Microplastics alter soil enzyme activities and microbial community structure without negatively affecting plant growth in an agroecosystem

Despite the enormous benefits that plastics bring to our daily lives, plastics accumulate in the environment, especially microplastics (MPs; defined as particles <5 mm), which can cause many problems and potential loss of ecosystem services. Current research has shown the significant impact of MPs on aquatic systems, but little is known about their effect on terrestrial systems, especially within agroecosystems. Here, we investigated the effect of MPs types (PS, PE and PVC) on plant growth, soil enzyme activities, and microbial communities. MPs had a positive, type-dependent influence on plant growth affecting both above and below-ground productivity. MPs, especially PVC increased dry weights (+69.51 and + 164.62), and root length (+54.81) relative to control. Although the activity of β-glucosidase, alkaline phosphatase, cellobiohydrolase, leucine-aminopeptidase, and dehydrogenase was suppressed by MPs except urease activity which was enhanced by MPs addition. The type of MPs in soil significantly altered C flow through the soil-plant system, indicating that MPs adversely affect many C-dependent soil functions. However, MPs (especially PVC) enhanced microbial biomass carbon (+14.88%) and altered the structure and metabolic status of the microbial community. MPs addition (especially PVC) greatly enhanced soil microbial structure (+29.59%; indicated by PLFAs) compared to control. Here we provide evidence that MPs can have significant effects on key pools and fluxes within the terrestrial C cycle, with responses being MPs type-dependent. Therefore, we concluded that MPs in soil are not benign and every step should be taken to restrict their access to the soil-plant system and their potential to transfer into the food chain.