Variations and Mutual Relations of Vegetation–Soil–Microbes of Alpine Meadow in the Qinghai-Tibet Plateau under Degradation and Cultivation

Artificial cultivation had been applied to recover the meadow suffering from serious degradation in the Qinghai–Tibet Plateau. Studies focusing only on the changes in vegetation, soil and microbes along the meadow degradation were insufficient, and artificial cultivation as an important part of succession was always neglected. Here, the variables of vegetation, soil, and soil bacteria are surveyed in four types of alpine meadow in the protected lands of the Qinghai–Tibet Plateau: intact alpine meadow (IAM), moderate degradation alpine meadow (MDAM), extreme degradation alpine meadow (black soil beach (BSB)), and artificial alpine grassland (AAG). The results indicated that degradation and cultivation significantly changed the characteristics of the vegetation community, physicochemical features of the soil, and soil bacterial community diversity. Soil bacteria took a considerably longer time to adapt to degradation and cultivation than vegetation and soil. Compared to IAM and BSB, ADAM and AAG had more specific bacteria identified by ANOVA and LEfSe analysis, implying an unstable state. Combined with vegetation and soil variables, it was speculated that the unstable AAG was not significantly improved from the degraded meadow, and also lagged significantly compared to IAM. Correlation analysis revealed that aboveground biomass, species richness, vegetation coverage, SOC, C/N, BD, WC, and pH were significantly associated with bacterial diversity under community level. Aboveground biomass was an effective indicator for soil bacterial gene copies. Redundancy analysis demonstrated that the soil bacterial community is mainly regulated by the vegetation coverage, Gleason index, Simpson index, TN, TP, and pH under phylum and genus level. Partial mantel test analysis indicated that the physicochemical features of the soil were the most important factor correlating with the soil bacterial community along the degradation and cultivation, compared to other environmental factors.