3.2 Soil microbial community structure
The relative abundances of major microbial phyla are illustrated (Fig.2a, b). Proteobacteria, Acidobacteria, Gemmatimonadetes, Planctomycetes, and Actinobacteria accounted for 83% of the total bacterial sequences, and Ascomycota, Basidiomycota, and chytridiomycota accounted for 78% of fungal. Bacteria alpha-diversity Chao1 and ACE indices did not significantly differ among the slope gradients. Simpson indices significantly differed among slope gradients and declined with increasing slope gradient (Table 3). These alpha-diversity indices had no significant differences between slope positions. Fungi alpha-diversity indices were not significantly affected by slope gradient or position. NMDS analysis based on the Bray-Curtis distance clustered bacterial and fungal communities, and distinct differences were observed in the communities’ composition (Fig. 2c, d). PERMANOVA revealed significant differences in bacterial and fungal community composition, which is significantly lower in the highest slope gradient level than in the other two levels. However, differences were not significant among slope positions (Table 4).