed over two-thirds of the fluxes of AIF and condensed tannins to soil. Fine root biochemistry was also less responsive than leaf litter to long-term simulated N deposition. Fine roots were the dominant source of difficult-to-decompose plant carbon fractions entering the soil at our four study sites. Based on our synthesis of the literature, this pattern appears to be widespread in boreal and temperate forests. |
| [163] | |
| [164] | Although nitrogen addition and recovery from degradation can both promote production of grassland biomass, these two factors have rarely been investigated in combination. In this study, we established a field experiment with six N-treatment (CK, 10, 20, 30, 40, 5065g65N65m61265yr611) on five fields with different degradation levels in the Inner Mongolian steppe of China from 2011–2013. Our observations showed that while the external nitrogen increased the aboveground biomass in all five grasslands, the magnitude of the effects differed with the severity of degradation. Fields with a higher level of degradation tended to have a higher saturation value (2065g65N65m61265yr611) than those with a lower degradation level (65<651065g65N m61265yr611). After three years of experimentation, species richness showed little change across degradation levels. Among the four functional groups of grasses, sedges, forbs and legumes, grasses shared the most similar response patterns with those of the whole community, demonstrating the predominant role that they play in the restoration of grassland under a stimulus of nitrogen addition. |
| [165] | Understanding the links between litter chemical transformations and functional microbial communities is key to elucidating the mechanisms of litter decomposition processes under nitrogen (N) and sulfur (S) deposition. Carbon (C)-13-labelled Pinus massoniana needles were incubated in a subtropical plantation forest soil exposed to: no amendment (Control), N amendments of 81 (N1) and 270 (N2) mg02kg 61021 , S amendments of 121 (S1) and 405 (S2) mg02kg 61021 and combined N and S amendments. Litter decomposition was measured as litter-derived carbon dioxide (CO 2 ) emissions and the litter C pools were partitioned using a two-pool model. Relationships between litter residue chemistry (assessed by 13 C nuclear magnetic resonance spectroscopy analysis) and microbial community composition (probed by phospholipid fatty acid analysis, PLFA) and activity (the metabolic quotient, q CO 2 ) were investigated. Over the 42002days incubation period, N and S additions (except N and S addition alone at low rate) significantly increased litter decomposition by 7.2–18.9% compared to the Control. Decomposition was stimulated by 10.2–61.9% during the initial 5602days (stage 1) and in contrast, 8.3–42.1% inhibition was measured during 57–42002days (stage 2) across the addition treatments. Stimulation on litter-derived CO 2 emissions under the N and S additions was largely dependent on the loss of O-alkyl C, a dominant component of the litter active C pool. During the initial 702days, N and S additions increased the ratio of fungal to bacterial PLFAs compared to the Control, which was accompanied by the increases in methoxyl C. The activity of microbes, particularly gram-negative bacteria, was also increased by N and S additions at stage 1, which was related to di-O-alkyl C. In contrast, fungal activity decreased under N and S additions at stage 2, accompanied by lowered C availability and increased methoxyl C. Alkyl C and aromatic C in the litter had positive relationships with the half-life of the slow C pool. Accordingly, the residue recalcitrance was increased under N and S additions compared with Control at stage 2, and was largely responsible for the inhibition of litter decomposition. Thus, N and S deposition is likely to increase the persistence of litter-derived recalcitrant C in subtropical forest soils in the long term. |
| [166] | Abstract Nitrogen (N) and sulfur (S) deposition are important drivers of global climate change, but their effects on litter decomposition remain unclear in the subtropical regions. We investigated the influences of N, S, and their interactions on the decomposition of 13C-labeled Pinus massoniana leaf litter. An orthogonal experiment with three levels of N (0, 81, and 270 mg N kg611 soil) and S (0, 121, and 405 mg S kg611 soil) was conducted. We traced the incorporation of 13C-litter into carbon dioxide (CO2), dissolved organic C (DOC), and microbial phospholipids. Over the 420-day incubation, litter decomposition did not respond to low N and S additions but increased under high levels and combined amendments (NS). However, litter-derived CO2 emissions were enhanced during the first 56 days, with a positive interaction of N × S. N additions promoted fungal growth, while S stimulated growth of Gram-positive bacteria, fungi, and actinobacteria. Increased decomposition was related to higher litter-derived DOC and fungi/bacteria ratio. Inversely, N and/or S amendments inhibited decomposition (N > NS > S) from day 57 afterwards, possibly due to C limitation and decreased abundances of Gram-negative bacteria and actinobacteria. These results suggested that N deposition interacted with S to affect litter decomposition, and this effect depended on N and S deposition levels and litter decomposition stage. |
| [167] | 放牧和围封通过影响植物群落结构和土壤微环境来调控草地生态系统的碳循环.该研究在内蒙古温带草原设置轻度放牧后围封、轻度放牧、重度放牧后围封、重度放牧4种样地,通过测定干旱年(2011年)和湿润年(2012年)地上、地下凋落物产量、质量及其分解速率和土壤养分含量,分析不同放牧强度对凋落物形成和分解的影响,以及围栏封育对生态系统恢复的作用.结果表明:重度放牧地上凋落物产量和分解速率均高于轻度放牧.干旱年轻度放牧样地地下凋落物产量和分解速率高于重度放牧,湿润年相反.短期围封显著提高了凋落物产量,轻度放牧样地围封后地上凋落物分解速率和养分循环加快,而重度放牧样地围封后地上凋落物分解减慢.因此,与重度放牧相比,轻度放牧草地的恢复更适合采用围栏封育措施;而重度放牧草地的恢复可能还需辅以必要的人工措施.降水显著促进地上、地下凋落物形成和分解.地下凋落物的生产和分解受降水年际波动影响较大,重度放牧草地对降水变化的敏感度比轻度放牧草地高.地上凋落物分解速率与凋落物N含量显著正相关,与土壤全N显著负相关,与地上凋落物C∶N和木质素:N相关性不大;地下凋落物分解速率与凋落物C、C∶N和纤维素含量显著负相关.该研究结果将为不同放牧强度的草地生态系统恢复和碳循环研究提供理论依据. |
| [168] | Anthropogenic acid deposition may lead to soil acidification, with soil buffering capacity regulating the magnitude of any soil pH change. However, little evidence is available from large-scale observations. Here, we evaluated changes in soil pH across northern China's grasslands over the last two decades using soil profiles obtained from China's Second National Soil Inventory during the 1980s and a more recent regional soil survey during 2001鈥2005. A transect from the central-southern Tibetan Plateau to the eastern Inner Mongolian Plateau, where Kriging interpolation provided robust predictions of the spatial distribution of soil pH, was then selected to examine pH changes during the survey period. Our results showed that soil pH in the surface layer had declined significantly over the last two decades, with an overall decrease of 0.63 units (95% confidence interval = 0.54鈥0.73 units). The decline of soil pH was observed in both alpine grasslands on the Tibetan Plateau and temperate grasslands on the Inner Mongolian Plateau. Soil pH decreased more intensively in low soil carbonate regions, while changes of soil pH showed no significant associations with soil cation exchange capacity. These results suggest that grassland soils across northern China have experienced significant acidification from the 1980s to 2000s, with soil carbonates buffering the increase in soil acidity. The buffering process may induce a large loss of carbon from soil carbonates and thus alter the carbon balance in these globally important ecosystems. |
| [169] | Abstract The contributions of environmental DNA to ecology are reviewed, focusing on diet, trophic interactions, species distributions and biodiversity assessment. Environmental DNA has the potential to dramatically improve quantitative studies in these fields. Achieving this, however, will require large investments of time and money into developing the relevant databases, models, and software. 0008 2012 Blackwell Publishing Ltd. |
| [170] | ( |
| [171] | The study took juveniles of T.ramosissima and A.sparsifolia as study objects,which are the key species of desert-oasis transition zone in the south fringe of the Taklimakan Desert.The trench method and root tracing method were used to excavate their whole root system.The aim of the experiment is to study the features of the biomass allocation,root / shoot ratio and root distribution of two plant juveniles under the same extra-arid habitant condition with comparing their differences.The results shows as follows:(1) Biomass allocation of two plant juveniles are obviously different.T.ramosissima allocates more biomass into shoots,whose root / shoot ratio is 0.75.On the contrary,A.sparsifolia allocates more biomass into roots with root / shoot ratio of 1.73.(2) Relationships between the root and the shoot of two plant juveniles are characterized by the allometry model,their correlation coefficients are larger than 0.83.(3) Root distribution of two plant juveniles is also significantly different.The root system of T.ramosissima is composed by a vertical main root and some horizontal lateral roots,whose root system distribution is like a Chinese character of "feng"(丰)in its soil vertical profiles.The root system of A.sparsifolia is composed of the tillers which are net-shaped,whose root system distribution in its soil vertical profiles is like a Chinese character of "gu"(古). |
| [172] | . . 凋落物分解作为生态系统物质养分循环过程的一个重要环节，对生物 地球化学循环起着非常重要的作用。在补充植物可利用土壤养分库的同时，释放光合作用固定的碳到大气中。目前，围绕不同类型生态系统的凋落物分解已经开展了 大量研究工作，其中以森林生态系统的研究居多。但是，凋落物分解的研究还有许多问题需要深入研究，例如，影响分解的各种因素的相对作用与交互作用、混合凋 落物分解中组分凋落物在混合效应（或非加性效应）中的作用、根系组织的分解及其影响机理、氮沉降对凋落物分解的影响等等。针对这些问题，本研究通过分析我 国主要的草甸草原——呼伦贝尔... |
| [173] | Atmospheric nitrogen (N) deposition caused by anthropogenic activities may alter litter decomposition and species composition, and then affect N cycling and carbon (C) sequestration in an ecosystem. Using the litterbag method, we studied the effects of N addition (CK: no N addition; low-N: 1 g N m (-2) y (-1) ; high-N: 2 g N m (-2) y (-1) ) on changes in mass remaining of shoot litter decomposition of three grasses (Stipa baicalensis, Carex pediformis and Leymus chinensis) over 28 months in the Hulun Buir meadow steppe of Inner Mongolia. The results showed that the addition of high and low N had no significant effect on the decomposition of single-species litter, but low N addition slightly inhibited the decomposition of litter mixtures. In addition, litter decomposition was strongly species dependent. Our results suggest that species type is likely the main determinant of litter decomposition, and low N deposition in natural ecosystems does not influence single-species litter decomposition. |
| [174] | |
| [175] | |
| [176] | Abstract Nitrogen addition has been shown to affect plant litter decomposition in terrestrial ecosystems. However, the way that nitrogen deposition impacts the relationship between plant litter decomposition and altered soil nitrogen availability is unclear. This study examined 18 co-occurring litter types in a subtropical forest in China in terms of their decomposition (one year of exposure in the field) with nitrogen addition treatment (0, 0.4, 1.6, and 4.0 mol N m612 year611) and soil fauna exclusion (litter bags with 0.1 and 2 cm mesh size). Results showed that the plant litter decomposition rate is significantly reduced because of nitrogen addition; the strength of the nitrogen addition effect is closely related to the nitrogen addition levels. Plant litters with diverse quality responded to nitrogen addition differently. When soil fauna was present, the nitrogen addition effect on medium-quality or high-quality plant litter decomposition rate was 6126% ± 5% and 6129% ± 4%, respectively; these values are significantly higher than that of low-quality plant litter decomposition. The pattern is similar when soil fauna is absent. In general, the plant litter decomposition rate is decreased by soil fauna exclusion; an average inhibition of 6117% ± 1.5% was exhibited across nitrogen addition treatment and litter quality groups. However, this effect is weakly related to nitrogen addition treatment and plant litter quality. We conclude that the variations in plant litter quality, nitrogen deposition, and soil fauna are important factors of decomposition and nutrient cycling in a subtropical forest ecosystem. This article is protected by copyright. All rights reserved. |
| [177] | Abstract Nitrogen (N) is a key limiting resource for aboveground net primary productivity (ANPP) in diverse terrestrial ecosystems. The relative roles of the rate and frequency (additions yr(-1)) of N application in stimulating ANPP at both the community- and species-levels are largely unknown. By independently manipulating the rate and frequency of N input, with nine rates (from 0 to 50鈥塯 N m(-2) year(-1)) crossed with two frequencies (twice year(-1) or monthly) in a temperate steppe of northern China across 2008-2013, we found that N addition increased community ANPP, and had positive, negative, or neutral effects for individual species. There were similar ANPP responses at the community- or species-level when a particular annual amount of N was added either twice year(-1) or monthly. The community ANPP was less sensitive to soil ammonium at lower frequency of N addition. ANPP responses to N addition were positively correlated with annual precipitation. Our results suggest that, over a five-year period, there will be similar ANPP responses to a given annual N input that occurs either frequently in small amounts, as from N deposition, or that occur infrequently in larger amounts, as from application of N fertilizers. |
| [178] | 为认识放牧对青藏高原东部中生性的高寒草甸草地和半湿生的沼泽草地凋落物分解的影响,在这两种草地上分别 设置了围栏和放牧样地,研究了其各自的混合凋落物样品和4个优势物种(发草Deschampsiacaespitos、鹅绒委陵菜Potentilla anserine、木里苔草Carexmuliensis、藏嵩草Kobresiatibetica)凋落物的分解和养分释放动态,这4个优势物种也大致 代表了当地沼泽草地生态系统在放牧和气候变暖驱动下逆行演替不同阶段的优势物种类群.结果表明,各优势物种凋落物的分解速率有显著差异；放牧在总体上促进 了凋落物的分解,但不同物种的响应有所不同；放牧对凋落物C的释放影响不显著或有抑制作用,但对N、P的释放具有一定促进作用.对各优势物种凋落物分解和 养分释放模式的分析表明,群落逆行演替过程中,凋落物分解和C释放加速,可能促进沼泽湿地退化的正反馈效应.草甸草地的退化标志物种鹅绒委陵菜具有较高的 凋落物质量和分解速度,反映了中生条件下植物应对牲畜啃食采用“逃避”而非“抵抗”策略的趋向. |
