草地生态系统碳库绝大部分分布在地下。根系是草地重要的碳汇、也是土壤有机碳的主要来源，由于测量方法限制，草地生态系统地下碳过程知之甚少,迫切需要开展深入研究。放牧是影响草地物质生产和碳循环的关键人为因素，明确放牧活动对草原生态系统碳库的影响，对全面理解我国陆地生态系统碳循环具有重要意义。 温性草甸草原是第一性生产力及土壤碳密度最高的温性草原类型。本项目依托呼伦贝尔草原生态系统国家重点野外实验站，基于大型草地放牧控制实验平台，利用稳定性同位素技术，研究不同放牧强度下草甸草原生物量分配、地下生物碳输入及碳素分解转移特征，探索草甸草原生物量碳与土壤碳之间的转化规律，建立稳定性同位素在地下碳素流动过程中的递减模型（碳素转化模型），揭示草甸草原生态系统地下碳库对放牧干扰的综合响应机理。不仅有助于全面理解放牧干扰下草原植被碳库的源汇机制，同时为草地放牧生态系统的有效管理提供基础依据和理论启示。

More than 80% of the grassland ecosystem's carbon distributes underground. The roots are important carbon sinks and mineral nutrient pools of grassland, and moreover, the main source of soil organic carbon(SOC). However, below-ground carbon process are poorly understood due to the restrictions of measurement methods and there is an urgent need for further research. Grazing is one of the major factors that control the net primary productivity(NPP) and carbon cycle of grassland ecosystem. The objective of this project, with new and more comprehensive methods and dataset, is to draw a better and conclusive understanding of the impact of grazing intensity on underground carbon dynamics of grassland ecosystem. In this study we selected temperate meadow steppe, which has the highest NPP and SOC in all temperate grassland types, to achieve the above specific objective. The research will be conducted in Hulun Buir, where the Huluner Grassland Ecosystem Research Station located. The station had built a grazing experiment platform in 2008, and carried out continuous observation during 2009-2013 to quantify the impact of six grazing gradients on grassland biodiversity, above- and below- ground biomass, carbon and nitrogen cycle, soil features and microbial properties. These studies raised new scientific issues which will be focused in this study. To address these scientific issues, we will adopt stable isotope techniques and in-growth soil core methods to explore the root biomass allocation, root carbon input, death and decomposition under different grazing intensity, to trace the underground carbon flow from root to soil carbon pool, to develop a carbon transfermation model to describe the diminishing of stable isotope C in underground carbon process, and to reveal the potential mechanism for response of grassland ecosystem carbon budget to grazing disturbance . The result will helpful for fully understanding of China's terrestrial ecosystem carbon cycle, and provide comprehensive knowledge for effective management of grazing ecosystems.