全球气候变化正改变着陆地生态系统的自然过程，尤其对干旱区荒漠生态系统的影响最为严重。降水的变化可以通过改变干旱区植被组成继而影响生态系统的结构和功能。了解C3和C4植物对水分变异的不同响应及适应机制对预测未来气候变化条件下C3、C4植物组成比例有重要的指导意义。本项目拟以准噶尔盆地古尔班通古特沙漠南缘不同光合途径共存C3和C4灌木为研究对象，利用稳定同位素技术，对比研究不同光合类型灌木水分来源、干旱适应特征和光合生理过程，探讨共存C3、C4灌木水分生态位特征及对土壤水分季节性变化和空间变化的响应机制。同时，结合盆栽控制试验，研究C3、C4灌木幼苗对模拟降水格局变化的光合生理响应和生长适应对策，探究降水变异对不同光合类型灌木幼苗存活的影响。拟开展研究对了解不同光合类型植物对水分变异的响应，探讨极端环境条件下荒漠植物与环境的相互关系，预测未来降水格局改变情况下荒漠植被特征有重要的理论指导意义。

Natural processes in terrestrial ecosystems, especially desert ecosystems in the arid area, are profoundly altered by human-induced global climate changes. The predicted variation in precipitation regimes (total amount, frequency and intensity) may modify structure and functioning of the desert ecosystems by changing vegetation composition. Therefore, understanding differential response and adaptation mechanisms between C3 and C4 plants to altered precipitation pattern is essential for the prediction of vegetation composition for the future precipitation regimes. For the desert ecosystems on southeast edge of Gurbantunggut desert, Tamarix ramosissima, Tamarix elongate, Reaumuria soongarica and Haloxylon ammodendron, Haloxylon persicum, Calligonum leucocladum, are the dominant C3 and C4 shrubs, respectively. We proposed a comparative study focus on differences between the two photosynthetic pathway shrubs in water sources, drought adaptation and carbon assimilation processes through the implication of stable isotope technique and other physiological measurements. The objectives are to characterize mechanisms underlying the coexistent C3 and C4 shrubs from the aspects of water utilization and adaptation. We also proposed a greenhouse precipitation intensity and frequency manipulation experiment to test the response of different photosynthetic pathway shrubs to altered precipitation patterns. Biomass, root distribution, leaf gas exchange and nonstructural carbohydrates will be measured to illustrate the underlying mechanisms of how C3 and C4 seedling adapt to variation in soil water availability. The proposed study will reveal potential difference between C3 and C4 shrubs in response to variation in water availability and underlying mechanisms, which are very important for understanding interactions between plant and environment in extremely harsh conditions. Moreover, the results of the proposed study are very useful for the prediction of desert ecosystem vegetation composition, especially composition of C3 and C4 plants, under the scenario of changed precipitation intensity and frequency.