Effects of Grazing Intensity on Soil Bacterial Community Structure of Stipa grandis Grasslands in Inner Mongolia, China

Grassland ecosystem is one of the indispensable ecosystem types in the world, accounting for approximately 30% of global land area. However, due to overgrazing and other human activities, grassland ecosystem is increasingly seriously degraded. Soil microorganism, as an important component of grassland soil ecology, plays a key role in litter decomposition, material metabolism and circulation. According to the results of large previous literature, soil microbial community structure could be affected by vegetation characteristics, soil properties and other environmental factors. Not surprisingly, soil microbial community structure could also be affected by different soil management strategies, including grazing intensity. As grazing could directly affect plant growth, soil porosity, nitrogen circulation and soil microbial community characteristics, the soil microbial community could be not only directly affected by grazing intensity, but also indirectly affected by the vegetation characteristics and soil properties that had changed with difference in grazing intensity. Therefore, there has been no unified conclusion about the effect of grazing intensity on soil microbial community. To further clarify this question, we utilized 16S amplifiers absolute quantitative sequencing technology to analyze the absolute abundance, diversity and composition of soil bacterial communities of Stipa grandis grasslands under different grazing intensity in Xilingol League, Inner Mongolia, China in this study. The correlations with soil bacterial communities and their corresponding environmental factors were also analyzed. Our results suggested that soil bacterial diversity decreased at first and then increased with the increase of grazing intensity, and the evenness had no significant variation with the difference in grazing intensity. Grazing intensity significantly affected the composition of soil bacterial communities at the phylum level: with the increase of grazing intensity, the abundance of Verrucomicrobia decreased at first and then increased, the abundance of Planctomycetes and Gemmatimonadetes significantly decreased, and the abundance of Nitrospirae significantly increased. According to the redundancy analysis with vegetation characteristics and soil properties, it indicated that the dominant soil bacterial phyla showed significant correlations with soil pH value, number of Gramineous species, aboveground biomass of Gramineous species, total aboveground biomass, soil organic matter content, available nitrogen content, available phosphorus and total nitrogen contents. This work could provide more scientific evidence for understanding of the effects of grazing intensity on soil bacterial community structure.