Live soil ameliorated the negative effects of biodegradable but not non-biodegradable microplastics on the growth of plant communities

Abstract Plastic pollution has become a global environmental problem. Alternative use of biodegradable plastics has been proposed to mitigate the pollution problem caused by the traditional non-biodegradable plastics but the relative impacts of both types of microplastics on plant community productivity and diversity remain unknown. Microplastics can affect growth of individual plants directly by altering plant physiological processes and indirectly by altering soil biota that in turn influence plant growth. However, it remains unknown whether soil biota can mediate impact of biodegradable and non-biodegradable microplastics on plant community productivity and diversity due to a lack of studies on the topic. Here, we performed a greenhouse experiment with six plant communities and five biodegradable and five non-biodegradable microplastics to test whether: 1) biodegradable microplastics have a less negative effect on plant community biomass production and diversity than non-biodegradable microplastics, and 2) soil microorganisms differentially mediate the effects of non-biodegradable and biodegradable microplastics on plant community biomass production and diversity. We employed a fully crossed factorial design to grow the six plant communities in the presence vs . absence of the 10 microplastics individually and in live soil vs . sterilized soil. Results show that live soil ameliorated the negative effects of biodegradable microplastics on shoot biomass of the plant communities, but microplastics suppressed plant community diversity more strongly in live soil than in sterilized soil regardless of microplastics types under averaged across all treatments. Furthermore, the specific microplastics polymers were the main drivers of these results. Synthesis and applications: Overall, our findings indicate that even biodegradable microplastics, e.g. PBS, which are considered environmentally friendly, still pose significant ecological risks to the structure and productivity of plant communities with potential implications for functioning of terrestrial ecosystems. Future studies may identify the specific taxa of soil microorganisms that may have degraded the microplastics that we studied, their rates of biodegradation, and the effects thereof on plant community structure and productivity under more natural field conditions in contrasting climatic conditions.