长江源区生源物质氮循环过程的解析对于变化环境下长江流域的生态环境保护具有重要意义。源区河流底质氮循环菌群对氮素循环起到重要作用，然而现阶段源区河流底质氮循环菌群特征及其对氮素转化的机制仍不清楚，难以实现变化环境下源区河流氮素循环过程的定量解析。本课题针对长江源区河流氮素的微生物转化过程，拟以源区河流底质氮循环关键微生物为研究对象，采用野外观测和室内模拟相结合的方法，首先研究径流变化下源区典型断面氮素和氮循环菌群的分布与变化规律，解析源区河流底质氮循环菌群特征，识别源区河流氮循环的主导功能微生物及关键转化步骤；其次研究氮循环菌群对源区径流、水质等因素的响应规律，阐明动水条件下源区河流底质氮循环菌群对环境因素的响应机制；在此基础上，探讨氮循环菌群的变化与氮素通量之间的动态交互关系，最终阐明长江源区河流底质氮循环菌群对氮转化的作用机制，为长江源区河流氮通量的定量解析和生态保护提供科学依据。

To predict the change in nitrogen fluxes precisely with the runoff variation in the source region of the Yangtze River, it is necessary to understand its nitrogen transformation process. The biological processes of nitrogen transformation are mainly carried out by nitrogen cycle microbial communities, however, the knowledge in the characteristics of nitrogen cycle microbial community and the microbial mechanism of nitrogen transformation processes in the source region is limited. The aim of this research is to study the microbial processes of nitrogen transformation in the source region of the Yangtze River through in situ and simulation experiments. The dominant microbial groups and the key steps of nitrogen transformation processes should be recognized first by analyzing the spatial and temporal distribution of nitrogen fluxes and the nitrogen cycle microbial community in some typical sections of the source region. Then the effect of dominate environmental variables to nitrogen cycle microbial communities in sediments will be performed to determine the responding mechanism of nitrogen cycle microbial communities to environmental variables under flowing water. At last, the interactions between nitrogen cycle microbial community and nitrogen fluxes will be analyzed to explore the microbial processes of nitrogen transformation in the source region of the Yangtze River. The above results could provide important information for the further mathematical modeling of nitrogen fluxes which is the scientific basis for environmental protection of the source region of the Yangtze River.