湿润亚热带山地生态国家重点实验室培育基地, 福州 350007
Effect of Dicranopteris dichotoma on spectroscopic characteristic of dissolved organic matter in red soil erosion area
ZHANGHao, LyuMao-Kui, XIEJin-Sheng通讯作者:
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可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(Michalzik & Matzner, 1999; 杨玉盛等, 2003)。它不仅影响着森林生态系统的能量交换, 而且直接参与生物地球化学循环, 尤其在全球碳循环过程中担当着重要角色(Kalbitz et al., 2007)。由于DOM在土壤有机质中的比例很小(<2%) (Andreasson et al., 2009), 在过去的碳循环研究中常被忽略, 但因其动态变化可以灵敏地反映土壤有机碳循环与平衡趋势(焦坤和李忠佩, 2005), 故而在森林生态系统中, DOM的来源、通量和迁移特征及其对土壤有机质的贡献受到重点关注(Schwendenmann & Veldkamp, 2005; Chang et al., 2007; Fujii et al., 2009; Carter et al., 2012), 如一些研究表明DOM对陆地生态系统的净生产力贡献高达11%-17% (Gielen et al., 2011), 20%-50%的森林土壤有机质可能来自DOM (Kalbitz & Kaiser, 2008), 在湿润的气候条件下, DOM对深层土壤有机质的贡献可能更大(Mccarthy, 2005), 但是林下植被对土壤DOM结构特征的影响仍不清楚。南方红壤侵蚀区植被恢复后, 林下分布着大片芒萁(Dicranopteris dichotoma)群落, 那么芒萁对土壤DOM结构特征影响如何? 随着植被恢复, 在土壤有机碳积累过程中芒萁担任何种角色? 目前对之尚不清楚。
目前关于DOM结构特征的研究采用的手段主要是光学技术, 其简单易操作, 不会对样品产生破坏, 而且分析高效, 分析结果所含信息丰富, 因此在DOM微观结构的研究中得到了广泛的应用。最为常用的就是紫外可见分光光谱和荧光光谱分析技术, 另外, 还有很多研究利用傅里叶变换红外光谱测定DOM的特征官能团, 更为详细地表征其结构特性(周江敏等, 2004; Carter et al., 2012; 刘翥等, 2015)。
鉴于此, 本研究在典型红壤侵蚀区福建省龙岩市长汀县河田镇选取不同恢复年限(0年, 13年, 31年) 的马尾松林为研究对象, 利用光学技术, 通过对比分析不同恢复年限马尾松林保留芒萁覆盖地、去除芒萁覆盖地和林下裸地土壤DOM光谱特征, 旨在分析植被恢复过程中林下植被芒萁对土壤DOM结构特征的影响, 揭示其在土壤有机碳积累过程中担任的角色, 为进一步理解植被恢复过程中土壤有机碳积累的机制提供科学依据。
1 材料和方法
1.1 研究区和试验地概况
研究区位于福建省龙岩市长汀县河田镇(116.30°-116.52° E, 25.55°-25.80° N), 该区地处福建省西南部, 属中亚热带季风气候, 年降水量1 737 mm, 年蒸发量1 403 mm, 年平均气温17.5-18.8 ℃, 平均无霜期260天, 年平均日照时间为1 924.6 h, ≥10 ℃积温为4 100-4 650 ℃。该区属于河谷盆地, 四周被低山高丘环抱, 海拔在300-500 m之间。该区原有地带性植被(常绿阔叶林)基本被破坏殆尽, 现有植被主要以马尾松次生林和人工林为主, 林下植被以芒萁为主。该区土壤为燕山运动早期形成的中粗粒花岗岩发育的红壤, 可蚀性高, 花岗岩风化壳深厚, 结构松散, 降雨侵蚀严重, 加之历史上该区植被破坏严重, 使河田镇成为全国水土流失极为严重的区域, 许多地方表土层丧失殆尽, 植被恢复困难。采用时空代换方案, 在红壤典型侵蚀区福建省龙岩市长汀县河田镇选择土壤母岩均为花岗岩的未治理地、恢复13年和31年的马尾松林地(表1)组成植被恢复年限序列。恢复13年和31年的马尾松林地治理前均为表土层土壤流失殆尽, 心土层出露, 本底条件与未治理地基本一致。
Table 1
表1
表1样地基本概况(平均值±标准偏差)
Table 1The basic background characteristics of sample plot (mean ± SD)
| 因子 Factor | 林分类型 Stand type | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Y0 | Y13 | Y31 | |||||||
| NRd | Rd | CK | NRd | Rd | CK | NRd | Rd | CK | |
| 治理历史 Management process | 土壤侵蚀严重 Suffer from serious soil erosion | 从2002年开始治理 Ecological restoration since from 2002 | 从1984年开始治理 Ecological restoration since from 1984 | ||||||
| 优势种 Dominant species | 马尾松, 芒萁 Pinus massoniana, Dicranopteris dichotoma | 马尾松, 芒萁 Pinus massoniana, Dicranopteris dichotoma | 马尾松, 芒萁 Pinus massoniana, Dicranopteris dichotoma | ||||||
| 平均树高 Average height of trees (m) | 2 | 7 | 13.7 | ||||||
| 平均胸径 Average diameter at breast height (cm) | 3.1 | 7.4 | 14 | ||||||
| 植株密度 Plant density (stems·hm-2) | 1 741 | 3 341 | 1 433 | ||||||
| 芒萁覆盖度 Coverage of Dicranopteris dichotoma (%) | 15 | 90 | 85 | ||||||
| 坡度 Slope (°) | 19 | 8 | 11 | ||||||
| 土壤有机碳 Soil organic carbon (g·kg-1) | 6.37 ± 0.12 | 3.42 ± 0.01 | 1.60 ± 0.14 | 10.16 ± 1.47 | 11.30 ± 1.28 | 8.09 ± 0.52 | 14.33 ± 4.78 | 14.23 ± 1.94 | 5.32 ± 0.54 |
| 总氮Total nitrogen (g·kg-1) | 0.61 ± 0.02 | 0.52 ± 0.19 | 0.26 ± 0.07 | 0.74 ± 0.04 | 0.66 ± 0.01 | 0.48 ± 0.09 | 0.91 ± 0.25 | 0.81 ± 0.02 | 0.36 ± 0.16 |
| pH | 4.37 ± 0.07 | 4.58 ± 4.58 | 4.67 ± 0.07 | 4.19 ± 0.07 | 4.39 ± 0.07 | 4.50 ± 0.04 | 4.24 ± 0.06 | 4.44 ± 0.03 | 4.69 ± 0.14 |
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1.2 样地调查和样品采集处理
于2014年8月上旬, 在每个林地设置3种处理: 保留芒萁覆盖、去除芒萁覆盖以及与之毗邻的林下未生长芒萁的裸露地。设置3个20 m × 20 m的标准样地, 每个标准样地分成4个10 m × 10 m的亚样方, 随机选取一个亚样方作为保留芒萁覆盖处理, 1个亚样方作为去除芒萁覆盖处理, 与之毗邻的林下裸地作为对照处理, 其面积和形状依每个样地实际裸露情况确定, 面积不少于100 m2。在去除芒萁一年后, 即2015年8月中旬, 用取土钻(内径为5 cm)在每个处理样地内取0-10 cm土层的土壤, 按S型随机多点(15个点)取样并混合。取回的部分新鲜土样在实验室拣去石砾、植物根系和大于2 mm的碎屑, 风干后过0.149 mm土壤筛, 存于密闭自封袋中, 用于土壤理化性质和土壤有机碳的测定。剩余的新鲜土样过2 mm土壤筛, 冷冻于-4 ℃冰箱中, 用于土壤DOM的浸提。1.3 实验方法
土壤理化性质测定: 土壤有机碳(SOC)和土壤全氮(TN)采用碳氮元素分析仪(Vario EL Max CN, Elementar Analysensystem GmbH, Langenselbold, Germany)测定, pH值使用CHN868型pH计(CHN868, Thermom, Orion, USA)测定。土壤DOM浸提: 样品DOM采用水浸提法(Wu et al., 2010), 取10 g鲜土于50 mL离心管中, 加入去离子水40 mL (水土比4:1, V:W), 振荡30 min (260 r·min-1), 离心10 min (4 000 r·min-1)后, 用0.45 μm滤膜过滤, 滤液用于DOC测定。
DOC浓度测定: 采用岛津TOC-V CPH有机碳分析仪(TOC-V CPH, Shimadzu, Japan)测定样品DOC浓度。
土壤DOM紫外光谱测定: 用紫外可见分光光度计(UV-2450, Shimadzu, Kyoto, Japan)测定波长为250、254和365 nm处的吸光值。
土壤DOM荧光光谱测定: 荧光光谱使用日立F7000仪器(F7000, Hitachi, Tokyo, Japan)进行测定, 激发和发射光栅狭缝宽度都为10 nm, 扫描速度 1 200 nm·min-1, 激发波长254 nm, 荧光发射光谱波长范围300-480 nm, 荧光同步光谱波长范围250-500 nm。
为了提高灵敏度, 紫外可见分光光度计吸收值测定和荧光光谱扫描前, 待测液均用2 mol·L-1 HCl将其pH值调至2。
