Meadow Degradation Affects Microbial Community Structure and Vegetation Characteristics by Increasing Soil pH

Abstract

Soil is the natural habitat for microorganisms, providing water and nutrients for vegetation, but the influence of meadow degradation on the “vegetation-soil-microorganism” system is still controversial, and the drivers of soil microbial and vegetation characteristics change are still unclear. This study explores in-depth the vegetation and soil changes in four different degradation levels, that is, non-degraded (ND), lightly degraded (LD), moderately degraded (MD), and severely degraded (SD), in the northeastern region of the Qinghai-Tibetan Plateau. Soil metagenomic sequencing methods were employed to understand the soil microbial and functional diversity and the factors that influence them. The findings indicated that alpine meadow degradation decreased the vegetation height, coverage, and above-ground biomass (AGB), but increased the vegetation diversity index. In addition, meadow degradation reduces soil properties (organic carbon, total nitrogen and phosphorus, available nitrogen and phosphorus) and enzyme activities (sucrase, cellulase, urease, and catalase) but increases soil pH. The copiotrophic groups (Actinobacteria, Ascomycota) decreased while oligotrophic groups (Acidobacteria, Glomeromycota) increased with meadow degradation. In particular, changes in vegetation characteristics and microbial community structure in alpine meadows are strongly influenced by changes in soil pH. In conclusion, the degradation of alpine meadows leads to the growth of some barren-tolerant species and deviation of soil pH from neutrality, which increases vegetation diversity but surface exposure reduces the vegetation richness, affects the type and amount of root secretions and changes in soil microbial communities, which reduce the fixation and release of soil nutrients. This study provides the theoretical basis for further analyzing the inner mechanism of alpine meadow degradation.