| [179] | Summary Biologically reactive nitrogen (Nr) enrichment threatens biodiversity in diverse ecosystems. Previous controlled N addition experiments may overestimate the effects of atmospheric Nr deposition on the rate of species loss, as it has been found that low frequency Nr additions, as used in traditional studies, lead to more rapid biodiversity loss. It remains unclear, however, whether the colonization of new species (gain) or extinction of old species (loss) is the cause of this difference. By independently manipulating the frequency (twice vs. monthly additions year611) and the rate (from 0 to 5002g N02m61202year611) of NH4NO3 inputs for six years in a temperate grassland of northern China, we aimed to examine the contribution of gain and loss of species to the reduction in species richness under different regimes of Nr inputs. Results showed that the gain of new species was higher at a high frequency of N addition than that at a low addition frequency, while loss of existing species was similar between the two frequencies of N addition. The number of new species gained decreased and old species lost increased with the increasing rate of Nr addition at both annual and five-year intervals. Cumulative gain of new species was negatively correlated with soil acidification, ammonium concentration and community biomass accumulation, whereas cumulative loss of old species was positively correlated with these variables. Our results revealed lower new species colonization results in lower species richness at low frequency of Nr addition. Findings from this study highlight the important role of N addition frequency in regulating the effects of Nr addition on community dynamics. To assess the effects of atmospheric Nr deposition on ecosystem structure and functioning, it is necessary to assess not only the dose but also the frequency of N addition. |
| [180] | Climate change scenarios that include precipitation shifts and nitrogen (N) deposition are impacting carbon (C) budgets in arid ecosystems. Roots constitute an important part of the C cycle, but it is still unclear which factors control root mass loss and nutrient release in arid lands. Litterbags were used to investigate the decomposition rate and nutrient dynamics in root litter with water and N-addition treatments in the Gurbantunggut Desert in China. Water and N addition had no significant effect on root mass loss and the N and phosphorus content of litter residue. The loss of root litter and nutrient releases were strongly controlled by the initial lignin content and the lignin:N ratio, as evidenced by the negative correlations between decomposition rate and litter lignin content and the lignin:N ratio. Fine roots ofSeriphidium santolinum(with higher initial lignin content) had a slower decomposition rate in comparison to coarse roots. Results from this study indicate that small and temporary changes in rainfall and N deposition do not affect root decomposition patterns in the Gurbantunggut Desert. Root decomposition rates were significantly different between species, and also between fine and coarse roots, and were determined by carbon components, especially lignin content, suggesting that root litter quality may be the primary driver of belowground carbon turnover. |
| [181] | Bacterial communities are the primary engineers during litter decomposition and related material cycling, and they can be strongly controlled by seasonal changes in temperature and other environmental factors. However, limited information is available on changes in the bacterial community from winter to the growing season as litter decomposition proceeds in cold climates. Here, we investigated the abundance and structure of bacterial communities using real-time quantitative PCR and denaturing gradient gel electrophoresis (DGGE) during a 2-year field study of the decomposition of litter of 4 species in the winter and growing seasons of an alpine forest of the eastern Tibetan Plateau. The abundance of the bacterial 16S rRNA gene was relatively high during decomposition of cypress and birch litter in the first winter, but for the other litters 16S rRNA abundance during both winters was significantly lower than during the following growing season. A large number of bands were observed on the DGGE gels, and their intensities and number from the winter samples were lower than those from the growing season during the 2-year decomposition experiment. Eighty-nine sequences from the bands of bacteria that had been cut from the DGGE gels were affiliated with 10 distinct classes of bacteria and an unknown group. A redundancy analysis indicated that the moisture, mass loss, and elemental content (e.g., C, N, and P) of the litter significantly affected the bacterial communities. Collectively, the results suggest that uneven seasonal changes in climate regulate bacterial communities and other decomposers, thus affecting their contribution to litter decomposition processes in the alpine forest. |
| [182] | The Long-Term Intersite Decomposition Experiment in China (hereafter referred to as LTIDE-China) was established in 2002 to study how substrate quality and macroclimate factors affect leaf litter decomposition. The LTIDE-China includes a wide variety of natural and managed ecosystems, consisting of 12 forest types (eight regional broadleaf forests, three needle-leaf plantations and one broadleaf plantation) at eight locations across China. Samples of mixed leaf litter from the south subtropical evergreen broadleaf forest in Dinghushan (referred to as the DHS sample) were translocated to all 12 forest types. The leaf litter from each of other 11 forest types was placed in its original forest to enable comparison of decomposition rates of DHS and local litters. The experiment lasted for 30 months, involving collection of litterbags from each site every 3 months. Our results show that annual decomposition rate-constants, as represented by regression fitted k-values, ranged from 0.169 to 1.454/year. Climatic factors control the decomposition rate, in which mean annual temperature and annual actual evapotranspiration are dominant and mean annual precipitation is subordinate. Initial C/N and N/P ratios were demonstrated to be important factors of regulating litter decomposition rate. Decomposition process may apparently be divided into two phases controlled by different factors. In our study, 0.75 years is believed to be the dividing line of the two phases. The fact that decomposition rates of DHS litters were slower than those of local litters may have been resulted from the acclimation of local decomposer communities to extraneous substrate. |
| [183] | |
| [184] | Abstract Elevated nitrogen (N) deposition to tropical forests may accelerate ecosystem phosphorus (P) limitation. This study examined responses of fine root biomass, nutrient concentrations, and acid phosphatase activity (APA) of bulk soil to five years of N and P additions in one old-growth and two younger lowland tropical forests in southern China. The old-growth forest had higher N capital than the two younger forests from long-term N accumulation. From February 2007 to July 2012, four experimental treatments were established at the following levels: Control, N-addition (150 kg N ha(-1) yr(-1)), P-addition (150 kg P ha(-1) yr(-1)) and N+P-addition (150 kg N ha(-1) yr(-1) plus 150 kg P ha(-1) yr(-1)). We hypothesized that fine root growth in the N-rich old-growth forest would be limited by P availability, and in the two younger forests would primarily respond to N additions due to large plant N demand. Results showed that five years of N addition significantly decreased live fine root biomass only in the old-growth forest (by 31%), but significantly elevated dead fine root biomass in all the three forests (by 64% to 101%), causing decreased live fine root proportion in the old-growth and the pine forests. P addition significantly increased live fine root biomass in all three forests (by 20% to 76%). The combined N and P treatment significantly increased live fine root biomass in the two younger forests but not in the old-growth forest. These results suggest that fine root growth in all three study forests appeared to be P-limited. This was further confirmed by current status of fine root N:P ratios, APA in bulk soil, and their responses to N and P treatments. Moreover, N addition significantly increased APA only in the old-growth forest, consistent with the conclusion that the old-growth forest was more P-limited than the younger forests. |
| [185] | Abstract The effects of nitrogen (N) and phosphorus (P) addition on litter decomposition are poorly understood in Tibetan alpine meadows. Leaf litter was collected from plots within a factorial N65×65P addition experiment and allowed to decompose over 708 days in an unfertilized plot to determine the effects of N and/or P addition on litter decomposition. Results showed that nutrient addition significantly affected initial P and P-related biochemical properties of litter from all four species. However, the responses of litter N and N-related biochemical properties to nutrient addition were quite species-specific. Litter C decomposition and N release were species-specific. However, N and P addition significantly affected litter P release. Ratios of Hemicellulose65+65Cellulose to N and P were significantly related to litter C decomposition; C:N ratio was a determinant of litter N release; and C:P and (Hemicellulose65+65Cellulose):P controlled litter P release. Overall, litter C decomposition was controlled by litter quality of different plant species, and strongly affected by P addition. Increasing N availability is likely to affect litter C decomposition more indirectly by shifting plant species composition than directly by improving litter quality, and may accelerate N and P cycles, but shift the ecosystem to P limitation. |
| [186] | Background and Aims: Atmospheric nitrogen (N) deposition has elevated rapidly in tropical regions where N-fixing tree species are widespread. However, the effect of N deposition on litter decomposition in forests with N-fixing tree species remains unclear. We examined the effect of N addition on litter decomposition and nutrient release in two tropical plantations with Acacia auriculiformis ( AA, N-fixing) and Eucalyptus urophylla ( EU, non-N-fixing) in South China. Methods: Three levels of N additions were conducted: control, medium-N (50 kg N ha yr.) and high-N (100 kg N ha yr.) in each plantation. Results: Initial decomposition rate ( k) for the control plots was faster in the AA plantation than in the EU plantation, but later in decomposition, larger fraction of slowly decomposing litter ( A) remained in the former. N addition increased the slow fraction ( A), decreasing soil microbial biomass and reducing acid-unhydrolyzable residue (AUR) degradation in the AA plantation. In the EU plantation, however, N additions significantly increased initial decomposition rate ( k) and soil N availability. Furthermore, N addition decreased litter carbon and N release (in the AA plantation), while litter phosphorus release also decreased in both plantations. Conclusions: With ongoing N deposition in future, tropical plantations with N-fixing tree species would potentially increase carbon accumulation and nutrient retention in forest floor by slowing litter decomposition. |
| [187] | Atmospheric nitrogen (N) deposition has accelerated in the last several decades due to anthropogenic activities, such as nitrogen fertilization, N-fixing plants cultivation and fossil fuel and biomass combustion. Increasing N deposition has become one of the important factors regulating N cycle in forest ecosystems. Forest ecosystems can retain part of deposited N in soil by biotic and abiotic mechanisms, but when N inputs exceed the capacity of soil retention, N losses will aggravate in terms of N oxide emission and/or nitrate leaching. The excess N input has threatened ecosystem health via acidification and eutrophication, causing declines in terrestrial biodiversity and forest productivity in forest ecosystems of Europe and North America. Recently, China has become one of the three areas that undergo severe N deposition in the world. Impacts of N deposition on soil N cycle in Chinese forest ecosystems have received increasing concern. In this paper, we reviewed the processes of soil N cycle and their responses to atmospheric N deposition based on available literature. The objective is to enhance our understanding on how N deposition affects soil N cycle in forest ecosystems and provide scientific information for sustainable forest management. The review mainly includes the following four aspects: (1) processes of soil N cycle and their controlling factors. These processes include biological N fixation (BNF), decomposition, mineralization, nitrification, denitrification, N oxide emission and NO 3 61 N leaching. The controlling factors of these processes are complicated and interactional. Only one of these factors altered may affect soil N cycle. For example, C/N is the factor that controls BNF, decomposition, mineralization and NO 3 61 N leaching. (2) Research methods and current results about studies are related to the impact of N deposition on soil N cycle in forest ecosystems. In general, the research methods are long-term simulated N deposition experiment, N deposition gradient method, roof clean rain method and 15 N tracing method. Effects of N deposition on soil N cycle vary depending on different initial N statuses and lengths of experiment. In “N-limited” forests, N deposition tended to have positive effect on soil N cycling processes, such as accelerating litter decomposition rate and N mineralization rate. However, such result generally showed in short-term fertilization experiments. In some long-term fertilization experiments, it showed that the negative effects would rise when the forests reached N saturation. Compared to “N-limited” forests in temperate region, N deposition tended to have negative or neutral effects in “N-rich” tropical forest. For example, N deposition promoted nitrification process in tropical forests. (3) Possible mechanisms for the effect of N deposition on soil N cycle: N deposition can affect soil N cycle through altering the chemical characteristic of forest substrates, the biomass and community composition of plant and microorganism. (4) Current problems and future research needs for the study about the effect of N deposition on soil N cycle: What role does regional diversity, changes in forest type, and interaction of carbon (C), N and phosphorus (P) play on the effect of N deposition on soil N cycle in forest ecosystems deserve our further study in the future. |
1
2000
... 土壤酸度是调控陆地生态系统生物多样性和生物地球化学循环的重要因子.人类活动产生的氮氧化合物(NOX)使草地生态系统土壤酸化现象越来越严重(
Is nitrogen deposition altering the nitrogen status of northern forests?
