Soil bacterial and fungal communities are linked with plant functional types and soil properties under different grazing intensities

Abstract

Abstract As a grassland management strategy in the typical steppe, livestock grazing can affect soil microbes and ecosystem functions via vegetation removal, trampling and manure deposition. However, the effects of grazing and its main consequences (e.g. the shifts in plant functional types and alterations in soil properties) on soil bacterial and fungal community composition remain unresolved. Taking advantage of a 5‐year grazing exclosure experiment that tested different grazing intensities [control: no grazing (G0); light: 0.75 sheep ha −1 (G1); moderate: 1.50 sheep ha −1 (G2); heavy: 2.25 sheep ha −1 (G3); and overgrazing: 3.00 sheep ha −1 (G4)], we examined grazing‐related changes in plant communities, soil chemistry and soil microbial communities. Grazing intensity affected the diversity and composition of soil bacterial and fungal communities via changes in plant species and soil nutrient contents. Increased grazing intensity reduced soil organic carbon (OC), suppressed the dominant bacterial phyla Proteobacteria and Bacteriodetes, and increased the abundance of oligotrophic bacteria in subordinate phyla (e.g. Verrucomicroba and Chloroflexi). Increased grazing intensity also promoted the dominant fungal phylum Ascomycetes because of the poor‐nutrient soil environment. The decreased soil carbon‐to‐nitrogen (C/N) ratio in the G2 treatment was associated with an effect on the fungal community composition. Structural equation modelling demonstrated that responses of the bacterial community to grazing intensity were related to changes in soil OC and soil pH, whereas the combination of C 4 plant community biomass and soil pH drove changes in the fungal community. Our study provides novel evidence that grazing affects plant functional group and soil chemistry through the soil pH and C/N ratio, which in turn affects bacterial and fungal communities. Highlights Heavy and overgrazing suppressed bacterial phylum Proteobacteria and increased fungal phylum Ascomycete . Soil OC was the predominant driver of changes in bacterial richness and community composition. C 4 plant community biomass modulated fungal richness and community composition.