Cropping systems reshape the distribution and risks of microplastics in soil aggregates in a karst agricultural...

Microplastics (MPs) represent persistent pollutants in agricultural soils, yet how cropping systems influence their distribution and risks within soil aggregates remains unclear, especially in fragile karst ecosystems. This study investigated the abundance, morphology, polymer composition, diversity, ecological risks, and loss potential of MPs within soil aggregates under plastic-mulched (flue-cured tobacco and chili pepper) and non-mulched (maize monoculture and intercropping) cropping systems in the Chishui River Basin, a typical karst region in Southwest China. The mean MP abundance was 1723 ± 527 items kg^-1, with predominant enrichment in coarse macro-aggregates (CMA; 50.84-69.04 %). Plastic-mulched systems accumulated approximately 46-76 % more MPs in CMA than non-mulched systems. These MPs were primarily transparent/black, film-shaped polyethylene, and as fibrous rayon particles in the 0.5-1 mm size range. Non-mulched systems, particularly intercropping, showed higher MP diversity and a shift in accumulation towards microaggregates, where the highest ecological risk indices were observed. The estimated MP loss intensity was 1.29-2.53 × 10⁷ items km^-2 yr^-1, with plastic-mulched crops contributing the most. Partial least squares-structural equation modeling (PLS-SEM) identified environmental factors (soil organic carbon, pH) as stronger drivers of MP pollution than socioeconomic factors (fertilizer and plastic film input). Our findings demonstrate that cropping systems fundamentally reshape the distribution and risk profile of MPs within the soil aggregates. This underscores the need for system-specific mitigation, such as adopting biodegradable films in mulched systems and straw mulching in maize intercropping systems to reduce respective MP sequestration and loss.