1
2003
... N添加形式包括硝酸铵、尿素和其他形式(NaNO3和混合肥等).大气湿沉降主要是NO3-、NH4+及少量可溶性有机氮经降水下降到地表, 采用硝酸铵的施肥方式能最大程度地模拟大气N沉降, 且硝酸铵含N量高达34%, 施肥后NH4+和NO3-都能被植物和土壤吸收, 因此施用硝酸铵是模拟N沉降实验中最常见和最有效的施肥方式(
Simple three-pool model accurately describes patterns of long-term litter decomposition in diverse climates.
2
2008
... 过去大多数的凋落物分解研究多为短期的原位观测, 近年来, 凋落物分解研究的时空尺度发生了变化.越来越多的研究将原位观测的凋落物分解实验进行整合, 通过对比不同生态系统类型、不同气候区凋落物分解的差异, 来研究大尺度上影响凋落物分解的因子(
... ).Adair等(2008)通过整合分析凋落物分解研究, 根据凋落物分解所需时间和分解的难易程度建立了凋落物三库模型, 描述凋落物分解的完整过程, 即易分解库、中期分解库和难分解库(
Climate, leaf litter chemistry and leaf litter decomposition in terrestrial ecosystems: A triangular relationship.
1
1997
... 凋落物质量, 即凋落物的相对可分解性.衡量凋落物质量的指标主要有C含量、N含量、磷(P)含量、木质素含量、纤维素含量, 以及它们之间的比值(
The freezer defrosting: Global warming and litter decomposition rates in cold biomes.
2
2006
... 影响凋落物分解的环境因子包括温度和降水.温度是调控生态系统生化过程和物质能量周转的关键因子, 对凋落物分解起主导作用(
... 调控凋落物分解的关键因子主要有环境因子、凋落物质量和生物因子等, 它们起作用的顺序通常为: 气候>凋落物质量>土壤生物(
Combining theory and experiment to understand effects of inorganic nitrogen on litter decomposition.
3
2001
... 近年来, 国内外****对N添加条件下的草地凋落物分解进行了研究, 但结果存在较大的不一致性, 如促进效应(
... 细菌和真菌是分解者, 在凋落物分解的各阶段中作用不同: 在前期, 真菌起主要作用; 在后期, 细菌起主要作用(
... 混合凋落物的实际分解速率偏离于期望分解速率时则称为混合凋落物的非加和性效应, 混合凋落物复杂的化学成分和丰富的空间异质性是影响混合凋落物分解时非加性效应产生的重要原因(
Nitrogen alters carbon dynamics during early succession in boreal forest.
1
2010
... 细菌和真菌是分解者, 在凋落物分解的各阶段中作用不同: 在前期, 真菌起主要作用; 在后期, 细菌起主要作用(
Litter decomposition of signalgrass grazed with different stocking rates and nitrogen fertilizer levels.
2
2014
... 自然生态系统中, 各种全球变化的现象(如全球变暖, 降水变化, N、P沉降, 以及紫外辐射等)时有发生, 且它们的交互作用无处不在.因此单独研究N沉降对凋落物分解过程的影响, 无法准确、全面地评估生态系统C循环和养分循环对未来全球变化响应的真实情况, 需要将其综合分析(
... 放牧和围封是人类管理和利用草地资源最普遍的方式, 是影响草地生态系统碳库和养分循环的重要人为因素.牲畜的啃食、排泄和踩踏作用可以改变地表植被特征、土壤环境(如温度、含水量等)及其养分含量, 影响凋落物分解(
Possible mechanisms leading to a delay in carbon stock recovery after land use change.
1
2007
... 凋落物分解是一个连续的生物降解过程, 影响凋落物分解的生物因子包括土壤动物、微生物及其产生的分解酶(
Tradeoffs and thresholds in the effects of nitrogen addition on biodiversity and ecosystem functioning: Evidence from Inner Mongolia grasslands.
2
2010
... N是草地生态系统的主要限制因子, N沉降使植物可有效利用的N增加, 减弱草地N限制, 促进植物生长, 凋落物产量和土壤C输入随之增多(
... 植物群落组成的改变包括物种的演替、优势种的定居和稀有物种的消失.N沉降会减弱物种丰富度, 改变草地植物群落组成, 使凋落物质量发生改变, 从而影响分解(
Long-term presence of tree species but not chemical diversity affect litter mixture effects on decomposition in a neotropical rainforest.
1
2011
... 混合凋落物的实际分解速率偏离于期望分解速率时则称为混合凋落物的非加和性效应, 混合凋落物复杂的化学成分和丰富的空间异质性是影响混合凋落物分解时非加性效应产生的重要原因(
Effect of N deposition on decomposition of plant litter and soil organic matter in forest systems.
1
1997
... N沉降加快营养元素循环, 促进凋落物形成过程中的营养元素再分配, 使凋落物中N、P含量增加(
Plant Litter-Decomposition, Humus Formation, Carbon Sequestration. Springer
1
2003
... 草地凋落物是由植物地上和地下部分产生并归还到土壤的所有有机质的总称, 是土壤C库的主要来源和维持土壤肥力的基础.凋落物分解是陆地生态系统养分循环的关键过程, 陆地生态系统中约90%的净初级生产量以凋落物的形式归还给土 壤, 其养分再循环供给植物的生长发育(
Decomposition rate and chemical changes in decomposing needle litter of Scots pine: Influence of chemical composition.
1
1980
... 近年来, 国内外****对N添加条件下的草地凋落物分解进行了研究, 但结果存在较大的不一致性, 如促进效应(
Litter decomposition in grasslands of Central North America (US Great Plains).
1
2009
... 影响凋落物分解的环境因子包括温度和降水.温度是调控生态系统生化过程和物质能量周转的关键因子, 对凋落物分解起主导作用(
Negative impact of nitrogen deposition on soil buffering capacity.
1
2008
... N沉降除提高土壤N有效性外, 还会造成土壤酸化, 土壤中H+和Al3+的浓度上升, 矿质阳离子(Ca2+、Mg2+、Na+等)浓度下降, 土壤质量变差, 阻碍植被和地下微生物群落的生长(
Understanding the dominant controls on litter decomposition.
1
2016
... 由此可见, 土壤过程和分解者对凋落物分解的影响是今后凋落物分解研究的重点.不同生态系统类型、不同凋落物分解阶段中影响分解的主导因子不同, 也可能存在一定的阈值, 使得主导凋落物分解的因子从一个转向另一个.因此, 重视小区域尺度上凋落物分解过程的研究、确定凋落物分解主导因子发生改变的原因和阈值是今后凋落物分解因子研究的关键(
Using litter chemistry controls on microbial processes to partition litter carbon fluxes with the Litter Decomposition and Leaching (LIDEL) Model.
1
2016
... 除了大时空尺度的凋落物分解研究外, 也有****关注更小的时空尺度, 研究一天内主导凋落物分解的因子, 结果表明主导白天和夜晚凋落物分解的因子不同——白天以非生物降解(光降解和热降解)为主, 而夜晚以微生物降解为主(
Microbial enzyme shifts explain litter decay responses to simulated nitrogen deposition.
1
2000
... 分解凋落物中木质素的酶类主要是多酚氧化酶, 在质量较差(木质素含量高)的凋落物中, N添加抑制多酚氧化酶活性, 阻碍了难分解物质的分解, 这是N添加抑制凋落物分解的重要机制(
Soil fauna alter the effects of litter composition on nitrogen cycling 290 in a mineral soil.
1
2011
... 凋落物分解是一个连续的生物降解过程, 影响凋落物分解的生物因子包括土壤动物、微生物及其产生的分解酶(
The nature of nutrient limitation in plant communities.
1
1986
... 植物群落组成的改变包括物种的演替、优势种的定居和稀有物种的消失.N沉降会减弱物种丰富度, 改变草地植物群落组成, 使凋落物质量发生改变, 从而影响分解(
Principles of Terrestrial Ecosystem Ecology. Springer
1
2002
... 大多数N添加研究持续时间太短, 其中85.5%的N添加研究持续时间不超过4年, 加上高的空间差异性, 我们无法准确地评估凋落物分解对N添加的响应(
Global change effects on crop photosynthesis and production in Mediterranean: The case of Crete, Greece.
1
2005
... 自然生态系统中, 各种全球变化的现象(如全球变暖, 降水变化, N、P沉降, 以及紫外辐射等)时有发生, 且它们的交互作用无处不在.因此单独研究N沉降对凋落物分解过程的影响, 无法准确、全面地评估生态系统C循环和养分循环对未来全球变化响应的真实情况, 需要将其综合分析(
a). Effects of nitrogen enrichment on belowground communities in grassland: Relative role of soil nitrogen availability vs. soil acidification.
2
2015
... 土壤酸度是调控陆地生态系统生物多样性和生物地球化学循环的重要因子.人类活动产生的氮氧化合物(NOX)使草地生态系统土壤酸化现象越来越严重(
... N沉降除提高土壤N有效性外, 还会造成土壤酸化, 土壤中H+和Al3+的浓度上升, 矿质阳离子(Ca2+、Mg2+、Na+等)浓度下降, 土壤质量变差, 阻碍植被和地下微生物群落的生长(
a). Effects of experimental nitrogen and phosphorus addition on litter decomposition in an old-growth tropical forest.
1
2013
... P是植物生长的重要限制因子, 控制着生态系统的关键过程.N添加后, 许多草地生态系统由N限制转向N饱和, 且N在生态系统中的归还速率高于P, 因此生态系统过程受到P限制.探究草地凋落物分解对N、P添加耦合效应的响应可为深入分析N、P添加对生态系统物质循环和能量流动产生的影响提供理论依据(
b). Effects of nitrogen deposition on carbon cycle in terrestrial ecosystems of China: A meta- analysis.
1
2015
... 近年来, 国内外****对N添加条件下的草地凋落物分解进行了研究, 但结果存在较大的不一致性, 如促进效应(
b). Responses of ammonia-oxidizing bacteria and archaea to nitrogen fertilization and precipitation increment in a typical temperate steppe in Inner Mongolia.
1
2013
... 土壤酸度是调控陆地生态系统生物多样性和生物地球化学循环的重要因子.人类活动产生的氮氧化合物(NOX)使草地生态系统土壤酸化现象越来越严重(
1
2000
... 在过去一个世纪里, 化石燃料燃烧、施肥等人类活动使全球大气氮(N)沉降量迅速增加.人类活动造成的N沉降量由1860年的31.6 Tg·a-1增加到20世纪90年代的103 Tg·a-1, 预计到2050年, 可能会增至195 Tg·a-1 (
Secondary metabolites of Pinus halepensis alter decomposer organisms and litter decomposition during afforestation of abandoned agricultural zones.
2
2014
... 凋落物质量, 即凋落物的相对可分解性.衡量凋落物质量的指标主要有C含量、N含量、磷(P)含量、木质素含量、纤维素含量, 以及它们之间的比值(
... ;
Plant secondary metabolites: A key driver of litter decomposition and soil nutrient cycling.
1
2016
... 凋落物质量, 即凋落物的相对可分解性.衡量凋落物质量的指标主要有C含量、N含量、磷(P)含量、木质素含量、纤维素含量, 以及它们之间的比值(
Nitrogen enrichment and plant communities.
