Effects of microplastic types and shapes on the community structure of arbuscular mycorrhizal fungi in different soil types

Arbuscular mycorrhizal fungi (AMF) play a crucial role in soil ecosystems by enhancing nutrient exchange, stabilizing soil structure, and improving water movement in soils. Microplastics (MPs), synthetic polymers smaller than five mm, pose an emerging threat to AMF by altering soil structure and chemistry, potentially disrupting these essential functions. This study examined how ten different microplastic types and shapes influenced AMF communities within the context of Grime's C-S-R (competitor-stress tolerator-ruderal) framework. We tested the effects of polypropylene, polyester, high-density polyethylene, polyethylene terephthalate, low-density polyethylene, polyvinyl chloride, and polystyrene on three distinct soils (Albic Luvisol, Haplic Chernozem, and Haplic Luvisol), examining MPs in forms of fibers, films, fragments, and mixtures, in a total of 15 treatments. Although general diversity indices based on the OTU level showed no significant changes, shifts occurred at the genus level. The soils were predominantly colonized by Funneliformis and an unidentified genus in Glomeraceae (incertae sedis); however, the addition of MPs increased the relative abundance of Diversispora and Claroideoglomus, while also subtly promoting Rhizophagus and Septoglomus. In particular, Claroideoglomus showed a notable increase in relative abundance in the most diverse Haplic Chernozem soil when exposed to fragment-shaped MPs and mixed MP types. According to Grime's C-S-R framework, these genera are classified as ruderals, except for Diversispora, a stress tolerator. Ruderals are known to thrive following disturbances, such as physical disruption of soil structure, a known effect of MPs, while MPs can also create stress conditions within the soil selecting stress tolerators. Our findings highlight the complex and soil-specific interactions between MPs and AMF, demonstrating that the effects of MPs on AMF are driven by the combined influence of soil types and MP properties.