,, 臧淑英,, 马大龙, 任建华, 李昊, 赵光影哈尔滨师范大学寒区地理环境监测与空间信息服务黑龙江省重点实验室,哈尔滨 150025Greenhouse gas fluxes from forest soil in permafrost regions of Greater Hinggan Mountains, Northeast China
WU Xiangwen,, ZANG Shuying,, MA Dalong, REN Jianhua, LI Hao, ZHAO GuangyingHeilongjiang Province Key Laboratory of Geographical Environment Monitoring and Spatial Information Service in Cold Regions, Harbin Normal University, Harbin 150025, China通讯作者:
收稿日期:2019-01-16修回日期:2020-09-4网络出版日期:2020-11-25
| 基金资助: |
Received:2019-01-16Revised:2020-09-4Online:2020-11-25
| Fund supported: |
作者简介 About authors
吴祥文(1991-), 男, 江苏连云港人, 博士生, 主要从事寒区冻土与气候变化研究。E-mail:
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吴祥文, 臧淑英, 马大龙, 任建华, 李昊, 赵光影. 大兴安岭多年冻土区森林土壤温室气体通量. 地理学报[J], 2020, 75(11): 2319-2331 doi:10.11821/dlxb202011004
WU Xiangwen, ZANG Shuying, MA Dalong, REN Jianhua, LI Hao, ZHAO Guangying.
1 引言
IPCC特别报告指出,受过去以及当前温室气体排放影响,全球变暖已导致地球平均气温较工业化之前的水平高出1 ℃[1]。大气中CO2、CH4和N2O浓度不断增加是造成气候变暖的关键因素[2]。温室气体浓度与生态系统碳、氮循环密切相关,其“源—汇”关系直接影响生态系统对气候变化的响应与反馈[3]。因此,3种温室气体通量的动态变化规律已成为全球气候变化研究的重要内容。全球气候变化直接影响多年冻土的演化和发展,气候变暖与多年冻土退化间的作用关系,已成为当今全球变化研究的热点问题。大兴安岭地区是中国高纬度多年冻土主要分布区之一,发育着兴安—贝加尔型多年冻土（面积约3.8×105 km2）[4,5]。多年冻土是重要的土壤碳库[6],其储量远高于大气圈碳库。高纬度多年冻土赋存条件脆弱,对气候变化响应敏感,气候变暖将造成冻土活动层厚度增加[7],释放封存的古碳和水,为微生物提供更大的生存空间和基质,增加土壤CO2、CH4和N2O等温室气体的释放,进而影响全球碳氮循环[8,9]。因此,了解高纬度多年冻土区温室气体通量变化特征,对认识多年冻土生态系统土壤碳氮循环及其对全球气候变化的响应具有重要科学意义。
森林生态系统是全球碳循环过程的重要参与者,它维持着地表86%的植物碳库和73%的土壤碳库[10,11]。在全球气候变暖背景下,不同优势树种的生境均会发生变化,影响森林生态系统的演替,改变森林土壤温室气体与大气间的交换,进而影响区域气候。Livesley等[12]和Jang等[13]研究发现,不同树种的冠层、根系及其分泌物均有差别,从而造成土壤理化性质、微生物群落组成和多样性的差异,影响温室气体排放通量。菊花等[14]研究发现,针叶林土壤生态系统代谢旺盛,CO2通量显著高于阔叶林。Leckie等[15]则认为针叶林凋落物中富含顽固性化合物,分解缓慢,减缓土壤碳氮矿化速率,造成针叶林土壤CO2通量较小。Wang等[16]研究发现针叶林下较厚的凋落物层截留降水,土壤含水量较低,比阔叶林土壤拥有更强的CH4吸收能力;Castro等[17]则认为2种林型土壤CH4通量差异不显著。而对阔叶林和针叶林土壤N2O通量研究的结论也各不相同,Butterbach-Bahl等[18]研究发现阔叶林下更易形成厌氧环境,造成土壤排放更多N2O;也有****认为2种林型土壤N2O排放通量相似或针叶林略高[19,20]。综上表明,不同林型对土壤CO2、CH4和N2O通量规律的影响尚不明晰,还需进一步探究。
大兴安岭地区是中国重要林业基地,同时也是欧亚大陆高纬度多年冻土区向南最突出的部分,受人类活动和气候变暖影响较为显著。目前关于中国东北地区温室气体研究主要包括野外原位观测和室内模拟培养实验,多集中于季节冻土区[21,22]和泥炭沼泽湿地[23,24],而有关大兴安岭多年冻土区森林土壤温室气体通量研究相对较少且多停留在定性描述阶段,缺乏定量评估。本研究连续观测（2016—2017年）大兴安岭多年冻土区生长季不同林型土壤温室气体通量的动态变化,为定量评估大兴安岭多年冻土退化所释放的温室气体在气候变暖过程中的贡献以及大兴安岭森林生态系统碳氮平衡提供科学依据。
2 研究区概况与研究方法
2.1 研究区概况
研究样地位于黑龙江漠河森林生态系统国家定位观测研究站实验区内（53°17′N~53°30′N, 122°06′E~122°27′E）。实验区地处大兴安岭的北坡,多低山丘陵,平均海拔为300~500 m;受寒温带大陆性季风气候控制,观测期年均温-3.3 ℃,气温年较差49.3 ℃,≥10 ℃年积温1436~2062 ℃,无霜期为86 d。观测期的年降水量442.9 mm。年均太阳辐射总量96~107 kcal·cm-2,日照时数2377~2625 h。地带性土壤为暗棕色森林土。主要植被组成：乔木层有兴安落叶松（Larix gmelinii）、山杨（Populus davidiana）、樟子松（Pinus sylvestris var. mongolica）、白桦（Betula platyphylla）等;灌木和草本有笃斯越橘（Vaccinium uliginosum）、兴安杜鹃（Rhododendron dauricum）、杜香（Ledum palustre）、红花鹿蹄草（Pyrola incarnata）等。依据样地选取的代表性和可行性原则,全面踏查后选取立地条件相似的典型区域设置100 m×100 m固定实验样地3块,包括大兴安岭多年冻土区最主要的3种典型林型：兴安落叶松林（LF）、樟子松林（PF）和白桦林（BF）。2.2 样品采集与处理
2.2.1 实验设置与实施 采用静态暗箱—气相色谱法野外原位观测大兴安岭多年冻土区3种典型森林土壤CO2、CH4和N2O气体通量。在3种林型的固定样地中沿对角线随机设置3个5 m×5 m样方,各样方间距至少20 m,进行温室气体样品采集,总共设置9个样方。静态箱主要由箱体（40 cm×40 cm×40 cm）和不锈钢基座（40 cm×40 cm×8 cm）两部分组成,取样前将带有凹槽的不锈钢基座提前1星期埋入样地,并保持固定不动以降低对周围环境的干扰。每次采样前提前1 d将罩箱区域地面以上植被剪除。箱体外部粘贴隔热遮光材料,减少外界环境影响,降低箱内温度扰动。箱顶预留3个孔,分别用于接通箱内风扇电源线、温度计探头和采样,3个孔均用橡胶塞密封。箱内安装12 V蓄电池供电风扇,取样时开启,使箱内气体浓度混合均匀。2.2.2 气体样品的采集与处理 样品采集时间为2016—2017年生长季（5—9月）,频率为每星期1次,选择天气晴朗的上午9:00—11:00进行气体样品采集。采样时将静态箱箱体放置于不锈钢基座的凹槽中,然后在凹糟中注水密封,用60 mL聚氯乙烯医用注射器在箱体水封后立即进行气体采集,依次每间隔10 min采集1次气体样品,0.5 h内共采集4个气体样品。采集的气体立即转移到气袋中保存运回实验室,使用美国Agilent公司生产的7890B型气相色谱仪测定。采集气体样品时同步测量气压,使用美国DeltaTrak公司生产的便携式温度计测定气温、箱内温度以及5 cm、10 cm和15 cm土层温度。
2.2.3 土壤样品的采集与处理 在采集气体样品的同时,同步采集土壤样品。每个样方内随机选取5个取样点（避开气体样品采集区）,清除出土壤表层,利用土钻分别采集0~15 cm土壤样品均匀混合成一个土样,每次采集9个土壤混合样品。采集的土样封存在自封袋中运回实验室,用于理化指标的测定（表1）。重量含水量采用烘干称重法测定;容重采用环刀法测定;pH值使用PHSJ-3F型酸度计测定;铵态氮（NH4+-N）、硝态氮（NO3--N）和全氮（TN）使用荷兰Skalar公司生产的SKALAR San++型连续流动分析仪测定;总有机碳（TOC）使用德国Jena公司生产的Multi C/N 3100型碳氮分析仪测定。
Tab. 1
表1
表1不同林型表层土壤基本理化性质
