Long-term no-tillage practice with re-used plastic film mulching exacerbates bacterial ecological risks in...

Re-used plastic-film (RUPF) mulching has emerged as an innovative and practical agricultural practice to reduce plastic use and the buildup of plastic waste in drylands in China. However, alterations in bacterial community colonisation mechanisms and ecological processes due to plastic contamination in RUPF mulching systems remain unclear. In this study, we examined the distribution and assembly of soil bacterial communities under two RUPF exposure scenarios, weathered plastic film plastisphere (WPS) and soil-buried plastic film plastisphere (BPS), and compared them to no-mulching ambient soil (CK). The findings revealed that WPS differed significantly from CK and BPS in terms of soil bacterial alpha- and beta-diversity. Bacterial diversity was reduced in WPS, while BPS showed no significant change compared to CK. Moreover, stochastic processes primarily influenced bacterial community assembly across all environments, whereas deterministic processes had a more pronounced effect on plastispheres than on CK. In WPS, the migration and diffusion of colonising bacteria was slow, whereas bacterial competition was more pronounced in BPS. The co-occurrence networks in the plastispheres were more intricate and unstable than those in CK. There were notable differences in bacterial functions between the plastisphere and CK soils, carbohydrate metabolism, amino acid metabolism, lipid metabolism, and xenobiotic biodegradation and metabolism decreased in WPS; whereas lipid metabolism and xenobiotic biodegradation and metabolism increased in BPS compared to that in CK. Notably, the profiles of human disease-related pathways, virulence factors, and pathogens were significantly higher in the plastisphere than that in CK, with WPS showing higher levels than BPS. Overall, our results emphasise that WPS has a more distinct bacterial composition and function, heightening the potential ecological risks compared to CK and BPS. These findings highlight the need for effective strategies to mitigate the risks of reusing plastic films in agricultural environments.