对青藏高原高寒草甸30%、60%和93%三种覆盖度下,多年冻土活动层的土壤水分随季节变化的观测研究,结果表明:多年冻土活动层土壤水分分布对植被覆盖变化响应强烈.年内不同时期,植被覆盖度为65%和30%的土壤表层20cm深度内水分含量及分布相似,每次降水后30%覆盖度土壤水分的变率略大于65%覆盖度的;而93%覆盖度土壤水分在年内解冻开始到冻结前均小于前两种覆盖类型;植被覆盖度越小,土壤冻结和融化响应时间越早,响应历时也越短;浅层土壤冻结和融化对植被覆盖度的响应程度较强,接近深层土壤冻结和融化对植被覆盖度的响应程度降低.覆盖度为30%和65%土壤水分在整个冻结过程的减少幅度比93%覆盖度土壤大10%～26%,而融化期水分增加幅度更大为1.5%～80%;土壤冻融的相变水量对植被覆盖度变化响应明显,植被覆盖度降低,土壤冻结和融化相变水量增大.由于受植被蒸腾与地表蒸散发和土壤温度梯度的影响,融化期土壤剖面的水分重新分配,总体上呈现水分向剖面上部和底部迁移,剖面中部60～80cm深度左右的土壤出现"干层".

Based on the analysis of soil moisture data in permafrost active layer with three vegetations in the alpine meadow of the Tibetan Plateau,the response of soil moisture in permafrost active layer to the change of vegetation is pronounced.It is found that the soil moisture distributions are similar within the depth of 20 cm in different time during the year for the vegetative coverage of 30% and 65%.After a precipitation,the change in soil moisture for vegetative coverage of 30% is slightly larger than that for vegetative coverage of 65%.The soil moisture for vegetative coverage of 93% is the lowest from the beginning of thawing to the beginning of freezing.The lower the vegetative coverage,the earlier the respond time of soil freezing and thawing,and the shorter the respond duration of soil thawing and freezing in the whole active layer.The dependence of soil thawing and freezing on vegetation will decrease with depth.The decrease of soil moisture for vegetative coverage of 30% and 65% during a freezing process is 10%~26% more than that for vegetative coverage of 93%,while the increase of soil moisture for vegetative coverage of 30% and 65% during a thawing process is 1 5%~80% more than that for vegetative coverage of 93%.The dependence of phase-change water amounts on vegetation is obvious;the lower the vegetative coverage,the more the phase-change water amounts.Soil moisture of the overall profile will redistribute,moving to the upper and bottom sectors of the active layer,and a dry sector appears in the depth range of 60~80 cm during thawing,because of transpiration by vegetation and evapotranspiration.