荒漠绿洲湿地凝结水形成特征及其生态作用

The dew formation and its ecological role have been paid much attention for a long time. Although the wetland is an important part of the desert-oasis ecosystem and has a unique microclimate characteristic in the desert climate, little research has been conducted to explore the dew formation characteristics and its ecological effects in desert-oasis wetland. As such, the proposed project will substantially contribute to solving those issues that the dew formation characteristics and its ecological effects in desert-oasis wetland ecosystem are now confronted, through field observations, control experiments and model simulation, combined with stable isotope and eddy correlation techniques depending on Linze Inland River Research Station, CERN as the field basement. There are three major concerns included in this project: 1) the formation processes of dew and its quantitative characteristics in desert-oasis wetland; 2) construction of mathematical model to evaluate dew amounts and simulation of the dew formation processes; 3) Mechanism of plant absorption and utilization and its water physiological response process to dew. Through our investigation, the threshold of the key meteorological factors will be determined when the dew occurs. The effects of the soil moisture on dew formation characteristics will be revealed. The relative contribution of dew to the total water utilization of dominant plants will be quantified and its effects on the plant community water balance will be estimated in desert-oasis wetland. The study will make for clearer understanding of the dew formation processes in the unique microclimate of desert-oasis wetland, and enrich the research content of dew in arid regions, as well as deepen the knowledge of the dew formation rules and its ecological roles.

干旱区凝结水的形成与作用研究得到了长期关注，湿地作为荒漠绿洲的重要组成部分，在荒漠气候背景下具有独特的小气候特征，但有关荒漠绿洲湿地凝结水的形成特征及其生态作用研究一直未给予重视。本项目以中国生态系统研究网络临泽内陆河流域研究站为依托，在河西走廊中部的荒漠绿洲区选择湿地观测场，采用野外定位观测、实验模拟、稳定同位素和涡动相关等技术，研究绿洲湿地土壤凝结水和冠层凝结水的发生规律及其关系，建立凝结水定量评估的方法，分析植物对凝结水的吸收利用机制及其水分生理响应过程。旨在确定凝结水发生的气象条件和关键气象要素的阈值，揭示土壤湿度对凝结水形成的影响，量化凝结水对绿洲湿地优势植物水分利用的贡献及其对绿洲湿地植物群落水量平衡的贡献，弥补荒漠绿洲湿地独特小气候条件下凝结水形成的知识缺陷，丰富干旱区凝结水的研究内容，加深对凝结水发生规律及其生态作用的认识。

凝结水是干旱区生态系统重要的水分补给来源，对于维持生态系统功能具有重要意义。荒漠绿洲湿地、砾质荒漠和沙质荒漠是荒漠绿洲生态系统的重要组成部分，不同微生境具有不同的小气候特征，不同小气候特征下凝结水形成特征、持续时间和生态作用可能各不相同。本项目以中国生态系统研究网络临泽站为依托，在甘肃河西走廊中部的荒漠绿洲区选择湿地、砾质荒漠和沙质荒漠观测场，开展了土壤凝结水形成规律；凝结水形成与关键气象因子间的关系；凝结水生态作用评估等研究。项目采用野外定位观测、实验模拟和稳定同位素等技术揭示了荒漠绿洲区不同生境凝结水形成特征，确定了凝结水发生的气象条件和关键气象要素的阈值，分析了典型植物水分生理对凝结水的响应，阐明了不同演替阶段人工固沙植被灌丛对凝结水形成的影响，初步评估了荒漠绿洲区凝结水的生态水文效应。研究发现，水分吸附过程是荒漠绿洲区凝结水形成的主要方式，凝结水主要发生在0-5cm的土壤层。植物生长季凝结水发生频率高，＞0.03 mm的日凝结量天数占整个凝结水发生天数的82 %。荒漠绿洲区沙质荒漠、砾质荒漠和绿洲湿地的生长季凝结水累积量占同期降水的16.7 %、6.6 %和32 %。近地面空气相对湿度、近地面气温、表层低温、气-地温差、气温-露点温差、风力都是影响凝结水形成的关键气象因子。沙质荒漠和砾质荒漠凝结水形成的平均相对湿度分别为50 %以上和30 %以上，风速阈值分别为＜4.3m/s和＜5.47m/s。不同演替阶段植被灌丛拦截了大气中的水汽输送，植被灌丛越大，其下土壤表层凝结水形成越难。在长期干旱条件下，凝结水的发生可以提高植物的水分状况和光合能力，其在改善植物长期生存在干旱环境中的不利影响方面发挥重要的作用。植物叶片吸收凝结水的能力与叶片本身的结构有关。本研究丰富了干旱区凝结水的研究内容，加深了对凝结水发生规律及其生态作用的认识。