Tab. 1
| 林型 | 年份 | pH | 容重 (g·cm-3) | 硝态氮 (mg·kg-1) | 铵态氮 (mg·kg-1) | 有机碳 (g·kg-1) | 全氮 (g·kg-1) |
|---|---|---|---|---|---|---|---|
| 兴安落叶松林 | 2016 | 5.50±0.11Aa | 1.01±0.08Aa | 2.65±1.01Aa | 5.31±0.75Ba | 47.47±1.77Aa | 3.78±0.63Aa |
| 2017 | 5.79±0.12Aa | 1.00±0.09Aa | 1.09±0.31Ab | 3.23±0.50Bb | 51.38±1.54Aa | 2.66±0.49Aa | |
| 樟子松林 | 2016 | 5.58±0.13Aa | 1.04±0.05Aa | 2.10±0.34Aa | 6.10±1.07Ba | 42.77±1.83Aa | 3.60±0.03Aa |
| 2017 | 5.52±0.16Aa | 1.05±0.07Aa | 1.10±0.46Aa | 4.27±0.63Bb | 46.69±1.65Aa | 2.27±0.18Aa | |
| 白桦林 | 2016 | 4.70±0.09Ba | 0.72±0.04Ba | 2.94±0.89Aa | 9.07±1.64Aa | 44.28±2.05Aa | 4.49±0.67Aa |
| 2017 | 4.58±0.10Ba | 0.69±0.05Ba | 1.60±0.49Ab | 6.80±1.34Ab | 46.26±1.46Aa | 2.47±0.22Ab |
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2.3 计算方法
温室气体通量计算公式：式中：F为所测气体通量（mg·m-2·h-1）;
全球增温潜势用来评价不同温室气体对气候变化影响的相对能力,计算公式：
式中：GWP为全球增温潜势（t·hm-2）;
3 结果分析
3.1 不同林型土壤温室气体通量变化规律
3.1.1 CO2通量季节变化规律 大兴安岭多年冻土区3种林型土壤CO2通量季节变化规律基本一致（图1a）,整个生长季均表现为排放通量,季节变化显著。2016—2017年间,5月上旬,CO2通量均出现小的排放峰值,春季维持在相对较低水平,夏季7—8月达到高排放期,秋季波动下降到低值。CO2通量范围65.88~883.59 mg·m-2·h-1,2016年表现为单峰型变化趋势,2017年则呈现双峰型。樟子松林土壤CO2通量于7月上旬到8月下旬进入排放高峰期,最高值（873.14 mg·m-2·h-1）出现在2016年8月9日。兴安落叶松林、白桦林土壤CO2通量排放高峰期集中在7月中旬到8月下旬,分别在2017年8月7日和8月13日达到排放最大值（883.59 mg·m-2·h-1、728.37 mg·m-2·h-1）。兴安落叶松林、樟子松林和白桦林土壤2年生长季CO2的排放总量分别为24.86 t·hm-2、27.04 t·hm-2、21.99 t·hm-2,樟子松林土壤CO2排放通量显著高于白桦林（表2）。图1
新窗口打开|下载原图ZIP|生成PPT图1大兴安岭多年冻土区3种林型土壤CO2(a)、CH4(b)和N2O(c)通量季节变化
Fig. 1Seasonal variations of CO2 (a), CH4 (b), and N2O (c) fluxes in different forest types
Tab. 2
表2
表2大兴安岭多年冻土区3种林型土壤CO2、CH4和N2O通量多重比较
Tab. 2
| 林型 | 年份 | CO2通量 (mg·m-2·h-1) | CH4通量 (μg·m-2·h-1) | N2O通量 (μg·m-2·h-1) |
|---|---|---|---|---|
| 兴安落叶松林 | 2016 | 329.96±25.46Aa | -33.84±5.43Ba | 14.23±2.92Aa |
| 2017 | 361.53±24.78Aa | -23.38±3.66Bb | 15.19±2.24Aa | |
| 樟子松林 | 2016 | 345.09±27.35Ab | -37.99±4.78Ba | 15.98±3.08Aa |
| 2017 | 402.75±23.93Aa | -27.63±5.87Ab | 18.11±3.36Aa | |
| 白桦林 | 2016 | 299.19±21.47Aa | -47.84±5.44Aa | 13.54±2.75Aa |
| 2017 | 315.59±22.19Ba | -33.55±5.85Ab | 13.80±2.79Aa |
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3.1.2 CH4通量季节变化规律 2016—2017年兴安落叶松林、樟子松林和白桦林3种林型生长季土壤CH4通量表现为吸收汇（图1b）,具有明显的季节波动规律。春季初期3种林型土壤均表现为CH4的弱吸收,吸收强度随时间推移而逐渐增强;春季末期到夏季则表现为强吸收,秋季呈现弱吸收。CH4通量范围为-93.29~-2.82 μg·m-2·h-1,2016年兴安落叶松林和樟子松林土壤表现为双吸收峰型,白桦林土壤表现为3吸收峰型;2017年均表现为双吸收峰型。兴安落叶松林、樟子松林和白桦林土壤分别在2016年的6月21日、6月27日和6月14日达到最大CH4吸收值（-77.84 μg·m-2·h-1、-82.40 μg·m-2·h-1和-93.29 μg·m-2·h-1）。白桦林2年生长季土壤CH4吸收总量（-2.95 kg·hm-2）分别是兴安落叶松林土壤（-2.10 kg·hm-2）、樟子松林土壤（-2.39 kg·hm-2）的1.40和1.23倍,不同林型间差异显著（表2）。
3.1.3 N2O通量季节变化规律 整个观测期3种林型土壤N2O均为排放通量,表现出相似的季节变化格局（图1c）。春季3种林型土壤N2O通量随着温度升高呈现波动上升趋势,至6月中旬达到最大排放峰值,之后缓慢下降并维持在较低水平。N2O通量范围-5.31~45.22 μg·m-2·h-1,2016年3种林型土壤N2O排放通量均为单峰型,季节变化较小;2017年兴安落叶松林和樟子松林表现为双峰型,白桦林则为单峰型,季节变化显著。3种林型土壤N2O通量均在2017年6月14日达到最大排放峰值,樟子松林和白桦林最大峰值较为接近（45.22 μg·m-2·h-1、44.29 μg·m-2·h-1）,高于兴安落叶松林（31.75 μg·m-2·h-1）（P < 0.05）。3种林型生长季土壤2年N2O排放总量表现为樟子松林（1.26 kg·hm-2）>兴安落叶松林（1.09 kg·hm-2）>白桦林（1.02 kg·hm-2）的排放规律。
3.2 气温和土壤温、湿度季节变化特征及与温室气体通量的关系
表3气象数据监测显示,研究区2017年生长季平均温度（13.8 ℃）高于2016年（13.3 ℃）,7月份温度较高;生长季平均降水量也表现出2017年（76.9 mm）高于2016年（73.4 mm）,全年降水量主要集中于生长季,雨热同期。Tab. 3
表3
表32016—2017年大兴安岭生长季各月气温和降水量
Tab. 3
| 月份 | 平均气温(°C) | 降水量(mm) | 日降水量> 0.1 mm天数(d) | 占年降水量比例(%) | ||||
|---|---|---|---|---|---|---|---|---|
| 2016年 | 2017年 | 2016年 | 2017年 | 2016年 | 2017年 | 2016年 | 2017年 | |
| 5 | 9.7 | 9.0 | 39.8 | 56.5 | 7 | 17 | 78.82 | 91.95 |
| 6 | 14.0 | 16.8 | 113.4 | 18.8 | 15 | 8 | ||
| 7 | 18.1 | 18.7 | 119.5 | 94.2 | 17 | 17 | ||
| 8 | 14.4 | 16.2 | 58.2 | 182.6 | 16 | 24 | ||
| 9 | 10.4 | 8.3 | 37.5 | 32.6 | 15 | 10 | ||
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由图2可知,兴安落叶松林、樟子松林和白桦林生长季土壤温度和气温的变化趋势相似。除2016年樟子松林土壤温度呈3峰型变化趋势外,其他林型土壤温度均表现为双峰型。3种林型5 cm、10 cm和15 cm土层温度变化范围为0.15~18.55 ℃,均在夏季达到最大值,且2017年夏季土壤平均温度（12.33 ℃）高于2016年夏季（11.61 ℃）。气温易受外界云层、树荫等环境扰动影响,波动较大,而土壤温度较为稳定,最大值出现时间较气温表现出滞后性。
