准噶尔盆地典型C3和C4灌木对水分变异的响应及适应机理

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.

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。

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。降水格局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/C4灌木和草本植物对降水变化响应和适应机制是预测全球变化背景下生态系统结构和功能的基础。本项目沿地下水梯度选取三种灌木群落（C4群落、C3/C4混合群落、C3群落），结合不同坡位原位模拟降雨量变化处理，通过测定不同植物类型气体交换参数和碳同位素组成、水氢氧同位素组成、草本层群落特征和生物量积累、土壤理化性状等，研究共存C3和C4灌木水分来源与水分利用策略和不同坡位草本植物对降雨变化的光合响应及生长适应机理。.研究结果表明，三种群落的C3和C4灌木具有相似水分利用季节变化规律，春季土壤表层水分充足，所有灌木对表层土壤水利用比例相对增高；夏季随着土壤表层水分含量的降低，转换利用更深层的水源。但不同群落灌木之间夏季水源有所不同。不同灌木中出现两种截然不同的用水模式，即相对保守的节水型模式和碳获取最优化的用水模式。C4灌木叶片所独有的CO2浓缩机制在其采用节水模式过程中起关键作用。共存荒漠植物之间不同的水分利用模式和响应机制不仅仅是自身水碳经济的权衡过程，而是共存过程中如何选择最有利的水分资源并以最有效方式利用的综合过程。降雨量比降雨频次对草本层片特征的影响更大。减雨增雨处理均显著改变了草本层片地上生物量。沙垄不同坡位草本层片地上生产力对减雨处理的敏感性存在差异，西坡显著强于东坡。沙垄不同坡位草本层片对降水处理具有一定稳定性，体现在草本层片优势物种没有改变，以及物种多样性改变不显著。极端干旱下优势物种通过分配更多的干物质到繁殖器官，并且提高后代萌发率使得自身的优势地位保持不变。研究结果对了解不同生活型荒漠植物对水分变异的响应、探讨极端环境下荒漠植物与水分的关系，预测降水格局改变下荒漠植被特征及其生态功能有重要理论意义。

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