Impacts of Bacillus velezensis inoculation on exogenous organic carbon mineralization and bacterial community composition in fumigated continuous-cropping obstacle soils

Chemical fumigants such as dazomet (DZ) and dimethyl disulfide (DMDS) effectively suppress soil-borne pathogens but there is uncertainty regarding the restoration of soil ecological functions in continuous cropping obstacles after fumigation, such as microbe-mediated organic carbon cycling. However, the mechanism by which microbial remediation measures enhance carbon mineralization activity after soil fumigation remains unclear. In this study, we conducted microcosm experiments to investigate the impacts of Bacillus velezensis inoculation on exogenous organic carbon (EOC) mineralization and bacterial community composition and interactions following chemical fumigation. Relative to fumigation alone, B. velezensis addition increased cumulative EOC mineralization by 27% in DZ-treated soils and by 22% in DMDS-treated soils. This enhancement was associated with the enrichment of core taxa and keystone species, which collectively increased microbial activity. Structural equation modeling further confirmed that core taxa (OTU56, belonging to Bacillus) induced positive interactions with indigenous species, which drove the observed enhancement in EOC mineralization. We conclude that B. velezensis facilitates the rapid recovery of soil carbon mineralization after fumigation by selectively reshaping the bacterial community and strengthening bacterial cooperative networks. This work provides a mechanistic framework for microbially driven ecological restoration of fumigant-impacted continuous-cropping obstacle soils and informs the development of sustainable soil-management practices in chemically challenged agroecosystems.