图2
新窗口打开|下载原图ZIP|生成PPT图2兴安落叶松林(a)、樟子松林(b)和白桦林(c)气温(Ta)与土壤温度季节变化
Fig. 2Seasonal variations of air temperature (Ta) and soil temperature in LF (a), PF (b), and BF (c)
3种林型土壤含水量变化趋势基本一致,除春季冻融期土壤含水量相对较高外,其他季节均维持在40%以下,季节变化较为明显（图3）。最大值出现在春季初期,随后波动下降;夏季受降水和蒸发的双重影响,在21.86%~37.73%之间波动,秋季逐渐降低。
图3
新窗口打开|下载原图ZIP|生成PPT图3大兴安岭多年冻土区3种林型土壤含水量季节变化
Fig. 3Seasonal variations of soil moisture in different forest types
由表4可知,2016—2017年兴安落叶松林、樟子松林和白桦林土壤CO2通量与5 cm、10 cm和15 cm土层温度极显著正相关（P < 0.01）,2017年兴安落叶松林土壤CO2通量受气温影响显著（P < 0.05）,温度是影响3种林型土壤CO2通量动态的关键环境因子。白桦林土壤CH4通量与10 cm土层温度呈极显著负相关（P < 0.01）,而与其他土层温度呈显著负相关（P < 0.05）。2017年樟子松林和白桦林土壤CH4通量与土壤含水量显著正相关（P < 0.05）。土壤CH4通量受到土壤温度和含水量共同影响。2年观测显示,土壤N2O通量受土壤含水量影响不显著,兴安落叶松林和樟子松林土壤N2O通量受气温影响显著（P < 0.05）,白桦林土壤N2O通量与15 cm土层温度显著负相关（P < 0.05）。
Tab. 4
表4
表4大兴安岭多年冻土区3种林型土壤温室气体通量与环境因子相关分析
Tab. 4
| 林型 | 年份 | 温室气体 | 土壤含水量 | 气温 | 土壤温度 | ||
|---|---|---|---|---|---|---|---|
| 5 cm | 10 cm | 15 cm | |||||
| 兴安落叶松林 | 2016 | CO2 | -0.409 | 0.425 | 0.849** | 0.874** | 0.815** |
| CH4 | 0.254 | -0.199 | -0.311 | -0.358 | -0.243 | ||
| N2O | -0.015 | 0.551** | 0.275 | 0.116 | -0.230 | ||
| 2017 | CO2 | -0.057 | 0.527* | 0.862** | 0.877** | 0.855** | |
| CH4 | 0.364 | -0.577** | -0.581* | -0.569** | -0.470* | ||
| N2O | -0.142 | 0.570** | 0.332 | 0.267 | 0.139 | ||
| 樟子松林 | 2016 | CO2 | -0.017 | 0.251 | 0.813** | 0.827** | 0.800** |
| CH4 | 0.194 | -0.324 | -0.402 | -0.398 | -0.385 | ||
| N2O | -0.131 | 0.403 | 0.021 | -0.066 | -0.175 | ||
| 2017 | CO2 | -0.099 | 0.418 | 0.891** | 0.890** | 0.787** | |
| CH4 | 0.599* | -0.446* | -0.287 | -0.261 | -0.317 | ||
| N2O | 0.020 | 0.531* | 0.223 | 0.148 | -0.009 | ||
| 白桦林 | 2016 | CO2 | -0.413 | 0.163 | 0.856** | 0.855** | 0.827** |
| CH4 | 0.425 | -0.297 | -0.658* | -0.592** | -0.477* | ||
| N2O | 0.068 | 0.423 | -0.281 | -0.352 | -0.411 | ||
| 2017 | CO2 | -0.382 | 0.365 | 0.828** | 0.839** | 0.780** | |
| CH4 | 0.556* | -0.550* | -0.644** | -0.617** | -0.540* | ||
| N2O | 0.259 | 0.207 | -0.294 | -0.348 | -0.511* | ||
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3.3 不同林型土壤温室气体全球增温潜势
全球增温潜势（GWP）以CO2作为参照气体,在100 a时间尺度上评价各温室气体对全球气候变化的相对影响,CH4和N2O的辐射影响分别是CO2的25倍和298倍[25]。由表5可知,大兴安岭多年冻土区森林土壤温室气体GWP表现为：樟子松林>兴安落叶松林>白桦林。整个观测期内,多年冻土区3种典型森林兴安落叶松林、樟子松林和白桦林土壤在100 a时间尺度上均表现为温室气体的“源”,2017年3种林型总GWP（39.413 t·hm-2）要高于2016年总GWP（35.293 t·hm-2）,表明大兴安岭多年冻土区森林土壤温室气体释放对全球气候变暖具有正反馈作用。Tab. 5
表5
表52016—2017年大兴安岭多年冻土区3种林土壤温室气体增温潜势 (t·hm-2)
Tab. 5
| 林型 | CO2 | CH4 | N2O | 综合增温潜势 | ||||
|---|---|---|---|---|---|---|---|---|
| 2016年 | 2017年 | 2016年 | 2017年 | 2016年 | 2017年 | 2016年 | 2017年 | |
| 兴安落叶松林 | 11.767 | 13.089 | -0.030 | -0.022 | 0.157 | 0.168 | 11.894 | 13.235 |
| 樟子松林 | 12.464 | 14.577 | -0.034 | -0.025 | 0.175 | 0.201 | 12.605 | 14.753 |
| 白桦林 | 10.687 | 11.303 | -0.043 | -0.031 | 0.150 | 0.153 | 10.794 | 11.425 |
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4 讨论
4.1 土壤CO2通量特征及影响因素
2016—2017年生长季观测发现,大兴安岭多年冻土区兴安落叶松林、樟子松林和白桦林土壤均为CO2排放源,且在夏季达到排放高峰期,这与Song等[26]和Li等[27]的研究结果相一致。生长季初期,3种林型土壤均出现短暂的高排放现象,其原因可能是由于冬季土壤冻结,植物呼吸以及土壤微生物活动产生的CO2被封存在土壤中;春季气温回升,冻结土壤随温度升高逐渐融化,据多年冻土监测系统监测显示,4月26日5 cm土壤融化,5月3日10 cm土壤融化,5月13日20 cm土壤融化,土壤融化后封存其中的CO2得以释放,形成小的排放高峰期,李攀等[28]也得出相似结果。春末气温持续升高,土壤融化后植物复苏,自养呼吸（主要为植被根系呼吸）和异养呼吸（主要为土壤微生物呼吸）作用逐渐增强,土壤CO2通量随之波动增加。研究区植被多属浅根系,凋落物也在土壤表层集聚,夏季良好的水热组合,促进根系呼吸作用和土壤微生物分解活动,使CO2达到排放高峰期[29]。秋季气温下降,植被逐渐凋落枯萎,微生物活性降低,土壤CO2通量也随之降低,这与相似纬度的俄罗斯西伯利亚、德国中部萨克森、奥地利等[30,31,32]地区研究结果相一致。2年数据对比发现,2016年生长季土壤CO2通量表现为单峰型,2017年生长季则呈现双峰型,与同步监测的土壤温度变化趋势相似,CO2通量与5 cm、10 cm和15 cm土层温度极显著正相关（表4）,这与耿元波等[33]研究结果一致。研究发现,樟子松林土壤CO2通量显著高于兴安落叶松林和白桦林,因樟子松林土壤温度高（图2）,微生物代谢活动强烈,林下腐殖质层分解较快,进而产生大量CO2释放到大气中。8月末受蒙古高压影响,冷空气来袭,研究区气温骤降,3种林型土壤CO2通量也随之下降。随后温度回升到同期正常水平,土壤CO2排放通量值也随温度回升而上升。对比表2和表6发现,受温度和有机质等因素的综合影响,本研究区土壤CO2通量高于亚北极地区以及青藏高原高寒冻土区,同时也高于部分中高纬季节冻土区土壤通量,但低于泥炭沼泽地区,在多年冻土区处于中等水平。Tab. 6
