随着人类活动强度的增加，通过大气干湿沉降输入到陆地生态系统的含氮化合物日益增多，氮沉降带来的生态效应已经成为当前全球变化研究的重点。然而，现有模拟氮沉降研究大多只探讨了单一形态的氮素化合物添加对生态系统结构与功能的影响，实际上大气氮沉降中含有不同化合物形态的有机氮和无机氮，其结论能否真实反映氮沉降对陆地生态系统的影响值得商榷。土壤氮素的富集会引起微生物群落结构和功能的改变，但是土壤微生物群落是否会对不同形态的氮素具有差异性响应还鲜为人知。本项目拟依托2013年在内蒙古草甸草原设置的氮素化合物添加实验平台，通过四种包括不同形态的有机和无机氮化合物添加，利用高通量测序和基因芯片技术，研究微生物群落组成和多样性及其功能基因对不同形态氮素添加的响应，结合植物和土壤环境因素的耦合分析，阐明微生物群落及其驱动的氮素转化过程的响应机理，该研究对于理解和预测温带草原氮沉降增加的生态效应有重要意义。

Nitrogen input through dry and wet deposition into terrestrial ecosystems is increasing rapidly with ever-increasing anthropogenic activities. The underlying mechanisms of the responses of diverse terrestrial ecosystems to N deposition have been widely studied. However, most of the the previous studies simulated N deposition through N addition with just one kind of nitrogen compounds, which can not reflect the real effects of atmosphere N deposition on the structure and function of natural ecosystems, as atmosphere deposited N includes different forms of organic and inorganic N. A growing body of evidence showed that N enrichment in soil has an effect on the structure and function of soil microbial communities, but it is still unclear if the responses of soil community communities to different forms of N will be different. In this proposed project, we will evaluate the microbial community diversity and composition, and functional genes using advanced techniques including GeoChip-based analysis of the functional genes and high-throughput sequencing of the 16S rRNA and ITS2 genes. The experiment will be conducted on the field of nitrogen compound addition of meadow grassland established since 2013 in the Inner Mongolia, Furthermore, we will try to elucidate the fundamental mechanisms of responses in the microbial communities and N transformation processes driven by microorganisms to the four different forms of N with comprehensive analysis of edaphic and vegetation parameters. Results from this project will improve our understanding of the responses of belowground communities to the increasing atmospheric N deposition and will have great implications for projecting the ecological impacts of N deposition in the temperate steppe of northern China.