Effects of microplastic particles on carbon source metabolism and bacterial community in freshwater lake sediments

Increasing microplastic (MP) pollution in freshwater lakes has profound impacts on microbial communities and biogeochemical processes. Lakes are important terrestrial carbon pools and among the most active habitats for the carbon biogeochemical cycle. However, the effects of MPs on microbial community and carbon metabolism in freshwater lakes remained poorly understood. In this study, a microcosmic experiment was performed to explore the effects of four widely used plastic particles on sediment microbial community and carbon metabolic activity through high-throughput sequencing and BIOLOG analysis. The results showed that polyethylene (PE) had little effect on the bacterial network complexity, community assembly pattern, and community stability, whereas polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) all reduced the bacterial network complexity, improved community stability and the contribution of the stochastic processes to community assembly. Adding MPs changed the number and taxonomy of keystone species in bacterial communities. BIOLOG analysis showed that PE increased carbon metabolic activity in sediments, however, PP, PS, and PVC all had different degrees of inhibition on carbon metabolism, among which PVC had the most significant inhibition. In addition, Mantel tests and db_RDA analyses suggested a significant effect of Fe(III) and NO₃^- content on sediment carbon metabolic activity. These results provided new insight for assessing the effects of MPs on the carbon cycle in freshwater lakes and deepen the understanding about the environmental effects of MPs in the aquatic system.