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。

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.