Quaternary volcanic activities influence core soil microorganisms in a typical steppe

Quaternary volcanic activities exert effects on microbial community compositions and structures, but the influences on typical steppes remain poorly understood. The aim of this study was to explore the influences of Quaternary volcanic activity on soil microorganisms in a typical steppe. The α-diversity results showed that the disturbance scope of volcanism is limited; once a certain distance from a volcano is reached, volcanism no longer affects soil microorganisms. Compared to bacterial communities, soil fungal communities seem to exhibit a stronger anti-interference ability under conditions of volcanic perturbation. A total of seven keystone taxa were identified by using analyses of co-occurrence networks and included six bacteria and one fungus, which suggested that soil bacteria may play a more significant role in the overall community structure and function than soil fungi. Compared to volcanic areas, typical steppes were enriched with more core soil microorganisms and had more highly modular networks (modularity: 0.296 vs 0.626), simpler community correlations (links: 369 vs 269) and stronger competitive relationships (positive/negative link ratio: 3.06 vs 1.89) among soil microbial communities. However, the volcanic area was enriched with arbuscular mycorrhizal fungi and showed improved bacterial metabolism. Multivariate regression tree (MRT) analyses indicated that the key potential drivers in volcanic areas and typical steppes were soil available phosphorus (AP) contents and C/N ratios, respectively. Structural equation models (SEMs) indicated that the same keystone taxa in different ecological environments are able to assume different functions, and that the causal relationships between the same keystone taxa and different environmental variables also differ. These results may provide crucial implications for understanding the effects of volcanic activity on the ecosystems of typical steppes.