青藏高原风火山流域坡面尺度活动层土壤水热时空变化特征

以风火山流域某阴坡坡顶、 坡底和阳坡坡底活动层土壤水热及气象资料为基础， 对青藏高原多年冻土区不同地形条件下的土壤水热时空变化特征进行了分析。结果表明： 在融化阶段， 除表层5 cm外， 阴坡坡底各深度土壤开始融化日期均比坡顶早， 比阳坡坡底晚； 阴坡坡脚各深度土壤含水量均大于坡顶和阳坡坡底。在冻结阶段， 开始冻结日期在阴坡坡底均比坡顶早， 但比阳坡坡底晚； 阴坡坡底各深度土壤含水量均高于坡顶相应土层的含水量， 在20 cm、 100 cm、 160 cm深处高于阳坡相应土层的含水量， 但在5 cm、 50 cm深处， 稳定冻结后两者的含水量差异较小。在整个冻融过程中， 阴坡坡底土壤温度对气温变化的响应弱于坡顶及阳坡坡底， 但其土壤水分对降水的响应强于坡顶及阳坡坡底。植被生长发育受水分和热量条件的制约， 不同地形条件下水热时空变化差异将影响植被空间分布特征。在未来气候变暖情况下， 上坡位植被可能因为水分胁迫而退化， 出现荒漠化现象， 而下坡位由于受侧向流的影响， 土壤水分对降水的响应强烈， 植被不会发生显著退化； 在不同坡向之间， 同一坡位阳坡植被退化程度可能大于阴坡。

Spatiotemporal variation characteristics of soil water content and temperature within active layer at slope scale in the Fenghuoshan basin， Tibetan Plateau

Based on the soil hydrothermal and meteorological data on top as well as bottom of the shady slope and bottom of the sunny slope on a slope of the Fenghuoshan basin， Tibetan Plateau， the spatial and temporal variability of soil water content and temperature under different topographic conditions were analyzed. The results show that in the thaw period， below the depth of 5 cm， the starting date of soil thawing on bottom of the shady slope was earlier than that on top of the slope， but was lagged to that on bottom of the sunny slope. The soil water content on bottom of the shady slope was higher than that on top of the shady slope and bottom of the sunny slope. In the freezing period， the starting date of soil freezing at all depths on bottom of the shady slope was earlier than that on top of the slope， but lagged to that on bottom of the sunny slope. The soil water content on bottom of the shady slope was higher than that in the corresponding soil layer on top of the shady slope， and at depths of 20 cm， 100 cm and 160 cm it was higher than that in the corresponding soil layer on the sunny slope， but at depths of 5 cm and 50 cm， the difference between the two was small after stable freezing. In the whole freezing-thawing process， the response of soil temperature on bottom of the shady slope to temperature change was weaker than that on top of the shady slope and bottom of the sunny slope， but the response of water content to rainfall was stronger than that on top of the shady slope and bottom of the sunny slope. Since vegetation growth and development is dependent on soil water content and temperature condition， the spatial and temporal variability of soil water content and temperature under different topographic conditions will affect the spatial distribution characteristics of vegetation. In the case of future climate warming， the vegetation on slope top may degrade and desertification will be appeared due to water deficit. While soil water on bottom of a slope responds strongly to rainfall and the vegetation will not degrade significantly. Between different slope directions， the degree of vegetation degradation may be greater on the sunny slope than on the shady slope.