松嫩草甸草原生产力干旱敏感性及其光合生理机制

As a result of rising atmospheric temperature associated intensification in global water cycle, frequent and intensified drought is predicted for the future. Drought may profoundly alter carbon cycling and plant community productivity, and eventually influence ecosystem service. As a water-prone vegetation type, grassland is very sensitive to altered precipitation regime associated fluctuation in soil water availability. Grassland vegetation composition, ecosystem carbon exchange and productivity are extremely vulnerable to extreme climate events, such as drought. Drought sensitivity of grassland vegetation structure and ecosystem processes and underlying mechanisms are poorly understood which impede the ability to predict potential drought impacts on ecosystem service. Through the combination of field drought manipulation and greenhouse pot water manipulation experiments, the proposed study aims to understand drought sensitivity of ecosystem structure and functions of Songnen meadow steppe focusing on ecosystem carbon exchange and productivity. For the in situ field study, drought treatments, including short-term drought and long-term rainfall reduction, will be imposed by the installation of high light permeability roof. Soil water content, leaf photosynthesis, ecosystem carbon exchange, vegetation composition and productivity during the drought period and rehydration period will be measured to quantify drought sensitivity of these key ecosystem structure and processes. Moreover, a pot experiment will be conducted to assess plant functional type differences in leaf photosynthesis drought response and quantify stomatal limitation and enzymatic limitation on leaf carbon assimilation. By the integration of measurements from leaf photosynthesis, ecosystem carbon exchange, vegetation composition, belowground and aboveground productivity, we hope to systematically assess drought response and adaptation of the meadow steppe in the Songnen Plain. Results of the proposed study are also valuable for the prediction of drought impacts on grassland vegetation composition and productivity and development of adaptive ecosystem management policies.

气候模型预测干旱频率和强度呈增加态势，将改变碳循环过程和植物群落生产力形成，最终影响生态系统服务功能。草地生产力对不同类型干旱扰动的抵抗力稳定性和恢复力稳定性存在差异，其光合生理机制尚不明晰。了解草地生产力干旱响应过程，从个体和群体水平揭示生产力干旱敏感性的光合生理机制，是构建模型预测干旱影响的基础。以松嫩草甸草原为研究对象，利用高透光率遮雨棚模拟不同强度短期干旱和长期降水减少，测量干旱期间及干旱胁迫解除后优势种叶片光合、生态系统碳交换、地上地下生产力和群落组成，量化草甸草原碳交换过程和生产力对干旱的敏感性。通过温室盆栽控水实验，研究不同干旱程度下松嫩草地不同功能群牧草光合固碳限制机制。本研究希望通过整合个体光合生理-群落物种组成-生态系统碳交换测量，系统性揭示松嫩草甸草原生产力对干旱的敏感性及其光合生理机制，为极端气候事件增加条件下草地结构和功能预测及适应性管理提供实验数据支持。

气候模型预测干旱频率和强度呈增加态势，将改变碳循环过程和生产力形成，最终影响生态系统服务功能。草地生产力对不同类型干旱扰动的抵抗力稳定性和恢复力稳定性存在差异，其光合生理机制尚不明晰。了解草地生产力干旱响应过程，从个体和群体水平揭示生产力干旱敏感性的光合生理机制，是构建模型预测干旱影响的基础。. 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，系统且深入地从个体-群体-生态系统多个层次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。不同功能群植物对干旱的响应和适应存在显著差异，C4牧草在遭受重度干旱胁迫后，其光合恢复过程长于C3植物。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。氮添加和干旱共同作用下，叶片呼吸碳损失占比显著增加，是导致生物量降低的主要原因。. 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。

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