青藏高原多年冻土区温室气体排放对活动层水热过程的响应及驱动机制

The hydrothermal processes of active layer play a pivotal role in the carbon and nitrogen cycling and biogeochemical cycles in permafrost, and the hydrothermal changes in different freezing and thawing stages are closely related to the dynamics of greenhouse gas emission. However, the influences of hydrothermal migration on greenhouse gas emissions in different freezing and thawing stages have not yet been systematically investigated, and the corresponding driving mechanisms are still not very clear. In this project, we will select an alpine meadow ecosystem in the Beiluhe permafrost region which is located in the hinterland of the Qinghai-Tibet Plateau and establish long-term observation plots in situ. The greenhouse gas emissions and hydrothermal processes in different freezing and thawing stages of the active layer would be systematically observed. Meanwhile the soil physical and chemical characteristics, the soil enzyme activities related to carbon and nitrogen conversion and the structures and functions of soil microbial community would be analyzed. The effects of the hydrothermal migration on soil physical and chemical traits, soil enzyme activities and soil microbial properties and their correlation with greenhouse gas emissions would be clarified, and the driving mechanisms of the freeze-thaw processes of active layer influencing the greenhouse gas emissions in the different freeze-thaw stages would be elucidated. This study will be of great significance for comprehensively and deeply understanding the regulatory mechanisms of the hydrothermal processes of active layer affecting the carbon and nitrogen cycling of the plateau, and will provide the basic data and theoretical basis for accurately evaluating the global climatic effects of greenhouse gas emissions from the permafrost regions of the Qinghai-Tibet Plateau.

活动层水热过程是驱动多年冻土碳、氮循环和生物地球化学循环的源动力，不同冻融阶段水热变化与温室气体排放动态密切相关，然而相关研究没有系统探讨不同冻融阶段水热迁移对温室气体排放的影响，并且相应的驱动机制仍不清楚。本项目以北麓河多年冻土区典型高寒草甸生态系统为研究对象，通过建立原位观测样地，对活动层不同冻融阶段温室气体排放和水热迁移进行系统观测，并对土壤物理化学性质、土壤碳氮转化相关的酶活性以及土壤微生物群落结构和功能进行分析，阐明水热迁移对土壤物理化学性质、酶活性和微生物学性质的影响及其与温室气体排放的相关性，揭示不同冻融阶段水热迁移对温室气体排放的驱动机制。该研究对于全面认识和深入理解活动层水热过程在高原碳氮循环中的调控机理具有重要意义，同时为准确评价青藏高原多年冻土区温室气体排放的全球气候效应提供基础数据和理论依据。

青藏高原多年冻土活动层水热过程对CO2、CH4、N2O等温室气体的排放影响强烈。项目通过野外原位试验和室内原状土柱模拟实验，对高寒草原、高寒草甸和高寒沼泽化草甸活动层土壤水热过程及其CO2、CH4、N2O排放进行了详细研究，全面完成了项目任务书中的各项研究内容和考核指标，取得了较为丰富的研究成果。.（1）明确了不同类型高寒草地土壤理化性质之间的差异。高寒草原、高寒草甸土壤含水量随深度而增加，高寒沼泽化草甸随深度增加呈下降趋势；高寒草原、高寒沼泽化草甸土壤重随深度增加而增加，高寒草甸变化不显著；高寒沼泽化草甸土壤总氮、有机碳含量及碳氮比最高，高寒草甸的最低。.（2）揭示了三类高寒草地土壤Rs通量的季节和日变化特征。夏季三种草地生态系统土壤CO2排放通量显著高于春季、秋季和冬季。在日变化上，生长季高寒草原、高寒草甸和沼泽化草甸Rs通量的日变化均呈双峰型变化特征，CO2排放通量最大值出现在16:00点至18:00之间，其次在凌晨02:00左右出现一个排放小高峰；非生长季三类高寒草地的土壤Rs通量的日变化均较为平缓且通量值较小。.（3）明确了三类高寒草地不同季节和冻融阶段N2O温室气体的排放特征。三类草地冬季、春季N2O通量比夏季、秋季高，且春季均处于N2O释放状态；植被地上部分对N2O通量影响显著，夏季上午促进N2O释放、下午起减弱作用，秋季主要表现为减弱生态系统N2O通量作用。.（4）揭示了活动层冻融深度变化影响CO2温室气体排放的规律，构建了基于土壤水分、温度、大气蒸汽压差、热通量的生态系统CO2排放SEM关系模型，阐明了不同类型高寒草地土壤CO2排放主控因子。.（5）阐明了高寒草甸活动层冻融过程对CO2温室气体排放的水热驱动机制，构建了不同冻融阶段土壤CO2温室气体排放关系模式，明确了活动层不同冻融阶段CO2温室气体的排放量及其占全年释放的比例。活动层一个冻融周期的CO2释放量约为1692.98±51.43gCO2/m2，其中：夏季融化阶段占61.32±0.32%、秋季冻结阶段占8.89±0.18%、冬季降温阶段占18.43±0.11%、春季升温阶段占11.29±0.11%。