土壤冻融格局变化及氮沉降对温带草地冬季土壤N2O排放的交互影响效应与机制

N2O is a greenhouse gas with a remarkable global warming potential, and it is also the dominant anthropogenic ozone depleting substance. Additionally, N2O losses from soil in temperate grassland can also affecting the nitrogen availabilities used by plant in ecosystems, which can further restrict the size of plant productivity and carbon sequestration potential. High N2O emission pulses are most likely to occur in the hot moments such as freezing-thawing of non-growing seasons and drying-rewetting periods during growing seasons. However, so far, most of the researches on N2O emission from temperate grassland in China were concentrated in growing season, and less touched about the non-growing season. The studies on the mechanisms of N2O emissions from soil in freezing and thawing period were even scarce. Thus, the accuracy of the prediction of N2O emissions and the recognition of mechanisms of nitrogen nutrition transform in grassland ecosystems in China were greatly restricted. Moreover, in the global change scenario, soil freezing and thawing patterns in temperate areas are changing and more nitrogen also deposits to the terrestrial ecosystems, which together aggravate the uncertainties of soil N2O emissions. In view of this, the project intends to conduct an in situ field simulation experiment to explore the interactive effects of nitrogen deposition and changes of soil freezing and thawing patterns on soil N2O emissions and their driving mechanisms. Here, the changes of freezing and thawing patterns will be simulated by changing snow cover. Meanwhile, N2O emission related factors such as water and temperature, carbon and nitrogen substrates and microbial mechanisms will be analyzed. The completion of the project will reduce the uncertainties of estimation in N2O emissions in China and it will also provide a strong theoretical and practical basis for the scientific management on grassland nitrogen nutrition, which leads to the enhancement of grassland productivity and the potential of carbon sequestration.

N2O是目前草地研究相对薄弱的温室效应气体，不仅大气增温效应显著，破坏臭氧层，同时其损失的多寡还决定着草地土壤中氮养分的存量，进而显著影响草地生产力及其碳汇强度。土壤冻融期与生长季干湿交替期被发现是中高纬度土壤N2O排放贡献最大的两个重要时期。但目前我国草地N2O排放研究多集中于生长季，较少考虑冬季，对冻融期的探讨更鲜有涉及，从而极大制约了草地N2O排放贡献估算的准确性以及对草地氮循环机制的深刻认识。当前日趋强烈的全球变化带来温带地区土壤冻融格局改变以及氮沉降的增加，将会进一步加剧预估结果的不确定性。鉴于此，本项目拟采用去雪、增雪，叠加氮素输入水平变化的野外模拟控制试验，初步探索冻融格局及氮输入变化对草地土壤N2O排放的影响，定量阐明不同时段土壤N2O的水热、碳氮底物以及微生物学驱动机制。研究结果有助于降低我国草地N2O排放研究的不确定性，同时也可为草地养分的科学管理提供重要的科学依据。

N2O是草地中研究相对薄弱的温室气体，它不仅大气增温效应显著，破坏臭氧层，同时其损失的多寡还决定着草地土壤中氮养分的存量，进而显著影响草地生产力及碳汇强度。土壤非生长季冻融期与生长季干湿交替期被发现是中高纬度土壤N2O排放贡献最大的两个重要时期。但目前我国草地N2O排放研究多集中于生长季，较少考虑非生长季，对不同冻融期的探讨更鲜有涉及，从而极大制约了草地N2O排放贡献估算的准确性以及对草地氮循环机制的深刻认识。当前日趋强烈的全球变化带来温带地区土壤冻融 格局改变以及氮沉降的增加，将会进一步加剧预估结果的不确定性。鉴于此，本项目开展了去雪、增雪以及氮素输入变化的野外原位模拟试验，初步探索非生长季不同冻融阶段（秋冬融冻阶段、深冬完全冻结阶段、冬春冻融阶段）雪被变化与氮沉降增加对温带典型草地土壤N2O排放的影响；定量阐述温带草地非生长季土壤N2O排放占年排放总量的贡献比例；科学揭示土壤水热、碳氮底物等环境因子以及微生物学特征对不同雪被和氮输入变化的差异响应；初步探讨非生长季不同冻融阶段土壤N2O排放响应不同雪被和氮输入变化的的主要环境驱动因子以及敏感微生物学指标。结果显示，N2O排放对不同雪被的响应及其主控因子与冻融阶段有关。施氮促进了非生长季和全年土壤N2O的排放，对照和施氮处理下非生长季土壤N2O占全年排放比例均达60%。土壤N2O排放受到土壤微生物量和群落结构、碳氮养分含量、水分多因子综合作用的影响，不同氮处理在不同冻融阶段对N2O排放的主控因子并不一致。对雪被变化敏感的微生物有浮霉菌门、硝化螺旋菌门及芽单胞菌门等物种，奇古菌门、疣微菌门及芽单胞菌门与环境因子有显著关系。研究成果有助于降低我国温带草地土壤N2O排放研究的不确定性，弥补非生长季温室气体排放及微生物响应敏感指标等数据的不足，提高对气候和环境变化应对的能力。同时，可以为草地碳氮养分的科学管理，实现草地生产力的提高和土壤温室气体的减排双重目标提供有力的理论与科学实践依据。