表6
表6不同冻土类型地区温室气体通量比较
Tab. 6
| 冻土类型 | 样地纬度 | 植被类型 | CO2通量(mg·m-2·h-1) | CH4通量(μg·m-2·h-1) | N2O通量 (μg·m-2·h-1) | 数据来源文献 |
|---|---|---|---|---|---|---|
| 多年冻土 | 亚北极67°03′N | 苔原 | 152.01 | 5.00 | 19.17 | [39] |
| 阿拉斯加65°10′N | 黑云杉 | 90.00±42.00 | -52.00±15.00 | 0.20±0.30 | [40] | |
| 东西伯利亚62°09′N | 泰加林 | 367.02 | 1.33 | [41] | ||
| 大兴安岭52°94′N | 泥炭地 | 2.27 | [24] | |||
| 巴音布鲁克42°53′N | 高寒草甸 | 76.70±23.10 | -54.20±6.90 | 20.40±4.20 | [42] | |
| 海北州37°37′N | 高寒草甸 | 4.80 | [43] | |||
| 季节冻土 | 德国48°17′N | 挪威云杉 | -14.20±1.30 | [44] | ||
| 伊春48°11′N | 落叶松沼泽 | 537.40 | 15.33 | [29] | ||
| 奥地利47°42′N | 山毛榉林 | 128.00±13.00 | -40.00±2.30 | 5.72±1.38 | [32] | |
| 长白山42°24′N | 针阔混交林 | 172.40±43.88 | -15.00±30.00 | 70.00±10.00 | [45] | |
| 北京东灵山40°01′N | 油松 | 182.00 | -79.00 | 50.00 | [19] | |
| 神农架31°36′N | 马尾松 | 107.03±12.11 | -14.10±3.38 | [14] |
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4.2 土壤CH4通量特征及影响因素
以往研究结果表明,CH4通量既有吸收[34,35],也有排放[36]。土壤水热条件直接或间接改变厌氧产甲烷菌和好氧甲烷氧化菌的群落特征,影响土壤CH4通量,因此不同生态系统条件下水热状况的差异导致土壤CH4通量也各不相同。本研究发现,兴安落叶松林、樟子松林和白桦林土壤CH4通量均表现为吸收汇。春季初期3种林型土壤表现为CH4弱吸收通量,推测其原因是冻融期土壤含水量相对较高,多年冻土区形成好氧/缺氧界面,活动层下部趋于形成厌氧环境,产甲烷菌通过还原作用产生CH4[37];而活动层上部趋于好氧环境,甲烷氧化菌活跃消耗CH4,因此观测到CH4弱吸收[38]。春季末期则为强吸收,一方面,随着温度不断升高,冻土活动层厚度进一步增大,为甲烷氧化菌提供较大的生存代谢场所,且冬季冻死微生物释放的C、N为其提供重要基质,有利于CH4的氧化[36];另一方面,雨季还未到来,蒸发作用逐渐加强,土壤出现短暂干旱期,有利于空气中CH4和氧气在土壤中传播,增加CH4氧化吸收量[34]。夏季受降水影响,土壤湿度增加,土壤CH4吸收量相对减少。秋季末期,研究区冷空气来袭,低温减缓土壤CH4吸收速率。2016、2017年生长季,3种林型土壤CH4平均吸收通量表现为白桦林>樟子松林>兴安落叶松林,阔叶林土壤CH4吸收通量高于针叶松林土壤,与Steudler等[46]的研究结果一致。分析其原因,兴安落叶松和樟子松林为壤质土,土壤紧实,通气性较差,而白桦林土壤容重相对较小（表1）,砾石含量相对较多,质地疏松,利于土壤中氧气输送,增强土壤中甲烷氧化酶和甲烷氧化微生物的活性,提高了白桦林土壤CH4的吸收能力[47]。此外,北方森林土壤的有效氮（NO3--N和NH4+-N）含量贫乏[48],本研究中不同林型土壤有效氮含量呈现出白桦林（5.10 mg·kg-1）显著高于樟子松林（3.39 mg·kg-1）和兴安落叶松林（3.07 mg·kg-1）（表1）,白桦林微生物可利用基质含量相对丰富,增强土壤CH4吸收能力。2017年生长季3种林型土壤CH4吸收通量均小于2016年,且与含水量以及土壤温度显著相关,可能由于2017年观测期土壤温度和湿度较高（图2、图3）,造成冻土中产甲烷菌的多样性和丰富度增加,提升冻土中类型II甲烷氧化菌（a-Proteobacteria）的重要性,消耗CH4能力增强,降低土壤CH4吸收速率[49,50]。对比表2和表6中不同冻土区的研究发现,CH4在沼泽湿地受淹水状况影响多为释放源,在林地多为吸收汇。本研究结果在多年冻土林区,CH4吸收通量较小,在季节冻土区受气候、水文等因素影响,通量大小各不相同,还需进一步分析探究。4.3 土壤N2O通量特征及影响因素
2年观测发现,生长季3种林型土壤N2O通量均表现为排放源。春季5月中旬至6月,土壤N2O通量均出现排放高峰期。主要原因可能是冬季土壤胶粒外部被冰层覆盖,内层仍留存未冻水膜形成厌氧环境,为反硝化反应提供了良好的场所,产生N2O的同时又阻止其外释,春季土壤融化,累积其中的N2O被释放到大气中[51];而土壤解冻期含水量较高且富含大量活性碳、氮等营养底物,有利于N2O的产生。研究区地处多年冻土区,受低温限制土壤氮矿化率较低,有效氮（NO3--N和NH4+-N平均值为3.86 mg·kg-1）含量相对较低且不足全氮的1%（表1）,夏季植被生长旺盛,吸收利用大量的有效氮,植被与微生物间形成竞争并占据优势,影响土壤硝化和反硝化作用[52];同时,夏季降雨频繁,浅层土壤干湿交替,均影响土壤N2O排放速率[53]。秋季受温度下降影响,控制土壤N2O生产过程的酶活性也降低,土壤N2O通量逐渐减小[54]。整个生长季,观测到樟子松林温度显著高于兴安落叶松林和白桦林,3种林型土壤N2O通量受温度驱动,与气温显著正相关（表4）,这一结果可解释樟子松林土壤N2O通量高于兴安落叶松林和白桦林。封克[55]研究发现,pH值介于5~6之间时酸性土壤N2O排放速率最大,高于或低于这个区间N2O排放速率均下降,这与本研究结果一致,白桦林土壤pH < 5（表1）,N2O排放速率低于樟子松林和兴安落叶松林,然而3种林型间土壤N2O通量差异不显著,林型不是影响土壤N2O通量的主要因素。对比表2和表6发现,本研究区土壤N2O通量在多年冻土区处于高排放水平,但低于中国季节冻土区。土壤中的N2O主要通过好氧硝化过程和厌氧反硝化过程产生,而这一系列反应受到气候变化、土壤理化性质以及凋落物含量、微生物种群等因素影响[41,42]。因此,还需深入研究该区域土壤硝化和反硝化作用过程及其与土壤底物浓度间的耦合关系,重新认识多年冻土生态系统温室气体N2O的排放机制。5 结论
（1）大兴安岭多年冻土区典型森林兴安落叶松林、樟子松林和白桦林生长季土壤是CO2、N2O的“源”和CH4的“汇”,3种温室气体通量具有明显的季节性差异,不同林型和年际间CO2和CH4通量差异显著。（2）通过2年研究发现,土壤温度和土壤含水量是影响高纬度多年冻土区不同林型土壤CO2、CH4和N2O通量的关键环境因子。5 cm、10 cm和15 cm土壤温度控制土壤CO2通量,而土壤温度和土壤含水量共同影响CH4通量,土壤N2O通量受气温影响较大。
（3）气候变暖背景下,3种林型土壤CO2、N2O排放速率随着温度升高而增加,CH4吸收速率随之降低,因此增强大气温室效应。在100 a时间尺度上,大兴安岭多年冻土区3种林型土壤温室气体对全球气候变暖具有正反馈作用。
气候变暖背景下,大兴安岭多年冻土区增温效应更显著,从而造成多年冻土土壤更加复杂的水热变化,直接或间接影响寒区森林生态过程,影响区域碳氮收支平衡。今后将综合运用稳定同位素示踪和分子生物学技术,深入解析多年冻土区土壤碳氮循环机理。