1
2010
... 植物群落组成的改变包括物种的演替、优势种的定居和稀有物种的消失.N沉降会减弱物种丰富度, 改变草地植物群落组成, 使凋落物质量发生改变, 从而影响分解(
Roots and associated fungi drive long- term carbon sequestration in boreal forest.
1
2013
... 细菌和真菌是分解者, 在凋落物分解的各阶段中作用不同: 在前期, 真菌起主要作用; 在后期, 细菌起主要作用(
Response of soil microbial biomass and community composition to chronic nitrogen additions at Harvard forest.
1
2004
... 细菌和真菌是分解者, 在凋落物分解的各阶段中作用不同: 在前期, 真菌起主要作用; 在后期, 细菌起主要作用(
Plant species traits are the predominant control on litter decomposition rates within biomes worldwide.
1
2008
... 凋落物质量, 即凋落物的相对可分解性.衡量凋落物质量的指标主要有C含量、N含量、磷(P)含量、木质素含量、纤维素含量, 以及它们之间的比值(
Atmospheric nitrate deposition and the microbial degradation of cellobiose and vanillin in a northern hardwood forest.
2
2004
... N沉降加快营养元素循环, 促进凋落物形成过程中的营养元素再分配, 使凋落物中N、P含量增加(
... 分解凋落物中木质素的酶类主要是多酚氧化酶, 在质量较差(木质素含量高)的凋落物中, N添加抑制多酚氧化酶活性, 阻碍了难分解物质的分解, 这是N添加抑制凋落物分解的重要机制(
Atmospheric water vapor as driver of litter decomposition in Mediterranean shrubland and grassland during rainless seasons.
1
2010
... 影响凋落物分解的环境因子包括温度和降水.温度是调控生态系统生化过程和物质能量周转的关键因子, 对凋落物分解起主导作用(
Microbial mechanisms mediating increased soil C storage under elevated atmospheric N deposition.
1
2013
... 细菌和真菌是分解者, 在凋落物分解的各阶段中作用不同: 在前期, 真菌起主要作用; 在后期, 细菌起主要作用(
Global analysis of nitrogen and phosphorus limitation of primary producers in freshwater, marine and terrestrial ecosystems.
1
2007
... N是草地生态系统关键的养分因子, 对植物的生长起十分重要的作用(
Incorporation of carbon from decomposing litter of two pioneer plant species into microbial communities of the detritusphere.
1
2011
... 凋落物分解是一个连续的生物降解过程, 影响凋落物分解的生物因子包括土壤动物、微生物及其产生的分解酶(
Harpole WS, de Mazancourt C (2010). Plant water use affects competition for nitrogen: Why drought favors invasive species in California.
1
2175
... 水分和N是干旱和半干旱草地生态系统的限制因子.随着地表温度的升高, 降水特征发生变化, 长期干旱和强降雨天气频繁发生(
Trends of nitrogen in air and precipitation: Model results and observations at EMEP sites in Europe, 1980-2003.
1
2008
... 欧美国家由于工农业较发达, N沉降研究起步早, 手段和技术相对成熟, 目前已经建立了系统而全面的跨地区大型监测网络.但对于N添加的研究一直只局限于森林生态系统, 直到20世纪90年代才有欧洲和北美的一些国家和地区对草地生态系统的响应进行研究(
Stoichiometry of leaf nitrogen and phosphorus of grasslands of the Inner Mongolian and Qinghai-Tibet Plateau in relation to climatic variables and vegetation organization levels.
1
2016
... 过去关于凋落物分解的研究集中在某一时间段内的静态研究, 而对凋落物分解整个过程中养分元素的转移路径、转移速率及其在植物、凋落物、土壤中的剩余情况等了解不足.生态化学计量学是生态学的一个新兴领域, 主要研究生物体与其所处环境之间的养分元素关系, 是分析生态系统养分循环过程的工具(
Effect of added nitrogen on plant litter decomposition depends on initial soil carbon and nitrogen stoichiometry.
1
2015
... N沉降改善草地生态系统的N状况, 导致N饱和和P限制(
Enzyme dynamics on decomposing leaf litter of Cistus incanus and Myrtus communisin in a Mediterranean ecosystem.
1
2000
... 凋落物分解是一个连续的生物降解过程, 影响凋落物分解的生物因子包括土壤动物、微生物及其产生的分解酶(
Experimentally simulated global warming and nitrogen enrichment effects on microbial litter decomposers in a Marsh.
1
2011
... 混合凋落物的实际分解速率偏离于期望分解速率时则称为混合凋落物的非加和性效应, 混合凋落物复杂的化学成分和丰富的空间异质性是影响混合凋落物分解时非加性效应产生的重要原因(
Leaf traits capture the effects of land use changes and climate on litter decomposability of grasslands across Europe.
1
2009
... 凋落物质量(N、木质素、纤维素、单宁等)的分析测定常采用化学分析法, 测定前都需要经过复杂的研磨、提取过程, 耗费时间长且存在较大的误差.目前, 有研究利用红外光谱分析(near-infrared spectrometry, NIRS)和代谢组学等新技术测定凋落物中的化合物含量.与化学分析法相比, 红外光谱分析技术免除了研磨、提取等复杂的步骤, 且可以同时测量凋落物中的多种化合物含量, 具有很强的整合性(
Anthropogenic N deposition slows decay by favoring bacterial metabolism: Insights from metagenomic analyses.
1
2016
... 近年来, 国内外****对N添加条件下的草地凋落物分解进行了研究, 但结果存在较大的不一致性, 如促进效应(
Linking litter decomposition of above- and below-ground organs to plant-soil feedbacks worldwide.
1
2013
... 细根是生态系统的重要组成部分, 它的死亡和分解对全球C收支和土壤养分循环有着重要的意义.与森林生态系统相比, 草地生态系统地下生产力高、根系周转速率快, 其根系分解的研究更应该受到研究者的重视(
Chronic nitrogen enrichment affects the structure and function of the soil microbial community in temperate hardwood and pine forests.
2
2004
... N是草地生态系统关键的养分因子, 对植物的生长起十分重要的作用(
... 凋落物分解是一个非常复杂的生物、物理、化学过程, 深受非生物因子(环境因子、土壤理化性质)、凋落物基质质量和生物因子(土壤微生物和酶活性)的影响, 且各因子间存在复杂的交互作用, 共同影响凋落物的形成和分解.N添加可通过改变土壤养分有效性、凋落物产量和质量、土壤生物及凋落物分解环境影响凋落物分解(
Nitrogen cycles: Past, present, and future.
1
2004
... 在过去一个世纪里, 化石燃料燃烧、施肥等人类活动使全球大气氮(N)沉降量迅速增加.人类活动造成的N沉降量由1860年的31.6 Tg·a-1增加到20世纪90年代的103 Tg·a-1, 预计到2050年, 可能会增至195 Tg·a-1 (
Impact of nitrogenous fertiliser-induced proton release on cultivated soils with contrasting carbonate contents: A column experiment.
1
2011
... 土壤酸度是调控陆地生态系统生物多样性和生物地球化学循环的重要因子.人类活动产生的氮氧化合物(NOX)使草地生态系统土壤酸化现象越来越严重(
Responses of microbial respiration to nitrogen addition in two alpine soils in the Qinghai-Tibetan Plateau.
1
2015
... 欧美国家由于工农业较发达, N沉降研究起步早, 手段和技术相对成熟, 目前已经建立了系统而全面的跨地区大型监测网络.但对于N添加的研究一直只局限于森林生态系统, 直到20世纪90年代才有欧洲和北美的一些国家和地区对草地生态系统的响应进行研究(
Decomposition dynamics in mixed-species leaf litter.
1
2004
... 草地凋落物是由植物地上和地下部分产生并归还到土壤的所有有机质的总称, 是土壤C库的主要来源和维持土壤肥力的基础.凋落物分解是陆地生态系统养分循环的关键过程, 陆地生态系统中约90%的净初级生产量以凋落物的形式归还给土 壤, 其养分再循环供给植物的生长发育(
The effect of microarthropods on litter decomposition depends on litter quality.
1
2016
... 凋落物分解是一个连续的生物降解过程, 影响凋落物分解的生物因子包括土壤动物、微生物及其产生的分解酶(
Diversity meetsdecomposition.
1
2010
... 凋落物分解是一个连续的生物降解过程, 影响凋落物分解的生物因子包括土壤动物、微生物及其产生的分解酶(
Effects of grazing and rainfall variability on root and shoot decomposition in a semi-arid grassland.
1
2009
... 放牧和围封是人类管理和利用草地资源最普遍的方式, 是影响草地生态系统碳库和养分循环的重要人为因素.牲畜的啃食、排泄和踩踏作用可以改变地表植被特征、土壤环境(如温度、含水量等)及其养分含量, 影响凋落物分解(
Biotic degradation at night, abiotic degradation at day: Positive feedbacks on litter decomposition in drylands.
1
2016
... 除了大时空尺度的凋落物分解研究外, 也有****关注更小的时空尺度, 研究一天内主导凋落物分解的因子, 结果表明主导白天和夜晚凋落物分解的因子不同——白天以非生物降解(光降解和热降解)为主, 而夜晚以微生物降解为主(
Fertilization effects on species density and primary productivity in herbaceous plant communities.
3
2000
... 草地凋落物是由植物地上和地下部分产生并归还到土壤的所有有机质的总称, 是土壤C库的主要来源和维持土壤肥力的基础.凋落物分解是陆地生态系统养分循环的关键过程, 陆地生态系统中约90%的净初级生产量以凋落物的形式归还给土 壤, 其养分再循环供给植物的生长发育(
... N是草地生态系统关键的养分因子, 对植物的生长起十分重要的作用(
... 凋落物分解是一个非常复杂的生物、物理、化学过程, 深受非生物因子(环境因子、土壤理化性质)、凋落物基质质量和生物因子(土壤微生物和酶活性)的影响, 且各因子间存在复杂的交互作用, 共同影响凋落物的形成和分解.N添加可通过改变土壤养分有效性、凋落物产量和质量、土壤生物及凋落物分解环境影响凋落物分解(
Four hypotheses about the effects of soil nitrogen availability on fine root production and turnover.
1
2007
... 根系的生产和储存是生态系统生产力的重要组成部分, 其分解对草地生态系统养分循环具有重要的意义, 但目前针对根系凋落物的研究很少(
Climate and litter quality differently modulate the effects of soil fauna on litter decomposition across biomes.
1
2013
... 调控凋落物分解的关键因子主要有环境因子、凋落物质量和生物因子等, 它们起作用的顺序通常为: 气候>凋落物质量>土壤生物(
N:P ratios influence litter decomposition and colonization by fungi and bacteria in microcosms.
1
2009
... 凋落物质量是导致N添加对凋落物分解影响不一致性的主要原因(
The role of polyphenols in terrestrial ecosystem nutrient cycling.
1
2000
... 凋落物质量, 即凋落物的相对可分解性.衡量凋落物质量的指标主要有C含量、N含量、磷(P)含量、木质素含量、纤维素含量, 以及它们之间的比值(
Competition for light causes plant biodiversity loss after eutrophication.
1
2009
... 根系的生产和储存是生态系统生产力的重要组成部分, 其分解对草地生态系统养分循环具有重要的意义, 但目前针对根系凋落物的研究很少(
Linkages between grazing history and herbivore exclusion on decomposition rates in mineral soils of subalpine grasslands.
1
2014
... 放牧和围封是人类管理和利用草地资源最普遍的方式, 是影响草地生态系统碳库和养分循环的重要人为因素.牲畜的啃食、排泄和踩踏作用可以改变地表植被特征、土壤环境(如温度、含水量等)及其养分含量, 影响凋落物分解(
生态化学计量学: 探索从个体到生态系统的统一化理论. 植物生态学报,
1
2010
... N沉降改善草地生态系统的N状况, 导致N饱和和P限制(
Response of aboveground biomass and diversity to nitrogen addition—A five-year experiment in semi-arid grassland of Inner Mongolia, China.
1
2016
... 植物群落组成的改变包括物种的演替、优势种的定居和稀有物种的消失.N沉降会减弱物种丰富度, 改变草地植物群落组成, 使凋落物质量发生改变, 从而影响分解(
Does background nitrogen deposition affect the response of boreal vegetation to fertilization?
