Multi-omics reveals microplastics disrupt nitrogen assimilation in hydrophytes

Abstract

Hydrophytes mitigate water eutrophication; however, microplastics (MPs) and nanoplastics (NPs) may affect nutrient removal. The underlying pathways through which MPs/NPs mediate disruptions in nitrogen assimilation remain unclear. This study investigates how polystyrene (PS) particles (0.1–100 μm) at freshwater-relevant concentrations (10–1000 μg/L) affect NH4+–N and NO3-–N removal by a typical hydrophyte—Myriophyllum aquaticum. For NH4+–N, the 0.1 μm PS (100 μg/L) treatment achieved the highest removal rate (92.02%), followed by 100 μm PS at 100 μg/L (91.28%). For NO3-–N, the 0.1 μm/1000 μg/L PS treatment removed 97.46%, while others reached 100% after 27 days. Larger PS particles (100 μm) enhanced nitrogen-specific uptake rates, whereas 0.5 μm PS (1000 μg/L) inhibited uptake. PS exposure altered plant biomass, chlorophyll content, soluble sugars, and activities of nitrogen metabolism enzymes (nitrate/nitrite reductase). Transcriptomics and metabolomics highlighted PS-induced disruptions in ammonia assimilation, TCA cycle, photosynthesis, and oxidative stress pathways. NO3-–N removal outperformed NH4+–N, likely due to M. aquaticum’s sensitivity to high ammonia. MPs/NPs exposure modulated expression of nitrogen uptake- and metabolism-related genes. The study underscores the complex size- and concentration-dependent impacts of MPs/NPs on aquatic plant-mediated nitrogen removal, emphasizing the need for tailored strategies to mitigate plastic pollution in freshwater ecosystems.