碳氮循环作为草原生态系统最基本的生态过程，调节和维持着生态系统生产力与稳定性。氮沉降增加作为全球变化的重要现象之一，其对草原生态系统碳氮循环的影响和反馈存在诸多不确定性。土壤微生物是碳氮循环过程的主要驱动力。研究土壤碳氮转化特征及其与微生物耦合关系是揭示这些不确定性，提高草原土壤碳积累，减少氮素损失的科学基础。本项目在内蒙古贝加尔针茅草原，设置模拟氮沉降野外控制试验，基于稳定性同位素技术和分子生物学方法，研究氮沉降增加背景下贝加尔针茅草原植物-土壤-微生物碳氮积累、分配格局和生态计量动态变化特征，以及土壤微生物群落及其介导碳氮循环的关键功能群结构和多样性演替规律，阐明草原植物-土壤-微生物碳氮转化特征与土壤微生物群落演替的耦合关系，为揭示氮沉降背景下草原土壤碳氮转化演变规律及其微生物学机制，全面分析和评估全球变化对草原生态系统的影响，以及为草地生物多样性保护和退化草地恢复提供科学依据。

Carbon and nitrogen cycles of grassland ecosystem, as the basic ecological processes, regulate and maintain ecosystem productivity and stability. Soil microbe is the main driving force of soil carbon and nitrogen cycling process. Enhanced atmospheric nitrogen deposition is one of the most important phenomena of global change, but its effect on the carbon and nitrogen cycles and their feedback in grassland ecosystem remains uncertain. Studying the coupling relationship between soil carbon/nitrogen transformation and microbial community succession is essential to reveal these uncertainties, and would provide scientific basis for improving the soil carbon accumulation and reducing the nitrogen losses. A field control experiment to simulate nitrogen deposition would be implemented in Inner Mongolia Stipa baicalensis steppe. Using stable isotope and molecular biology technologies, we would reveal the characteristics of organic carbon and nitrogen reserves, distribution patterns and ecological stoichiometry from plant-soil-microbes system. Meanwhile, the changes of soil microbial community and the main related functional groups responding to carbon and nitrogen transformation and their succession regulation would be explored in this project. This study would reveal the coupling relationship between soil carbon-nitrogen transformation and microbial community succession, and then provide a theoretical basis for the analysis and evaluation of global change effects on grassland ecosystem, and provide scientific basis for the reasonable utilization of grassland, the biodiversity conservation and the restoration of degraded grassland.