1
2013
... N是草地生态系统的主要限制因子, N沉降使植物可有效利用的N增加, 减弱草地N限制, 促进植物生长, 凋落物产量和土壤C输入随之增多(
Interactive effects of elevated CO2, N deposition and climate change on plant litter quality in a California annual grassland.
1
2005
... 水分和N是干旱和半干旱草地生态系统的限制因子.随着地表温度的升高, 降水特征发生变化, 长期干旱和强降雨天气频繁发生(
Grass litter responses to warming and N addition: Temporal variation in the contributions of litter quality and environmental effects to decomposition.
2
2015
... 近年来, 国内外****对N添加条件下的草地凋落物分解进行了研究, 但结果存在较大的不一致性, 如促进效应(
... 大多数N添加研究持续时间太短, 其中85.5%的N添加研究持续时间不超过4年, 加上高的空间差异性, 我们无法准确地评估凋落物分解对N添加的响应(
Carbon sequestration in ecosystems: The role of stoichiometry.
1
2004
... N沉降改善草地生态系统的N状况, 导致N饱和和P限制(
Nitrogen effects on decomposition: A five- year experiment in eight temperate sites.
1
2008
... 凋落物质量是导致N添加对凋落物分解影响不一致性的主要原因(
Response of decomposing litter and its microbial community to multiple forms of nitrogen enrichment.
2
2012
... N沉降加快营养元素循环, 促进凋落物形成过程中的营养元素再分配, 使凋落物中N、P含量增加(
... N添加的浓度范围和梯度的设置是造成诸多实验结果存在差异的主要原因, 其设置的合理性也是影响实验结果的重要指标.通过总结, N添加实验的浓度范围在10-640 kg·hm-2·a-1, 很多研究只是单纯设置高、中、低3个N添加梯度, 缺乏一定的理论依据(
Quantification of effects of season and nitrogen supply on tree below-ground carbon transfer to ectomycorrhizal fungi and other soil organisms in a boreal pine forest.
1
2010
... 细菌和真菌是分解者, 在凋落物分解的各阶段中作用不同: 在前期, 真菌起主要作用; 在后期, 细菌起主要作用(
中国草地地下生物量研究进展
1
2005
... 在过去一个世纪里, 化石燃料燃烧、施肥等人类活动使全球大气氮(N)沉降量迅速增加.人类活动造成的N沉降量由1860年的31.6 Tg·a-1增加到20世纪90年代的103 Tg·a-1, 预计到2050年, 可能会增至195 Tg·a-1 (
2
... 在过去一个世纪里, 化石燃料燃烧、施肥等人类活动使全球大气氮(N)沉降量迅速增加.人类活动造成的N沉降量由1860年的31.6 Tg·a-1增加到20世纪90年代的103 Tg·a-1, 预计到2050年, 可能会增至195 Tg·a-1 (
... P是植物生长的重要限制因子, 控制着生态系统的关键过程.N添加后, 许多草地生态系统由N限制转向N饱和, 且N在生态系统中的归还速率高于P, 因此生态系统过程受到P限制.探究草地凋落物分解对N、P添加耦合效应的响应可为深入分析N、P添加对生态系统物质循环和能量流动产生的影响提供理论依据(
Diversity of shrub tree layer, leaf litter decomposition and N release in a Brazilian Cerrado under N, P and N plus P additions.
1
2010
... 室内分解培养法是指在实验室内模拟凋落物自然分解状态, 此方法多用于控制实验, 研究光照、水分、温度等因子的变化对凋落物分解过程的影响(
Effects of nitrogen addition and litter properties on litter decomposition and enzyme activities of individual fungi.
1
2014
... 近年来, 国内外****对N添加条件下的草地凋落物分解进行了研究, 但结果存在较大的不一致性, 如促进效应(
Nitrogen lichen community changes through differential species responses.
1
2012
... 凋落物质量是导致N添加对凋落物分解影响不一致性的主要原因(
Foliar litter decomposition in an alpine forest meta-ecosystem on the eastern Tibetan Plateau.
1
2016
... 过去大多数的凋落物分解研究多为短期的原位观测, 近年来, 凋落物分解研究的时空尺度发生了变化.越来越多的研究将原位观测的凋落物分解实验进行整合, 通过对比不同生态系统类型、不同气候区凋落物分解的差异, 来研究大尺度上影响凋落物分解的因子(
Global pattern of leaf litter nitrogen and phosphorus in woody plants.
1
2010
... 分解凋落物中木质素的酶类主要是多酚氧化酶, 在质量较差(木质素含量高)的凋落物中, N添加抑制多酚氧化酶活性, 阻碍了难分解物质的分解, 这是N添加抑制凋落物分解的重要机制(
Effects of long-term nitrogen addition on microbial enzyme activity in eight forested and grassland sites: Implications for litter and soil organic matter decomposition.
1
2009
... N沉降加快营养元素循环, 促进凋落物形成过程中的营养元素再分配, 使凋落物中N、P含量增加(
Incorporation studies of NH4+ during incubation of organic residues by 15N-CPMAS-NMR-spectroscopy.
4
1997
... 目前, 国内外已有很多研究关注N沉降对凋落物分解过程产生的影响, 也有****对N沉降影响森林生态系统凋落物分解的研究结果进行汇总整理(
... N沉降加快营养元素循环, 促进凋落物形成过程中的营养元素再分配, 使凋落物中N、P含量增加(
... 分解凋落物中木质素的酶类主要是多酚氧化酶, 在质量较差(木质素含量高)的凋落物中, N添加抑制多酚氧化酶活性, 阻碍了难分解物质的分解, 这是N添加抑制凋落物分解的重要机制(
... N添加的浓度范围和梯度的设置是造成诸多实验结果存在差异的主要原因, 其设置的合理性也是影响实验结果的重要指标.通过总结, N添加实验的浓度范围在10-640 kg·hm-2·a-1, 很多研究只是单纯设置高、中、低3个N添加梯度, 缺乏一定的理论依据(
Nitrogen additions and litter decomposition: A meta-analysis.
1
2008
... 根系的生产和储存是生态系统生产力的重要组成部分, 其分解对草地生态系统养分循环具有重要的意义, 但目前针对根系凋落物的研究很少(
Above- and below-ground responses to nitrogen addition in a chihuahuan desert grassland.
1
2012
... N是草地生态系统的主要限制因子, N沉降使植物可有效利用的N增加, 减弱草地N限制, 促进植物生长, 凋落物产量和土壤C输入随之增多(
Nitrogen limitation of net primary productivity in terrestrial ecosystems is globally distributed.
1
2008
... 混合凋落物的实际分解速率偏离于期望分解速率时则称为混合凋落物的非加和性效应, 混合凋落物复杂的化学成分和丰富的空间异质性是影响混合凋落物分解时非加性效应产生的重要原因(
Effects of nitrogen addition on the mixed litter decomposition in Stipa baicalensis steppe in Inner Mongolia.
2
2016
... 近年来, 国内外****对N添加条件下的草地凋落物分解进行了研究, 但结果存在较大的不一致性, 如促进效应(
... 混合凋落物的实际分解速率偏离于期望分解速率时则称为混合凋落物的非加和性效应, 混合凋落物复杂的化学成分和丰富的空间异质性是影响混合凋落物分解时非加性效应产生的重要原因(
模拟氮沉降对温带草原凋落物质量的影响. 生态学杂志,
1
2016
... 凋落物质量是导致N添加对凋落物分解影响不一致性的主要原因(
外加氮源对杉木叶凋落物分解及土壤养分淋失的影响. 植物生态学报,
1
2000
... 同位素示踪法是指在实验室或野外条件下用15N、13C同位素进行跟踪, 并与PLFA、PCR等生物化学技术结合, 研究凋落物分解过程中C、N元素在凋落物-微生物-土壤连续体中的转移方向、转移速率等.有研究采用同位素标记技术与PLFA相结合, 将用13C标记的凋落物置于土壤中分解, 测定凋落物分解产生的13CO2、土壤和微生物中的13C以及土壤微生物群落组成, 可对不同种类凋落物分解过程中C的转移路径和微生物对不同C源的利用情况进行动态监测(
Different fates of deposited NH4+ and NO3- in a temperate forest in northeast China: A 15N tracer study.
1
2016
... 影响凋落物分解的环境因子包括温度和降水.温度是调控生态系统生化过程和物质能量周转的关键因子, 对凋落物分解起主导作用(
Litter decomposition and nutrient release as affected by soil nitrogen availability and litter quality in a semiarid grassland ecosystem.
1
2010
... 过去大多数的凋落物分解研究多为短期的原位观测, 近年来, 凋落物分解研究的时空尺度发生了变化.越来越多的研究将原位观测的凋落物分解实验进行整合, 通过对比不同生态系统类型、不同气候区凋落物分解的差异, 来研究大尺度上影响凋落物分解的因子(
热带亚热带森林叶凋落物交互分解的研究. 中山大学学报自然科学版,
2004
2
... 凋落物分解是一个连续的生物降解过程, 影响凋落物分解的生物因子包括土壤动物、微生物及其产生的分解酶(
... N添加形式包括硝酸铵、尿素和其他形式(NaNO3和混合肥等).大气湿沉降主要是NO3-、NH4+及少量可溶性有机氮经降水下降到地表, 采用硝酸铵的施肥方式能最大程度地模拟大气N沉降, 且硝酸铵含N量高达34%, 施肥后NH4+和NO3-都能被植物和土壤吸收, 因此施用硝酸铵是模拟N沉降实验中最常见和最有效的施肥方式(
不同氮添加量和添加方式对南亚热带4个主要树种幼苗生长的影响
2
2015
... 近年来, 国内外****对N添加条件下的草地凋落物分解进行了研究, 但结果存在较大的不一致性, 如促进效应(
... 放牧和围封是人类管理和利用草地资源最普遍的方式, 是影响草地生态系统碳库和养分循环的重要人为因素.牲畜的啃食、排泄和踩踏作用可以改变地表植被特征、土壤环境(如温度、含水量等)及其养分含量, 影响凋落物分解(
Nitrogen deposition and its ecological impact in China: An overview.
3
2011
... 在过去一个世纪里, 化石燃料燃烧、施肥等人类活动使全球大气氮(N)沉降量迅速增加.人类活动造成的N沉降量由1860年的31.6 Tg·a-1增加到20世纪90年代的103 Tg·a-1, 预计到2050年, 可能会增至195 Tg·a-1 (
... N添加的浓度范围和梯度的设置是造成诸多实验结果存在差异的主要原因, 其设置的合理性也是影响实验结果的重要指标.通过总结, N添加实验的浓度范围在10-640 kg·hm-2·a-1, 很多研究只是单纯设置高、中、低3个N添加梯度, 缺乏一定的理论依据(
... 同位素示踪法是指在实验室或野外条件下用15N、13C同位素进行跟踪, 并与PLFA、PCR等生物化学技术结合, 研究凋落物分解过程中C、N元素在凋落物-微生物-土壤连续体中的转移方向、转移速率等.有研究采用同位素标记技术与PLFA相结合, 将用13C标记的凋落物置于土壤中分解, 测定凋落物分解产生的13CO2、土壤和微生物中的13C以及土壤微生物群落组成, 可对不同种类凋落物分解过程中C的转移路径和微生物对不同C源的利用情况进行动态监测(
Enhanced nitrogen deposition over China.
1
2013
... 欧美国家由于工农业较发达, N沉降研究起步早, 手段和技术相对成熟, 目前已经建立了系统而全面的跨地区大型监测网络.但对于N添加的研究一直只局限于森林生态系统, 直到20世纪90年代才有欧洲和北美的一些国家和地区对草地生态系统的响应进行研究(
Nitrogen deposition promotes phosphorus uptake of plants in a semi-arid temperate grassland.
2
2016
... 目前, 国内外已有很多研究关注N沉降对凋落物分解过程产生的影响, 也有****对N沉降影响森林生态系统凋落物分解的研究结果进行汇总整理(
... 水分和N是干旱和半干旱草地生态系统的限制因子.随着地表温度的升高, 降水特征发生变化, 长期干旱和强降雨天气频繁发生(
氮沉降对凋落物分解的影响研究进展. 世界林业研究,
1
2014
... 水分和N是干旱和半干旱草地生态系统的限制因子.随着地表温度的升高, 降水特征发生变化, 长期干旱和强降雨天气频繁发生(
Nitrogen and water availability interact to affect leaf stoichiometry in a semi-arid grassland.
