松嫩草地主要C3和C4植物对水分变异的光合生理响应及生长适应对策

Global climate changes, especially changes in precipitation regime, influence ecosystem processes and functioning in arid and semiarid regions through affecting ratios of different plant functional groups (C3 vs C4) in the vegetation composition. Thus, it is important to understand sensitivity of C3 and C4 plants to water availability and variability as well as their growth adaptation and underlying photosynthetic physiological mechanisms for the purpose of predicting the contribution of plant functional group differed in photosynthetic pathways to the vegetation under future variation in precipitation regime..We proposed a water manipulation (intensity and frequency) experiment to test whether there are differences between C3 and C4 plants in response to water variability using co-ocurring C3 and C4 grasses in the Songnen grassland. To further explore growth adaptation of these grasses differed in photosynthetic pathway, we will measure the allocation of accumulated biomass among different organs. We also attempt to understand the plasticity of leaf functional traits (size and density of stomata and leaf cross-sectional anatomy) and their response to variation in plant water conditions. Overall, we hope to elucidate differences in the underlying photosynthetic physiological mechanisms between C3 and C4 plants in response to water availability and variability through measuring leaf gas exchange, chlorophyll fluorescence, the activity of photosynthetic enzymes and the efficiency of CO2 concentrating mechanisms (C4 species). The results of the proposed study will provide experimental data for the prediction of the vegetation composition of the grasslands in the Northern China under the future precipitation regime.

全球气候变化，尤其是降水格局变化，可能通过改变干旱半干旱区植被中不同功能群植物（如C3 vs C4）组成而影响生态系统过程和功能。预测未来降水格局变化条件下植被中C3和C4植物比率，需要了解C3和C4植物对水分变异的敏感性及其生长适应和光合生理机制。.拟通过模拟降水数量和频率变化，研究松嫩草地共存C3和C4禾本科植物光合速率、生长速率、水分利用效率对水分变异的敏感性；通过测量不同器官生物量比率，从分配计量角度阐述C3和C4植物对水分变异的生长适应；通过观察叶片特征和超微结构，来了解C3和C4植物叶片结构的可塑性和对水分变异的适应；最后，利用气体交换和叶绿素荧光测量及稳定性同位素分析来明确光合的限制性因子，并通过测定酶活性、光化学效率和C4植物CO2富集机制效率揭示不同光合途径植物对水分变异敏感性的光合生理机制；最终为未来降水格局变化条件下，预测中国北方草地植被类型组成变异提供试验数据支持。

全球气候变化，尤其是降水格局变化，可能通过改变干旱半干旱区植被中不同功能群植物（如C3 vs C4）组成而影响生态系统过程和功能。预测未来降水格局变化条件下植被中C3和C4植物比率及草地生态系统服务功能改变，需要了解C3和C4植物对水分变异的敏感性及其生长适应和光合生理机制。. 本项目从草地植物光合途径差异入手，以未来全球变化中关键因素（降水格局改变）为实验处理，利用盆栽控制实验、稳定性同位素技术结合光合气体交换测量、碳代谢关键生理过程及酶活性测量，研究了松嫩草地代表性C3和C4禾草对降水格局变化的响应和适应机制。发现降水格局变化能够显著影响不同光合途径植物生物量积累，也能够改变不同光合途径牧草竞争格局。两种光合途径牧草生物量积累不仅受模拟降雨量变化影响，在低降雨量处理下，模拟降水频率变化能够显著改变生物量形成和生物量分配。不同光合途径牧草均能够调整光合产物在地上和地下的分配来适应土壤水分条件变化。此外，C3和C4禾草对干旱适应机制存在差异，C3禾草通过调控气孔导度来有效利用水分，复水后能够快速恢复光合固碳能力；而C4禾草受干旱胁迫后，气孔恢复较慢，表明其碳代谢主要受酶损伤等其它生理过程影响，复水后恢复较慢。C4禾草叶片解剖结构受环境条件变化影响，但是C4禾草能够调整叶肉细胞C4循环（C4 cycle）和维管束鞘细胞C3循环（C3 cycle），维持一定的CO2富集机制效率，适应环境变化。不同种C4禾草在维持CO2富集机制效率能力上存在差异，与其光合系统I产能和叶绿体排布（chloroplast movement）调节能力有关系。. 研究结果不仅揭示了松嫩草地不同光合途径植物对模拟降水格局变化的响应和适应机制，增进了关于C3和C4禾草对未来环境变化的适应策略的了解。有助于预测全球变化，尤其是降水格局变化条件下，中国北方草地，特别是松嫩草地植被组成变化和生产力形成，进而制定草地优化利用政策。