Polymer-environment interplay drives microplastic degradation in a surface-flow wetland: New insights into bacterial assembly, network structure, and function across aquatic and sedimentary habitats.

It remains unclear how polymer types (petroleum- vs. bio-based) and environmental media interact to affect microplastic (MP) biodegradation in wetlands. We conducted a 120-day in situ experiment, incubating five MPs (polylactic acid PLA, polyurethane PU, polyethylene terephthalate PET, polyethylene PE, and polypropylene PP) in a surface-flow wetland. A distinct degradation order was observed: PU (15.2 ± 3.2% in sediment; 12.0% ± 3.9% in water) > PE (11.9% ± 2.9%; 8.2% ± 4.0%) > PLA (4.4% ± 2.2%; 5.0% ± 3.1%) ≈ PET (2.4% ± 1.5%; 7.1% ± 3.5%) ≫ PP (0.0-0.3%), showing faster degradation of most petroleum-based MPs than bio-based PLA. Integrating 16S rRNA sequencing, co-occurrence network analysis, neutral and null model analyses, we demonstrated plastisphere community assembly was governed by deterministic habitat filtering (>85% contribution) over polymer type. Functional specialization diverged between habitats, with aquatic plastispheres being enriched in nitrate reducers and aromatic hydrocarbon degraders (Nitrospira, Methyloversatilis, and Hydrogenophaga), whereas sedimentary ones were dominated by plastic/polysaccharide degraders (Psychrobacter and Microbulbifer). Co-occurrence networks contrasted sharply, being high-modularity/low-connectivity structures in water but low-modularity/high-connectivity ones in sediment. Structural equation modeling identified the plastisphere microbiome as the direct degradation driver. This degradation is enhanced by light irradiation (loadings: 0.888) in water and but is inhibited by the contents of organic matter (-0.738), DGT-labile Fe (-0.876) and S (-0.876) in sediment. These findings underscore the critical interplay between habitat and polymer type in controlling MP fate in wetlands.