土壤DOM红外光谱测定: 用FTIR光谱仪(Nicolet Magna FTIR 550, Thermo, Waltham, USA)测定红外光谱, 将1 mg冷冻干燥的土壤DOM样品与400 mg干燥的KBr (光谱纯)磨细混匀, 在10 t·cm-2压强下压成薄片并维持1 min, 测定并记录其光谱, 波谱扫描范围为4 000-400 cm-1。
1.4 计算方法和数据处理
使用UV-2450 (岛津)紫外可见分光光度计检测待测液在波长254 nm处的吸收值来表征其芳香化程度(Akagi et al., 2007; Wu et al., 2010), 即芳香化指数(AI)。E2:E3值表征待测样中DOM平均分子量的大小, 该值越大表明平均分子量越小, 计算公式为 E2:E3 = UV250:UV365 (Peuravuori & Pihlaja, 1997)。
荧光发射光谱中Σ435-480 nm区域与Σ300- 345 nm区域的峰面积比值被称为荧光发射光谱腐殖化指数(HIXem), 荧光同步光谱波长460与345 nm处荧光强度的比值被称为荧光同步光谱腐殖化指数(HIXsyn)(Kalbitz et al., 1999)。
所有数据通过软件Excel 2013进行统计处理, 利用软件SPSS 19.0进行方差分析和皮尔逊相关分析, 相关图表全部用Origin 9.0软件完成。
2 结果和分析
2.1 马尾松林土壤DOM的数量特征
本研究采用土壤可溶性有机碳(DOC)的含量来表征土壤中DOM的数量。Y0、Y13、Y31马尾松林芒萁覆盖地土壤DOC含量分别是林下裸地的7.61倍、4.83倍、5.47倍(图1A), 去除芒萁一年后, 土壤DOC的含量显著下降, 分别是林下裸地的1.84倍、4.12倍、4.73倍(p < 0.05), 表明芒萁对土壤DOM数量有显著影响。DOC在土壤总有机碳(SOC)中分配比例的变化趋势同土壤DOC含量的变化基本相同(图1B), Y0马尾松林林下裸地显著低于芒萁覆盖地(p < 0.05), 而去除芒萁处理一年后其比例已经和林下裸地没有明显差异, 同样, Y13和Y31保留芒萁处理的DOC占SOC的比例均显著高于林下裸地, 且去除芒萁处理一年后其比例已经显著降低, 但仍显著高于林下裸地(p < 0.05), 显然, 芒萁覆盖增加了DOC在SOC中的分配比例。
显示原图|下载原图ZIP|生成PPT图1土壤可溶性有机质(DOM)数量变化(平均值±标准偏差)。不同小写字母表示同一恢复年限不同处理间各指标间差异显著(p < 0.05); 不同大写字母表示同一处理不同恢复年限间各指标间差异显著(p < 0.05)。CK, 林下裸地; NRd, 芒萁覆盖地; Rd, 去除芒萁覆盖地。Y0, 未治理地; Y13, 恢复13年马尾松林地; Y31, 恢复31年马尾松林地。
-->Fig. 1Variation of the quantity of soil dissolved organic matter (DOM) (mean ± SD). Different lowercase letters stand for the significant difference between different experimental treatments in the same vegetation restoration years (p < 0.05). Different capitals stand for the significant difference between the different vegetation restoration years in the same experimental treatment (p < 0.05). CK, control; NRd, not removed Dicranopteris dichotoma; Rd, removed D. dichotoma. Y0, without ecological restoration; Y13, ecological restoration for 13 years; Y31, ecological restoration for 31 years.
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2.2 马尾松林土壤DOM的紫外光谱特征
Y0马尾松林林下裸地土壤DOM的AI显著小于芒萁覆盖地(p < 0.05), 去除芒萁一年后, 已和林下裸地无差异(图2A); 同样, Y13和Y31马尾松林林下裸地土壤DOM的AI值均显著低于芒萁覆盖地, 且去除芒萁一年后, 其AI值显著降低, 但仍显著高于林下裸地(p < 0.05), 这些结果表明, 去除芒萁后土壤DOM的腐殖化程度逐渐接近林下裸地, 证明芒萁对维持土壤DOM的芳香化程度具有明显作用, 而且随着马尾松林恢复年限增加, 芒萁覆盖地土壤DOM的芳香化程度显著增加, 而林下裸地没有明显差异, 表明芒萁是控制土壤DOM腐殖化程度的主要因素。Y0马尾松林林下裸地E2:E3明显高于芒萁覆盖地, 且去除芒萁一年后E2:E3也显著升高, 有接近林下裸地的趋势, 但仍明显低于林下裸地(p < 0.05) (图2B)。同样, Y13和Y31马尾松林林下裸地E2:E3明显高于芒萁覆盖地, 但去除芒萁一年后E2:E3与芒萁覆盖地无差异, 以上结果表明芒萁覆盖地土壤DOM平均分子量明显大于林下裸地。另外, Y13和Y31马尾松林芒萁覆盖地土壤E2:E3显著低于Y0 (p < 0.05), 而这种差异在去除芒萁和林下裸地处理上表现尤为显著, 这意味着芒萁是影响土壤DOM分子量大小的主要因素。
显示原图|下载原图ZIP|生成PPT图2土壤可溶性有机质(DOM)的紫外光谱特征(平均值±标准偏差)。不同小写字母表示同一恢复年限不同处理间各指标间差异显著(p < 0.05)。CK, 林下裸地; NRd, 芒萁覆盖地; Rd, 去除芒萁覆盖地。Y0, 未治理地; Y13, 恢复13年马尾松林地; Y31, 恢复31年马尾松林地。E2:E3, 波长在250 nm和365 nm处的紫外可见光光度值之比。
-->Fig. 2Characteristics of soil dissolved organic matter (DOM) ultraviolet spectrum (mean ± SD). Different lowercase letters stand for the significant difference between different experimental treatments in the same vegetation restoration years (p < 0.05). CK, control; NRd, not removed Dicranopteris dichotoma; Rd, removed D. dichotoma. Y0, without ecological restoration; Y13, ecological restoration for 13 years; Y31, ecological restoration for 31 years. E2:E3, the ratio of ultraviolet-visible light absorption photometric quantity at 250 nm wavelength to ultraviolet-visible light absorption photometric quantity at 365 nm wavelength.
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2.3 马尾松林土壤DOM的荧光光谱特征
不同恢复年限马尾松林不同处理下的土壤DOM荧光发射光谱峰型图相似(图3), 但特征峰荧光强度差异明显, 特别是不同恢复年限的马尾松林林下植被芒萁被去除一年后, 土壤DOM各基团在对应波长上荧光强度明显降低, 意味着去除芒萁后土壤DOM结构中荧光基团在减少。Y0和Y13马尾松林芒萁覆盖地、去除芒萁地、林下裸地的土壤DOM的波峰对应的波长主要集中在340-355 nm之间, 未见明显的波峰位移显现, 而Y31马尾松林林下植被的不同处理引起了土壤DOM波峰的明显位移, 芒萁覆盖地DOM的波峰位于发射荧光光谱波长(λem) = 408 nm处, 而林下裸地的波峰位于λem = 353 nm处, 去除芒萁一年后, DOM的波峰位于λem = 402 nm处, 这意味着芒萁覆盖地土壤DOM分子内的共轭体系更多。另外, Y31马尾松林土壤DOM荧光光谱波峰位移明显, Y0和Y13马尾松林却未发现土壤DOM荧光光谱波峰明显位移, 表明芒萁覆盖对DOM分子结构的影响是一个长期缓慢的过程。不同恢复年限的马尾松林在不同处理下的土壤DOM荧光同步光谱峰型图相似(图4), 但不同恢复年限、不同处理间特征峰出现的位置大致相同, 相对峰面积却不同。土壤DOM荧光同步光谱特征峰中: 同步荧光光谱波长(λsyn)在280-290 nm处表
显示原图|下载原图ZIP|生成PPT图3土壤可溶性有机质(DOM)荧光发射光谱特征。CK, 林下裸地; NRd, 芒萁覆盖地; Rd, 去除芒萁覆盖地。Y0, 未治理地; Y13, 恢复13年马尾松林地; Y31, 恢复31年马尾松林地。λem, 发射荧光光谱波长。
-->Fig. 3Characteristics of dissolved organic matter (DOM) emission fluorescence spectrum. CK, control; NRd, not removed Dicranopteris dichotoma; Rd, removed D. dichotoma. Y0, without ecological restoration; Y13, ecological restoration for 13 years; Y31, ecological restoration for 31 years. λem, emission fluorescence spectrum wavelength.
