光合产物的分配和利用是草地植物群落适应环境条件变化的重要策略之一。降水格局变化将显著改变光合产物在不同组分之间的配置，进而影响草地碳循环。然而，关于光合产物分配，尤其是地下碳分配的研究十分有限，极大地限制了我们预测草地结构功能对未来降水格局变化响应的能力。拟通过野外原位模拟降水变化处理，研究松嫩草甸草原植被组成和生态系统气体交换对土壤水分条件改变的响应；测量13C标记光合产物在地上地下生态系统之间的分配，明晰光合产物分配的控制机制，比较分析光合产物在根系和微生物组分间分配、利用和周转；最终揭示草甸草原通过调整地下碳分配以应对水分条件改变的生态适应机制。本项目以地下碳分配为切入点，量化光合产物在生态系统不同组分间的配置和利用，阐释草甸草原地下碳分配对降水格局变化的响应及其生态适应机制。本研究将加深对草地碳循环过程及其控制机制的了解，也有助于预测草甸草原结构和功能对降水格局变化的响应和适应。

As an important component of terrestrial ecosystems, grassland ecosystem structure and functioning are very sensitive to global changes, especially variation in precipitation regimes. Allocation and utilization of photosynthates are essential components of grassland ecosystem carbon cycling; they are highly influenced by the availability of soil moisture. Moreover, carbon allocation, especially belowground carbon allocation, is an important strategy that plant communities are often imply for the adaptation to the changed environmental conditions. In the current literature, there is a knowledge gap about the allocation and utilization of recently fixed carbohydrates, especially how photosynthates being used in the underground part of the ecosystem. However, this knowledge is required for the prediction of how grassland response to predicted alteration in precipitation regimes. We proposed an in situ precipitation manipulation experiment focusing on the response of photosynthates allocation and utilization, particularly belowground carbon allocation. Vegetation composition and photosynthesis at plant and community levels will be studied to understand how vegetation structures and capacity of carbon assimilation will be affected by altered precipitation regimes. 13CO2 labelling approach will be implied to investigate photosynthates allocation between aboveground and belowground components. We will also analyze soil microbial community composition and their isotopic signature to illustrate the utilization of recently fixed carbohydrates. Root respiration and root carbohydrate pools will be characterized to demonstrate how plant adjust root activities to adapt to the altered soil moisture conditions. Overall, we aim to explore how meadow steppe dominated by Leymus chinensis respond and adapt to altered precipitation regimes from the perspective of carbon allocation, especially belowground carbon allocation. The results of the proposed study are essential for the prediction of the response of meadow steppe to future changes in precipitation patterns.