1
2012
... N沉降加快营养元素循环, 促进凋落物形成过程中的营养元素再分配, 使凋落物中N、P含量增加(
Convergent responses of nitrogen and phosphorus resorption to nitrogen inputs in a semiarid grassland.
1
2013
... 同位素示踪法是指在实验室或野外条件下用15N、13C同位素进行跟踪, 并与PLFA、PCR等生物化学技术结合, 研究凋落物分解过程中C、N元素在凋落物-微生物-土壤连续体中的转移方向、转移速率等.有研究采用同位素标记技术与PLFA相结合, 将用13C标记的凋落物置于土壤中分解, 测定凋落物分解产生的13CO2、土壤和微生物中的13C以及土壤微生物群落组成, 可对不同种类凋落物分解过程中C的转移路径和微生物对不同C源的利用情况进行动态监测(
Connecting litter quality, microbial community and nitrogen transfer mechanisms in decomposing litter mixtures.
1
2012
... N添加的浓度范围和梯度的设置是造成诸多实验结果存在差异的主要原因, 其设置的合理性也是影响实验结果的重要指标.通过总结, N添加实验的浓度范围在10-640 kg·hm-2·a-1, 很多研究只是单纯设置高、中、低3个N添加梯度, 缺乏一定的理论依据(
The responses of soil respiration to nitrogen addition in a temperate grassland in northern China.
1
2016
... 草地凋落物分解的研究对象分为单种凋落物和混合凋落物.单种凋落物分解的研究集中在草地优势种.优势种是草地群落的重要组成部分, 在一定程度上决定草地生态系统的属性, 草地优势种的研究是不同尺度凋落物分解研究的基础.因此, 研究草地优势种凋落物分解对N沉降的响应是理解N沉降影响凋落物分解的关键(
Landscape-ecological and population aspects of the strategy of restoration of 443 disturbed lands.
1
2010
... 凋落物分解是一个非常复杂的生物、物理、化学过程, 深受非生物因子(环境因子、土壤理化性质)、凋落物基质质量和生物因子(土壤微生物和酶活性)的影响, 且各因子间存在复杂的交互作用, 共同影响凋落物的形成和分解.N添加可通过改变土壤养分有效性、凋落物产量和质量、土壤生物及凋落物分解环境影响凋落物分解(
Direct and indirect effects of nitrogen deposition on litter decomposition.
1
2008
... N沉降改善草地生态系统的N状况, 导致N饱和和P限制(
Stoichiometric controls on carbon, nitrogen, and phosphorus dynamics in decomposing litter.
2
2010
... 草地凋落物是由植物地上和地下部分产生并归还到土壤的所有有机质的总称, 是土壤C库的主要来源和维持土壤肥力的基础.凋落物分解是陆地生态系统养分循环的关键过程, 陆地生态系统中约90%的净初级生产量以凋落物的形式归还给土 壤, 其养分再循环供给植物的生长发育(
... 凋落物分解是一个复杂的物理、化学、生物过程, 包括淋溶, 机械破碎, 有机物转化, 以及土壤动物、微生物的消化作用等.调控凋落物分解的关键因素有环境因子、凋落物质量和生物因子, 且各因子之间存在复杂的相互关系(
Macroclimate and lignin control of hardwood leaf litter fecomposition dynamics.
2
1978
... 凋落物质量是导致N添加对凋落物分解影响不一致性的主要原因(
... 过去大多数的凋落物分解研究多为短期的原位观测, 近年来, 凋落物分解研究的时空尺度发生了变化.越来越多的研究将原位观测的凋落物分解实验进行整合, 通过对比不同生态系统类型、不同气候区凋落物分解的差异, 来研究大尺度上影响凋落物分解的因子(
A theoretical model of litter decay and microbial interaction.
2
2006
... N添加形式包括硝酸铵、尿素和其他形式(NaNO3和混合肥等).大气湿沉降主要是NO3-、NH4+及少量可溶性有机氮经降水下降到地表, 采用硝酸铵的施肥方式能最大程度地模拟大气N沉降, 且硝酸铵含N量高达34%, 施肥后NH4+和NO3-都能被植物和土壤吸收, 因此施用硝酸铵是模拟N沉降实验中最常见和最有效的施肥方式(
... 凋落物质量(N、木质素、纤维素、单宁等)的分析测定常采用化学分析法, 测定前都需要经过复杂的研磨、提取过程, 耗费时间长且存在较大的误差.目前, 有研究利用红外光谱分析(near-infrared spectrometry, NIRS)和代谢组学等新技术测定凋落物中的化合物含量.与化学分析法相比, 红外光谱分析技术免除了研磨、提取等复杂的步骤, 且可以同时测量凋落物中的多种化合物含量, 具有很强的整合性(
Effects of nitrogen deposition rates and frequencies on the abundance of soil nitrogen-related functional genes in temperate grassland of northern China.
1
2015
... 植物群落组成的改变包括物种的演替、优势种的定居和稀有物种的消失.N沉降会减弱物种丰富度, 改变草地植物群落组成, 使凋落物质量发生改变, 从而影响分解(
Different growth responses of C3 and C4 grasses to seasonal water and nitrogen regimes and competition in a pot experiment.
2
2008
... 过去关于凋落物分解的研究集中在某一时间段内的静态研究, 而对凋落物分解整个过程中养分元素的转移路径、转移速率及其在植物、凋落物、土壤中的剩余情况等了解不足.生态化学计量学是生态学的一个新兴领域, 主要研究生物体与其所处环境之间的养分元素关系, 是分析生态系统养分循环过程的工具(
... 同位素示踪法是指在实验室或野外条件下用15N、13C同位素进行跟踪, 并与PLFA、PCR等生物化学技术结合, 研究凋落物分解过程中C、N元素在凋落物-微生物-土壤连续体中的转移方向、转移速率等.有研究采用同位素标记技术与PLFA相结合, 将用13C标记的凋落物置于土壤中分解, 测定凋落物分解产生的13CO2、土壤和微生物中的13C以及土壤微生物群落组成, 可对不同种类凋落物分解过程中C的转移路径和微生物对不同C源的利用情况进行动态监测(
Microbial utilization of rice straw and its derived biochar in a paddy soil.
1
2016
... 植物群落组成的改变包括物种的演替、优势种的定居和稀有物种的消失.N沉降会减弱物种丰富度, 改变草地植物群落组成, 使凋落物质量发生改变, 从而影响分解(
Effects of nitrogen additions on a Leymus Chinensis population in a typical steppe of Inner Mongolia.
1
2005
... 近年来, 国内外****对N添加条件下的草地凋落物分解进行了研究, 但结果存在较大的不一致性, 如促进效应(
Litter decomposition and C and N dynamics as affected by N additions in a semi- arid temperate steppe, Inner Mongolia of China.
1
2014
... 在过去一个世纪里, 化石燃料燃烧、施肥等人类活动使全球大气氮(N)沉降量迅速增加.人类活动造成的N沉降量由1860年的31.6 Tg·a-1增加到20世纪90年代的103 Tg·a-1, 预计到2050年, 可能会增至195 Tg·a-1 (
Changes in biomass carbon stocks in China’s grasslands between 1982 and 1999. Global Biogeochemical Cycles, 21,
2
2007
... 由此可见, 土壤过程和分解者对凋落物分解的影响是今后凋落物分解研究的重点.不同生态系统类型、不同凋落物分解阶段中影响分解的主导因子不同, 也可能存在一定的阈值, 使得主导凋落物分解的因子从一个转向另一个.因此, 重视小区域尺度上凋落物分解过程的研究、确定凋落物分解主导因子发生改变的原因和阈值是今后凋落物分解因子研究的关键(
... N添加的浓度范围和梯度的设置是造成诸多实验结果存在差异的主要原因, 其设置的合理性也是影响实验结果的重要指标.通过总结, N添加实验的浓度范围在10-640 kg·hm-2·a-1, 很多研究只是单纯设置高、中、低3个N添加梯度, 缺乏一定的理论依据(
Litter decomposition: What controls it and how can we alter it to sequester more carbon in forest soils?
1
2010
... 欧美国家由于工农业较发达, N沉降研究起步早, 手段和技术相对成熟, 目前已经建立了系统而全面的跨地区大型监测网络.但对于N添加的研究一直只局限于森林生态系统, 直到20世纪90年代才有欧洲和北美的一些国家和地区对草地生态系统的响应进行研究(
不同退化程度羊草草原碳收支对模拟氮沉降变化的响应. 环境科学,
1
2015
... P是植物生长的重要限制因子, 控制着生态系统的关键过程.N添加后, 许多草地生态系统由N限制转向N饱和, 且N在生态系统中的归还速率高于P, 因此生态系统过程受到P限制.探究草地凋落物分解对N、P添加耦合效应的响应可为深入分析N、P添加对生态系统物质循环和能量流动产生的影响提供理论依据(
Phosphorus enrichment affects litter decomposition, immobilization, and soil microbial phosphorus in wetland mesocosms.
2000
The hemiparasitic angiosperm Bartsia alpina has the potential to accelerate decomposition in sub-arctic communities.
1
... 混合凋落物的实际分解速率偏离于期望分解速率时则称为混合凋落物的非加和性效应, 混合凋落物复杂的化学成分和丰富的空间异质性是影响混合凋落物分解时非加性效应产生的重要原因(
Vegetation and soil respiration: Correlations and controls.
1
2000
... 植物群落组成的改变包括物种的演替、优势种的定居和稀有物种的消失.N沉降会减弱物种丰富度, 改变草地植物群落组成, 使凋落物质量发生改变, 从而影响分解(
Effects of resource additions on species richness and ANPP in an alpine meadow community.
2010
3
1984
... 凋落物质量, 即凋落物的相对可分解性.衡量凋落物质量的指标主要有C含量、N含量、磷(P)含量、木质素含量、纤维素含量, 以及它们之间的比值(
... 放牧和围封是人类管理和利用草地资源最普遍的方式, 是影响草地生态系统碳库和养分循环的重要人为因素.牲畜的啃食、排泄和踩踏作用可以改变地表植被特征、土壤环境(如温度、含水量等)及其养分含量, 影响凋落物分解(
... N沉降除提高土壤N有效性外, 还会造成土壤酸化, 土壤中H+和Al3+的浓度上升, 矿质阳离子(Ca2+、Mg2+、Na+等)浓度下降, 土壤质量变差, 阻碍植被和地下微生物群落的生长(
Soil bacterial and fungal communities across a pH gradient in an arable soil.
1
2010
... 细菌和真菌是分解者, 在凋落物分解的各阶段中作用不同: 在前期, 真菌起主要作用; 在后期, 细菌起主要作用(
Fungal and bacterial growth responses to N fertilization and pH in the 150-year “park grass” UK grassland experiment.
1
2011
... N是草地生态系统的主要限制因子, N沉降使植物可有效利用的N增加, 减弱草地N限制, 促进植物生长, 凋落物产量和土壤C输入随之增多(
Legacies of precipitation fluctuations on primary production: Theory and data synthesis.
1
2012
... 室内分解培养法是指在实验室内模拟凋落物自然分解状态, 此方法多用于控制实验, 研究光照、水分、温度等因子的变化对凋落物分解过程的影响(
Microbial activities during the early stage of laboratory decomposition of tropical leaf litters: The effect of interactions between litter quality and exogenous inorganic nitrogen.
1
2003
... 除了大时空尺度的凋落物分解研究外, 也有****关注更小的时空尺度, 研究一天内主导凋落物分解的因子, 结果表明主导白天和夜晚凋落物分解的因子不同——白天以非生物降解(光降解和热降解)为主, 而夜晚以微生物降解为主(
Forest composition modifies litter dynamics and decomposition in regenerating tropical dry forest.
1
2016
... 近年来, 国内外****对N添加条件下的草地凋落物分解进行了研究, 但结果存在较大的不一致性, 如促进效应(
Increased rainfall variability and N addition accelerate litter decomposition in a restored prairie.
1
2015
... 凋落物分解是一个非常复杂的生物、物理、化学过程, 深受非生物因子(环境因子、土壤理化性质)、凋落物基质质量和生物因子(土壤微生物和酶活性)的影响, 且各因子间存在复杂的交互作用, 共同影响凋落物的形成和分解.N添加可通过改变土壤养分有效性、凋落物产量和质量、土壤生物及凋落物分解环境影响凋落物分解(
氮沉降对内蒙古温带草原土壤酶活性影响的试验研究
2
2014
... 凋落物网袋法是现在凋落物分解研究最常用的方法, 其原理是在不可降解的尼龙网袋中(袋的大小为15-600 cm2, 孔径为2-10 mm)装入一定量的凋落物, 然后将网袋直接接触地表或埋置在深度为5-10 cm的土壤中(
... 细根是生态系统的重要组成部分, 它的死亡和分解对全球C收支和土壤养分循环有着重要的意义.与森林生态系统相比, 草地生态系统地下生产力高、根系周转速率快, 其根系分解的研究更应该受到研究者的重视(
Global patterns in root decomposition: Comparisons of climate and litter quality effects.
