Increasing soil microplastic diversity decreases community biomass via its impact on the most dominant species

Abstract

Ecosystems experience strong microplastic pollution and the ecological impacts of microplastic pollution have received increasing attention. While an ecosystem can be contaminated by different numbers of microplastics, no study has tested the impacts of the diversity of microplastic types on plant communities. We constructed an experimental plant community with six plant species in soils with three levels of microplastic diversity (1, 2 and 4 microplastic types) using six types of common microplastics differing in chemical composition and/or morphology, i.e., polystyrene foams (EPS), polyethylene fibers (PET), polypropylene fibers (PP), polyethylene beads (HDPE), polylactic beads (PLA), and polyamide beads (PA6). Different microplastic types in the soil differed significantly in their impacts on total and shoot biomass of the plant community, but not on its species evenness. Interestingly, total, shoot and root biomass of the plant community decreased significantly with increasing soil microplastic diversity. This was because shoot biomass of the dominant species Lolium perenne decreased significantly with increasing soil microplastic diversity. Consequently, species evenness of the plant community tended to be higher in the treatment with two and four microplastic types than in the treatment with only one type. Therefore, microplastic diversity in the soil can influence productivity of plant communities. These results highlight the importance of taking microplastic diversity into account when testing the ecological impacts of microplastics.