Effect of biodegradable films on microplastic distribution and microbial community composition in paddy soil

Biodegradable plastic film (BF) has been widely used in agriculture owing to concerns over microplastic (MP) contamination and its potential risks to agricultural sustainability. Elucidating the distribution of MP and the role of microbial communities in their biodegradation is crucial for evaluating the effectiveness of BF in paddy soil. In this study, soil samples were collected from typical paddies in southern China. The MP composition was analyzed by Fourier-transform infrared spectroscopy. Metagenomic sequencing was conducted to identify MP degradation genes and characterize microbial communities. The results revealed that BF-mulched soil had significantly higher MP abundance in the 0.25–0.1 mm size range than soil with a history of no film use as a comparator (CK) (P < 0.05). Similarly, BF had a significantly higher abundance of particular MP types than the CK (P < 0.05). Five main types of MP biodegradation pathways were identified in both BF and CK samples. Over 26 functional genes and 10 genera were associated with the biodegradation of the top five polymer types. However, only a subset of genes and genera significantly differed between BF and CK samples, particularly in the degradation of di(2-ethylhexyl) phthalate, polyethylene and other polymers (P < 0.05). At the functional level, similar genera contributed to MP degradation. However, the relative contributions of these genera varied depending on the polymer type. Overall, BF use led to more efficient MP degradation into simpler structures than in CK. Although the total MP content did not significantly differ between BF and CK samples, BF use had altered the composition and abundance of MP-degrading bacterial communities in the sampled paddy soil. This enhanced biodegradation efficiency under BF use further supports agricultural sustainability in paddy systems.