2
2001
... 草地凋落物是由植物地上和地下部分产生并归还到土壤的所有有机质的总称, 是土壤C库的主要来源和维持土壤肥力的基础.凋落物分解是陆地生态系统养分循环的关键过程, 陆地生态系统中约90%的净初级生产量以凋落物的形式归还给土 壤, 其养分再循环供给植物的生长发育(
... 凋落物分解是一个复杂的物理、化学、生物过程, 包括淋溶, 机械破碎, 有机物转化, 以及土壤动物、微生物的消化作用等.调控凋落物分解的关键因素有环境因子、凋落物质量和生物因子, 且各因子之间存在复杂的相互关系(
Root traits predict decomposition across a landscape-scale grazing experiment.
2
2014
... N沉降加快营养元素循环, 促进凋落物形成过程中的营养元素再分配, 使凋落物中N、P含量增加(
... 凋落物网袋法是现在凋落物分解研究最常用的方法, 其原理是在不可降解的尼龙网袋中(袋的大小为15-600 cm2, 孔径为2-10 mm)装入一定量的凋落物, 然后将网袋直接接触地表或埋置在深度为5-10 cm的土壤中(
Litter quality impacts on grassland litter decomposition are differently dependent on soil fauna across time.
2
2003
... 根系的生产和储存是生态系统生产力的重要组成部分, 其分解对草地生态系统养分循环具有重要的意义, 但目前针对根系凋落物的研究很少(
... 细根是生态系统的重要组成部分, 它的死亡和分解对全球C收支和土壤养分循环有着重要的意义.与森林生态系统相比, 草地生态系统地下生产力高、根系周转速率快, 其根系分解的研究更应该受到研究者的重视(
Factors controlling decomposition rates of fine root litter in temperate forests and grasslands.
1
2014
... 影响凋落物分解的环境因子包括温度和降水.温度是调控生态系统生化过程和物质能量周转的关键因子, 对凋落物分解起主导作用(
全球气候变暖对凋落物分解的影响.
2
2014
... 自然生态系统中, 各种全球变化的现象(如全球变暖, 降水变化, N、P沉降, 以及紫外辐射等)时有发生, 且它们的交互作用无处不在.因此单独研究N沉降对凋落物分解过程的影响, 无法准确、全面地评估生态系统C循环和养分循环对未来全球变化响应的真实情况, 需要将其综合分析(
... 放牧和围封是人类管理和利用草地资源最普遍的方式, 是影响草地生态系统碳库和养分循环的重要人为因素.牲畜的啃食、排泄和踩踏作用可以改变地表植被特征、土壤环境(如温度、含水量等)及其养分含量, 影响凋落物分解(
Effect of nitrogen deposition and management practices on fine root decomposition in Moso bamboo plantations.
1
2017
... 植物群落组成的改变包括物种的演替、优势种的定居和稀有物种的消失.N沉降会减弱物种丰富度, 改变草地植物群落组成, 使凋落物质量发生改变, 从而影响分解(
Terricolous lichens as indicators of nitrogen deposition: Evidence from national records.
2012
2
2014
... 细菌和真菌是分解者, 在凋落物分解的各阶段中作用不同: 在前期, 真菌起主要作用; 在后期, 细菌起主要作用(
... 水分和N是干旱和半干旱草地生态系统的限制因子.随着地表温度的升高, 降水特征发生变化, 长期干旱和强降雨天气频繁发生(
Considering fungal: bacterial dominance in soils—Methods, controls and ecosystem implications.
1
2010
... 植物群落组成的改变包括物种的演替、优势种的定居和稀有物种的消失.N沉降会减弱物种丰富度, 改变草地植物群落组成, 使凋落物质量发生改变, 从而影响分解(
Functional- and abundance-based mechanisms explain diversity loss due to N fertilization.
3
2005
... 在过去一个世纪里, 化石燃料燃烧、施肥等人类活动使全球大气氮(N)沉降量迅速增加.人类活动造成的N沉降量由1860年的31.6 Tg·a-1增加到20世纪90年代的103 Tg·a-1, 预计到2050年, 可能会增至195 Tg·a-1 (
... 大多数N添加研究持续时间太短, 其中85.5%的N添加研究持续时间不超过4年, 加上高的空间差异性, 我们无法准确地评估凋落物分解对N添加的响应(
... ;
Simulated atmospheric nitrogen deposition alters decomposition of ephemeral roots.
1
2015
... N添加的浓度范围和梯度的设置是造成诸多实验结果存在差异的主要原因, 其设置的合理性也是影响实验结果的重要指标.通过总结, N添加实验的浓度范围在10-640 kg·hm-2·a-1, 很多研究只是单纯设置高、中、低3个N添加梯度, 缺乏一定的理论依据(
Effects of long-term nitrogen deposition on fine root decomposition and its extracellular enzyme activities in temperate forests.
1
2016
... 调控凋落物分解的关键因子主要有环境因子、凋落物质量和生物因子等, 它们起作用的顺序通常为: 气候>凋落物质量>土壤生物(
Decomposition in terrestial ecosystems.
1
1979
... 放牧和围封是人类管理和利用草地资源最普遍的方式, 是影响草地生态系统碳库和养分循环的重要人为因素.牲畜的啃食、排泄和踩踏作用可以改变地表植被特征、土壤环境(如温度、含水量等)及其养分含量, 影响凋落物分解(
Vegetation dynamics and plant species interactions under grazed and ungrazed conditions in a western European salt marsh.
1
2003
... 同位素示踪法是指在实验室或野外条件下用15N、13C同位素进行跟踪, 并与PLFA、PCR等生物化学技术结合, 研究凋落物分解过程中C、N元素在凋落物-微生物-土壤连续体中的转移方向、转移速率等.有研究采用同位素标记技术与PLFA相结合, 将用13C标记的凋落物置于土壤中分解, 测定凋落物分解产生的13CO2、土壤和微生物中的13C以及土壤微生物群落组成, 可对不同种类凋落物分解过程中C的转移路径和微生物对不同C源的利用情况进行动态监测(
Particle size alters litter diversity effects on decomposition.
1
2009
... 土壤酸度是调控陆地生态系统生物多样性和生物地球化学循环的重要因子.人类活动产生的氮氧化合物(NOX)使草地生态系统土壤酸化现象越来越严重(
Interactive effects of warming and increased nitrogen deposition on 15N tracer retention in a temperate old field: Seasonal trends.
1
2009
... 凋落物质量, 即凋落物的相对可分解性.衡量凋落物质量的指标主要有C含量、N含量、磷(P)含量、木质素含量、纤维素含量, 以及它们之间的比值(
Are decomposition and N release from organic mulches determined mainly by their chemical composition?
2
2006
... N沉降加快营养元素循环, 促进凋落物形成过程中的营养元素再分配, 使凋落物中N、P含量增加(
... 混合凋落物的实际分解速率偏离于期望分解速率时则称为混合凋落物的非加和性效应, 混合凋落物复杂的化学成分和丰富的空间异质性是影响混合凋落物分解时非加性效应产生的重要原因(
Do leaf traits and nitrogen supply affect decomposability rates of three Mediterranean species growing under different competition levels?
1
2013
... N沉降改善草地生态系统的N状况, 导致N饱和和P限制(
Terrestrial phosphorus limitation: Mechanisms, implications, and nitrogen-phosphorus interactions.
1
2010
... 混合凋落物的实际分解速率偏离于期望分解速率时则称为混合凋落物的非加和性效应, 混合凋落物复杂的化学成分和丰富的空间异质性是影响混合凋落物分解时非加性效应产生的重要原因(
Nitrogen addition stimulates forest litter decomposition and disrupts species interactions in Patagonia, Argentina.
1
2011
... 调控凋落物分解的关键因子主要有环境因子、凋落物质量和生物因子等, 它们起作用的顺序通常为: 气候>凋落物质量>土壤生物(
Global decomposition experiment shows soil animal impacts on decomposition are climate-dependent.
1
2008
... 凋落物质量(N、木质素、纤维素、单宁等)的分析测定常采用化学分析法, 测定前都需要经过复杂的研磨、提取过程, 耗费时间长且存在较大的误差.目前, 有研究利用红外光谱分析(near-infrared spectrometry, NIRS)和代谢组学等新技术测定凋落物中的化合物含量.与化学分析法相比, 红外光谱分析技术免除了研磨、提取等复杂的步骤, 且可以同时测量凋落物中的多种化合物含量, 具有很强的整合性(
Litter chemistry changes more rapidly when decomposed at home but converges during decomposition-transformation.
1
2013
... 根系的生产和储存是生态系统生产力的重要组成部分, 其分解对草地生态系统养分循环具有重要的意义, 但目前针对根系凋落物的研究很少(
Nitrogen addition increases the production and turnover of the lower-order roots but not of the higher-order roots of Bothriochloa ischaemum.
1
2017
... N沉降改善草地生态系统的N状况, 导致N饱和和P限制(
氮沉降对森林土壤有机质和凋落物分解的影响及其微生物学机制. 生态学报,
1
2013
... 过去关于凋落物分解的研究集中在某一时间段内的静态研究, 而对凋落物分解整个过程中养分元素的转移路径、转移速率及其在植物、凋落物、土壤中的剩余情况等了解不足.生态化学计量学是生态学的一个新兴领域, 主要研究生物体与其所处环境之间的养分元素关系, 是分析生态系统养分循环过程的工具(
生态系统碳氮磷元素的生态化学计量学特征. 生态学报,
1
2008
... 干旱和半干旱草原的非生长季漫长, 植被覆盖率低, 地表温湿度变化剧烈.大多数研究认为, 非生长季的低温使微生物休眠或者死亡, 非生长季的凋落物分解几乎停滞, 很少有研究关注非生长季的凋落物分解(
冬季土壤呼吸: 不可忽视的地气CO2交换过程. 植物生态学报,
1
2007
... 影响凋落物分解的环境因子包括温度和降水.温度是调控生态系统生化过程和物质能量周转的关键因子, 对凋落物分解起主导作用(
环境因素对干旱半干旱区凋落物分解的影响研究进展. 应用生态学报,
4
2013
... 根系的生产和储存是生态系统生产力的重要组成部分, 其分解对草地生态系统养分循环具有重要的意义, 但目前针对根系凋落物的研究很少(
... 放牧和围封是人类管理和利用草地资源最普遍的方式, 是影响草地生态系统碳库和养分循环的重要人为因素.牲畜的啃食、排泄和踩踏作用可以改变地表植被特征、土壤环境(如温度、含水量等)及其养分含量, 影响凋落物分解(
... ;
... 细根是生态系统的重要组成部分, 它的死亡和分解对全球C收支和土壤养分循环有着重要的意义.与森林生态系统相比, 草地生态系统地下生产力高、根系周转速率快, 其根系分解的研究更应该受到研究者的重视(
Effects of land use and precipitation on above- and below-ground litter decomposition in a semi-arid temperate steppe in Inner Mongolia, China.
1
2015
... 细菌和真菌是分解者, 在凋落物分解的各阶段中作用不同: 在前期, 真菌起主要作用; 在后期, 细菌起主要作用(
Ecological linkages between aboveground and belowground biota.
1
2004
... 凋落物分解是一个连续的生物降解过程, 影响凋落物分解的生物因子包括土壤动物、微生物及其产生的分解酶(
Exploring relationships between enzyme activities and leaf litter decomposition in a wet tropical forest.
1
2013
... 影响凋落物分解的环境因子包括温度和降水.温度是调控生态系统生化过程和物质能量周转的关键因子, 对凋落物分解起主导作用(
In situ litter decomposition and litter quality in a Mojave Desert ecosystem: Effects of elevated atmospheric CO2 and interannual climate variability.
