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

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.

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。

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对未来降水格局变化响应的能力。. 本项目结合野外原位模拟降雨量变化处理和盆栽控制实验，利用稳定性13C标记技术以及光合生理等常规植物生理生态学研究方法，系统且深入地研究了羊草草甸草原光合固碳过程，光合产物地上地下分配和地下光合产物分配利用策略。研究结果表明，野外原位模拟降雨变化处理显著影响土壤含水量和地上生物量，但未显著改变物种多样性、物种均匀度指数、物种丰富度等植被特征。降雨变化处理显著影响生态系统CO2交换，羊草草甸草原主要碳固定时期集中在生长季早期。干旱对羊草草甸草原地上生产力影响随干旱胁迫强度的增加呈现指数形式增长，氮添加加剧了羊草草甸草原地上生物量的干旱敏感性；然而，羊草草甸草原具有很强的干旱影响恢复能力，60天连续干旱处理第2年地上生物量得到全面恢复。干旱处理显著影响光合产物在地上和地下分配，随着干旱强度的增加，地下碳分配逐渐增加，根冠比逐渐增大；此外，地下根分布也发生变化，10-30 cm深根占比随土壤水分亏缺加剧而逐渐增加。羊草能够通过与菌根真菌共生，增强干旱响应和适应能力；菌根真菌对植物干旱抵抗力在不同光合途径植物之间存在差异，C3植物羊草受益程度大于C4植物牛鞭草。稳定性13C标记实验结果表明干旱处理增加地下光合产物分配比例。同时，干旱导致呼吸速率的降低。. 通过整合分析干旱胁迫条件下植物叶片光合生理特征、植物群落组成、生态系统气体交换、地上地下光合产物分配和地下光合产物分配利用，发现羊草采用多重策略适应干旱胁迫，揭示了羊草草甸草原适应降水格局变化的生态学机制，为未来降水变化背景下羊草草甸草原结构和功能预测奠定了理论基础。