Biome regulates the effects of long-term grazing on soil microbial diversity

IntroductionLivestock overgrazing represents one of the most destructive uses of land in terrestrial ecosystems and threatens biodiversity. However, understanding the effects of livestock overgrazing on below-ground soil microbial diversity is limited, despite soil microbes representing the majority of biodiversity and determining ecosystem functioning.Materials and MethodsTo investigate the effects of overgrazing on soil microbial richness, a long-term grazing exclusion experiment was conducted at six sites including three meadow steppes and three typical steppes in northern China.ResultsOur results revealed that overgrazing decreased bacterial and fungal richness across temperate steppes in northern China, and the biome could regulate the overgrazing effects, especially for fungal richness. Specifically, the negative effects of overgrazing on microbial richness were highly significant in typical steppes while not significant in meadow steppes that contained higher plant diversity and precipitation. Partial least-squares path model showed that overgrazing affected soil microbial richness in highly complex ways, and the affected pathways were different in meadow steppes and typical steppes. The direct negative effects of grazing and their indirect negative effects via soil properties resulted in a significant decrease in microbial richness in typical steppes. In meadow steppes, the indirect beneficial effects via plant attributes offset the direct negative effects of grazing. Consequently, the soil microbial community in meadow steppe resisted overgrazing disturbance.ConclusionOur study illuminates the complex and highly biome-dependent grazing effects and pathways on soil microbiota and indicates that meadow steppe may be more resistant or resilient to human disturbance than typical steppe. These findings suggest that different grasslands might be managed differently considering their intrinsic characteristics to help biodiversity conservation. Moreover, future research should focus on the underlying mechanisms of grazing effects on soil microbial richness. Besides grazing-induced plant and soil traits changes, other potential pathways could strongly influence soil microbial diversity.