土壤水分是连接气候变化和植被覆盖动态的关键因子,以长江源区北麓河一级支流左冒西孔曲典型小流域为研究对象,通过观测降水特征、植被覆盖情况、土壤特性、土壤水分变化、入渗过程以及蒸散发和凝结,分析了不同植被覆盖下土壤水分变化与降水之间的响应关系.结果表明:研究区内高寒草甸土壤水分对降水的响应存在十分明显的滞后现象,滞后时间较长;当植被退化较为严重时,20 cm深度范围内土壤水分对降水有一定响应,深层土壤比较干燥,对降水的响应微弱;在保持其原有植物建群和较高覆盖度时,土壤持水能力增强,深层土壤含水量明显提高,土壤水分变化剧烈,对降水的响应深度达到40 cm以下.较高的植被覆盖能有效改善土壤物理结构、提高土壤有机质含量,促进降水入渗.植物根系导致的较大孔隙优先流运动以及根系吸水作用影响了土壤水分对降水的响应和土壤水分的空间分布.不同植被覆盖度下,土壤水分的蒸散发与凝结具有明显差异,高覆盖度的高寒草甸土壤,蒸散发量较小,凝结水量较大.

Soil moisture connects climate change dynamic. In this paper, is the key factor which and vegetation coverage the typical catchment of Zuomaoxikongqu in the headwaters of the Yangtze River was taken as an example. Based on the observations of precipitation, vegetation coverage, soil moisture,infiltration, evapotranspiration and condensation, the relationship is analyzed between soil moisture and precipitation under different vegetation coverage conditions. The study indicates that there is a significant delayed response of soil moisture to precipitation under different vegetation coverage,with a long lag time. When the vegetation degradation is seriously, soil moisture within the depth of 20 cm responds to precipitation to a certain extent,while in the deeper soil layer, which is rather dry, the response is insignificant. When the original plant community is kept with a higher coverage, the water retention ability would be enhanced, and the soil moisture content in deeper layers has been greatly improved. The depth, at which the change of soil moisture is distinct with soil moisture response to precipitation, is deeper than 40 cm. Higher vegetation coverage can improve the physical and chemical characteristics of soil, with an accelerated water infiltration. The plant roots influence the response of soil moisture to precipitation, because of preferential flow and water-absorption caused by plant roots. There ex- ists a big difference in surface evapotranspiration and condensation under different vegetation coverage. Alpine meadow with high vegetation coverage has an apparent effect of reducing evapotranspiration and increasing condensate water.