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显示原图|下载原图ZIP|生成PPT图4土壤可溶性有机质(DOM)的荧光同步光谱特征。CK, 林下裸地; NRd, 芒萁覆盖地; Rd, 去除芒萁覆盖地。Y0, 未治理地; Y13, 恢复13年马尾松林地; Y31, 恢复31年马尾松林地。λsyn, 同步荧光光谱波长。
-->Fig. 4Characteristics of dissolved organic matter (DOM) synchronization fluorescence spectrum. CK, control; NRd, not removed Dicranopteris dichotoma; Rd, removed Dicranopteris dichotoma. Y0, without ecological restoration; Y13, ecological restoration for 13 years; Y31, ecological restoration for 31 years. λsyn, synchronous fluorescence spectrum wavelength.
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征DOM分子中的蛋白质基团(如芳香氨基酸), 在375-385 nm处表征DOM分子中的芳香性脂肪基团, 在450-490 nm处表征DOM分子中的木质素基团, 而各类峰的相对面积大小表征分子个基团含量的多少(刘翥等, 2015)。Y0马尾松林芒萁覆盖地土壤DOM荧光同步光谱在λsyn = 285 nm附近的相对峰面积明显大于林下裸地, 去除芒萁一年后, 该区的相对峰面积与裸地基本相同; 同样, Y13马尾松林芒萁覆盖地土壤DOM荧光同步光谱在λsyn为 285、381和453 nm附近的相对峰面积均大于林下裸地, 去除芒萁一年后, 在λsyn = 285 nm附近的峰面积明显减小, 但仍大于林下裸地, 而λsyn为381和453 nm附近的相对峰面积与林下裸地几乎无差别, 但仍大于林下裸地; Y31马尾松林与之相似, 芒萁覆盖地土壤DOM在λsyn为285、379和453 nm附近的相对峰面积均大于林下裸地, 去除芒萁一年后, 该区对应特征峰面积均有明显的减小趋势, 但仍大于林下裸地, 这表明芒萁对土壤中DOM分子内的蛋白质基团、芳香性脂肪酸基团和木质素基团的维持有重要的作用, 并且在Y0马尾松林这种不稳定的生态系统中这种作用表现得更为明显。图4还表明, 随着恢复年限的不断增加, 土壤DOM的特征峰在不断增加, 芒萁覆盖地表现尤为明显,说明芒萁是影响土壤DOM分子复杂程度的主要因素。
Y0马尾松林林下裸地土壤DOM的HIXem和HIXsyn均显著低于芒萁覆盖地(p < 0.05), 去除芒萁一年后, 土壤的HIXem无明显变化, 但仍显著高于林下裸地(p < 0.05), 而HIXsyn显著低于芒萁覆盖地
(p < 0.05), 与林下裸地接近(图5); Y13马尾松林下裸地土壤DOM的HIXem和HIXsyn均显著低于芒萁覆盖地(p < 0.05), 去除芒萁一年后, HIXem和HIXsyn变化不明显, 却仍显著高于林下裸地(p < 0.05); Y31马尾松林下裸地土壤DOM的HIXem和HIXsyn显著低于芒萁覆盖地(p < 0.05), 去除芒萁一年后, 土壤DOM的HIXem接近林下裸地的趋势明显, HIXsyn显著降低, 但仍明显高于林下裸地(p < 0.05), 显然, 芒萁覆盖地土壤DOM分子腐殖化程度更高, 分子结构更复杂, 去除芒萁一年后, 土壤DOM分子的腐殖化程度均有不同程度的降低, 这意味着芒萁对土壤DOM腐殖化程度的维持有深刻影响, 并且这个影响过程是一个长期缓慢的过程。
2.4 马尾松林土壤DOM的红外光谱特征
土壤DOM存在5类特征峰: 4 000-3 000 cm-1 (与氢键键合的—COOH、醇、苯酚中的—OH伸缩振动吸收峰)、1 625-1 690 cm-1 (苯环、烯烃类和分子间或分子内形成氢键的羧酸中—C==O的伸缩振动峰)、1 600-1 425 cm-1 (苯环上C==C骨架振动)、 1 000-1 250 cm-1 (多糖类、醇类、羧酸类及脂类—C—O—伸缩振动吸收峰)、460-680 cm-1 (苯环上—C—H面外弯曲振动吸收峰)(占新华等, 2007; 肖彦春和窦森, 2008)。Y0马尾松林芒萁覆盖地土壤DOM红外光谱图在3 250-3 750 cm-1和1 000- 1 250 cm-1均存在一个强而宽的吸收峰(图6), 前者表明与氢键键合的—COOH、醇、苯酚中的—OH的存在, 后者表明多糖类、醇类、羧酸类及脂类—C—O—的存在, 这类羟基和—C—O主要来源于DOM中纤维素、糖类及淀粉等碳水化合物, 另外还有1 625- 1 690 cm-1和460-680 cm-1两个弱而窄的吸收峰以及1 600-1 425 cm-1的弱吸收峰证实了芳香类物质的存在, 其中特征峰3 546 cm-1和3 409 cm-1的N-H伸缩振动以及1 687 cm-1的N-H的弯曲振动, 证明酰胺类物质的存在, 然而林下裸地土壤DOM的特征峰明显没有芒萁覆盖地的丰富, 它仅有3 250- 3 750 cm-1和1 000-1 250 cm-1以及460-680 cm-1这几个弱而窄的吸收峰, 并且吸收比例也明显弱于芒萁覆盖地, 去除芒萁一年后, 土壤DOM的红外光谱特征峰与芒萁覆盖地差异不明显, 但有接近CK的趋势; Y31马尾松林土壤DOM红外光谱特征与Y0年相同, 林下裸地红光光谱特征峰明显没有芒萁覆盖地土壤DOM的丰富, 并且吸收比例也要明显低于芒萁覆盖地, 去除芒萁一年后, 土壤DOM红外光谱 特征峰与芒萁覆盖地差异不明显, 但有接近林下裸地的趋势; 特别的是, Y13马尾松林处理之间土壤DOM红外光谱的变化趋势并不明显, 芒萁覆盖地、去除芒萁地和林下裸地土壤DOM光谱上的特征峰型基本相似, 吸收比例也基本相同, 这可能与Y13马尾松林处于壮年期, 林分密度大, 林下即使无芒萁覆盖也可获得相当数量和质量的DOM有关。由此可见, 林下裸地土壤DOM较芒萁覆盖地含有更多羟基、羧酸类以及碳水化合物等结构简单且易迁移的物质, 去除芒萁一年后, 与芒萁覆盖地之间差异不明显, 这也意味着芒萁可以保持DOM分子的复杂程度, 维持其稳定性, 但这种影响作用可能是一个长期缓慢的过程。
显示原图|下载原图ZIP|生成PPT图5土壤可溶性有机质(DOM)的荧光光谱特征(平均值±标准偏差)。不同小写字母表示同一恢复年限不同处理间各指标间差异显著(p < 0.05)。CK, 林下裸地; NRd, 芒萁覆盖地; Rd, 去除芒萁覆盖地。Y0, 未治理地; Y13, 恢复13年马尾松林地; Y31, 恢复31年马尾松林地。HIXem, 发射荧光光谱腐殖化指数; HIXsyn, 同步荧光光谱腐殖化指数。
-->Fig. 5Characteristics of dissolved organic matter (DOM) fluorescence spectrum (mean ± SD). Different lowercase letters stand for the significant difference between different experimental treatments in the same vegetation restoration years (p < 0.05). CK, control; NRd, not removed Dicranopteris dichotoma; Rd, removed D. dichotoma. Y0, without ecological restoration; Y13, ecological restoration for 13 years; Y31, ecological restoration for 31 years. HIXem, emission fluorescence spectrum humification index; HIXsyn, synchronous fluorescence spectrum humification index.
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显示原图|下载原图ZIP|生成PPT图6土壤可溶性有机质(DOM)的红外光谱特征。CK, 林下裸地; NRd, 芒萁覆盖地; Rd, 去除芒萁覆盖地。Y0, 未治理地; Y13, 恢复13年马尾松林地; Y31, 恢复31年马尾松林地。
-->Fig. 6Characteristics of dissolved organic matter (DOM) fourier infrared transmission spectrum. CK, control; NRd, not removed Dicranopteris dichotoma; Rd, removed D. dichotoma. Y0, without ecological restoration; Y13, ecological restoration for 13 years; Y31, ecological restoration for 31 years.