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Eddy Covariance technique (EC) achieves the direct measurement on ecosystem carbon, nitrogen and water fluxes, and it provides scientific data for accurately assessing ecosystem functions in mitigating global climate change. This paper briefly reviewed the construction and development of Chinese terrestrial ecosystem flux observation and research network (ChinaFLUX), and systematically introduced the design principle and technology of the terrestrial ecosystem carbon, nitrogen and water fluxes coordinated observation system of ChinaFLUX. In addition, this paper summarized the main progress of ChinaFLUX in the ecosystem carbon, nitrogen and water exchange and environmental controlling mechanisms, the spatial pattern of carbon, nitrogen and water fluxes and biogeographical mechanisms, and the regional terrestrial ecosystem carbon budget assessment. Finally, the prospects and emphases of the terrestrial ecosystem carbon, nitrogen and water fluxes coordinated observation of ChinaFLUX are put forward to provide theoretical references for the development of flux observation and research in China.
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Large quantities of organic carbon are stored in frozen soils (permafrost) within Arctic and sub-Arctic regions. A warming climate can induce environmental changes that accelerate the microbial breakdown of organic carbon and the release of the greenhouse gases carbon dioxide and methane. This feedback can accelerate climate change, but the magnitude and timing of greenhouse gas emission from these regions and their impact on climate change remain uncertain. Here we find that current evidence suggests a gradual and prolonged release of greenhouse gas emissions in a warming climate and present a research strategy with which to target poorly understood aspects of permafrost carbon dynamics.
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On the basis of analyses of the importance of cryospheric researches in China and the current status of cryospheric sciences over the world, this paper addresses some key issues and main contents that must be handled at present. Generally, the impacts of cryospheric changes on climate, sea level and physical environments receive worldwide concerns, whereas in China, cryospheric changes are of great importance in ecology, fresh water, physical environments and climate since China has a most developed cryosphere among countries in mid- and low-latitudes. The key issues that should be currently addressed are: i) fluctuation mechanisms of different types of glaciers in responses to climate changes and the scale-conversion in water resources assessments of glaciers; ii) modeling of water and heat exchanges between frozen soil and vegetation; iii) parameterization of physical processes in the cryosphere as well as their coupling with climate models. Towards full solution of these key issues, works in following three aspects should be highlighted, i.e. cyrospheric processes and their responses to climate changes, influences of cryospheric changes, and adaptation strategies for cryospheric changes.
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DOI:10.1126/science.1204588URL [本文引用: 1]
Immune clearance and resource limitation (via red blood cell depletion) shape the peaks and troughs of malaria parasitemia, which in turn affect disease severity and transmission. Quantitatively partitioning the relative roles of these effects through time is challenging. Using data from rodent malaria, we estimated the effective propagation number, which reflects the relative importance of contrasting within-host control mechanisms through time and is sensitive to the inoculating parasite dose. Our analysis showed that the capacity of innate responses to restrict initial parasite growth saturates with parasite dose and that experimentally enhanced innate immunity can affect parasite density indirectly via resource depletion. Such a statistical approach offers a tool to improve targeting of drugs or vaccines for human therapy by revealing the dynamics and interactions of within-host regulatory mechanisms.
