Microplastic-induced agricultural soil carbon dynamics: A global meta-analysis of property-dependent effects and underlying mechanisms.

Microplastics (MPs) pollution in agricultural soils alters global carbon cycling, yet the underlying mechanisms remain poorly understood. Through a global meta-analysis of 1230 observations from 89 studies, we show that MPs exposure increased soil organic carbon (SOC) by 27.1%, dissolved organic carbon (DOC) by 16.3%, CO2 emission by 39.1%, and microbial biomass carbon (MBC) by 19.1%, while reducing soil pH and nitrate nitrogen. Biodegradable MPs exert stronger impacts on total carbon, CO2 emission, and MBC than conventional MPs, partly reflecting short-term incubation conditions. Lower MPs concentrations show positive linear effects on SOC, DOC, and MBC, whereas high concentrations shift the CO2 turning point. Particles > 100 μm enhance MBC, whereas smaller fractions show mixed effects. Fiber-shaped MPs promote SOC and CO2 via three-dimensional networks. Organic amendments produce type- and time-dependent effects on carbon indicators. Model averaging identifies MPs concentration and background SOC as dominant predictors. Structural equation modeling reveals conventional MPs favor physical pathways while biodegradable MPs favor biological pathways (reducing Gram-negative bacteria and enhancing network connectivity). Temporal responses peak at 30-60 days, with maximal responses in weakly acidic soils and high-clay soils. Our findings provide a preliminary mechanistic framework and morphology-specific insights for risk assessment in agricultural systems.