Shift in microbial communities mediated by vegetation-soil characteristics following subshrub encroachment in a semi-arid grassland

Subshrub encroachment is a frequently occurring phenomenon in arid and semi-arid area, altering the plant community structure and function. However, the effects of the encroachment process on soil bacterial communities are poorly understood on the Loess Plateau, China. In this study, we assessed the changes in soil properties and vegetation characteristics, and their association with alterations in soil bacterial communities in grasslands subjected to different subshrub (Artemisia sacrorum Ledeb.) encroachment intensities (no subshrub encroachment, light subshrub encroachment, moderate subshrub encroachment, and heavy subshrub encroachment). Our results indicated that heavy subshrub encroachment significantly increased plant aboveground biomass and bacterial diversity, but adversely affected plant diversity. Heavy and moderate subshrub encroachment significantly increased soil organic carbon, total nitrogen and water content. Subshrub encroachment at all intensities increased community weighted mean trait values of leaf carbon content, leaf nitrogen content, leaf phosphorus content, specific leaf area, but decreased leaf dry matter content and community functional dispersion. In addition, subshrub encroachment altered the composition of plant and bacterial communities. The partial least squares structural equation model indicated that subshrub encroachment indirectly influenced bacterial communities by affecting vegetation characteristics and soil properties. The determinants of bacterial diversity were vegetation structures (community weighted mean trait values of specific leaf area and plant community composition) and soil properties (organic carbon content, alkaline hydrolysis nitrogen, total phosphorus, available phosphorus, and soil water content). The composition of bacterial community was primarily regulated by plant aboveground biomass and soil properties. Overall, the results of this study improved our understanding of the impact of subshrub encroachment on soil bacteria community on Loess Plateau, and the processes underlying the alterations in the soil bacterial community by subshrub encroachment.