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3 讨论
近期的研究发现, 新近凋落物和土壤腐殖质分解以及土壤根系周转及其分泌物和微生物代谢产物是土壤DOM的主要来源(Chang et al., 2007; Wu et al., 2010; 刘翥等, 2015), 而本研究中马尾松林下裸地立地条件极差, 其凋落物数量、根系周转速度和分泌物数量以及土壤微生物代谢产物远没有林下芒萁覆盖地丰富(Xie et al., 2013; 张浩等, 2016), 造成不同恢复年限马尾松林下芒萁覆盖地土壤DOM数量显著高于林下裸地(p < 0.05), 去除芒萁覆盖一年后, 土壤DOM数量降低明显, 说明了林下芒萁是影响土壤DOM数量的主要因素。与林下裸地相比, 芒萁覆盖下的土壤, 凋落物输入的数量和种类更为丰富, 并且土壤中遍布芒萁的根系, 能够产生大量的根系分泌物和根系脱落物, 此类活性有机碳恰好是微生物生命活动的主要能量源(Zhao et al., 2012; 张浩等, 2016), 而微生物正常生命活动会产生大量微生物代谢产物。林下芒萁覆盖地土壤DOM在SOC中的分配比例明显高于林下裸地, 且芒萁去除一年后, 该比例明显下降, 而DOM作为土壤微生物可直接分解利用的主要碳源, 其在土壤有机碳中所占的比例大小表征了土壤可供给微生物能量大小的潜力(Zhao et al., 2012; 张浩等, 2016), 因此, 芒萁覆盖地土壤可提供足够的碳源给微生物, 维持其正常的代谢活动, 当微生物自身代谢所需碳源得到满足后, 土壤有机碳水平便处于动态平衡当中, 由此可见, 芒萁覆盖地土壤有积累土壤有机碳的潜力(Hagedorn, et al., 2000), 即林下芒萁对土壤有机碳积累具有积极的作用。植被类型不同, 土壤DOM结构差异明显(李海涛等, 2007), 显然, 林下芒萁覆盖地土壤DOM的光谱学特征与林下裸地不同。本研究的紫外光谱显示, 林下芒萁覆盖地土壤DOM的AI显著高于林下裸地, E2:E3值却与之相反, 意味着芒萁覆盖地土壤DOM芳香化程度更高, 且分子量更大, 结构更为复杂(Chang et al., 2007), 而去除芒萁一年后, 土壤DOM的AI值显著降低, E2:E3值却未见明显变化, 表明芒萁去除后, 土壤DOM的芳香化程度在降低, 但分子量变化却不明显。研究发现因芒萁凋落物养分含量低、质量差(Zhao et al., 2012), 所以芒萁群落下常常覆盖着一层厚厚的芒萁枯死物, 其分解后会产生大量的芳香类物质, 这是导致芒萁覆盖地土壤DOM芳香化程度较高的主要原因。
如前所述, 林下芒萁覆盖地土壤荧光发射光谱也表明芒萁覆盖地土壤DOM结构中含有更多的荧光基团, 即腐殖化物质, 并且Y31马尾松土壤DOM荧光发射光谱特征峰位置发生明显位移, 从裸地到芒萁覆盖地特征峰位置明显向长波方向移动, 说明芒萁覆盖地土壤DOM的共轭体系增加, 分子结构更为复杂, 而Y0和Y13马尾松林的这种波峰位置移动并不明显, 这可能与不同恢复程度的森林生态系统对于土壤DOM结构变化快慢程度的控制机制不同有关。芳香环是常见的共轭体系, 它是形成土壤腐殖质的基础, 腐殖质分子的中心常常是一个稠环或者易生稠环的芳香核(朱鹤健, 1992), 因而和AI的结果一致。荧光同步光谱结果类似, 芒萁覆盖地土壤DOM结构中含有更多的蛋白质基团、芳香性脂肪酸基团和木质素基团, 且去除芒萁一年后, 土壤DOM各基团特征峰均有不同程度的降低, 证实了芒萁是土壤DOM结构复杂程度的主要影响因素。许多研究证实, 林下裸地因其立地条件差, 且缺少林下植被芒萁覆盖, 所以DOM的输入源(凋落物、根系周转和分泌物、微生物代谢产物)远不如芒萁覆盖地丰富(Hagedorn et al., 2000; Zhao et al., 2012), 而且源于芒萁枯落物的DOM中含有许多聚合程度高的难分解组分, 其分解产物中含有许多结构复杂的大分子化合物(周国模和姜培坤, 2004), 这不仅有利于土壤DOM腐殖化程度的提高, 而且有利于其腐殖质的形成, 导致其易被土壤胶体吸附(Kaiser, 1997), 增强其化学稳定性, 有利于土壤有机碳的积累。红外光谱显示, 林下裸地土壤DOM比芒萁覆盖地含有更多的羟基、羧酸类以及碳水化合物中的烷氧基等结构简单易迁移的物质, 这与AI和HIX的规律吻合, 但芒萁去除一年后, 红外光谱谱图上的特征峰减少不明显, 也说明芒萁对土壤DOM的结构特征的影响是一个持久缓慢的过程。
4 结论
不同恢复年限的马尾松林芒萁覆盖地, 因其凋落物数量、根系周转和分泌物以及微生物代谢产物明显多于林下裸地, 故而芒萁覆盖地土壤DOM数量更多, 可供给微生物足够的碳源, 维持土壤有机碳的动态平衡, 利于土壤有机碳积累。从DOM光谱学特征判断, 林下芒萁覆盖地土壤DOM比林下裸地的芳香化程度和腐殖化程度更高, DOM的分子量更大, 结构更为复杂, 易于被土壤胶粒吸附, 维持其化学稳定, 利于土壤有机碳积累, 即芒萁在土壤有机碳积累过程中具有明显的积极作用。The authors have declared that no competing interests exist.
参考文献 原文顺序
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被引期刊影响因子
| [1] | The dissolved organic matter (DOM) in soils is essentially defined by the way in which it is obtained. Therefore, we need to understand as to how pre-treatment of a soil will affect the characteristics of DOM, since this fraction may be strongly influenced by a soil's water content. The effect of two different pre-treatments on DOM from the A-horizons of a large variety of ecosystems and regions were compared. In both cases the soils were allowed to air-dry. In one case the air-dried soil was directly extracted (AD), while in the other case it was preincubated for 1 week at 50% of its water holding capacity (INCU). AD is simpler, but INCU brings the soil, and especially its microbial population, back to a standardised state, which is more representative of the usual state in the field. Both methods are used whenever an adjustment of the soil water content is essential to compare different regions or to eliminate short term weather effects. A significant regression indicated that the dissolved organic carbon (DOC) extracted from INCU samples was only 20% of AD DOC. Both the absorptivity (UV absorption divided by DOC) of 86% of the samples, and a fluorescence emission spectrum based Humification Index in all cases increased as a result of preincubation. This would indicate that labile compounds released during drying were metabolised during the incubation. However, the magnitude of this increase varied, and no correlation with soil organic and microbial carbon, pH, or texture could be detected. The results show that DOM extracted from AD and INCU soils is not comparable and that the differences are mainly due to the impact of air-drying on the microbial activity. |
| [2] | The biodegradability of dissolved organic carbon (DOC) in different fractions from the forest floor was studied. Soil leachate (SL, the soil solution in macropores which is freely drained from forest floor after rainfall), the soil matrix solution (SMS, the soil solution in meso-/micropores of the soil matrix), and soil water extracts (SWE) from two different beech forest floors were compared. Zero-tension and tension lysimeters were used to collect SL and SMS, respectively. Loss of DOC (during 21 days) and respiration of CO 2 鈥揅 (during 7 days) were used as conventional measures of the availability of DOC. Bacterial production, measured using the leucine incorporation technique, and bacterial growth efficiency were also estimated. All methods were used to study differences in biodegradability between plots with and without ground flora ( Deschampsia flexuosa or Anemone nemorosa) and different type of forest floor (with an organic (O) horizon or a mull (A) horizon). There were no differences in bioavailability of DOC from soil solutions extracted from plots with and without ground flora. The bioavailability of DOC in the different collected soil solutions varied, however. DOC in SWE was the most available, with a mean of 39% of DOC-loss in 21 days, and 18% of DOC being respired in 7 days. DOC in soil matrix solution was the least available of the soil solutions (7% respired), significantly less than DOC in soil leachate (11% respired). The methods measuring biodegradation of DOC, DOC-loss and CO 2 鈥揅 respiration gave similar results and were comparable to bacterial production and bacterial growth efficiency, with the exception of SWE from the O-horizon at the D. flexuosa site, which had low bacterial production and bacterial growth efficiency, indicating a limitation of the bacterial growth. This study is one of the first to use bacterial production and bacterial growth efficiency for measuring bioavailability in terrestrial environments, giving an extra dimension for the process of biodegradation of DOC. |
| [3] | We present a model that considers UV-absorbing dissolved organic matter (DOM) to consist of two components (A and B), each with a distinct and constant spectrum. Component A absorbs UV light strongly, and is therefore presumed to possess aromatic chromophores and hydrophobic character, whereas B absorbs weakly and can be assumed hydrophilic. We parameterised the model with dissolved organic carbon concentrations [DOC] and corresponding UV spectra for c. 1700 filtered surface water samples from North America and the United Kingdom, by optimising extinction coefficients for A and B, together with a small constant concentration of non-absorbing DOM (0.80mgDOCL鈭1). Good unbiased predictions of [DOC] from absorbance data at 270 and 350nm were obtained (r2=0.98), the sum of squared residuals in [DOC] being reduced by 66% compared to a regression model fitted to absorbance at 270nm alone. The parameterised model can use measured optical absorbance values at any pair of suitable wavelengths to calculate both [DOC] and the relative amounts of A and B in a water sample, i.e. measures of quantity and quality. Blind prediction of [DOC] was satisfactory for 9 of 11 independent data sets (181 of 213 individual samples). |
