Impacts of Microplastics on Soil Characteristics, Microbial Diversity and Greenhouse Gas Emissions: A Review

Soil microplastics (MPs) pollution has emerged as a global concern, yet its integrated impacts on soil biogeochemical cycles and greenhouse gas (GHG) fluxes remain incompletely understood. This review synthesizes studies from 2019 to 2026 on MP interactions with soil physicochemical properties, microbial communities, and GHG dynamics, emphasizing carbon and nitrogen cycling. MPs actively modify soil processes rather than acting as inert particles. Fiber and film MPs alter pore architecture, bulk density, and water retention, affecting aeration and microbial habitats. For carbon cycling, MPs modify DOC, MBC, and EOOC pools and trigger polymer-specific priming effects that range from positive to negative depending on polymer composition, with net outcomes varying across studies. For nitrogen cycling, MP-induced shifts in NO₃^--N and NH₄⁺-N availability and in nitrification and denitrification pathways yield variable N₂O responses; notably, certain biodegradable polymers suppress N₂O emissions in a dose-dependent manner, contrasting with the neutral or stimulatory effects of conventional plastics. Microbial communities shift functionally, with enrichment of plastic-degrading taxa, increased Proteobacteria, reduced overall bacterial abundance, and promoted fungi, while the plastisphere forms a distinct habitat from bulk soil. GHG responses are highly context-dependent, varying with polymer type, concentration, shape, aging, soil properties, and experimental conditions, and should not be generalized. Future research should prioritize environmentally relevant doses, polymer mixtures, long-term field experiments, co-pollutant scenarios, and integration of MP-derived degradation products into carbon models. Addressing these gaps will advance understanding of MP-soil-climate interactions and support evidence-based risk assessment.