Changes in surface vegetation cover,soil organic carbon and soil microorganisms associated with al-pine grassland desertification in Northwest Sichuan were explored.We studied the surface vegetation cover, aboveground and underground biomass and the vertical distribution of soil organic carbon and microorganisms in different grassland on sandy soils using repeated sampling.The results showed that with aggravation of de-sertification,vegetation cover and aboveground and underground biomass decreased sharply.Compared with grassland not undergoing desertification,aboveground biomass of grassland suffering mild,medium,heavy and severe desertification was decreased by 13.0%,91.8%,76.5% and 40.6% respectively.Underground biomass decreased by 21.4%,44.0%,83.4% and 94.7% respectively.With the increase of the degree of desertifica-tion,soil organic carbon and humus carbon fractions showed a declining trend,most obvious in the 0-20 cm soil layer.There were differences among different soil layers but there were no differences between grassland undergoing heavy and severe desertification.The degree of desertification also influenced the number of soil mi-croorganisms (bacteria,fungi,actinomycetes)and microbial biomass carbon and nitrogen;desertification re-duced all of these soil traits.%为探究川西北高寒沙化草地地表植被、土壤有机碳和微生物的特征，采用样地调查方法，研究了不同沙化程度草地地表植被状况及土壤有机碳、腐殖质碳、微生物数量和微生物量碳、氮的差异特征。结果表明，1）随沙化严重程度增加，植被群落盖度、植被地上和地下生物量急剧下降。与未沙化草地相比，轻度沙化、中度沙化、重度沙化和极重度沙化草地地上生物量分别降低了12．95％，40．60％，76．53％和91．78％，地下生物量分别降低了21．44％，44．00％，83．41％和94．65％。2）土壤有机碳、腐殖质碳组分均随着沙化程度的提高而呈下降的趋势，且0～20 cm土层变化最为显著。不同沙化草地各土层之间也存在差异，但重度和极重度沙化草地各土层之间没有显著差异。3）随着沙化程度的加剧，土壤微生物（细菌、真菌、放线菌）数量和微生物量碳、氮产生显著变化。土壤沙化加剧会导致土壤微生物数量、微生物量碳、氮含量显著降低，破坏土壤微生物群落结构。
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