多年冻土区活动层土壤水分对不同高寒生态系统的响应

土地覆被变化对土壤水分的影响是生态水文学和流域水文学研究的关键问题，基于长江源典型多年冻土区不同高寒草地土壤水分的观测，结合降水、生物量（包括地上和地下）和土壤理化性质，研究了活动层土壤水分变化对不同高寒生态系统的响应. 结果表明：高寒草甸生物量、土壤养分含量均比高寒草原高，且对降水响应更为强烈，致使高寒草甸土壤水分变异性弱于高寒草原. 在土壤完全融化阶段，高寒草甸土壤活动层存在一个低含水层（50 cm左右）和两个相对高含水层（20 cm和120 cm），但高寒草原土壤水分在活动层剖面上有随深度逐渐增大的一致性趋势；在秋季冻结过程中，高寒草甸土冻结起始日滞后于高寒草原土3~15 d；在春季融化阶段，高寒草原土更高的含冰量需要更多的融化潜热. 此外，表层土壤中（0~20 cm），高寒草甸土比高寒草原土有更大的持水特性，而在活动层中下部则呈现完全相反的结果，不同高寒生态系统的演替改变了土壤的水热迁移过程.

Response of soil moisture within the permafrost active layer to different alpine ecosystems

The influence of vegetation change on the soil moisture is one of the key subjects in study of eco-hydrology and hydrology. In this paper, based on soil moisture in the active layer, plant biomass, soil physical and chemical properties in permafrost regions on the source regions of the Yangtze River, the response of soil moisture to different alpine ecosystems was studied. The results showed that the biomass and nutrient in the alpine meadow are higher and the response to precipitation is more intense than those in alpine steppe, which subsequently result in smaller soil moisture variability in the alpine meadow. In the soil completely thaw phase, soil moisture content is relatively lower at the depth of around 0.5 m, but higher at 0.2 m and 1.2 m depths for alpine meadow. However, the soil moisture gradually increases from the surface to the bottom of the active layer in alpine steppe. In the freezing process, the first day of alpine meadow freezing is 3-15 days' lag behind, as compared with that in alpine steppe. In the thawing process, the alpine steppe, which is rich in ice, needs more latent heat for thawing as compared with alpine meadow. Meanwhile, the water holding capacity in alpine meadow is more than that in alpine steppe in the surface layer from 0 to 0.2 m depth, but it is opposite in the middle and bottom. In conclusion, the succession of different alpine systems may change the processes of heat-moisture migration.