Interactive effects of microplastics and arbuscular mycorrhizal fungi on grassland communities

Societal Impact Statement Grassland plant communities contribute significantly to global biodiversity but face numerous man‐made pressures which may interfere with their ecological functions. One such pressure receiving increasing scientific, political, and public attention is microplastic pollution. Despite multifaceted effects on individual plants, plant‐community responses are rarely assessed. We show that, over two growing seasons, microplastics differentially affect the productivity and structure of experimental grassland communities, with various effects depending on initial community composition, microplastic characteristics, and plant‐mycorrhiza interactions. As grasslands facilitate ecological processes (e.g., carbon storage) and provide ecosystem services (e.g., food and water supply), our findings highlight the need for actions to preserve those important functions. Summary Terrestrial microplastic pollution is receiving increasing public and scientific attention. While diverse microplastic effects on individual plants' physiology, morphology, and productivity are known, how such effects transmit to the community level remains poorly understood. However, as grassland plant communities are central agents for ecosystem functioning and ecosystem services, assessing how microplastics may interfere with such functions is indispensable. To reduce this gap, we tested how six types of artificial particles and their interactions with arbuscular mycorrhizal fungi (AMF) affect the productivity and composition of plant communities representing dry and mesic grasslands over 17 months. Effects were strongest in the mesic, less diverse community type. Without artificial particles, community biomass was higher with AMF but lower without AMF, while AMF did not affect community biomass if artificial particles were present. Compared with glass, microplastics increased diversity with AMF but decreased it without AMF. Importantly, most effects depended on AMF inoculation and material type and concentration, revealing no universal pattern of microplastic pollution on grassland communities. Next to providing first evidence that microplastic effects on plant communities might change over time, our results highlight that such effects likely depend on particle and community characteristics and that responses differ between community traits such as productivity and diversity. Advancing the knowledge about ecological effects of microplastic pollution in terrestrial systems will require a stronger emphasis on community‐level experiments as well as incorporating temporal dynamics and the diversity of plastic pollution. Such work is essential to anticipate how accumulating plastic waste may alter grassland ecosystem functioning.