DOI:10.11821/dlxb201811008URL [本文引用: 1]
-1. This increase was mainly observed in the topsoil (0-20 cm). Forest, grassland, and cropland SOC storage increased by 2.52±0.77, 0.40±0.78, and 0.07±0.31 Pg C, respectively, which can be attributed to the several ecological restoration projects and agricultural practices implemented. On the other hand, SOC storage in wetlands declined by 0.76±0.29 Pg C, most likely due to the decrease in wetland area and SOC density. These results, combined with those of vegetation C sink (0.100 Pg C yr-1), show that the net C sink in Chinese terrestrial ecosystems was about 0.201±0.061 Pg C yr-1, which offsets 14.85%-27.79% of the C emissions from fossil fuels from the 1980s to the 2010s. These estimates of soil C sink based on field measured data supported the premise that China's terrestrial ecosystems have a large C sequestration potential, and further emphasized the importance of forest protection and reforestation to increase SOC storage capacity.]]>
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DOI:10.1111/gcb.2009.15.issue-2URL [本文引用: 1]
DOI:10.1007/s11284-006-0041-9URL [本文引用: 1]
Methane is one of the strongest of the greenhouse gases, being 30-fold more radiatively active than carbon dioxide on a molar basis. In addition, its atmospheric concentrations have increased by 1% per year since the Industrial Revolution. As such, the dynamics of methane is of great importance for the prediction of global climatic changes caused by increasing concentrations of greenhouse gases in the atmosphere. One of the most important biological sinks for methane is forest soils, where methanotrophic bacteria oxidize methane to carbon dioxide. Based on data mined from a review of the literature, we determined that the mean methane oxidation rate was 1.90mgCH4m−2day−1 and that the main variables controlling this rate were soil water content and inorganic nitrogen in the soils. In contrast, the effects of temperature and pH are minimal. In addition to reviewing the literature, we monitored methane oxidation rates in a temperate forest soil in Korea on a monthly basis for a year, using a static chamber method. The mean oxidation rate was 1.96mgCH4m−2day−1 and was positively correlated with nitrate concentration in the soil.]]>
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DOI:10.1139/x04-028URL [本文引用: 1]
DOI:10.1007/s11104-010-0408-0URL [本文引用: 1]
2O, CH4 and CO2. One coniferous plantation was composed of Pinus massoniana (PM), and the three broadleaf plantations were Castanopsis hystrix (CH), Michelia macclurei (MM) and Mytilaria laosensis (ML). We found that mean soil N2O and CO2 emissions in the PM plantation were 4.34μgN m−2 h−1 and 43.25mg C m−2 h−1, respectively, lower than those in the broadleaf plantations (>5.25μgN m−2 h−1 and >56.38mg C m−2 h−1). The PM plantation soil had higher mean CH4 uptake (39.03μg C m−2 h−1) than the broadleaf plantation soils (<32.67μg C m−2 h−1). Variations in soil N2O emissions among tree species could be primarily explained by the differences in litter C:N ratio and soil total N stock. Differences in soil CH4 uptake among tree species could be mostly attributed to the differences in mean soil CO2 flux and water filled pore space (WFPS). Litter C:N ratio could largely account for variations in soil CO2 emissions among tree species. This study confirms that there is no GHG benefit of converting PM plantation to broadleaf plantations in subtropical China. Therefore, the future strategy of tree species selection for substituting in place of large coniferous plantations in subtropical China needs to consider the potential effects of tree species on soil-atmosphere GHG exchanges.]]>
DOI:10.1029/94GB02651URL [本文引用: 1]
DOI:10.1023/A:1015825615309URL [本文引用: 1]
During 4 years continuous measurements of N-trace gas exchange were carried out at the forest floor-atmosphere interface at the Höglwald Forest that is highly affected by atmospheric N-deposition. The measurements included spruce control, spruce limed and beech sites. Based on these field measurements and on intensive laboratory measurements of N2-emissions from the soils of the beech and spruce control sites, a total balance of N-gas emissions was calculated. NO2-deposition was in a range of –1.6 –2.9 kg N ha–1 yr–1 and no huge differences between the different sites could be demonstrated. In contrast to NO2-deposition, NO- and N2O-emissions showed a huge variability among the different sites. NO emissions were highest at the spruce control site (6.4–9.1 kg N ha–1 yr–1), lowest at the beech site (2.3–3.5 kg N ha–1 yr–1) and intermediate at the limed spruce site (3.4–5.4 kg N ha–1 yr–1). With regard to N2O-emissions, the following ranking between the sites was found: beech (1.6–6.6 kg N ha–1 yr–1) >> spruce limed (0.7–4.0 kg N ha–1 yr–1) > spruce control (0.4–3.1 kg N ha–1 yr–1). Average N-trace gas emissions (NO, NO2, N2O) for the years 1994–1997 were 6.8 kg N ha–1 yr–1 at the spruce control site, 3.6 kg N ha–1 yr–1 at the limed spruce site and 4.5 kg N ha–1 yr–1 at the beech site. Considering N2-losses, which were significantly higher at the beech (12.4 kg N ha–1 yr–1) than at the spruce control site (7.2 kg N ha–1 yr–1), the magnitude of total gaseous N losses, i.e. N2-N + NO-N + NO2-N + N2O-N, could be calculated for the first time for a forest ecosystem. Total gaseous N-losses were 14.0 kg N ha–1 yr–1 at the spruce control site and 15.5 kg N ha–1 yr–1 at the beech site, respectively. In view of the huge interannual variability of N-trace gas fluxes and the pronounced site differences in N-gas emissions it is concluded that more research is needed in order to fully understand patterns of microbial N-cycling and N-gas production/emission in forest ecosystems and mechanisms of reactions of forest ecosystems to the ecological stress factor of atmospheric N-input.]]>
DOI:10.1016/j.atmosenv.2018.10.045URL [本文引用: 3]
URL [本文引用: 1]
Seasonal dynamics of N2O flux and its controlling factors for four representative temperate forests in northeastern China were examined with a static closed chamber-gas chromatograph technique. These forests were Korean pine (Pinus koraiensis) plantation, Dahurian larch (Larix gmelinii) plantation, Mongolian oak (Quercus mongolica) forest and hardwood broadleaved forest (dominated by Fraxinus mandshurica, Juglans mandshurica, and Phellodendron amurense). The results showed that all ecosystems were overall atmospheric N2O source during the growing season. The N2O flux (μg·m-2·h-1) decreased in order of the hardwood broadleaved forest (210±49)>the pine plantation (176±46)>the larch plantation (98±59)>the oak forest (16±126). Overall, there was no consistent seasonal pattern in N2O flux for the four ecosystems. The N2O flux was significantly positively correlated to soil gravimetric water content (0〖KG-*2〗-〖KG-*7〗10 cm depth) consistently for all ecosystems, but significantly negatively correlated to NO3--N content for each ecosystem. However, the responses of N2O flux to soil temperature and NH4+-N differed among the ecosystems. The N2O fluxes for the coniferous plantations were positively correlated to NH4+-N, but not correlated to the soil temperature at 5 cm depth; while those for the broadleaved forests displayed an opposite trend. The soil water content was the dominator of soil N2O emission for the forests in 2007 perhaps resulting from relative drought in the year. Interactions of vegetation type, environmental factor, and nitrogen availability to soil N2O emission should be further studied in the future. ]]>
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DOI:10.1016/j.catena.2018.02.026URL [本文引用: 1]
DOI:10.1016/j.scitotenv.2017.10.246URL [本文引用: 2]
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DOI:10.1016/j.ecoleng.2017.05.033URL [本文引用: 1]
DOI:10.1016/j.soilbio.2014.10.026URL [本文引用: 1]
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DOI:10.11707/j.1001-7488.20100702URL [本文引用: 2]
