Abstract: Arbuscular mycorrhizal fungi (AMF) play an important role in plant nutrient absorption and soil nutrient transformation in forests. The community structure of AMF is sensitive to the regeneration and succession of vegetation. Here, the composition and diversity of AMF in soil organic layer and mineral layer were measured by the high-throughput sequencing method to explore the effects of forest conversion from a fir (Abies faxoniana) secondary forest and a spruce (Picea aspirata) plantation on AMF diversity in subalpine forests. The results showed that a total of 923 fungi OTUs were obtained from both forests, belonging to 9 families, 10 genera and 36 species. The Glomus was the dominant AMF group. The humified litter layer had the highestabundance and diversity of AMF in both forests. Forest conversion affected the abundance anddiversity of AMF. Compared to the secondary forest, plantation had higher abundance of Glomus but lower abundance ofDiversispora and Acaulospora. Moreover, the Shannon index, Ace index and Chao index of AMF in the plantation were lower than those in the secondary forest. The results of non-metric multidimensional (NMDS) analysis showed that forest conversion significantly affected the β diversity of AMF. The redundancy analysis (RDA) results showed that pH and total phosphorus concentration were two main factors affecting the diversity and abundance of AMF. These results suggest that forest conversion can change the diversity of AMF in subalpine forests and that secondary forests can provide more favorable living conditions for the AMF and thus facilitate the diversity of AMF.

Key words: forest conversion, arbuscular mycorrhizal fungi, species diversity, subalpine forest.