Abstract:

Ali alpine desert zone in Qinghai-Tibet Plateau were selected as the investigation regions，vegetation and soil profiles in 30 sample plots were surveyed, soil organic carbon, size composition, and other index were measured. The results show:（1）The Ali alpine desert zone main distribute in spread over lake basin ,broad valley ,the foot of the slope, alluvial-proluvial fan with altitude of 4 000-5 000 m,soil there are thin soil thickness, high gravel proportion in soil surface, severe desertification and low soil organic carbon. The contents of soil organic carbon demonstrate the reduction tendency from subalpine prairie soil, alpine prairie soil, subalpine desert steppe soil, subalpine desert steppe soil to alpine desert soil. The contents of soil organic carbon had the significance reduction from alpine prairie soil to subalpine desert steppe soil, subalpine desert steppe soil, and alpine desert soil.（2）The contents of soil organic carbon in 8 kinds of plant association showed a reduction tendency from steppe to desert steppe and desert. The contents of soil organic carbon of stipa spp-Orinus thoroldii steppe and Stipa purpurea steppe higher highly significance than Stipa caucasica steppe, Artemisia wellbyi bushwood, Ajania fruticulosa desert, Ceratoides latens desert, and Ceraloides compacta desert. The contents of soil organic carbon of Stipa caucasica steppe, Ajania fruticulosa desert, Ceratoides latens desert higher significance than Krascheninnikovia compacta desert.（3）Correlation analysis of soil organic carbon with altitude,gravel concentration in surface and soil thickness showed the reducation of soil organic carbon and increase of gravel proportion in soil surface with the rise altitude.Overgraze of livestock and wild animal maybe is the principal factor that bring about vegetation degradation and lead to the reducation of soil organic carbon in alpine desert zone.

Key words: Tibet, alpine desert zone, soil, organic carbon