Differential responses of soil microbial community structure and function to conventional and biodegradable microplastics

Biodegradable plastics have attracted increasing attention as substitutes for conventional plastics; however, they may release a greater quantity of microplastics (MPs) than conventional plastics over a certain period. Currently, knowledge regarding the impacts of biodegradable MPs (BMPs) on soil microbial communities is scarce. This study explored the impacts of nine common BMPs (polylactic acid [PLA], poly (butylene adipate- co -terephthalate) [PBAT], poly (butylene succinate) [PBS], polycaprolactone [PCL], polyhydroxyalkanoates [PHA], and polyhydroxy butyrate [PHB]) and conventional MPs (CMPs) (polyethylene [PE], polypropylene [PP], and polyvinyl chloride [PVC]) on the structure and function of soil microbial communities after incubation in soil for 180 d. After incubation, the apparent morphology and the intensity of surface functional group absorption peaks of PCL, PHA, PBAT, PBS, PVC, PLA, and PHB exhibited pronounced changes. Among these, PCL, PHA, PBAT, PVC, and PBS experienced varying degrees of weight loss, with reduction rates of 12.8 ± 6.5%, 5.60 ± 4.25%, 1.14 ± 0.25%, 0.652 ± 0.956%, and 0.194 ± 0.030%, respectively. PLA and PCL had minimal effects on soil urease, dehydrogenase, and β-glucosidase activities. Meanwhile, most PBAT, PBS, PHA, and PHB substantially increase these enzyme activities by 7.01–55.9% when compared to that achieved with the control; however, no consistent pattern was observed for PE, PP, and PVC. Most MPs did not significantly affect the richness or diversity of soil bacterial communities, except for PP, PCL, PBS, and PHA. PLA, PCL, PBS, PHA, and PHB significantly altered the relative abundance of several bacterial families, including Xanthomonadaceae , Microscillaceae , Comamonadaceae , Sphingomonadaceae , Nocardioidaceae , Gemmatimonadaceae , Vicinamibacteraceae , Gaiellaceae , and SC_I_84 . PBAT, PCL, and PHA substantially increased the abundance of most soil carbon- and nitrogen-cycle genes, whereas PBS and PHB showed opposite trends; no marked effects were observed for PE, PP, PVC, and PLA. Collectively, BMPs—particularly PHB, PHA, PBS, and PCL—exerted stronger influences on soil microorganisms than CMPs. Taken together, these findings demonstrate distinct and material-specific responses of soil microorganisms to common CMPs and BMPs. • BMPs underwent varying degrees of degradation after being incubated in soil for 180 d. • Most BMPs exhibited more pronounced effects on soil microbial communities compared to CMPs. • PBS, PHB, PCL, PHA, and PBAT exhibited different effects on most soil C/N cycling genes. • CMPs did not influence the abundance of soil C/N cycling genes.