毛乌素沙地依赖地下水的旱柳水分胁迫恢复期用水来源

Groundwater-Dependent Plants (GDP) are widely distributed in arid regions that would suffer water stress after groundwater pumping. However, the sources of plant water use during recovery periods are unclear, which hinders the study on the mechanism of water stress recovery. In the groundwater and ecology experimental field station of MLR, willows, a widely distributed GDP in the Muus sandland, are subject to water stress triggered by continuous groundwater pumping. During pumping, sap flow of stem and roots, soil moisture and potential and water table were monitored, and isotopic compositions of xylem water, soil moisture and groundwater were analyzed. The indicator of full recovery will be identified through the comparison of sap flow between the stressed and unstressed willows. Based on the isotopic compositions of water bodies, water sources during recovery periods will be determined using a linear multiple source model and the role of rainfall played to water stress mitigation will be studied as well as the difference of water sources before and after rainfall. Sap flow variations of main and lateral roots will be analyzed to quantitatively assess the role of hydraulic lift to water stress recovery in combination of soil moisture and soil potential data. Quantitative assessment of the contribution of soil water and groundwater to water stress recovery and the exploration of water stress recovery mechanism by this study will lay a theoretical basis for the harmonious co-existence between human and nature.

旱区广泛分布依赖地下水的植物，地下水开采会导致其受到水分胁迫，对于胁迫恢复期植物用水来源尚不清楚，阻碍了对水力胁迫恢复机制的揭示。本申请选取毛乌素沙地广泛分布的依赖地下水的旱柳为研究对象，依托国土资源部地下水与生态野外试验站，通过连续抽水使旱柳遭受水分胁迫，开展树干（根）液流、土壤水分（势）和地下水动态观测，分析植物水、土壤水和地下水的氢氧稳定同位素组分；通过对比受水分胁迫和未受胁迫旱柳的树干液流，建立植物完全恢复的标识；根据不同水体的同位素特征，利用多源线性混合模型厘定胁迫恢复期的水分来源，揭示降雨前后水分来源的差异，查明降雨对植物水分胁迫消除的作用机制；分析夜间主根、侧根液流的变化特征，结合不同深度土壤水分（势）的动态变化，定量评价水力提升在植物水分胁迫恢复中发挥的作用。本研究将定量确定土壤水、地下水对水分胁迫恢复的贡献，探讨水分胁迫恢复机制，为实现人与自然的和谐共生提供理论依据。

旱区广泛分布着依赖地下水的植物，地下水开采会导致其受到水分胁迫，对于胁迫恢复期植物用水来源尚不清楚，阻碍了对水力胁迫恢复机制的揭示。本项目以毛乌素沙地为研究区，综合采用野外试验和同位素技术相结合的方法，定量分析了旱柳水分胁迫后恢复期消耗水分来源；确定了土壤水、地下水对旱柳水分胁迫恢复的优先等级。首先利用分析大气降水、土壤水、地下水以及旱柳枝干水分等氢氧稳定同位素特征的方法，总结形成水分胁迫恢复期植物的用水策略和机制；其次，开展了基于人工抽水的依赖地下水植物水分胁迫与消除实验研究；在此基础上，建立了系统动力学的植物水分胁迫与消除数学模拟模型；最后结合气象要素、旱柳树干液流、地下水位动态特征，借助土壤水总水头分布规律，分析了土壤水水力提升在植被水分胁迫恢复中发挥的作用。研究结果表明：可以将树干液流强度的变幅作为分析旱柳受到水分胁迫完全恢复的判识标识；旱柳生长的适生水位是2-4m，胁迫水位是5m；结合树干液流、气象要素、地下水位，综合分析了旱柳根系耗水影响下土壤水分运移的动力学过程；通过分析土壤水分、旱柳树干水分、地下水以及大气降水的氢氧稳定同位素特征，结合土壤水分总水头分布图，综合分析得出旱柳在受到水分胁迫后恢复过程中，优先消耗大气降水，然后才是土壤水，在地下水位达到水分胁迫水位以浅时，旱柳根系迅速转换为吸收地下水。项目的研究确定了旱柳在受到水分胁迫后恢复期用水来源，探讨了旱柳生长水分胁迫的恢复机制。该成果对于指导旱区植被生态恢复，实现水与生态的和谐发展具有重要的理论和实践价值。