The seasonal variation and the influence factors of emission fluxes of greenhouse gas (CO2, N2O and CH4) from the soil ofLarix gmelinii-Betula ovalifolia-Carex schmidtii swamp, Larix gmelinii-Betula ovalifolia-Vaccinium uliginosum-moss swamp and Larix gmelinii-Ledum palustre var. anjustum-Sphagnum magellanicum swamp were studied during the growing season by static opaque chamber-GC technique in Xiaoxing′an Mountains of China. The results showed that: 1）The patterns of seasonal variation of emission fluxes of CO2 from the soil of the three forested swamp communities all were a single-peak curve, high in summer(651.4～823.6 mg·m-2h-1), lower in spring and autumn(233.3～310.0 mg·m-2h-1); That of Emission fluxes of N2O from the three communities respectively were 0.010～0.049, 0.012～0.020 and 0.010～0.080 mg·m-2h-1, and their seasonal changes were in a order of summer ＞spring＞autumn, spring＞summer＞autumn, and autumn＞spring＞summer respectively; Emission fluxes of CH4 from the three communities were -0.083～0.037,-0.122～0.078 and-0.05～0.026 mg·m-2h-1, that was the soil emitted CH4in spring and autumn, absorbing CH4 in summer; emitted CH4 in spring, absorbed CH4 in summer and autumn, and emitted CH4 in spring and summer, absorbed CH4 in autumn respectively in the three communities. 2）In the three communities, temperature of the soil (＜30 cm ) was the main affecting factors of CO2emission; Higher temperature of the soil (＜30 cm ) and lower water table were the main affecting factors of N2O emission; Water table was the main affecting factors of CH4 emission; The soil with lower water table emitted CH4, while the soil with higher water table absorbed CH4. 3）During the growing season, the soils of the three forested swamps all were the sources of CO2(20.8～25.2 t·hm-2), higher in summer, and lower in spring and autumn; The soils all were the sources of N2O (0.192～1.128 kg·hm-2). The soil ofLarix gmelinii-Betula ovalifolia-Carex schmidtii swamp emitted more N2O than the other two. The soils of Larix gmelinii-Betula ovalifolia-Carex schmidtii swamp and Larix gmelinii-Betula ovalifolia-Vaccinium uliginosum-moss swamps both were strong sinks of CH4 (1.152～1.200 kg·hm-2), but the soils of Larix gmelinii-Ledum palustre var. anjustum-Sphagnum magellanicum swamp were a weak sources of CH4 (0.168 kg·hm-2). 4） The emission of greenhouse gases from the soil of Larix gmelinii-Betula ovalifolia-Carex schmidtii swamp was higher (CO2:25.4 t·hm-2) than others (CO2： 20.8～21.2 t·hm-2). The greenhouse gas all were composed of CO2 mainly (99.63%～99.93%), few N2O and CH4 (0.19%～0.92% and 0.02%～0.10%).]]>
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DOI:10.1134/S1067413615020071URL [本文引用: 1]
DOI:10.1007/s12665-015-4241-xURL [本文引用: 1]
DOI:10.1007/s11104-015-2771-3URL [本文引用: 2]
DOI:10.11821/xb201009003URL [本文引用: 1]
Leymus chinensis steppe in Xilin River Basin of Inner Mongolia, China. Soil temperature and moisture are the most important factors affecting CO2 flux. Soil temperature was the main factor influencing respiration rates. Exponential models based on soil temperature can explain large percent of CO2 efflux variations (R2 = 0.375-0.655) excluding data of low soil water conditions. Soil moisture can also effectively explain some variations of soil and ecosystem respiration (R2 = 0.314-0.583), but it can not explain much of variation of soil microbial respiration (R2 = 0.063). Low soil water content (≤5%) inhibited CO2 efflux though soil temperature was high. Rewetting the soil after a long drought resulted in substantial increases in CO2 flux at high temperature. Bi-variable models based on soil temperature at 5 cm depth and soil water content at 0-10 cm depth can explain about 70% of variations of CO2 effluxes. The contribution of soil respiration to ecosystem respiration averaged 59.4%, ranging from 47.3% to 72.4%; the contribution of root respiration to soil respiration averaged 20.5% , ranging from 11.7% to 51.7% . The contribution of soil to ecosystem respiration was a little overestimated and root to soil respiration underestimated because of increased soil water content that occurred as a result of plant removal.]]>
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DOI:10.11821/xb201209002URL [本文引用: 2]
P. australis. Measurements were taken at three tidal stages. Potential rates of methane production and oxidation from the marsh sediments were also estimated in situ in summer and winter using acetylene as a methane oxidation inhibitor. We devised a ‘hanging' enclosed static chamber to measure methane transport and emission directly from single stems of P. australis on days of neap tide. Methane emission from the P. australis tidal marsh showed a seasonal variation in all the three tidal stages, and reached a maximum during the summer when soil temperature was relatively high. The ranges of methane flux were 0.69-40.95, 0.26-9.57 and 0.74-22.10 mg m-2 h-1 before the flood, during the flood/ebb and after the ebb respectively and the average methane fluxes were 7.53, 2.19 and 4.93 mg m-2 h-1, respectively. Methane production and oxidation potentials in summer were all higher than those in winter. Methane concentrations within the lacunal of the P. australis stems were the greatest at the base and decreased faster compared with stem height, which start at the stem base, and showed lower lacunal methane concentrations at daytime and higher lacunal methane concentrations at night-time. On an annual basis, the average methane transport and emission of a single P. australis culm was 33.67 μg·culm-1·h-1. These methane transport rates differed between growth stages, with the highest transport and emission detected within the stage of fastest plant growth. Nearly half (43.4%) of the whole plant transport and emission occurred from P. australis culms nearest the ground (0-20 cm above the ground). We estimated that plant-mediated methane transport contributed 2.3%-28.5% of the total methane emission within this P. australis-dominated marsh.]]>
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DOI:10.1016/j.scitotenv.2016.10.219URL [本文引用: 1]
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DOI:10.1016/S1164-5563(01)01067-6URL [本文引用: 1]
DOI:10.1111/gcb.13563URLPMID:27862698 [本文引用: 1]
Rapidly rising temperatures in the Arctic might cause a greater release of greenhouse gases (GHGs) to the atmosphere. To study the effect of warming on GHG dynamics, we deployed open-top chambers in a subarctic tundra site in Northeast European Russia. We determined carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2 O) fluxes as well as the concentration of those gases, inorganic nitrogen (N) and dissolved organic carbon (DOC) along the soil profile. Studied tundra surfaces ranged from mineral to organic soils and from vegetated to unvegetated areas. As a result of air warming, the seasonal GHG budget of the vegetated tundra surfaces shifted from a GHG sink of -300 to -198 g CO2 -eq m(-2) to a source of 105 to 144 g CO2 -eq m(-2) . At bare peat surfaces, we observed increased release of all three GHGs. While the positive warming response was dominated by CO2 , we provide here the first in situ evidence of increasing N2 O emissions from tundra soils with warming. Warming promoted N2 O release not only from bare peat, previously identified as a strong N2 O source, but also from the abundant, vegetated peat surfaces that do not emit N2 O under present climate. At these surfaces, elevated temperatures had an adverse effect on plant growth, resulting in lower plant N uptake and, consequently, better N availability for soil microbes. Although the warming was limited to the soil surface and did not alter thaw depth, it increased concentrations of DOC, CO2, and CH4 in the soil down to the permafrost table. This can be attributed to downward DOC leaching, fueling microbial activity at depth. Taken together, our results emphasize the tight linkages between plant and soil processes, and different soil layers, which need to be taken into account when predicting the climate change feedback of the Arctic.
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DOI:10.1111/j.1747-0765.2008.00309.xURL [本文引用: 2]
DOI:10.1016/j.chemosphere.2012.02.077URL [本文引用: 2]
To assess the effects of nitrogen (N) deposition on greenhouse gas (GHG) fluxes in alpine grassland of the Tianshan Mountains in central Asia, CH4, CO2 and N2O fluxes were measured from June 2010 to May 2011. Nitrogen deposition tended to significantly increase CH4 uptake, CO2 and N2O emissions at sites receiving N addition compared with those at site without N addition during the growing season, but no significant differences were found for all sites outside the growing season. Air temperature, soil temperature and water content were the important factors that influence CO2 and N2O emissions at year-round scale, indicating that increased temperature and precipitation in the future will exert greater impacts on CO2 and N2O emissions in the alpine grassland. In addition, plant coverage in July was also positively correlated with CO2 and N2O emissions under elevated N deposition rates. The present study will deepen our understanding of N deposition impacts on GHG balance in the alpine grassland ecosystem, and help us assess the global N effects, parameterize Earth System models and inform decision makers. (C) 2012 Elsevier Ltd.
DOI:10.1016/j.soilbio.2010.02.011URL [本文引用: 1]
DOI:10.1016/j.envpol.2011.06.025URL [本文引用: 1]
Based on multi-year measurements of CH(4) exchange in sub-daily resolution we show that clear-cutting of a forest in Southern Germany increased soil temperature and moisture and decreased CH(4) uptake. CH(4) uptake in the first year after clear-cutting (-4.5 +/- 0.2 mu g C m(-2) h(-1)) was three times lower than during the pre-harvest period (-14.2 +/- 1.3 mu g C m(-2) h(-1)). In contrast, selective cutting did not significantly reduce CH4 uptake. Annual mean uptake rates were -1.18 kg C ha(-1) yr(-1) (spruce control), -1.16 kg C ha(-1) yr(-1) (selective cut site) and -0.44 kg C ha(-1) yr(-1) (clear-cut site), respectively. Substantial seasonal and inter-annual variations in CH(4) fluxes were observed as a result of significant variability of weather conditions, demonstrating the need for long-term measurements. Our findings imply that a stepwise selective cutting instead of clear-cutting may contribute to mitigating global warming by maintaining a high CH(4) uptake capacity of the soil. (C) 2011 Elsevier Ltd.
