Plastisphere-mediated nitrogen cycling and N2O emissions in inland waters: A systematic review

Plastic pollution in inland aquatic ecosystems fosters unique microbial biofilms, termed the “plastisphere”, act as a potent mediator of biogeochemical cycles. This systematic review synthesizes evidence that the plastisphere disrupts nitrogen (N) cycle and amplifies emissions of nitrous oxide (N 2 O). By creating stratified microenvironments with sharp oxygen gradients, microplastics selectively enrich microbial guilds responsible for N transformations. Conventional polymers (polyethylene, polyvinyl chloride) enrich nitrifying bacteria ( Nitrosomonas and Nitrospira ), increasing the abundance of functional marker genes for ammonia oxidation ( amoA ) and nitrite oxidation ( nxrB ). Simultaneously, these and other polymers (polystyrene) promote denitrifying taxa ( Dechloromonas , Thauera , and Flavobacterium ), elevating genes for nitrite reduction ( nirK, nirS ), a key step in N 2 O production. The gene responsible for N 2 O reduction ( nosZ ) is frequently suppressed. This imbalance is quantified by the ( nirK + nirS )/ nosZ ratio, where a higher value indicates a greater genetic potential for N 2 O to be produced rather than reduced to N 2 , is a primary mechanism for N 2 O accumulation. Biodegradable polymers introduce a complex paradox: while they may inhibit classic nitrifiers, they create anoxic microinches that favor alternative pathways like nitrifier-denitrification and support distinct denitrifier communities, resulting in substantial N 2 O yields. The direction and magnitude of these effects are critically determined by polymer chemistry and size. We identify research priorities, including long-term field studies and advanced isotopic methods, essential for developing predictive models and effective mitigating strategies. • Plastic biofilms create potent greenhouse gas hotspots in inland waters. • Key nitrogen-transformation genes are dysregulated within the plastisphere. • Biodegradable plastics can unexpectedly intensify N 2 O emissions. • Nanoparticles shift effects from microbial selection to direct toxicity. • Polymer chemistry is a primary determinant of microbial functional shifts.