基于稳定同位素的西南岩溶区典型生态系统水分耗散规律研究

The karst area of Southwest China is one of the typical vulnerable areas of China, and it is suffering enhancing pressure of water resource shortage in the context of climate change and human activities in the case of ecosystem degradation and karst desertification. Water is one of the most important environmental limiting factors in plant growing and ecological construction in this area. As a result, it is of significance to reveal the patterns of water transport and exchange within typical karst ecosystems. This study will do systematic monitoring of environmental and plant stable isotopes to reveal water transport and exchange characteristics of a field (orchard) and a secondary shrub karst ecosystem in Chongqing. To assess how water uptake, stomatal conductance and water use efficiency of plants response to water availability, this study will monitor and analyze the variability of hydrogen and oxygen stable isotopes of precipitation, epikarst water, soil water, xylem water of plants and oxygen and carbon stable isotopes of bulk leaf of plants. Combining the stable isotopes of surface vapor, this study will partition the evapotranspiration and reveal the seasonality of evaporation and transpiration of each individual ecosystem. Based on the isotopic, atmospheric and soil data, this study would also do the quantitative partition of the components of water cycle in such two ecosystems using the stable isotopic and eddy covariance techniques. The results of this study would benefit our understanding of the water cycle characteristics of karst ecosystems and provide useful information for water management in karst areas of Southwest China.

西南岩溶区是我国典型的生态脆弱区，在气候变化和人类活动增强的背景下，地表可有效利用水资源愈加缺乏、生态退化和石漠化加剧，水分是岩溶区植物生长和开展生态建设的重要限制因子。在西南岩溶区选择典型生态系统进行水分耗散规律研究具有重要意义。本项目拟针对岩溶区农田（园地）和次生灌丛典型生态系统进行综合的稳定同位素监测研究。通过开展降水、表层岩溶水、土壤水、植物木质部水氢氧稳定同位素和叶片氧、碳稳定同位素监测，从植物水分利用、叶片气孔导度和水分利用效率方面阐明主要植物对环境水分变化的适应机制；结合地表水汽稳定同位素监测，揭示地表蒸散水汽组成结构基本特征及其季节变化规律；在此基础上，利用同位素质量守恒、水量平衡原理和涡度相关技术，实现生态系统水循环通量的定量区分。该项目有助于深入认识岩溶区水循环规律，为岩溶生态系统水资源优化管理提供理论依据。

西南岩溶区生态脆弱，水分是这一地区植物生长和开展生态建设的重要限制因子，研究西南岩溶生态系统水分耗散规律显得尤为重要。本研究在西南典型岩溶槽谷开展了系统的降水、表层岩溶水、土壤水、植物木质部水、叶片水和水汽氢氧稳定同位素、叶片碳稳定同位素综合监测研究。结果表明：1）阔叶灌木、阔叶乔木和针叶乔木树种具有不同的水分利用模式，其对表层土壤水、深层土壤水和表层岩溶水的依赖性依次逐渐增强，对应着从强到弱的环境水分胁迫；2）阔叶树种叶片水分利用效率主要受环境水分、大气湿度和叶片功能性状（如比叶面积）等综合影响，且浅根系植物更为显著，而针叶树种叶片水分利用效率则主要受环境水分、大气温度和叶片气孔行为等综合影响，阔叶和针叶树种叶片气孔行为都与大气温度（尤其是露点）具有显著相关性；3）基于稳定同位素方法的地表蒸散发分割表明，研究区植物蒸腾水汽在蒸散水汽中所占的比例（T/ET）平均值为81.4%，在夏季最低（76.2%）而春季最高（89.1%），饱和水气压差（VPD）是影响T/ET最重要的环境气象因子。该研究深化了对西南岩溶湿润区植物环境水分适应性的理解，增强了对西南岩溶生态系统水循环规律的认识，可以为西南岩溶生态系统生态建设提供理论依据。