Soil properties rather than plant production strongly impact soil bacterial community diversity along a desertification gradient on the Tibetan Plateau

Grassland desertification is an important environmental issue that has detrimental impacts on the sustainable development of grasslands and human residential environments. Soil microbial community structure might dramatically change during desertification processes because microorganisms are one of the major drivers of ecological processes through their interactions with plants and soil. However, knowledge on the driving factors of microbial diversity changes during the desertification process in alpine grasslands is still lacking. Using a spatial sequence instead of a time successional sequence method, five desertification gradients in alpine steppe were chosen to investigate the changes in soil properties, plants and microbial communities during grassland desertification and to determine the factors that drive microbial community changes. Community coverage, species diversity indices and aboveground biomass gradually decreased from potential to severely heavy desertification gradients (HDs), while species richness and belowground biomass showed unimodal patterns (p < .05). Soil water content and total nitrogen showed gradual decreasing trends, while soil bulk density and gravel content showed opposite trends (p < .05). In addition, both the Shannon diversity index and the Chao1 richness index of soil bacteria increased gradually. The structural equation model showed that of the factors, soil total nitrogen (82.3% of total effect) and soil bulk density (41.4% of total effect) were the most important soil factors affecting soil bacterial diversity. However, community aboveground (43.4% of total effect) and belowground production (13.9% of total effect) were not the primary factors affecting soil microbial diversity. This result suggests that soil microbial diversity during grassland desertification is primarily driven by changes in soil properties, and the effects of vegetation composition and production are relatively small. These findings contribute to the mechanistic understanding of soil microbial diversity by linking changes in soil properties and plant production during desertification processes in alpine ecosystems.