[Mechanisms of Interaction Between Microplastics and Carbon and Nitrogen Transformations in Aquatic Environments]

As a new global pollutant， microplastics （MPs） are widely distributed in various types of water bodies and significantly interfere with carbon and nitrogen transformations in aquatic ecosystems by altering the physicochemical properties and microbial community structure of water bodies. We systematically investigated the mechanisms by which MPs affect carbon and nitrogen cycling in marine and riverine environments： In marine ecosystems， MPs interfered with key processes such as decomposition of organic matter and nitrification and denitrification by altering the optical properties of the water column， adsorbing pollutants， and disrupting the microbial communities and enzyme activities， releasing dissolved organic matter， exacerbating ocean acidification， and contributing to the release of greenhouse gases （e.g.， CO₂， CH₄， and N₂O） emissions. In riverine ecosystems， MPs altered hydrological conditions and adsorbed nutrients mainly through shading effects， affecting photosynthetic efficiency and dissolved oxygen levels and then interfering with carbon and nitrogen transformations， and their impacts showed significant spatial and temporal heterogeneity. Biodegradable microplastics rapidly degraded and released small-molecule organic matter in the short term， significantly promoted microbial activity， accelerated organic carbon mineralization and CO₂ and CH₄ emissions， and enhanced N₂O generation. Non-biodegradable microplastics， on the other hand， mainly accumulated over time by physically damaging the organisms， hindering nutrient uptake， and acting as a pollutant carrier， and NBMPs indirectly interfered with the carbon and nitrogen cycle by aggregating with microorganisms to accelerate sedimentation and altering the vertical fluxes of carbon and nitrogen and benthic habitats. Future research could focus on the transport and transformation patterns of MPs， microbial regulation mechanisms， bioconcentration effects， and their coupling with multiple environmental pressures such as climate change and acidification and develop effective prevention， control， and remediation strategies.