Abstract:A field experiment was conducted on the Tibet plateau Stipa bungeana grassland to investigate the effects of arbuscular mycorrhizal fungi (AMF) inoculation on S. bungeana growth and its phosphorus uptake, and on soil microbial communities under unsterilized condition. The results showed that AMF inoculation increased the AMF spore density, infection rate and infection intensity in rhizosphere soil significantly, but had less effect on arbuscule richness. The infection rate of AMF increased with its increasing spore density, and the plant dry weight and P uptake of S. bungeana increased significantly with AMF infection rate. Similar results were observed in S. bungeana root dry weight and its P content. AMF inoculation increased the acid and alkaline phosphatase activities and bacterial biomass in rhizosphere soil, but had less effect on fungal and actinomyces communities. The infection effect of AMF varied with inoculation treatments , being in the sequence of Glomus mosseae+G. intraradices+Scutellospora calospora＞G. mosseae+G. aggregatum＞Glomus sp.＞G. mosseae＞G. mosseae+ G. etunicatum+G. intraradices+S. erythropa＞G. geosporum.