1
2003
... N添加形式包括硝酸铵、尿素和其他形式(NaNO3和混合肥等).大气湿沉降主要是NO3-、NH4+及少量可溶性有机氮经降水下降到地表, 采用硝酸铵的施肥方式能最大程度地模拟大气N沉降, 且硝酸铵含N量高达34%, 施肥后NH4+和NO3-都能被植物和土壤吸收, 因此施用硝酸铵是模拟N沉降实验中最常见和最有效的施肥方式(
Foliar uptake and release of inorganic nitrogen compounds in Pinus sylvestris L. and Picea abies (L.) Karst.
1
1992
... 植物群落组成的改变包括物种的演替、优势种的定居和稀有物种的消失.N沉降会减弱物种丰富度, 改变草地植物群落组成, 使凋落物质量发生改变, 从而影响分解(
Global response patterns of terrestrial plant species to nitrogen addition.
1
2008
... 在过去一个世纪里, 化石燃料燃烧、施肥等人类活动使全球大气氮(N)沉降量迅速增加.人类活动造成的N沉降量由1860年的31.6 Tg·a-1增加到20世纪90年代的103 Tg·a-1, 预计到2050年, 可能会增至195 Tg·a-1 (
Response of ecosystem carbon exchange to warming and nitrogen addition during two hydrologically contrasting growing seasons in a temperate steppe.
1
2009
... 干旱和半干旱草原的非生长季漫长, 植被覆盖率低, 地表温湿度变化剧烈.大多数研究认为, 非生长季的低温使微生物休眠或者死亡, 非生长季的凋落物分解几乎停滞, 很少有研究关注非生长季的凋落物分解(
川西亚高山森林凋落物分解初期土壤动物对红桦凋落叶质量损失的贡献. 应用生态学报,
1
2012
... 细根是生态系统的重要组成部分, 它的死亡和分解对全球C收支和土壤养分循环有着重要的意义.与森林生态系统相比, 草地生态系统地下生产力高、根系周转速率快, 其根系分解的研究更应该受到研究者的重视(
Fine roots are the dominant source of recalcitrant plant litter in sugar maple-dominated northern hardwood forests.
1
2015
... 草地凋落物分解的研究对象分为单种凋落物和混合凋落物.单种凋落物分解的研究集中在草地优势种.优势种是草地群落的重要组成部分, 在一定程度上决定草地生态系统的属性, 草地优势种的研究是不同尺度凋落物分解研究的基础.因此, 研究草地优势种凋落物分解对N沉降的响应是理解N沉降影响凋落物分解的关键(
混合凋落物分解非加和性效应研究进展. 环境科学与技术,
1
2012
... N是草地生态系统的主要限制因子, N沉降使植物可有效利用的N增加, 减弱草地N限制, 促进植物生长, 凋落物产量和土壤C输入随之增多(
Response of aboveground biomass and diversity to nitrogen addition along a degradation gradient in the Inner Mongolian steppe, China.
1
2015
... 同位素示踪法是指在实验室或野外条件下用15N、13C同位素进行跟踪, 并与PLFA、PCR等生物化学技术结合, 研究凋落物分解过程中C、N元素在凋落物-微生物-土壤连续体中的转移方向、转移速率等.有研究采用同位素标记技术与PLFA相结合, 将用13C标记的凋落物置于土壤中分解, 测定凋落物分解产生的13CO2、土壤和微生物中的13C以及土壤微生物群落组成, 可对不同种类凋落物分解过程中C的转移路径和微生物对不同C源的利用情况进行动态监测(
Characterization of organic carbon in decomposing litter exposed to nitrogen and sulfur additions: Links to microbial community composition and activity.
2
2017
... 根系的生产和储存是生态系统生产力的重要组成部分, 其分解对草地生态系统养分循环具有重要的意义, 但目前针对根系凋落物的研究很少(
... 细菌和真菌是分解者, 在凋落物分解的各阶段中作用不同: 在前期, 真菌起主要作用; 在后期, 细菌起主要作用(
Stage-specific response of litter decomposition to N and S amendments in a subtropical forest soil.
2
2016
... 放牧和围封是人类管理和利用草地资源最普遍的方式, 是影响草地生态系统碳库和养分循环的重要人为因素.牲畜的啃食、排泄和踩踏作用可以改变地表植被特征、土壤环境(如温度、含水量等)及其养分含量, 影响凋落物分解(
... 细根是生态系统的重要组成部分, 它的死亡和分解对全球C收支和土壤养分循环有着重要的意义.与森林生态系统相比, 草地生态系统地下生产力高、根系周转速率快, 其根系分解的研究更应该受到研究者的重视(
内蒙古温带草原不同放牧强度和围栏封育对凋落物分解的影响. 植物生态学报,
1
2016
... 土壤酸度是调控陆地生态系统生物多样性和生物地球化学循环的重要因子.人类活动产生的氮氧化合物(NOX)使草地生态系统土壤酸化现象越来越严重(
Significant soil acidification across northern China’s grasslands during 1980s-2000s.
1
2012
... 草地凋落物分解的研究方法有凋落物网袋法、现量估算法、室内分解培养法等, 随着分子生物学技术的迅速发展, 同位素示踪、磷脂脂肪酸分析(PLFA)、DNA/RNA等方法为凋落物分解和土壤微生物研究提供了新手段, 有利于凋落物分解的微生物学和酶学机制研究.未来生态学研究的一个发展趋势是将传统生态学研究与这些新技术手段相结合(
The future of environmental DNA in ecology.
2
2012
... 植物群落组成的改变包括物种的演替、优势种的定居和稀有物种的消失.N沉降会减弱物种丰富度, 改变草地植物群落组成, 使凋落物质量发生改变, 从而影响分解(
... N沉降加快营养元素循环, 促进凋落物形成过程中的营养元素再分配, 使凋落物中N、P含量增加(
氮沉降对草原凋落物分解的影响. 农业资源与环境学报,
1
2013
... 根系的生产和储存是生态系统生产力的重要组成部分, 其分解对草地生态系统养分循环具有重要的意义, 但目前针对根系凋落物的研究很少(
Characteristics of biomass allocation and root distribution of Tamarix ramosissima Ledeb. and Alhagi sparsifolia Shap. seedlings.
3
2010
... 近年来, 国内外****对N添加条件下的草地凋落物分解进行了研究, 但结果存在较大的不一致性, 如促进效应(
... 混合凋落物的实际分解速率偏离于期望分解速率时则称为混合凋落物的非加和性效应, 混合凋落物复杂的化学成分和丰富的空间异质性是影响混合凋落物分解时非加性效应产生的重要原因(
... N添加形式包括硝酸铵、尿素和其他形式(NaNO3和混合肥等).大气湿沉降主要是NO3-、NH4+及少量可溶性有机氮经降水下降到地表, 采用硝酸铵的施肥方式能最大程度地模拟大气N沉降, 且硝酸铵含N量高达34%, 施肥后NH4+和NO3-都能被植物和土壤吸收, 因此施用硝酸铵是模拟N沉降实验中最常见和最有效的施肥方式(
呼伦贝尔草甸草原主要优势植物地上部凋落物和根系组织分解过程及其控制机制
2013
Effects of species and low dose nitrogen addition on litter decomposition of three dominant grasses in Hulun Buir Meadow Steppe.
1
2013
... 调控凋落物分解的关键因子主要有环境因子、凋落物质量和生物因子等, 它们起作用的顺序通常为: 气候>凋落物质量>土壤生物(
Rates of litter decomposition in terrestrial ecosystems: Global patterns and controlling factors.
1
2008
... 自然生态系统中, 各种全球变化的现象(如全球变暖, 降水变化, N、P沉降, 以及紫外辐射等)时有发生, 且它们的交互作用无处不在.因此单独研究N沉降对凋落物分解过程的影响, 无法准确、全面地评估生态系统C循环和养分循环对未来全球变化响应的真实情况, 需要将其综合分析(
土壤微生物对气候变暖和大气N沉降的响应. 植物生态学报,
1
2007
... 凋落物质量是导致N添加对凋落物分解影响不一致性的主要原因(
Litter quality mediated nitrogen effect on plant litter decomposition regardless of soil fauna presence.
2016
a). Productivity depends more on the rate than the frequency of N addition in a temperate grassland.
2
2015
... N添加形式包括硝酸铵、尿素和其他形式(NaNO3和混合肥等).大气湿沉降主要是NO3-、NH4+及少量可溶性有机氮经降水下降到地表, 采用硝酸铵的施肥方式能最大程度地模拟大气N沉降, 且硝酸铵含N量高达34%, 施肥后NH4+和NO3-都能被植物和土壤吸收, 因此施用硝酸铵是模拟N沉降实验中最常见和最有效的施肥方式(
... 凋落物网袋法是现在凋落物分解研究最常用的方法, 其原理是在不可降解的尼龙网袋中(袋的大小为15-600 cm2, 孔径为2-10 mm)装入一定量的凋落物, 然后将网袋直接接触地表或埋置在深度为5-10 cm的土壤中(
放牧对青藏高原东部两种典型高寒草地类型凋落物分解的影响. 生态学报,
2012
b). Fewer new species colonize at low frequency N addition in a temperate grassland.
2
2015
... N添加形式包括硝酸铵、尿素和其他形式(NaNO3和混合肥等).大气湿沉降主要是NO3-、NH4+及少量可溶性有机氮经降水下降到地表, 采用硝酸铵的施肥方式能最大程度地模拟大气N沉降, 且硝酸铵含N量高达34%, 施肥后NH4+和NO3-都能被植物和土壤吸收, 因此施用硝酸铵是模拟N沉降实验中最常见和最有效的施肥方式(
... N添加的浓度范围和梯度的设置是造成诸多实验结果存在差异的主要原因, 其设置的合理性也是影响实验结果的重要指标.通过总结, N添加实验的浓度范围在10-640 kg·hm-2·a-1, 很多研究只是单纯设置高、中、低3个N添加梯度, 缺乏一定的理论依据(
a). Effects of increased summer precipitation and nitrogen addition on root decomposition in a temperate desert.
2015
b). Variations in bacterial communities during foliar litter decomposition in the winter and growing seasons in an alpine forest of the eastern Tibetan Plateau.
2
2015
... 凋落物分解是一个复杂的物理、化学、生物过程, 包括淋溶, 机械破碎, 有机物转化, 以及土壤动物、微生物的消化作用等.调控凋落物分解的关键因素有环境因子、凋落物质量和生物因子, 且各因子之间存在复杂的相互关系(
... 干旱和半干旱草原的非生长季漫长, 植被覆盖率低, 地表温湿度变化剧烈.大多数研究认为, 非生长季的低温使微生物休眠或者死亡, 非生长季的凋落物分解几乎停滞, 很少有研究关注非生长季的凋落物分解(
Factors influencing leaf litter decomposition: An intersite decomposition experiment across China.
1
2008
... N沉降改善草地生态系统的N状况, 导致N饱和和P限制(
微生物对分解底物碳氮磷化学计量的响应和调节机制. 植物生态学报,
1
2016
... N添加形式包括硝酸铵、尿素和其他形式(NaNO3和混合肥等).大气湿沉降主要是NO3-、NH4+及少量可溶性有机氮经降水下降到地表, 采用硝酸铵的施肥方式能最大程度地模拟大气N沉降, 且硝酸铵含N量高达34%, 施肥后NH4+和NO3-都能被植物和土壤吸收, 因此施用硝酸铵是模拟N沉降实验中最常见和最有效的施肥方式(
Nutrient limitation in three lowland tropical forests in southern china receiving high nitrogen deposition: Insights from fine root responses to nutrient additions.
2013
a). Changes in litter quality induced by nutrient addition alter litter decomposition in an alpine meadow on the Qinhai- Tibet Plateau.
2016
b). Effects of nitrogen addition on litter decomposition and nutrient release in two tropical plantations with N2-fixing vs. non-N2-fixing tree species.
3
2016
... 目前, 国内外已有很多研究关注N沉降对凋落物分解过程产生的影响, 也有****对N沉降影响森林生态系统凋落物分解的研究结果进行汇总整理(
... N沉降改善草地生态系统的N状况, 导致N饱和和P限制(
... 在N沉降背景下, 探究植物吸收的N在植物-凋落物-土壤-大气中分解、释放、转移的方式和路径对深入研究N沉降对生态系统C循环的影响具有十分重要的意义.但是, N添加条件下植物、凋落物和土壤C:N:P化学计量比对凋落物分解的影响及其微生物学和酶学机制研究不足(
Impacts of nitrogen deposition on soil nitrogen cycle in forest ecosystems: A review.
2015
