Mycorrhizal-specific responses of rhizosphere soil properties and fine-root traits to polystyrene microplastic addition in a temperate mixed forest

While microplastic impacts on aquatic and agricultural systems are well-documented, their impacts on forest ecosystems remain poorly understood. We assessed how microplastic addition affects rhizosphere soil properties and fine-root traits for ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) associations in a mixed temperate forest. In ECM-associated soils, microplastics increased nitrogen availability and nitrate reductase activity but decreased phosphorus and phosphatase activity; AM-associated soils showed the opposite pattern. Morphologically, ECM roots exhibited reduced branching but increased hyphal density and colonization. Conversely, AM roots displayed increased specific root length and tip density but decreased cortical thickness and tissue density. These divergent, mycorrhizal-specific responses suggest that increasing microplastic pollution may fundamentally alter nutrient cycling and species composition dynamics in temperate forests. After microplastic addition, rhizosphere nitrogen increased but phosphorus decreased in ectomycorrhizal trees, while arbuscular mycorrhizal trees showed an opposite trend of lower nitrogen and higher phosphorus in rhizosphere soil, based on a field study in Changbai Mountain Nature Reserve, China.