pH and Pb co-regulate soil bacterial communities and C/N/S Cycling processes in valley-type landfills under multi-factor interactions.

Valley-type landfills, a globally widespread source of contamination, produce leachate that significantly affecting adjacent soils. Clarifying leachate's contribution to global biogeochemical cycles requires investigating soil bacterial communities related to C/N/S cycling, but few studies have explored interactive effects of multiple factors (season, soil layer, distance). To fill this gap, 144 soil samples were collected across three hydrological seasons (dry, normal, wet) from a representative valley-type landfill in southern Sichuan, China. Results showed that leachate exposure increased the relative abundances of dominant phyla such as Proteobacteria (by over 200%) and Acidobacteriota (by over 30%), as well as Acidobacteriota's genus Pseudolabrys, while reducing the relative abundance of the sensitive phylum Chloroflexi by 50%. During normal and wet seasons, bacterial diversity at leachate-affected sites was up to twice that of clean soil, with more complex co-occurrence networks. Redundancy analysis and partial least squares path modeling (PLS-PM) revealed that soil pH (positive) and Pb (negative) were key factors regulating bacterial communities and C/N/S cycling functions. Distance emerged as the dominant predictor of bacterial community and function in random forest analyses. This work elucidates the response of C/N/S cycling-related bacterial communities and functions to leachate under multi-factor interactions, providing a scientific basis for understanding valley-type landfills' role in global biogeochemical cycles.