| [4] | Forest ecosystems in Taiwan are frequently influenced by typhoons that cause large amounts of litter input to the soil. The rapid decomposition of such litter under the high precipitation and temperature conditions may trigger nutrient losses via seepage. Our goal was to investigate the effects of exceptionally high inputs of Chamaecyparis obtusa var. formosana leaves to the soil on the solute fluxes and concentrations of mineral elements, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in a Lithic Leptosol. We simulated the effect of a typhoon by adding the annual aboveground litterfall (4600kgha 611 ) and about 3 times the annual litterfall (13,900kgha 611 ) as fresh leaves in a single event to small manipulation plots. All plots were also subjected to the natural litterfall. Soil solution was collected 4 months before and 15 months following the litter manipulation in 14 days intervals underneath the forest floor with free draining lysimeters and by ceramic suction cups at 60cm depth. The 3-fold litter addition caused increased fluxes of K, Mg, Ca, and NH 4 in forest floor percolates as compared to the 1-fold litter treatment. DOC and DON fluxes also increased, but this was only statistically significant for DON. DON was the dominant form of N both in forest floor percolates and in seepage. The 3-fold litter manipulation increased the seepage fluxes of K, DON, and DOC relative to the 1-fold treatment with largest differences recorded for K, reaching 12.4kgha 611 15month 611 . The fluxes of DOC with forest floor percolates and with seepage in both treatments exceeded published values by far. Our results suggest that the decomposition of large amounts of fresh leaf litter may trigger K losses from the ecosystem via seepage, whereas the probability for additional N and DOC losses is moderate. For Ca and Mg, additional losses seem to be rather unlikely. |
| [5] | . Leaching of dissolved organic carbon (DOC) from the organic horizon is an important process involved in translocation and stabilization of organic matter in forest soils. Despite there being many studies on the DOC fluxes in temperate forest soils, very little information is available in tropical forest soils. The roles of DOC leaching in soil organic carbon cycle were evaluated by quantifying the fluxes of DOC in throughfall and soil solution in the Ultisols under tropical secondary and pristine forests in East Kalimantan, Indonesia. The fluxes of DOC in the soil profiles are highest from the O horizon (470–56202kg C ha 61 1 yr 61 1), decreasing markedly in the A and B1 horizons of the two Ultisols studied. DOC fluxes from the O horizon are comparable to those of temperate forests because of the greater amounts of precipitation, substantial C input (3.7–4.302Mg C ha 61 1 yr 61 1) and its rapid decomposition (4.2–5.402Mg C ha 61 1 yr 61 1). The proportion of DOC leaching to C input in the O horizon (12.7–13.2%) is similar to Spodosols under boreal and temperate forests. DOC leached from the O horizon appears to be an important carbon source into mineral soils, even in tropical regions. At the same time, DOC leaching contributed to eluviation of Al and Fe from the O horizon and their illuviation in the subsurface soil horizons. It was quantitatively shown that DOC leaching is important to the translocation of organic matter, Al and Fe in the acidic Ultisols in tropical forests, as well as the soils under boreal and temperate forests that undergo podzolization. |
| [6] | Efforts to increase our understanding of the terrestrial carbon balance have resulted in a dense global network of eddy covariance towers, which are able to measure the net ecosystem exchange of CO 2 , H 2 O and energy between ecosystems and the atmosphere. However, the typical set-up on an eddy covariance tower does not monitor lateral CO 2 - and carbon fluxes such as dissolved organic carbon (DOC). By ignoring DOC fluxes eddy covariance-based CO 2 balances overestimate the carbon sink of ecosystems as part of the DOC drains into the inland waters and get respired outside the footprint of the eddy covariance tower. In this study we quantify 7 years (2000–2006) of DOC fluxes from a temperate Scots pine forest in Belgium and analyse its inter-annual variability. On average, 1002gC02m 612 02year 611 is leached from the pine forest as DOC. If the DOC fluxes are considered relative to the gross ecosystem carbon fluxes we see that DOC fluxes are small: 0.802±020.2% relative to gross primary productivity, 1.002±020.3% relative to ecosystem respiration, and (2.402±020.4%) relative to soil respiration. However, when compared to net fluxes such as net ecosystem productivity and net biome productivity the DOC flux is no longer negligible (1102±027% and 17%, respectively), especially because the DOC losses constitute a systematic bias and not a random error. The inter-annual variability of the DOC fluxes followed that of annual water drainage. Hence, drainage drives DOC leaching at both short and long time scales. Finally, it is noted that part of the carbon that is leached from the ecosystem as DOC is respired or sequestered elsewhere, so the physical boundaries of accounting should always be reported together with the carbon budget. |
| [7] | In forest ecosystems, organic solutes play prominent roles in pollutant and nutrient transport. This study, conducted in subalpine forested Humaquepts in Switzerland, investigated the influence of redox conditions and flow processes on dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). In the mineral soil, concentrations of DOC were higher under reduced than under oxidized con... |
| [8] | 本文通过田间采样分析和室内培育试验,研究了不同利用年限的3种 红壤水田土壤中溶解有机C(DOC)的含量动态和生物降解特征.结果表明:土壤DOC的含量随土壤深度而降低,二者具有显著负相关性.0～30cm土壤 DOC的含量及其占总C比例随土壤有机C含量的升高而增大.DOC的季节变化明显,主要与气候因素有关;降雨和灌水可显著提高DOC的含量,是落干时含量 的1.44～2.50倍.淋溶试验结果表明,从试验开始,淋滤液中DOC的浓度呈增加趋势,至21天时达到最大,其后又趋下降.在49天的培养期 内,DOC的分解速率为31%～58%,其中低分子量组分能在数天内降解掉.不同土壤间DOC的分解速率有明显差异. |
| [9] | |
| [10] | The elemental composition and spectroscopic properties of dissolved fulvic acids isolated from different sampling media (topsoil, ground and surface water) of a natural fen area (high portion of organic soils) were examined to reveal the effects of land use history. These effects need to be known if dissolved humic substances are to be a major factor in identifying the impact of present and future changes in land use. Dissolved fulvic acids (topsoil, groundwater) from highly degraded peatlands (due to a long-term agricultural use) exhibit lower C/N ratios, higher absorption in the UV spectra, and higher absorption at 1,620 cm 鈭1 in the FTIR spectra compared with fulvic acids from relatively intact peatlands. These properties illustrate that long-term agricultural use with high inputs results in increased aromatic structures and a further humification of dissolved fulvic acids due to very strong peat decomposition compared with relatively intact peatlands. Synchronous fluorescence spectra also indicate the higher level of aromatic structures within fulvic acids isolated from sites with long-term agricultural use (high peat decomposition) compared with a land use history resulting in a lower peat decomposition. The different sources of fulvic acids in surface water (precipitation, runoff, interflow, groundwater) are the main reason for these effects not being detected in fulvic acids isolated from surface water. Short-term changes in land use characterized by a transition from crop farming to an unimproved grassland were found not to affect the spectroscopic properties of dissolved fulvic acids. A humification index deduced from the synchronous fluorescence spectra is proposed. We have strong evidence that dissolved humic substances indicate changes in the environmental conditions (both anthropogenic and natural) of wetlands with a high proportion of organic soils. |
| [11] | Dissolved organic matter (DOM) is often considered the most labile portion of organic matter in soil and to be negligible with respect to the accumulation of soil C. In this short review, we present recent evidence that this view is invalid. The stability of DOM from forest floor horizons, peats, and topsoils against microbial degradation increases with advanced decomposition of the parent organic matter (OM). Aromatic compounds, deriving from lignin, likely are the most stable components of DOM while plant-derived carbohydrates seem easily degradable. Carbohydrates and N-rich compounds of microbial origin produced during the degradation of DOM can be relatively stable. Such components contribute much to DOM in the mineral subsoil. Sorption of DOM to soil minerals and (co-)precipitation with Al (and probably also with Fe), especially of the inherently stable aromatic moieties, result in distinct stabilization. In laboratory incubation experiments, the mean residence time of DOM from the Oa horizon of a Haplic Podzol increased from <30 y in solution to >90 y after sorption to a subsoil. We combined DOM fluxes and mineralization rate constants for DOM sorbed to minerals and a subsoil horizon, and (co-)precipitated with Al to estimate the potential contribution of DOM to total C in the mineral soil of a Haplic Podzol in Germany. The contribution of roots to DOM was not considered because of lack of data. The DOM-derived soil C ranges from 20 to 55 Mg ha-1 in the mineral soil, which represents 19%-50% of the total soil C. The variation of the estimate reflects the variation in mineralization rate constants obtained for sorbed and (co-)precipitated DOM. Nevertheless, the estimates indicate that DOM contributes significantly to the accumulation of stable OM in soil. A more precise estimation of DOM-derived C in soils requires mineralization rate constants for DOM sorbed to all relevant minerals or (co-)precipitated with Fe. Additionally, we need information on the contribution of sorption to distinct minerals as well as of (co-)precipitation with Al and Fe to DOM retention. |
