Optimized soil bacterial structure following grazing exclusion promotes soil nutrient cycling and plant growth

Abstract

Grazing exclusion is a common grassland restoration strategy, and the effectiveness on optimizing plant species community, increasing vegetation diversity and biomass, and improving soil fertility, has been widely documented in literatures. Soil bacterial community, as one of important ecological components, closely relates to plants and soil features. However, there is no definite conclusion of grazing exclusion effects on various ecological components, especially on soil bacterial community. To clarify this question, we compared the soil bacterial community characteristics and their corresponding vegetation characteristics and soil properties on one 40 years-grazing exclusion (GE) and three free grazing (FG) areas within a Leymus chinensis steppe of Inner Mongolia, China. Our results showed that grazing exclusion could significantly increase the soil bacterial abundance, and optimize the soil bacterial structure, with the synergistic increase of the soil bacterial diversity. The abundance of Euryarchaeota, Verrucomicrobia, Nitrospirae, Proteobacteria, Elusimicrobia, Latescibacteria, and Microgenomates phyla, some taxa of which involved in the N and P cycles, increased significantly following grazing exclusion, while the abundance of Chloroflexi, Firmicutes, Thaumarchaeota, and Pacearchaeota phyla which are often considered to contain many pathogens, decreased significantly. The bacterial phyla increased by grazing exclusion have a significant positive correlation with vegetation biomass and diversity, and soil alkali-hydrolyzable nitrogen content, total nitrogen content, total phosphorus content, organic matter content and water content. The reducing of pathogenic abundance after grazing exclusion provides a healthier environment for plant growth. This work indicates that grazing exclusion optimizes the soil bacterial structure to promote the growth of plants in more sufficient soil nutrients and healthier soil environments, making the enclosed grassland soil ecology form a virtuous circle.