土壤氧化亚氮通量对增温的响应及其微生物学机制：以水分条件不同的两种高寒草地为例

Nitrous oxide (N2O) emissions induced by climate warming may play an important role in regulating atmospheric N2O concentrations. However, our understanding of underlying microbial mechanisms of soil N2O flux remains limited. In this project, we will focus on two types of alpine grasslands with completely different moisture conditions, carry out experimental warming studies in alpine steppe and alpine swamp meadow using the same experimental design based on the coordinated distributed experiments (CDE) design scheme, and try to examine the effects of warming on soil N2O flux, soil potential nitrification rates and denitrification rates, abundance and community structures of soil N cycling microorganisms (ammonia oxidizing bacteria, ammonia oxidizing archaea and denitrifying bacteria). Furthermore, we will use structural equation modeling (SEM) to analyze the quantitative relationships between soil N2O flux and independent variables such as soil properties, soil potential nitrification and denitrification rates, soil N-cycling microbial abundance and community structures. This project could enhance our knowledge about the responses of soil N2O flux to experimental warming and their underlying microbial mechanisms, and provide important scientific basis for understanding the dynamics of the soil N cycle in alpine grasslands under warming scenarios.

气候变暖导致的土壤氧化亚氮(N2O)释放可能在调节大气N2O浓度中扮演重要角色。然而，目前学术界对于调控土壤N2O通量的微生物机制的认识还相对薄弱。为此，本项目以两种水分条件完全不同的高寒草地生态系统为对象，基于国际上正在倡导的Coordinated Distributed Experiments(CDE)设计方案，采用完全一致的实验设计在高寒草原和高寒沼泽草甸中开展增温实验研究，考察增温对两种生态系统中土壤N2O通量、土壤硝化反硝化潜势和N循环功能微生物(氨氧化细菌，氨氧化古菌和反硝化细菌)丰度和群落结构的影响。同时，基于结构方程模型分析不同自变量(土壤理化性质、土壤硝化反硝化潜势、土壤N循环功能微生物丰度和群落结构)与土壤N2O通量之间的定量关系。本项目的实施有望阐明高寒生态系统土壤N2O通量对增温的响应及其微生物学机制，并为理解气候变暖背景下高寒生态系统土壤氮循环的变化提供科学基础。

气候变暖导致的土壤氧化亚氮(N2O)释放可能在调节大气N2O浓度中扮演重要角色。然而，目前学术界对于气候变暖背景下土壤N2O排放调控机制的认识还相对薄弱。为此，本项目以高寒草地生态系统为对象，使用透明开顶箱(OTCs)模拟气候变暖，并基于静态箱法测定了2014和2015年生长季(5-10月)的土壤N2O通量，同时利用定量PCR技术测定了表层(0-10 cm)土壤中氮循环功能微生物(氨氧化细菌，氨氧化古菌和反硝化细菌)的基因丰度，进而揭示土壤N2O通量和氮循环功能微生物群落丰度对增温的响应以及N2O排放的调控机制。结果显示：增温处理导致2014和2015年生长季表层(0-10 cm)土壤温度分别升高了1.7 和1.6 度，土壤体积含水量下降了2.5%和3.3%，其他土壤理化性质并未发生显著变化。土壤N2O通量和氮循环微生物功能基因丰度呈现显著的年际差异，然而增温对土壤N2O通量和氮循环微生物功能基因丰度无显著影响。在生长季尺度上，增温导致的土壤N2O变化量与土壤水分的变化量呈显著正相关，而与土壤温度的变化量之间没有显著相关关系。以上结果表明，土壤含水量调控高寒草地生态系统N2O排放对增温的响应，增温导致的土壤干旱会抵消增温对土壤N2O排放的促进作用，意味着未来评估气候变暖情景下土壤N2O排放量时需考虑增温引发的土壤干旱等间接效应。