Response of soil property and microbial community to biodegradable microplastics, conventional microplastics and straw residue

The application of biodegradable plastics is considered crucial steps in addressing plastic pollution. However, due to their high sensitivity to light, heat, and biological factors, biodegradable plastics are more likely to break down into microplastics, which could enter the soil environment. Therefore, it is urgent to study the effects of biodegradable microplastics in soil ecosystems. In this study, we investigated the impact of microplastics derived from poly (butylene adipate-co-terephthalate) (PBAT), which is commonly used for making biodegradable mulching film, on soil properties and microbial communities, and compared the impacts of PBAT microplastics with those of conventional polyethylene (PE) microplastics, biodegradable polylactic acid (PLA) microplastics, and straw residue. The results showed that 0.5 % (w/w) of PE and PLA microplastics exhibited minimal impact on soil parameters after an incubation of 100 d at 30 degrees C, while PBAT microplastics significantly increased dissolved organic carbon (DOC) content and microbial biomass and significantly reduced available nitrogen (NH4+-N and NO3--N) content, potential nitrification rate and beta-glucosidase activity. Although PBAT had insignificant effect on soil bacterial community structure, it increased the relative abundance of several Proteobacteria members, such as Ramlibacter, Bradyrhizobium, Ellin6067 and Pedomicrobium. In terms of fungi, PBAT significantly reduced community diversity and altered community structure, mainly enriching the genera of Acrophialophora and Tetracladium, which are potential pathogens or bioplastic degraders. Interestingly, as a relatively easily degradable natural polymer/organic matter, straw showed a weaker effect than PBAT. This was probably because straw residue differed from plastic in composition, with the recalcitrant components being dominant at the later stage of incubation, which caused nutrient depletion and the die-off of microbes enriched during early stages. This study highlights the profound impacts of PBAT microplastics on soil ecosystems.