| [12] | Dissolved organic matter (DOM) contributes to organic carbon either stored in mineral soil horizons or exported to the hydrosphere. However, the main controls of DOM dynamics are still under debate. We studied fresh leaf litter and more decomposed organic material as the main sources of DOM exported from the forest floor of a mixed beech/oak forest in Germany. In the field we doubled and excluded aboveground litter input and doubled the input of throughfall. From 1999 to 2005 we measured concentrations and fluxes of dissolved organic C and N (DOC, DON) beneath the Oi and Oe/Oa horizon. DOM composition was traced by UV and fluorescence spectroscopy. In selected DOM samples we analyzed the concentrations of phenols, pentoses and hexoses, and lignin-derived phenols by CuO oxidation. DOC and DON concentrations and fluxes almost doubled instantaneously in both horizons of the forest floor by doubling the litter input and DOC concentrations averaged 82聽mg聽C聽l 鈭1 in the Oe/Oa horizon. Properties of DOM did not suggest a change of the main DOM source towards fresh litter. In turn, increasing ratios of hexoses to pentoses and a larger content of lignin-derived phenols in the Oe/Oa horizon of the Double litter plots in comparison to the Control plots indicated a priming effect: Addition of fresh litter stimulated microbial activity resulting in increased microbial production of DOM from organic material already stored in Oe/Oa horizons. Exclusion of litter input resulted in an immediate decrease in DOC concentrations and fluxes in the thin Oi horizon. In the Oe/Oa horizon DOC concentrations started to decline in the third year and were significantly smaller than those in the Control after 5聽years. Properties of DOM indicated an increased proportion of microbially and throughfall derived compounds after exclusion of litter inputs. Dissolved organic N did not decrease upon litter exclusion. We assume a microbial transformation of mineral N from throughfall and N mineralization to DON. Increased amounts of throughfall resulted in almost equivalently increased DOC fluxes in the Oe/Oa horizon. However, long-term additional throughfall inputs resulted in significantly declining DOC concentrations over time. We conclude that DOM leaving the forest floor derives mainly from decomposed organic material stored in Oe/Oa horizons. Leaching of organic matter from fresh litter is of less importance. Observed effects of litter manipulations strongly depend on time and the stocks of organic matter in forest floor horizons. Long-term experiments are particularly necessary in soils/horizons with large stocks of organic matter and in studies focusing on effects of declined substrate availability. The expected increased primary production upon climate change with subsequently enhanced litter input may result in an increased production of DOM from organic soil horizons. |
| [13] | |
| [14] | 选取中亚热带福建三明格氏栲天然林及其转换而成的木荷、锥栗及福建柏等3种人工林表层土壤（0—10 cm）可溶性有机质（DOM）为对象,对其数量和光谱学特征进行了研究,以探讨森林转换对土壤DOM的影响。结果表明,天然林转换成上述3种人工林后,0—5 cm土壤可溶性有机碳（DOC）浓度显著降低（P〈0.05）,降低程度分别为66.1%,69.9%及29.4%,可溶性有机氮（DON）浓度也有所下降;除福建柏外,其余两种人工林5—10 cm土壤DOC及DON浓度均低于天然林。各林分0—5 cm土壤DOC及DON浓度均高于5—10 cm土层。两个土层中,天然林土壤DOM的芳香化及腐殖化程度均显著高于人工林（P〈0.05）,但荧光效率值低于人工林;荧光光谱图显示,天然林土壤DOM在芳香性脂肪族及木质素类复杂结构荧光基团处的吸收大于人工林;各林分土壤DOM傅里叶红外光谱出现吸收谱带的位置相似,其中吸收强度最大的为形成氢键的—OH的伸缩振动,此外还有芳香性CC伸缩振动、有机羧酸盐COO-反对称伸缩振动、碳水化合物中烷氧基C—O的振动等,人工林土壤DOM中碳水化合物的比例增加是其结构简单的主要原因。土壤DOM中结构复杂、分子量大的组分不易向下迁移;天然林与人工林间土壤DOM数量及光谱学特征的差异主要与凋落物输入及营林措施的干扰有关;本研究所涉及的3种人工林中,福建柏更有利于土壤养分的累积。 |
| [15] | |
| [16] | Summary Dissolved organic nitrogen and carbon (DOC) are significant in the C and N cycle in terrestrial ecosystems. Little is known about their dynamics in the field and the factors regulating their concentrations and fluxes. We followed the fluxes and concentrations of the two in a Norway spruce ( Picea abies (L.) Karst.) forest ecosystem in Germany from 1995 to 1997 by sampling at fortnightly intervals. Bulk precipitation, throughfall, forest floor percolates from different horizons and soil solutions from different depths were analysed for major ions, dissolved organic N and DOC. The largest fluxes and concentrations were observed in percolates of the Oi layer, which contain amino N and amino sugar N as the major components. The average ratio of dissolved organic C to N in forest floor percolates corresponded to the C/N ratio of the solid phase. Concentrations and fluxes were highly dynamic with time and decreased with depth. The largest fluxes in forest floor percolates occurred when the snow melted. The concentrations and fluxes of dissolved organic N were significantly correlated with DOC, but the correlation was weak, indicating different mechanisms of release and consumption. The dynamics of dissolved organic N and DOC in forest floor percolates were not explained by pH and ionic strength of the soil solution nor by the water flux, despite large variations in these. Furthermore, the release of these fractions from the forest floor was not related to the quality and amount of throughfall. Concentrations of dissolved organic N in forest floor percolates increased with soil temperature, while temperature effects on DOC were less pronounced, but their fluxes from the forest floor were not correlated with temperature. In the growing season concentrations of both dissolved organic N and C in forest floor percolates decreased with increasing intensity of throughfall. Thus, the average throughfall intensity was more important than the amount of percolate in regulating their concentrations in forest floor percolates. Our data emphasize the role of dissolved organic N and DOC in the N and C cycle of forest ecosystems. |
| [17] | The number- and weight-averaged molecular weights of different isolated humic fractions and unfractionated organic matter from natural water samples were measured using high-performance size-exclusion chromatography (HPSEC). The chromatograms obtained, with sodium acetate as the mobile phase on a TSK G3000SW high-speed column, provided illustrative information about the nature of the dissolved organic matter that was not available with phosphate buffer eluents. The calibration of the column system merely with protein standards generated misleading information about the molecular weight and size distribution of humic solutes. Instead, the present results support the utilization of polystyrene-sulphonates (PSS) either alone or together with certain other model compounds for the calibration of HPSEC in studying molecular weights of humic solutes. The data obtained with the HPSEC system indicate that the average molecular weight of humic solutes is distinctly lower than is generally assumed. Besides, aquatic humic solutes also contain some very large-sized though minor constituents, leading to a fairly polydisperse mixture. Number-averaged molecular weights obtained using the HPSEC system were 4鈥5-fold greater than those from vapour-pressure osmometry. Bulk spectroscopic properties such as molar absorptivity at 280 nm and the quotient, ja:math , correlated strongly with the total aromaticity and averaged molecular weights of all the humic solutes. This observation suggests that bulk spectroscopic properties can be applied, as a first approximation, for estimating the size of humic solutes and their aromaticity in natural surface waters. |
