Soil depth exerts greater effect on bacterial community than spatial structure in Longmenshan fault zone

The diversity patterns and drivers of soil microbial communities across spatial distances have been extensively investigated over the recent years. However, whether microbial communities in surface and subsurface soils showed an identical spatial distribution pattern at a small regional scale has not been fully confirmed. For this, we investigated the linkage between soil water content (SWC), pH as well as nutrient contents and soil bacterial diversity and communities in different soil layers in the Longmenshan fault zone in Sichuan Province, China. Our investigation indicated that surface soil bacterial communities were positively correlated with SWC and pH (P < 0.05), whereas those in the subsurface correlated with soil organic carbon and its fractions (P < 0.05). Bacterial community co-occurrence network structures differed significantly across soil layers. Compared to subsurface soils, surface soils had more nodes, larger network diameters, and longer average paths. The keystone species belonged to Rokubacteriales in the surface, and in the subsurface soil, they belonged to Chryseobacterium, while no keystone species were found in the subsoil. Spatial distance showed a smaller effect (4%-7%) on community structure, indicating that various soil factors represent key regulatory factors for bacterial community shifts. Collectively, soil depth showed a considerably higher effect than spatial distance on soil bacterial community composition and network properties in Longmenshan fault zone, with key species differing across soil layers. These results could provide an essential basis for further investigation of microbial functions in soil ecosystem heterogeneity and maintaining soil health.

Soil water content served as the main driver of changes in surface soil bacterial diversity and community. Spatial structure had a greater influence on surface soil bacterial communities and diversity. Soil depth had a significantly higher effect on soil bacterial community composition and network properties than site. Our results may provide insights into the impact of microbial functions on biodiversity and ecosystem service functions.