干旱沙区固沙植物生存的生态水文机理研究

Plant water use strategy and the adaptive mechanisms of plant survival under drought stress have always been the key issues of ecohydrology in arid desert regions. After recording more than 50 years of sand-binding vegetation succession in the Shapotou area on the southeastern edge of the Tengger Desert, the dominant species have gradually evolved from artificial woody plants into herb based natural plant communities. However, the coverage of woody plants eventually stabilized at 10% under harsh environmental conditions, such as the rainfall infiltration interception and the deep level of groundwater that cannot be used by revegetated plants. And also, some plants in the revegetated areas had gained the ability to self-regulate. Observations of these natural phenomena have inspired us to consider what are the ecohydrology mechanisms of plant survival in such a stable community of sand binding vegetation? Hence, in this study, three typical sand-fixing plants, Caragana korshinskii, Artemisia ordosica and Heaysarum scoparum were selected, based on the control experiments, stable isotopic analysis and combined with the long-term monitoring and mathematical models, the magnitude of hydraulic redistribution of soil water by plants roots, stemflow, and the foliar water uptake capacity were quantified. And then, its relationship with plant growth and transpiration were analyzed. Finally, the key eco-hydrological regulation mechanisms of plant survival and its threshold response to rainfall gradient were determined. Our goal was to provide a scientific basis for understanding plant water use mechanisms and to obtain new insights into the in the stability of vegetation and ecosystem management in revegetated desert areas.

植物对水分的利用对策及其在干旱胁迫下生存的适应机制一直是干旱区生态水文学研究的核心内容。腾格里沙漠东南缘建立的固沙植被体系经过50 余年的演变，并在降水入渗受阻和地下水不能被植物所利用的情况下，灌木的盖度始终稳定在10%左右，其稳定性维持的生态水文学机理是什么？本项目将选择沙坡头固沙植被区广泛栽植的三种（半）灌木：柠条（Caragana korshinskii）、油蒿（Artemisia ordosica）和花棒（Heaysarum scoparum）为研究对象，以控制试验和同位素示踪为主，结合长期定位监测和数学模型方法，量化不同固沙植物根系水力再分配、树干径流和叶片吸水的存在性、发生时间、数量特征及其与植物蒸腾和生长的关系，揭示影响典型固沙植物生存的关键生态水文调控机制及其对降水的响应阈值，为干旱沙区植被恢复与重建后的植被稳定性及其变化趋势评价提供理论依据。

植物对水分的利用对策及其在干旱胁迫下生存的适应机制一直是干旱区生态水文学研究的核心内容。腾格里沙漠东南缘建立的固沙植被体系经过60 余年的演变，并在降水入渗受阻和地下水不能被植物所利用的情况下，灌木的盖度始终稳定在10%左右，其稳定性维持的生态水文学机理是什么？为此，本项目选择沙坡头固沙植被区广泛栽植的三种植物：柠条、油蒿和花棒为研究对象，以长期定位监测、控制实验、同位素示踪和模型模拟等方法，量化了三种植物的根系水力再分配、树干径流和叶片吸水的存在性、发生时间、数量特征及其与植物蒸腾和生长的关系，确定了影响典型固沙植物生存的关键生态水文调控机制及其对降水的响应阈值。结果表明：三种典型的荒漠植物柠条、油蒿和花棒的叶片均具有吸收水分的能力，其单位面积叶片吸水量分别在3.032-11.025、5.869-24.765、3.333-24.899 mg•cm-2之间变化。三种植物群落叶片水分吸收的能力达到300-800 g/m2，相当于同期降雨量0.3-0.8mm。柠条、油蒿和花棒的水力再分配在0.01-0.18，0.01-0.05和0.02-0.25 mm/d 之间变化，平均值分别为0.08、0.03 和 0.11 mm/d。水力再分配贡献率与蒸腾速率呈显著对数相关关系。以干旱沙区植物生存的生态水文学机理作为目标层，根系水力再分配（U1）、树干径流（U2）、叶片吸水（U3）3为准则层建立了干旱沙区植物生存的综合评价层次结构模型。通过分析，我们确定降水、土壤水分、植物凌晨水势和植物冠层结构为影响干旱沙区植被水分利用的主要环境因子。并确定了U1、U2和U3所占的比例分别为38.76%，44.36%和16.88%。当单次降水量在0-1 mm时，植物适应干旱的主要对策为叶片吸水；而当降水量在1-5 mm之间变化时，树干径流起主要作用；当降水量大于5mm时，根土界面的水力再分配是植物适应干旱的主要对策。本研究结果将加深我们对荒漠生态系统不同功能型物种利用水资源方式和策略的理解，为干旱沙区植被恢复与重建后的植被稳定性及其变化趋势评价提供理论依据。