大兴安岭多年冻土区泥炭地-大气间碳交换对气温升高和冻土退化的潜在响应研究

Wetlands in mid-high latitude of northern region play an important role in global carbon cycling. Carbon release from wetland soils caused by temperature increase and permafrost degradation is among the most important feedbacks of northern ecosystems to the climate change. With the on-going change of heat and permafrost conditions, what is the trend of the carbon exchange between the wetland ecosystems and the atmosphere and to what extent will the trend respond to climate change still need quantitative and systematic researches. The project plans to select a typical peatland in the permafrost region of the Greater Khingan Mountains which lie at the southern edge of the permafrost zone of Eurasia as the research object. By using the continuous field observations, in situ simulated experiments, long-term laboratory soil incubation experiments and model simulation, the coupling between temperature increase, permafrost degradation, plants carbon fixation and the release of CO2 and CH4 by soil organic matters will be systematically studied. The potential variation of soil carbon pool and the carbon exchange between the peatland and the atmosphere under different future climate scenarios will be quantitatively predicted. The research work could provide scientific data and theoretical support for quantifying the long term variation and climate feedback of wetland carbon balance in permafrost regions of mid-high latitude. It could also provide scientific support in evaluating the stability of wetland carbon pool in the northern permafrost region of our country under the background of the global change.

北方中高纬度地区的沼泽湿地在全球碳循环中发挥着重要的作用，气温升高和多年冻土退化引起的该区沼泽湿地的碳释放是当前北方生态系统对气候变化的最重要的响应之一。关于全球变化背景下我国中高纬多年冻土区湿地与大气间的碳交换将发生怎样的改变以及将在何种程度上响应气候变化，目前仍缺乏定量、系统的研究。项目拟选取位于欧亚大陆多年冻土带南缘、对气候变化敏感性高的大兴安岭多年冻土区的泥炭地为研究对象，采用野外连续观测、原位增温模拟、长期室内培养实验和过程模型相结合的研究方法，探讨气温升高和冻土退化、土壤碳库分解以及生态系统碳收支之间的耦合关系，进而定量评估未来不同气候变化情景下泥炭地土壤有机碳库以及湿地-大气间碳交换的潜在变化。研究工作可为量化中高纬多年冻土区湿地碳收支的长期变化和气候反馈，评估全球变化背景下我国北方多年冻土区湿地土壤碳库的稳定性提供科学数据和理论支持。

项目针对气候变化背景下大兴安岭多年冻土区泥炭地生态系统碳交换的长期变化具有较大不确定性这一科学问题，通过连续4年的研究：(1)明确了多年冻土区泥炭地-大气间含碳温室气体通量的时空变化特征。连续的通量观测结果表明，冻土区泥炭地生长季CO2净吸收量为92.6gC-CO2m-2，CH4排放量为0.8gC-CH4m-2，冻土区泥炭地目前为大气碳汇，年累积固碳量为79.7gCm-2；土壤温度和冻土融深的变化直接影响了CH4排放的季节变化，局域微地貌和因地形波动引起的水分条件的变化导致了CH4排放的空间变异；约2℃的原位增温显著促进了泥炭地碳排放，CO2和CH4排放分别增加了39%和27%。(2)考察了冻土区泥炭地从活动层到多年冻土层土壤有机碳分解和CH4释放的温度敏感性。从表层到永冻土层，CO2和CH4的温度敏感性(Q10)分别在1.4-2.8和3.0-40之间变化；温度升高可显著提高泥炭地土壤短期内的碳排放，但在超过约一年的长时间尺度上，CO2分解和CH4释放都趋于稳定的低排放。(3)结合长时间序列的高精度实测数据，对过程模型CoupModel进行结构调整、参数率定和校验，模型可较好地模拟泥炭地生态系统的水热过程和生态系统碳交换的季节变化。(4)评估了大兴安岭多年冻土区泥炭地生态系统的碳收支对未来气候变化和冻土退化的潜在响应。RCP2.6、RCP6.0和RCP8.5三种代表性浓度路径情景下，无论泥炭地是否发生灌木入侵，在无人为干扰的情况下，生态系统总初级生产力、呼吸排放和净碳累积的未来长期变化都表现为增强的趋势，灌木入侵会进一步增加泥炭地生态系统的碳交换和净碳累积能力。研究工作可为评估全球变化背景下我国中高纬多年冻土区湿地土壤碳库的稳定性和分解风险、量化多年冻土区湿地碳收支的长期变化提供科学依据，同时可为我国温室气体排放清单的制定以及应对全球变化、减缓湿地碳库损失的科学管理提供参考。