Interactive effects of soil characteristics and polymer types reveal patterns of denitrifying bacteria enrichment in the soil plastisphere

The plastisphere impact on nitrogen (N) biogeochemical processes in soil ecosystems remains poorly understood. This study investigated the N-transforming microbiota in the plastispheres of four microplastic (MP) types in paddy soils with varying physicochemical properties. We further assessed the plastisphere's potential for denitrification and nitrous oxide (N₂O) production. Our results demonstrate that polyethylene (PE) and polystyrene (PS) plastispheres exhibited a higher abundance of N-functional genes than those formed on polyvinyl chloride (PVC) and polylactic acid (PLA). In strongly acidic paddy soil, MPs acted as microbial refugia, promoting the accumulation of denitrifiers and associated functional genes. Notably, plastispheres were highly enriched in narG in soils characterized by low nitrate (NO₃⁻) levels and a high dissolved organic carbon (DOC)/NO₃⁻ ratio. Denitrifiers, such as Dechloromonas and Pseudomonas, were more prevalent in plastispheres than in soil. Compared to soil, the narG-type denitrifying community in plastispheres exhibited lower diversity but more positive interactions. Furthermore, we observed that plastispheres significantly contributed to N₂O production, with denitrification rates increasing by 5.04- to 5.76-fold in soil extracts. These findings highlight the ecological role of plastispheres in soil N cycling and identify plastispheres as a previously unrecognized source of N₂O emissions in paddy soils.