Profile distribution patterns and assembly processes of microbial communities in arid saline-alkali loess

Microorganisms are distributed throughout the soil profile and play key roles in ecosystem function restoration. However, little is known about the vertical distribution patterns and assembly processes of soil microbial community, especially in arid saline-alkali loess. In this study, typical saline-alkali loess cores were collected from central Gansu province to examine variations in microbial diversity, community structure and assembly process along soil depths by 16S rDNA and ITS amplicon high-throughput sequencing. The results showed that Actinobacteriota , Proteobacteria , Chloroflexi , Firmicutes , Ascomycota , and Basidiomycota dominated across soil depths, with clear shifts in community composition along the profile. Bacterial diversity followed linear descent, “U” or unimodal patterns with depths, whereas fungal diversity decreased linearly. Bacterial co-occurrence network complexity declined from topsoil (0–20cm) to subsoil (20–40cm and 40–80 cm), while fungal networks were more complex and tightly connected in the middle layer (20–40 cm) compared with the topsoil and deeper layer. Null model analysis indicated that bacterial community assembly processes was primarily governed by deterministic processes, whereas fungal community assembly was mainly driven by stochastic processes (dispersal limitation mainly). These findings help elucidate the spatial patterning and assembly mechanisms of soil microbial communities in arid, saline-alkali loess.