Effects of long-term plastic film mulching on microplastic and phthalate esters pollution in salt-affected soils: Microbial community shifts and enrichment of putative degraders

The long-term accumulation and spatial distribution of microplastics (MPs) and their degradation products, particularly phthalate esters (PAEs), as well as their consequent impacts on soil microbial communities and functional interactions in plastic-mulched fields, remain inadequately understood. This study systematically examined these dynamics in salinized cotton agroecosystems by analyzing soil samples collected from fields subjected to 1-30 years of continuous plastic film mulching. The composition and abundance of MPs, PAEs, and microbial community composition were characterized and quantified. Results showed that polyethylene (PE) was the predominant MP type detected in soil, with its abundance increasing significantly with prolonged mulching duration, reaching 5.80 × 10 items kg after 30 years. Surface soil (0-20 cm) contained twice the MP content of deeper layers. Di(2-ethylhexyl) phthalate (DEHP), accounting for 44 % of total PAEs, reached 0.72 mg kg in surface soil after 30 years. Long-term mulching elevated bacterial diversity and enhanced the co-occurrence network complexity. However, accumulation of MPs and PAEs disrupted the structural complexity of bacterial co-occurrence networks while enhancing overall bacterial connectivity. The dominant phyla were Proteobacteria, Actinobacteria, Gemmatimonadota, and Bacteroidota, including putative MP-degrading taxa such as the family Pyrinomonadaceae (genus PSRF01). This study provides a theoretical foundation for the restoration of salinized farmlands and the mitigation of plastic contamination in agricultural ecosystems.