青海湖芨芨草干草原植被退化对土壤温湿特征的影响

Effect of Soil Temperature and Volumetric Moisture Content on Vegetation Degeneration over the Achnatherum splendens Steppe around the Qinghai Lake,China

芨芨草(Achnatherum splendens)干草原目前退化严重,但对土壤温湿特征的驱动机理仍不清楚。利用2011年连续观测资料分析环青海湖区域的芨芨草干草原原生植被和典型退化区域的0 cm、5 cm、10 cm、20 cm、40 cm和80 cm土壤温度和5 cm、10 cm、20 cm、40 cm和80 cm土壤容积含水量。结果表明:植被退化直接导致0 cm和5 cm表层土壤温度日极大值显著升高了39.04%和13.91%,温度日极小值显著降低,温度日较差升高;而10 cm以下温度日特征无显著响应。原生植被区0 cm逐日土壤温度在植物生长季(5—9月)极显著降低,非生长季5 cm和10 cm则略高。芨芨草植被改变了土壤年均温度垂向扩散特征。植被退化间接导致土壤5 cm土壤容积含水量升高了35.20%,10 cm无差别,20 cm以下显著降低,同时降低了系统土壤含水量的时间稳定性。特征聚类分析结果表明,芨芨草干草原土壤温湿特征对植被退化的综合响应主要表现在7—8月。

Achnatherum splendens steppe is one of the dominated vegetation types around the Qinghai Lake in Qinghai Province, China, but it has been degenerated seriously. However, its driving effect on soil temperature and moisture content is still unclear. The continuously-measured data were used to analyze the soil temperature and volumetric moisture content in soil layers at 0, 5, 10, 20, 40 cm and 80 cm and 5, 10, 20, 40 cm and 80 cm in depth over the native vegetation area and the typical degenerated area of the steppe in whole 2011. The results showed that the vegetation degeneration resulted directly in a significant increase of topsoil maximum temperature at 0 and 5 cm in depth （39.04% and 13.91% respectively）, the daily minimum temperature was significantly de- creased, the daily range of soil temperature was increased, but there was no significant response of daily tempera- ture of soil deeper than 10 cm to vegetation degeneration. Daily topsoil temperature was decreased obviously in plant growing season from May to September, but that at soil layers of 5 cm and 10 cm in depth was slightly in- creased in non-growing season. There was a vertical diffusion of annual soil temperature under the A. splendens canopy and litters as well as in rhizosphere. Vegetation degeneration resulted indirectly in an increase of soil volu- metric moisture content （35.20%） at 5 cm but a significantly decrease at 20 cm. Moreover, the temporal stability of soil moisture content was reduced. The cluster analysis revealed that the comprehensive response of soil tempera- ture and moisture content to the degeneration of A. splendens steppe occurred mainly during the period from July to August.