| [18] | Although tropical wet forests play an important role in the global carbon (C) and nitrogen (N) cycles, little is known about the origin, composition, and fate of dissolved organic C (DOC) and N (DON) in these ecosystems. We quantified and characterized fluxes of DOC, DON, and dissolved inorganic N (DIN) in throughfall, litter leachate, and soil solution of an old-growth tropical wet forest to assess their contribution to C stabilization (DOC) and to N export (DON and DIN) from this ecosystem. We found that the forest canopy was a major source of DOC (23202kg C ha –1 y –1 ). Dissolved organic C fluxes decreased with soil depth from 27702kg C ha –1 y –1 below the litter layer to around 5002kg C kg C ha –1 y –1 between 0.75 and 3.5m depth. Laboratory experiments to quantify biodegradable DOC and DON and to estimate the DOC sorption capacity of the soil, combined with chemical analyses of DOC, revealed that sorption was the dominant process controlling the observed DOC profiles in the soil. This sorption of DOC by the soil matrix has probably led to large soil organic C stores, especially below the rooting zone. Dissolved N fluxes in all strata were dominated by mineral N (mainly NO 3 61 ). The dominance of NO 3 – relative to the total amount nitrate of N leaching from the soil shows that NO 3 – is dominant not only in forest ecosystems receiving large anthropogenic nitrogen inputs but also in this old-growth forest ecosystem, which is not N-limited. |
| [19] | To better understand the impact of converting native forests to intensively managed plantations on soil carbon (C) and nitrogen (N) dynamics in subtropical China, we examined the seasonal patterns of water-soluble organic C (WSOC) and N (WSON) concentrations in soils in Chinese chestnut (Castanea mollissima Blume) (CF) and bamboo (Phyllostachys praecox C.D. Chu & C.S. Chou) plantation forests (... |
| [20] | |
| [21] | Recovery of carbon stocks after afforestation in degraded lands provides a management practice to mitigate rising atmospheric carbon dioxide concentrations, however carbon accumulation after afforestation of severely eroded lands is poorly understood. Large areas of the red soils in subtropical China suffer from severe erosion and have very low carbon density. We investigated above- and below-ground carbon pools in bare land on a severely eroded red soil (BL), a Pinus massoniana plantation that had been established on bare land in 1981(PM) and a nearby secondary forest (SF) in southeastern China. The ecosystem carbon pool in PM (130.102±027.202Mg02C02ha 611 ) was 10 times higher than in BL (13.002±021.302Mg02C02ha 611 ), and 22% lower than that in SF (166.702±027.002Mg02C02ha 611 ) ( p 02<020.05). The above ground biomass carbon pool was 91.902±024.802Mg02C02ha 611 in PM, similar to 98.202±025.502Mg02C02ha 611 in SF. The soil organic carbon (SOC) pool (to 102m depth) in PM (38.202±023.402Mg02C02ha 611 ) was 2.9 times higher than that in BL (13.002±021.302Mg C ha –1 ), but was significantly lower than that in SF (68.502±022.502Mg C ha –1 ). About 70% of the organic C to 102m depth was stored in the top 4002cm in the two forests. The storage of light fraction organic carbon (LFOC) at the 0–6002cm depth in PM was significantly higher than that in BL, but not significantly different from that in SF. PM had significantly higher proportions of LFOC to SOC for all soil depths in comparison with BL and SF ( p 02<020.05). The mean accumulation rates of ecosystem carbon pools, aboveground biomass carbon pools, and SOC pools in PM were 4.8802±020.25, 3.8302±020.16, and 1.0502±020.0902Mg02C02ha 611 02yr 611 , respectively. Our results indicate that afforestation of severely eroded red soils with P. massoniana may be a successful forest management practice to achieve rapid carbon accumulation. |
| [22] | 可溶性有机物质 (Dissolved Organic Matter)是森林生态系统主要的可移动碳库及重要的养分库。系统综述了森林生态系统 DOM的来源、组成、性质、季节动态 ;DOM释放与存留机制及影响因素 ;森林生态系统 DOM的流动及干扰对 DOM动态影响等。已有研究表明 DOM在森林生态系统 C、N、P循环、成土作用、污染物迁移等方面起着重要作用。今后森林生态系统 DOM的研究应集中于以下几方面 :(1 )确定森林生态系统中 DOM源和汇 ;(2 )评价森林水文条件对 DOM释放与存留的调节作用 ;(3)探讨全球气候变化对森林生态系统 DOM的影响 ;(4)可溶性有机氮 (Dissolved Organic Nitrogen)、可溶性有机磷 (DissolvedOrganic Phosphorus)动态与可溶性有机碳 (Dissolved Organic Carbon)动态的差别。 |
| [23] | |
| [24] | 试验研究了典型红壤侵蚀区不同植被恢复年限（0,11,31a）的表层（0—10cm）和深层（60—80cm）土壤有机碳矿化特征。结果表明：深层土壤有机碳84d累积矿化量或潜在矿化量显著低于表层土壤,植被恢复则显著增加了表层和深层土壤累积矿化量或潜在矿化量（P〈0.05）,相关分析显示土壤有机碳累积矿化量或潜在矿化量与WSOC、MBC和SOC显著（P〈0.05）或极显著（P〈0.01）相关,表明碳矿化底物数量是决定土壤碳累积矿化量或潜在矿化量的主导因子;对照表层土壤的矿化速率常数（k）高于深层土壤的,植被恢复降低了表层土壤的k值（P〈0.05）,对深层土壤的k值却没有显著影响;而深层土壤矿化率显著高于表层土壤,且植被恢复后均显著降低（P〈0.05）,相关分析显示土壤有机碳矿化率与微生物代谢熵呈极显著的正相关（P〈0.01）,表明微生物碳利用效率是影响土壤碳矿化率的重要因素,而深层土壤微生物碳利用效率显著低于表层土壤,但植被恢复可以改善侵蚀红壤的环境条件,提高土壤微生物的碳利用效率,从而增强土壤固碳能力。 |
| [25] | Dicranopteris is a common fern distributed throughout tropical and subtropical regions of the world. It often forms a mat-like understory, especially in open areas. A forest floor dominated by Dicranopteris plays an important role in ecosystem dynamics, but is often overlooked in ecological research. We conducted an experiment by removing overstory or understory Dicranopteris to compare their effects on soil microclimate, litter decomposition, soil decomposer food web and ecosystem nutrient cycling. Results of our field study showed that removal of a Dicranopteris -dominated understory leads to increased soil temperature and reduced soil moisture, subsequently, altering the components of the soil food web (microbial community, nematode and microarthropod densities) and reducing ecosystem processes of litter decomposition. When present, Dicranopteris forms a dense understory layer in subtropical and tropical regions, which is favorable for sustaining soil microclimates and acts as the major driver of soil biota and ecological processes in intensive forest ecosystems. |
| [26] | 为了解侵蚀型红壤不同植被恢复后,土壤有机碳的演变状况,采集了持续时间为17年和9年的2个定位试验点土壤样品,分析了土壤总有机碳、微生物量碳、水溶性碳和矿化态碳含量。结果表明:侵蚀型红壤植被恢复后,土壤总有机碳和各类活性碳含量均明显增加,并随着恢复时间的延长,土壤各类碳含量显著上升。同样是杉木林,恢复17年的土壤(0～20cm)总有机碳、微生物量碳、水溶性碳和矿化态碳的含量分别是恢复9年土壤的2 18倍、2 95倍、2 25倍和2 01倍。不同处理比较来看,木荷林土壤各类碳含量明显高于杉木林土壤,黑麦草处理矿化态碳含量明显高于恢复时间相同的杉木和胡柚处理。分析了各处理活性碳占总有机碳的比例发现,植被恢复17年的2个处理,土壤微生物量占总有机碳比例明显高于恢复9年的3个处理;恢复时间分别为17年和9年的2个杉木处理,土壤水溶性碳占总有机碳比例明显较高,而矿化态碳占总有机碳比例明显偏低;黑麦草处理矿化态碳占总有机碳比例明显高于恢复时间相同的杉木和胡柚处理。从相关分析来看,土壤总有机碳、微生物量碳、水溶性碳及矿化态碳两两之间相关性均达极显著水平(P0 01);土壤各类碳与土壤全氮、水解氮、有效磷含量之间也具有极显著相关性。 |
| [27] | |
| [28] |
1
2007
... 使用UV-2450 (岛津)紫外可见分光光度计检测待测液在波长254 nm处的吸收值来表征其芳香化程度(
Bioavailability of DOC in leachates, soil matrix solutions and soil water extracts from beech forest floors.
1
2009
... 可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(
Freshwater DOM quantity and quality from a two-component model of UV absorbance.
2
2012
... 可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(
... 目前关于DOM结构特征的研究采用的手段主要是光学技术, 其简单易操作, 不会对样品产生破坏, 而且分析高效, 分析结果所含信息丰富, 因此在DOM微观结构的研究中得到了广泛的应用.最为常用的就是紫外可见分光光谱和荧光光谱分析技术, 另外, 还有很多研究利用傅里叶变换红外光谱测定DOM的特征官能团, 更为详细地表征其结构特性(
Soil fluxes of mineral elements and dissolved organic matter following manipulation of leaf litter input in a Taiwan Chamaecyparis forest.
3
2007
... 可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(
... 近期的研究发现, 新近凋落物和土壤腐殖质分解以及土壤根系周转及其分泌物和微生物代谢产物是土壤DOM的主要来源(
... 植被类型不同, 土壤DOM结构差异明显(
Fluxes of dissolved organic carbon in two tropical forest ecosystems of East Kalimantan, Indonesia
1
2009
... 可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(
The importance of dissolved organic carbon fluxes for the carbon balance of a temperate Scots pine forest.
1
2011
... 可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(
Effects of redox conditions and flow processes on the mobility of dissolved organic carbon and nitrogen in a forest soil.
2
2000
... 近期的研究发现, 新近凋落物和土壤腐殖质分解以及土壤根系周转及其分泌物和微生物代谢产物是土壤DOM的主要来源(
... 如前所述, 林下芒萁覆盖地土壤荧光发射光谱也表明芒萁覆盖地土壤DOM结构中含有更多的荧光基团, 即腐殖化物质, 并且Y31马尾松土壤DOM荧光发射光谱特征峰位置发生明显位移, 从裸地到芒萁覆盖地特征峰位置明显向长波方向移动, 说明芒萁覆盖地土壤DOM的共轭体系增加, 分子结构更为复杂, 而Y0和Y13马尾松林的这种波峰位置移动并不明显, 这可能与不同恢复程度的森林生态系统对于土壤DOM结构变化快慢程度的控制机制不同有关.芳香环是常见的共轭体系, 它是形成土壤腐殖质的基础, 腐殖质分子的中心常常是一个稠环或者易生稠环的芳香核(
红壤稻田土壤溶解有机碳含量动态及其生物降解特征.
1
2005
... 可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(
Dissolved organic matter sorption on subsoil and minerals studied by 13C-NMR and DRIFT spectroscopy.
