Changes of soil microbial community under different degraded gradients of alpine meadow

• We investigated how soil microbial composition and their diversity are impacted by meadow degradation.
• We analyzed how the changes in microbial community with degradation correlated to shifts in plant and soil attributes.
• Neither bacterial nor fungal diversity paralleled plant diversity with degradation.
• Higher sensitivity of fungal community to meadow degradation than bacterial community was found.
• Severe meadow degradation apparently increased the relative abundance of pathogenic fungi compared with original meadow.

Changes in soil bacterial and fungal composition and their diversity with degradation degrees (i.e. non-degraded (ND), moderately degraded (MD) and severely degraded (SD) meadows) were investigated in a Tibetan alpine meadow using the Illumina MiSeq. Proteobacteria, Actinobacteria, and Acidobacteria were predominant bacteria in the studied meadow soils, regardless of degradation. ND and MD exhibited no significant differences in bacterial species composition and diversity, while SD significantly altered bacterial composition and increased their diversity compared with ND and MD. Sordariomycetes was predominant fungal class in ND, however, a shift in the fungal class from it to Dothideomycetes was found with increasing degradation level. Moreover, SD apparently increased the relative abundance of pathogenic fungi compared with ND. Degradation significantly shifted fungal species composition and increased their diversity. Soil nutrient conditions could explain 33.8 and 35.6% of the variance in bacterial and fungal composition, respectively. In addition, 25.3 and 21.7% of the variance in bacterial and fungal composition, respectively, were explained by plant properties. However, neither bacterial nor fungal diversity paralleled plant diversity with degradation. Soil silt to sand ratio was the best predictor of shifts in bacterial α-diversity with degradation degrees (R2 > 0.46), while fungal α-diversity was most closely associated with changes in soil available potassium (R2 > 0.66). Together, these results suggest that changes of microbial diversity and plant diversity was decoupled under degradation process, and degradation could increase the potential risk of plant diseases and decrease health of the alpine ecosystem.