Grazing Changed Plant Community Composition and Reduced Stochasticity of Soil Microbial Community Assembly of Alpine Grasslands on the Qinghai-Tibetan Plateau

Abstract

Grazing is a substantial threat to the sustainability of grassland ecosystems, while it is uncertain about the variety of plant and soil microbial community and the linkages between them limit the comprehensive understanding of grazing ecology. We conducted an experiment on the effects of the grazing regimes rotational grazing (RG), continuous grazing (CG), and grazing exclusion (GE) on an alpine meadow in Qinghai-Tibetan Plateau. The differences of plant community composition, soil microbial community assembly mechanism, and taxonomic and functional composition between grazing regimes were examined, and the relationship between plant species and the soil microbes was assessed by constructing a co-occurrence network. The results showed that the plant community composition varied with the grazing regimes, while the soil microbial community composition did not vary with the grazing regimes. The soil bacterial functional composition was similar under RG and CG, while the soil fungal functional composition was similar under GE and RG. The soil microbial community under all grazing regimes was assembled mainly according to stochastic rather than deterministic mechanisms, and RG and CG reduced the relative importance of the stochastic ratio. At the microbial phylum level, CG and GE increased the relative abundance of Acidobacteria and Armatimonadetes and CG and RG increased the relative abundance of Elusimicrobia. In the network of plant species and soil microbial classes, plants and bacteria themselves were mainly positively linked (symbiosis and promotion), while plants and soil microbes were mainly negatively linked (competition). There were five microbial generalists in the network, which connected with many microbes, and four showed no difference in their abundance among the grazing regimes. Overall, the stable key microbes in the network and the fact that many of the plants are unconnected with microbes weakened the impact of grazing-induced changes in the plant community on soil microbes, probably resulting in the stable soil microbial community composition. Moreover, there was still a dominant and tolerant plant species, Kobresia pygmaea, that connected the plant and microbial communities, implying that the dominant plant species not only played a crucial role in the plant community but also acted as a bridge between the plants and soil microbes; thus, its tolerance and dominance might stabilize the soil microbial community.

Response of soil microbial α‐diversity to grazing in grassland ecosystems: A meta‐analysis

“…In this study, grazing intensity caused changes in soil pH, SWC, and SOC, and moderate and heavy grazing significantly reduced AGB (Figure 2a). These changes in vegetation and soil physical and chemical characteristics will affect soil microbial diversity, which also shows that the changes in microbial diversity caused by different grazing intensities are the overall effect of plant–soil system (Lamb et al, 2010; Li, Dong, et al, 2022).…”

Fertilization can accelerate the pace of soil microbial community response to rest‐grazing duration in the three‐river source region of China

“…This may be due to long‐term rest‐grazing and fertilization, changes in aboveground vegetation types, increase in aboveground vegetation litter, plants which need nitrogen‐rich habits, changes in plant root exudates, and changes in soil physicochemical properties (Zong et al., 2021). Changes in soil environment and vegetation may result in reduced microbial biomass (Li, Yang, et al., 2023). Therefore, in the restoration of degraded alpine meadows, rest‐grazing and fertilization measures according to local conditions should be adopted to achieve good ecological effects.…”

Variable effects of long‐term livestock grazing across the western United States suggest diverse approaches are needed to meet global change challenges

“…Plant traits related to grazing response are complex combinations of photosynthetic pathway, life history, growth form, morphology, and paleoecology linked to herbivore community composition and abundance (Briske, 1996; Diaz et al, 2007). Livestock grazing can have large impacts on plant community composition by increasing or decreasing the competitive advantage of dominant species (Lezama et al, 2014; Koerner et al, 2018; Li, Dong, et al, 2022; Li, He, et al, 2022).…”

“…Livestock grazing can have large impacts on plant community composition by increasing or decreasing the competitive advantage of dominant species (Lezama et al, 2014;Koerner et al, 2018;Li, Dong, et al, 2022;Li, He, et al, 2022).…”