Effects of phthalic acid esters released from long-term agricultural film mulching on soil properties, bacterial communities, and functions in Xinjiang cotton field.

The global use of transparent agricultural films has raised significant concerns about the contamination of phthalate esters (PAEs). Despite these concerns, field studies on PAE accumulation due to long-term agricultural film use remain limited. This study focuses on cotton fields in Xinjiang with varying mulching durations (0-30 years) to explore the accumulation of PAEs and their effects on soil physicochemical properties, enzyme activities, microbial metabolic functions, and community structure. Results reveal that with the increase in mulching duration, the ∑PAEs content in the soil did not follow a linear growth trend, but instead exhibited a pattern of initial increase followed by a decrease. The peak concentration was observed in the 8th year, reaching 6.40 mg/kg. This decline is attributed to multiple factors, including microbial adaptation, decreased film degradation, and soil uptake of residual compounds. The accumulation and degradation of PAEs significantly altered soil pH and organic matter content. Both soil enzyme activity and microbial metabolic activity showed a three-phase fluctuation over time, initially increasing, then decreasing, and finally increasing again, highlighting the microbial response to environmental PAE-induced stress. Similarly, the diversity and composition of bacterial communities exhibited analogous fluctuations. The analysis of keystone species abundance, assessment of co-occurrence network complexity, and evaluation of their ecological functions in carbon, nitrogen, and sulfur cycling collectively underscore the potential risks posed by PAEs in long-term mulched cotton fields to soil health and ecosystem stability. In summary, this study provides comprehensive field-based evidence that long-term use of agricultural mulching films leads to dynamic changes in PAEs accumulation, which in turn affect soil physicochemical properties, microbial functions, and ecosystem stability, thereby underscoring the ecological risks associated with prolonged plastic film application in agroecosystems.