Polymer-specific impacts of nanoplastics on sediment bacterial communities and ecosystem functionality in Poyang Lake wetlands

The widespread environmental persistence of nanoplastics (NPs) poses critical threats to aquatic ecosystems, yet their impacts on sediment bacterial communities and ecosystem functionality remain poorly characterized. Through a 180 days microcosm experiment integrating 16S rRNA sequencing and structural equation modeling (SEM), we investigated the ecological effects of NPs (polyethylene, PE, and polypropylene, PP) on sediment bacterial communities. PE significantly increased sediment bacterial richness (Chao1 index: 555±36.57 vs. CK: 546.33±52.48), whereas large-particle/high-concentration PP exhibited the lowest diversity. Proteobacteria (30%–40%) and Actinobacteriota (15%–18%) dominated community composition across treatments. At the genus level, NPs type significantly restructured dominant taxa composition. Moreover, PE amendments significantly increased total organic carbon (TOC; +9.4%) and nitrate retention (NO3−-N; +21.4%), whereas PP reduced TOC (−10.3%), total phosphorus (TP; −46.3%), and available phosphorus (AP; −36.6%). Enzymatic analyses demonstrated polymerdependent effects: PE inhibited urease activity by 45.7% relative to controls, whereas PP stimulated nitrate reductase activity by 316.3%, indicating distinct metabolic adaptations. Functional profiling predicted NP-induced enrichment of nitrogen fixation, methylotrophy, and chemoheterotrophy pathways. Notably, PP treatments selectively enriched genetic traits associated with stress tolerance and virulence potential. Structural equation modeling elucidated cascading interdependencies among microbial diversity, sediment geochemistry, enzymatic profiles, and functional gene dynamics. Our results demonstrate that polymer type is a stronger driver of microbial functional shifts than particle size in wetland sediments, emphasizing the need for tailored mitigation strategies to protect wetland ecosystem integrity from plastic pollution.