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DOI:10.1038/341314a0URL [本文引用: 1]
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DOI:10.1038/nature07276URLPMID:18784722 [本文引用: 1]
Old-growth forests remove carbon dioxide from the atmosphere at rates that vary with climate and nitrogen deposition. The sequestered carbon dioxide is stored in live woody tissues and slowly decomposing organic matter in litter and soil. Old-growth forests therefore serve as a global carbon dioxide sink, but they are not protected by international treaties, because it is generally thought that ageing forests cease to accumulate carbon. Here we report a search of literature and databases for forest carbon-flux estimates. We find that in forests between 15 and 800 years of age, net ecosystem productivity (the net carbon balance of the forest including soils) is usually positive. Our results demonstrate that old-growth forests can continue to accumulate carbon, contrary to the long-standing view that they are carbon neutral. Over 30 per cent of the global forest area is unmanaged primary forest, and this area contains the remaining old-growth forests. Half of the primary forests (6 x 10(8) hectares) are located in the boreal and temperate regions of the Northern Hemisphere. On the basis of our analysis, these forests alone sequester about 1.3 +/- 0.5 gigatonnes of carbon per year. Thus, our findings suggest that 15 per cent of the global forest area, which is currently not considered when offsetting increasing atmospheric carbon dioxide concentrations, provides at least 10 per cent of the global net ecosystem productivity. Old-growth forests accumulate carbon for centuries and contain large quantities of it. We expect, however, that much of this carbon, even soil carbon, will move back to the atmosphere if these forests are disturbed.
DOI:10.1038/ismej.2007.84URLPMID:18180745 [本文引用: 1]
Archaeal populations are abundant in cold and temperate environments, but little is known about their potential response to climate change-induced temperature changes. The effects of temperature on archaeal communities in unamended slurries of weakly acidic peat from Spitsbergen were studied using a combination of fluorescent in situ hybridization (FISH), 16S rRNA gene clone libraries and denaturing gradient gel electrophoresis (DGGE). A high relative abundance of active archaeal cells (11-12% of total count) was seen at low temperatures (1 and 5 degrees C), and this community was dominated by Group 1.3b Crenarchaeota and the euryarchaeal clusters rice cluster V (RC-V), and Lake Dagow sediment (LDS). Increasing temperature reduced the diversity and relative abundance of these clusters. The methanogenic community in the slurries was diverse and included representatives of Methanomicrobiales, Methanobacterium, Methanosarcina and Methanosaeta. The overall relative abundance and diversity of the methanogenic archaea increased with increasing temperature, in accordance with a strong stimulation of methane production rates. However, DGGE profiling showed that the structure of this community changed with temperature and time. While the relative abundance of some populations was affected directly by temperature, the relative abundance of other populations was controlled by indirect effects or did not respond to temperature.
DOI:10.1016/j.soilbio.2008.08.020URL [本文引用: 1]
AbstractThe abundance, activity, and temperature response of aerobic methane-oxidizing bacteria were studied in permafrost-affected tundra soils of northeast Siberia. The soils were characterized by both a high accumulation of organic matter at the surface and high methane concentrations in the water-saturated soils. The methane oxidation rates of up to 835 nmol CH4 h−1 g−1 in the surface soils were similar to the highest values reported so far for natural wetland soils worldwide. The temperature response of methane oxidation was measured during short incubations and revealed maximum rates between 22 °C and 28 °C. The active methanotrophic community was characterized by its phospholipid fatty acid (PLFA) concentrations and with stable isotope probing (SIP). Concentrations of 16:1ω8 and 18:1ω8 PLFAs, specific to methanotrophic bacteria, correlated significantly with the potential methane oxidation rates. In all soils, distinct 16:1 PLFAs were dominant, indicating a predominance of type I methanotrophs. However, long-term incubation of soil samples at 0 °C and 22 °C demonstrated a shift in the composition of the active community with rising temperatures. At 0 °C, only the concentrations of 16:1 PLFAs increased and those of 18:1 PLFAs decreased, whereas the opposite was true at 22 °C. Similarly, SIP with 13CH4 showed a temperature-dependent pattern. When the soils were incubated at 0 °C, most of the incorporated label (83%) was found in 16:1 PLFAs and only 2% in 18:1 PLFAs. In soils incubated at 22 °C, almost equal amounts of 13C label were incorporated into 16:1 PLFAs and 18:1 PLFAs (33% and 36%, respectively). We concluded that the highly active methane-oxidizing community in cold permafrost-affected soils was dominated by type I methanotrophs under in situ conditions. However, rising temperatures, as predicted for the future, seem to increase the importance of type II methanotrophs, which may affect methane cycling in northern wetlands.]]>
DOI:10.1002/ppp.v31.1URL [本文引用: 1]
DOI:10.1111/gcb.15119URLPMID:32301539 [本文引用: 1]
Soil nitrification, an important pathway of nitrogen transformation in ecosystems, produces soil nitrate that influences net primary productivity, while the by-product of nitrification, nitrous oxide, is a significant greenhouse gas. Although there have been many studies addressing the microbiology, physiology, and impacting environment factors of soil nitrification at local scales, there are very few studies on soil nitrification rate over large scales. We conducted a global synthesis on the patterns and controlling factors of soil nitrification rate normalized at 25 degrees C by compiling 3,140 observations from 186 published articles across terrestrial ecosystems. Soil nitrification rate tended to decrease with increasing latitude, especially in the Northern Hemisphere, and varied largely with ecosystem types. The soil nitrification rate significantly increased with mean annual temperature (MAT), soil nitrogen content, microbial biomass carbon and nitrogen, soil ammonium, and soil pH, but decreased with soil carbon:nitrogen and carbon:nitrogen of microbial biomass. The total soil nitrogen content contributed the most to the variations of global soil nitrification rate (total coefficient = 0.29) in structural equation models. The microbial biomass nitrogen (MBN; total coefficient = 0.19) was nearly of equivalent importance relative to MAT (total coefficient = 0.25) and soil pH (total coefficient = 0.24) in determining soil nitrification rate, while soil nitrogen and pH influenced soil nitrification via changing soil MBN. Moreover, the emission of soil nitrous oxide was positively related to soil nitrification rate at a global scale. This synthesis will advance our current understanding on the mechanisms underlying large-scale variations of soil nitrification and benefit the biogeochemical models in simulating global nitrogen cycling.
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DOI:10.1016/j.agrformet.2011.02.001URL [本文引用: 1]
Savanna soil was generally a net CH4 sink that equated to between -2.0 and -1.6 kg CH4 ha(-1) y(-1) with no clear seasonal pattern in response to changing soil moisture conditions. Irrigation in the dry season significantly reduced soil gas diffusion and as a consequence soil CH4 uptake. There were short periods of soil CH4 emission, up to 20 mu g C m(-2) h(-1), likely to have been caused by termite activity in, or beneath, automated chambers. Soil CO2 fluxes showed a strong bimodal seasonal pattern, increasing fivefold from the dry into the wet season. Soil moisture showed a weak relationship with soil CH4 fluxes, but a much stronger relationship with soil CO2 fluxes, explaining up to 70% of the variation in unburnt treatments. Australian savanna soils are a small N2O source, and possibly even a sink. Annual soil CH4 flux measurements suggest that the 1.9 million km(2) of Australian savanna soils may provide a C sink of between -7.7 and -9.4 Tg CO2-e per year. This sink estimate would offset potentially 10% of Australian transport related CO2-e emissions. This CH4 sink estimate does not include concurrent CH4 emissions from termite mounds or ephemeral wetlands in Australian savannas. (C) 2011 Elsevier B.V.]]>
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