Differentiating microbial taxonomic and functional responses to physical disturbance in bulk and rhizosphere soils

The rhizosphere is an important hotspot of soil microbial activity, diversity, and functions. Despite being a microbial hotspot, studies have seldom addressed the differences in the response of the microbial community in bulk and rhizosphere soils to domestic animal disturbance. Here, we investigated grassland disturbance by physical uprooting behaviours of Tibetan pigs (Sus scrofa domesticus) on bacterial taxonomy and functions in three soil types: Histosols, Fluvisols, and Gleysols which are dominant on the Qinghai-Tibet Plateau. We found that after 8 years of continued disturbance, compared to the undisturbed sites, disturbance consistently reduced rhizosphere bacterial α diversity (by 34.6% on average), restructured taxonomic communities, and weakened their carbon substrate utilization capacities in all soil types. The relative abundance of the phyla Proteobacteria, Actinobacteria, and Bacteriodetes increased, but the relative abundance of Acidobacteria, Chloroflexi, and Nitrospirae decreased in the rhizosphere under disturbance. In contrast, most detected taxonomic changes in bulk soils were minor, and their changing directions were divergent among studied soil types. Compared to the undisturbed, carbon utilization potential by rhizosphere microbes decreased under disturbance and the decrease extent was stronger (by 30.4% on average) than that in bulk soil. The strengthened environmental filtering, imposed by the significant reduction of soil water-holding capacity and nutrient contents as well as the physical destruction of soil aggregates after disturbance, provided mechanistic insight into the extensive microbial restructuring within the rhizosphere. These results may have implications for recognizing changed root-microbe interactions and ecological processes in disturbed soils for better understanding soil ecology under intensified herding activities. © 2020 John Wiley & Sons, Ltd.