Contrasting the roles of plastisphere and soil in shaping antibiotic resistome under flooding and co-pollution stress.

Plastisphere has emerged as a distinctive ecological niche in soil, yet its roles in shaping antibiotic resistome under environmental disturbances remain poorly understood. In this study, we examined the influence of co-contamination with imidacloprid and copper on antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and microbial functional traits within soil and plastisphere microhabitats under flooding conditions. Pollutant exposure at environmentally relevant concentrations promoted ARG and MGE enrichment, with stronger effects as pollutant number increased. Under combined pollution, ARG abundance increased up to 5.59- and 2.42-fold in the plastisphere and soil under non-flooded conditions, and 2.62- and 2.75-fold under flooding. However, flooding reduced ARG abundance under combined pollution to 0.31- and 0.64-fold relative to non-flooded conditions. Nevertheless, the plastisphere maintained consistently stronger ARG-MGE associations. Functional trait analyses revealed that plastisphere microbes possessed higher GC content, smaller genomes, and faster growth rates than their soil counterparts, consistent with the Black Queen Hypothesis. Lower GC content and enhanced anaerobic metabolism were associated with greater ARG abundance, highlighting trait-mediated enrichment of ARGs in plastisphere biofilm habitats. Structural equation modeling further identified flooding-driven anaerobic respiration, microbial community composition, pollutant number, and MGE abundance as key determinants of ARG dynamics in the plastisphere, whereas ARG abundance in soil was primarily influenced by pollutant number and community composition. Collectively, these findings identify the plastisphere as a distinct reservoir of antibiotic resistance shaped by flooding and multiple chemical stressors, and emphasize the role of microbial functional traits in mediating ARG enrichment.