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Non-synergistic effects of microplastics and submerged macrophytes on sediment microorganisms involved in carbon and nitrogen cycling
Summary
This study used genomic analysis to look at how polystyrene microplastics and aquatic plants (submerged macrophytes) together influence the microbial communities in lake sediments that control nutrient cycling. Rather than amplifying each other's effects, the two factors acted independently — microplastics increased microbial diversity while the plants shaped which metabolic functions dominated. The finding suggests that the ecological impact of microplastics in lakes cannot be predicted by looking at microplastics alone, without accounting for the vegetation already present.
Submerged macrophyte communities play a crucial role in regulating sediment carbon and nitrogen cycling in lake ecosystems. However, their interactions with emerging pollutants such as polystyrene microplastics (PS-MPs) remain poorly understood. In this study, we employed metagenomic analysis to examine the combined effects of submerged macrophyte communities and PS-MPs on sediment microbial communities, focusing on microbial populations, functional genes, and metabolic pathways involved in carbon and nitrogen cycling. Our results revealed a non-synergistic interaction between macrophyte communities and PS-MPs in shaping sediment biogeochemical processes. While increasing PS-MPs concentrations (from 0.5 to 2.5 % w/w) significantly enhanced microbial diversity (species richness increased from 533 to 1301), the presence of macrophytes moderated this response. Notably, we observed differential selective pressures on functional genes involved in key carbon and nitrogen cycling steps, particularly amoAB and amoC, nirS, and nirK, indicating distinct shifts in microbial functional groups. Furthermore, we identified complex substrate-pathway interactions: nitrate and ammonium differentially influenced fermentation and methanogenesis, while inorganic carbon positively regulated nitrate dissimilatory reduction. These findings provide novel insights into the regulatory mechanisms of submerged macrophytes in sediment biogeochemical cycling under microplastic stress, highlighting their potential role in maintaining ecosystem functions in contaminated aquatic environments.
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