Effects of grazing intensity on diversity and composition of rhizosphere and non-rhizosphere microbial communities in a desert grassland.

Overgrazing-induced grassland degradation has become a serious ecological problem worldwide. The diversity and composition of soil microbial communities are sensitive to grazing disturbances. However, our understanding is limited with respect to the effects of grazing intensity on bacterial and fungal communities, especially in plant rhizosphere. Using a long-term grazing experiment, we evaluated the diversity and composition of microbial communities in both rhizosphere and non-rhizosphere soils under three grazing intensities (light, moderate, and heavy grazing) in a desert grassland and examined the relative roles of grazing-induced changes in some abiotic and biotic factors in affecting the diversity and composition of microbial communities. Our results showed that soil bacteria differed greatly in diversity and composition between rhizosphere and non-rhizosphere zones, and so did soil fungi. Moderate and heavy grazing significantly reduced the rhizosphere bacterial diversity. Grazing intensity substantially altered the bacterial composition and the fungal composition in both zones but with different mechanisms. While root nitrogen and soil nitrogen played an important role in shaping the rhizosphere bacterial composition, soil-available phosphorus greatly affected the non-rhizosphere bacterial composition and the fungal composition in both soils. This study provides direct experimental evidence that the diversity and composition of microbial communities were severely altered by heavy grazing on a desert grassland. Thus, to restore the grazing-induced, degraded grasslands, we should pay more attention to the conservation of soil microbes in addition to vegetation recovery.