Do historically accumulated microplastics affect soil CO2 emissions and their temperature sensitivity in plastic-film mulched soils?

Microplastics have been reported to promote soil respiration in controlled experimental settings; however, the relationship between historically accumulated microplastics and soil carbon dioxide (CO 2 ) dynamics remains unclear. In this study, 67 soil samples were collected from agricultural fields under plastic film mulching, and an incubation experiment was conducted across a temperature gradient to quantify soil CO 2 emissions and their temperature sensitivity (Q 10 ). Soil microplastic abundance, chemical properties, and microbial parameters were also measured. Microplastic abundance ranged from 0.4 × 10 4 to 4.7 × 10 4 pieces kg −1 dry soil, with corresponding mass contents of 0.9–43.4 mg kg −1 dry soil. Due to the relatively low level of microplastic accumulation observed, no significant correlations were observed between historically accumulated microplastic concentrations (expressed either as particle count or mass) and soil CO 2 emissions or Q 10 values. Instead, Actinobacteria appeared to be a primary regulator of both CO 2 emissions and their thermal adaptation, whereas soil organic matter and the carbon to nitrogen ratio acted as secondary factors influencing CO 2 emissions and Q 10 , respectively. Redundancy analysis indicated a positive relationship between microplastics abundance/content and Actinobacteria , suggesting that field-realistic microplastic pollution may indirectly regulate soil carbon dynamics through its influence on Actinobacteria . Overall, our findings reveal no significant relationships between microplastics and soil CO 2 dynamics, implying that the ecological risks of historically accumulated microplastics in soil carbon cycling require further investigation.