生物结皮影响下沙漠土壤表面凝结水的形成与变化特征

在水资源匮乏的沙漠生境,凝结水是植物、生物结皮、无脊椎和脊椎小动物的重要水分来源之一.采用微渗计法对比研究3种生物结皮类型(藻结皮、地衣结皮和苔藓结皮)和自然裸沙对地表凝结水量及凝结水蒸散过程的影响.微渗计的规格为内径6 cm,高3.5 cm的PVC管.研究结果表明:不同类型地表的总凝结水量之间存在极显著的差异(P < 0.01),总凝结水量随生物结皮发育水平呈显著增加的趋势,依次为:裸沙 < 藻结皮 < 地衣结皮 < 苔藓结皮,即生物结皮的存在有利于沙漠地表凝结水的形成.不同类型地表凝结水量的日均值有所差异.对于同一地表类型,凝结水量的最大值为最小值的数倍.黎明时,苔藓结皮的凝结水量最大,而裸沙的凝结水量最小,地衣结皮和藻结皮居中.凝结现象自20:00～22:00,次日8:00～9:00结束.大多数日出后凝结现象仍继续发生.不同类型地表的凝结及蒸散过程经历2个阶段:日出前凝结水量呈缓慢增加的趋势,日出后随温度的升高凝结水量快速减少,其中以苔藓结皮凝结水量下降最为迅速.凝结水量主要受温度、大气湿度、凝结面类型、气象条件和生境等方面因素的影响.

The influence of biological soil crusts on dew deposition and characteristics of soil surface in Gurbantunggut Desert

In desert environments, dew is an important source of moisture for plants, biological soil crusts, invertebrates and small vertebrates. In this paper, measurements were taken to investigate the effects of three different types of biological soil crusts (algae, lichen, moss) and bare sand on dew deposition, dew duration and evaporation pattern in Gurbantunggut Desert. Dew quantities were measured using micro-lysimeters with a diameter of 6 cm and a height of 3.5 cm. The results indicated that the total dew amounts of different soil surface types were significantly different (p < 0.01), it increased with the development of biological soil crusts, in the following order: sand < algae crust < lichen crust < moss crust. It can be concluded that the occurrence of biological soil crusts benefited dew deposition. Average daily dew amounts varied along with different soil surfaces. During the period of this study, for each type of crust studied, the maximum amount of dew was several times greater than the minimum. Moss crust was characterized by having the greatest amount of dew at dawn, whereas bare sand yielded the lowest amount of dew, lichen crust and algae crust exhibited intermediate values. Dew deposition began at 20:00-22:00 and ended at 8:00-9:00 the next morning. A continuous dew deposition even after sunrise was also observed. The time course of dew accumulation and drying on different soil surfaces could be divided into two parts: dew amounts increased gradually before sunrise, and after then dew amounts decreased rapidly with higher temperature. Dew deposition was mainly affected by air temperature near the surface, soil temperature, the air relative humidity and the kind of surface. The data, thus, indicated the important effect of biological soil crusts on dew formation and may assist in evaluating the significant ecological role of dew in the arid and semi-arid environments.