Subsurface drainage influences the structure and assembly of soil bacterial and fungal communities in salinized cotton field

Exploring the impact of subsurface drainage on microbial community structures in saline-alkali soils is of great significance for maintaining the sustainability of saline-alkali fields. In this study, seven field treatments were designed in cotton fields: two drain depth (0.8 and 1.1 m) and three drain spacing (10, 20, and 30 m) treatments, as well as no drainage (control). Soil samples were obtained in the seedling and flowering and boll-setting (FBS) stages, and the soil properties and microbial communities (bacteria and fungi) were analyzed. The results displayed that compared with the control group, soil salt was significantly decreased in all subsurface drainage treatments. Subsurface drainage treatments have no effect on microbial richness and diversity. Both drain depth and spacing had significant effects on bacterial and fungal composition structures in the seedling stage, but only drain depth significantly altered soil microbial composition structures in the FBS stage. Based on the null model, the assembly of soil microbial communities was mainly driven by stochastic processes. The contributions of the deterministic process for soil bacterial community assembly at the seedling stage and FBS stage were 18.1% and 22.1%, respectively. In contrast, soil fungal community assembly was mainly determined by dispersal limitation and drift.