草地是全球碳循环的重要组分。放牧是天然草地最主要的利用方式，并影响草地碳循环。稳定碳同位素技术是研究生态系统光合作用与碳循环生态学过程的有效工具。项目选取内蒙古荒漠草原，进行放牧与围封的处理，同时在放牧样地栽培羊草（C3）和糙隐子草（C4）并做碳同位素标记试验，分析研究放牧对内蒙古荒漠草原植物群落不同功能群及其标记的典型植物叶片、茎部、根系、凋落物、根际土及土壤呼吸气体的稳定碳同位素比值（δ13C）的动态变化，量化荒漠草原系统光合产物在不同环节的分配比例及其对放牧的响应，探讨放牧强度引起荒漠草原地上与地下部碳同位素变化的分馏机制及草原土壤碳动态变化过程和调控机制，为草原退化监测、恢复和重建提供新的微观指标和新思路。对于深入认识草地生态系统碳循环过程和准确估算全球碳平衡有着重要意义。

Grassland is an important component of the global carbon cycle. Grazing is the most important use of natural grassland and affects the grassland carbon cycle. Stable carbon isotope techniques are effective tools for studying ecosystem photosynthesis and ecology processes of carbon cycle. This project will conduct in Inner Mongolia desert steppe with four treatments grazing and no grazing and at the same time cultivate Leymus chinensis (C3) and Cleistogenes squarrosa (C4) in the grazing plot and conducte carbon isotope labeling tests to analyze the effect of grazing intensities on dynamic changes of stable carbon isotope ratios (δ13C) of different functional groups of plant communities and of two typical plants leaves, stems, roots, litter, rhizosphere soil and soil respiration gas, we will quantify the distribution of photosynthetic products of different links on desert steppe system and its response to grazing, we will explore the fractionation mechanism of carbon isotope changes in the aboveground and belowground parts of desert steppe and the dynamic process and regulation mechanism of soil carbon in grassland, which would provide new micro-indicators and new ideas for grassland degradation monitoring, restoration and reconstruction. It is of great significance for understanding the carbon cycle of grassland ecosystems and accurately estimating global carbon balance.