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Nanoplastics reshape nitrogen cycling in submerged macrophyte systems: A metagenomic perspective
Summary
Scientists found that tiny plastic particles (nanoplastics) can mess with how water plants and their bacteria clean up nitrogen pollution in aquatic ecosystems—low levels of plastic slightly helped, but higher levels disrupted the microbial communities that keep waterways healthy. This matters because these aquatic systems help filter our water supplies, and this study adds to growing evidence that nanoplastic pollution—the same tiny particles increasingly found in human blood and organs—can disrupt natural processes we depend on, even before we fully understand the direct effects on our own bodies.
Nanoplastics (NPs) pose a potential risk to aquatic ecosystems. Submerged macrophytes are critical for nitrogen removal, but how nitrogen cycling responds to NP-induced stress remains unclear. This study used Myriophyllum aquaticum to evaluate nitrogen cycling in submerged macrophyte-sediment systems exposed to 100 nm polystyrene (PS) NPs at 10, 100, and 1000 μg/L, integrating stable isotope tracing and metagenomic profiling to explore microbial community and nitrogen-cycling gene responses across rhizosphere and non-rhizosphere compartments. Low PS-NP exposure (10 μg/L) slightly increased the NH-N removal efficiency to 81.5%, whereas medium and high PS-NP exposures (100 and 1000 μg/L) reduced the NH-N removal efficiency, with values around 70.9%. Low doses stimulated nitrification (NO-N accumulation) and high doses inhibited NO emissions; δN tracing showed disrupted NH-N to N reduction. Plant-only microcosms had the highest NO release (1.37 mg, 1.5% of total N). Metagenomics revealed concentration-dependent, spatially distinct microbial community shifts: low PS-NPs increased rhizosphere α-diversity, while high concentrations depleted Proteobacteria, enriched Acidobacteria/Bacteroidetes, and reduced key nitrogen-cycling genera (e.g., Dechloromonas, Accumulibacter). In the rhizosphere, denitrification genes (nirK/S,nosZ) were upregulated by 2.5- and 3-fold, respectively, while DNRA (nrfA) and nitrogen fixation (nifH) genes were downregulated by 1.7- and 2.3-fold. Network and canonical correspondence analyses indicated stronger environmental filtering in bulk sediments (explaining 52.0% of variance) and spatially structured nitrogen metabolic pathway reorganization. These findings show concentration-dependent PS-NP exposure differentially shapes microbial community composition and nitrogen-cycling functions in rhizosphere and bulk sediments.