Abstract: 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 decreased, the daily range of soil temperature was increased, but there was no significant response of daily temperature 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 increased 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 volumetric 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 temperature and moisture content to the degeneration of A. splendens steppe occurred mainly during the period from July to August.

Key words: Achnatherum splendens, steppe, soil moisture content, soil temperature, native vegetation, vegetation degeneration, cluster analysis, Qinghai Lake