1
1997
... 如前所述, 林下芒萁覆盖地土壤荧光发射光谱也表明芒萁覆盖地土壤DOM结构中含有更多的荧光基团, 即腐殖化物质, 并且Y31马尾松土壤DOM荧光发射光谱特征峰位置发生明显位移, 从裸地到芒萁覆盖地特征峰位置明显向长波方向移动, 说明芒萁覆盖地土壤DOM的共轭体系增加, 分子结构更为复杂, 而Y0和Y13马尾松林的这种波峰位置移动并不明显, 这可能与不同恢复程度的森林生态系统对于土壤DOM结构变化快慢程度的控制机制不同有关.芳香环是常见的共轭体系, 它是形成土壤腐殖质的基础, 腐殖质分子的中心常常是一个稠环或者易生稠环的芳香核(
Spectroscopic properties of dissolved humic substances—A reflection of land use history in a fen area.
1
1999
... 荧光发射光谱中Σ435-480 nm区域与Σ300- 345 nm区域的峰面积比值被称为荧光发射光谱腐殖化指数(HIXem), 荧光同步光谱波长460与345 nm处荧光强度的比值被称为荧光同步光谱腐殖化指数(HIXsyn)(
Contribution of dissolved organic matter to carbon storage in forest mineral soils.
1
2008
... 可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(
Response of dissolved organic matter in the forest floor to long-term manipulation of litter and throughfall inputs.
1
2007
... 可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(
亚热带红壤丘陵区四种人工林凋落物分解动态及养分释放.
1
2007
... 植被类型不同, 土壤DOM结构差异明显(
中亚热带森林转换对土壤可溶性有机质数量与光谱学特征的影响.
3
2015
... 目前关于DOM结构特征的研究采用的手段主要是光学技术, 其简单易操作, 不会对样品产生破坏, 而且分析高效, 分析结果所含信息丰富, 因此在DOM微观结构的研究中得到了广泛的应用.最为常用的就是紫外可见分光光谱和荧光光谱分析技术, 另外, 还有很多研究利用傅里叶变换红外光谱测定DOM的特征官能团, 更为详细地表征其结构特性(
... 征DOM分子中的蛋白质基团(如芳香氨基酸), 在375-385 nm处表征DOM分子中的芳香性脂肪基团, 在450-490 nm处表征DOM分子中的木质素基团, 而各类峰的相对面积大小表征分子个基团含量的多少(
... 近期的研究发现, 新近凋落物和土壤腐殖质分解以及土壤根系周转及其分泌物和微生物代谢产物是土壤DOM的主要来源(
Carbon fluxes in soil.
1
2005
... 可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(
Dynamics of dissolved organic nitrogen and carbon in a Central European Norway spruce ecosystem.
1
1999
... 可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(
Molecular size distribution and spectroscopic properties of aquatic humic substances.
1
1997
... E2:E3值表征待测样中DOM平均分子量的大小, 该值越大表明平均分子量越小, 计算公式为 E2:E3 = UV250:UV365 (
The role of dissolved organic carbon, dissolved organic nitrogen, and dissolved inorganic nitrogen in a tropical wet forest ecosystems.
1
2005
... 可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(
Dissolved soil organic carbon and nitrogen were affected by conversion of native forests to plantations in subtropical China.
3
2010
... 土壤DOM浸提: 样品DOM采用水浸提法(
... 使用UV-2450 (岛津)紫外可见分光光度计检测待测液在波长254 nm处的吸收值来表征其芳香化程度(
... 近期的研究发现, 新近凋落物和土壤腐殖质分解以及土壤根系周转及其分泌物和微生物代谢产物是土壤DOM的主要来源(
土壤腐殖质各组分红外光谱研究.
1
2008
... 土壤DOM存在5类特征峰: 4 000-3 000 cm-1 (与氢键键合的—COOH、醇、苯酚中的—OH伸缩振动吸收峰)、1 625-1 690 cm-1 (苯环、烯烃类和分子间或分子内形成氢键的羧酸中—C==O的伸缩振动峰)、1 600-1 425 cm-1 (苯环上C==C骨架振动)、 1 000-1 250 cm-1 (多糖类、醇类、羧酸类及脂类—C—O—伸缩振动吸收峰)、460-680 cm-1 (苯环上—C—H面外弯曲振动吸收峰)(
Rapid accumulation of carbon on severely eroded red soils through afforestation in subtropical China.
1
2013
... 近期的研究发现, 新近凋落物和土壤腐殖质分解以及土壤根系周转及其分泌物和微生物代谢产物是土壤DOM的主要来源(
森林生态系统DOM的来源、特性及流动.
1
2003
... 可溶性有机质(DOM)是指能够通过0.45 μm筛孔且溶于水、酸或碱溶液的不同分子大小和有机结构的混合体(
水溶性有机物与多环芳烃结合特征的红外光谱学研究.
1
2007
... 土壤DOM存在5类特征峰: 4 000-3 000 cm-1 (与氢键键合的—COOH、醇、苯酚中的—OH伸缩振动吸收峰)、1 625-1 690 cm-1 (苯环、烯烃类和分子间或分子内形成氢键的羧酸中—C==O的伸缩振动峰)、1 600-1 425 cm-1 (苯环上C==C骨架振动)、 1 000-1 250 cm-1 (多糖类、醇类、羧酸类及脂类—C—O—伸缩振动吸收峰)、460-680 cm-1 (苯环上—C—H面外弯曲振动吸收峰)(
侵蚀红壤区植被恢复对表层与深层土壤有机碳矿化的影响.
3
2016
... 近期的研究发现, 新近凋落物和土壤腐殖质分解以及土壤根系周转及其分泌物和微生物代谢产物是土壤DOM的主要来源(
... ;
... ;
Dicranopteris-dominated understory as major driver of intensive forest ecosystem in humid subtropical and tropical region.
4
2012
... 近期的研究发现, 新近凋落物和土壤腐殖质分解以及土壤根系周转及其分泌物和微生物代谢产物是土壤DOM的主要来源(
... ), 而微生物正常生命活动会产生大量微生物代谢产物.林下芒萁覆盖地土壤DOM在SOC中的分配比例明显高于林下裸地, 且芒萁去除一年后, 该比例明显下降, 而DOM作为土壤微生物可直接分解利用的主要碳源, 其在土壤有机碳中所占的比例大小表征了土壤可供给微生物能量大小的潜力(
... 植被类型不同, 土壤DOM结构差异明显(
... 如前所述, 林下芒萁覆盖地土壤荧光发射光谱也表明芒萁覆盖地土壤DOM结构中含有更多的荧光基团, 即腐殖化物质, 并且Y31马尾松土壤DOM荧光发射光谱特征峰位置发生明显位移, 从裸地到芒萁覆盖地特征峰位置明显向长波方向移动, 说明芒萁覆盖地土壤DOM的共轭体系增加, 分子结构更为复杂, 而Y0和Y13马尾松林的这种波峰位置移动并不明显, 这可能与不同恢复程度的森林生态系统对于土壤DOM结构变化快慢程度的控制机制不同有关.芳香环是常见的共轭体系, 它是形成土壤腐殖质的基础, 腐殖质分子的中心常常是一个稠环或者易生稠环的芳香核(
不同植被恢复对侵蚀型红壤活性碳库的影响.
1
2004
... 如前所述, 林下芒萁覆盖地土壤荧光发射光谱也表明芒萁覆盖地土壤DOM结构中含有更多的荧光基团, 即腐殖化物质, 并且Y31马尾松土壤DOM荧光发射光谱特征峰位置发生明显位移, 从裸地到芒萁覆盖地特征峰位置明显向长波方向移动, 说明芒萁覆盖地土壤DOM的共轭体系增加, 分子结构更为复杂, 而Y0和Y13马尾松林的这种波峰位置移动并不明显, 这可能与不同恢复程度的森林生态系统对于土壤DOM结构变化快慢程度的控制机制不同有关.芳香环是常见的共轭体系, 它是形成土壤腐殖质的基础, 腐殖质分子的中心常常是一个稠环或者易生稠环的芳香核(
应用光谱分析技术研究土壤水溶性有机质的分组及其结构特征.
1
2004
... 目前关于DOM结构特征的研究采用的手段主要是光学技术, 其简单易操作, 不会对样品产生破坏, 而且分析高效, 分析结果所含信息丰富, 因此在DOM微观结构的研究中得到了广泛的应用.最为常用的就是紫外可见分光光谱和荧光光谱分析技术, 另外, 还有很多研究利用傅里叶变换红外光谱测定DOM的特征官能团, 更为详细地表征其结构特性(
1
... 如前所述, 林下芒萁覆盖地土壤荧光发射光谱也表明芒萁覆盖地土壤DOM结构中含有更多的荧光基团, 即腐殖化物质, 并且Y31马尾松土壤DOM荧光发射光谱特征峰位置发生明显位移, 从裸地到芒萁覆盖地特征峰位置明显向长波方向移动, 说明芒萁覆盖地土壤DOM的共轭体系增加, 分子结构更为复杂, 而Y0和Y13马尾松林的这种波峰位置移动并不明显, 这可能与不同恢复程度的森林生态系统对于土壤DOM结构变化快慢程度的控制机制不同有关.芳香环是常见的共轭体系, 它是形成土壤腐殖质的基础, 腐殖质分子的中心常常是一个稠环或者易生稠环的芳香核(
