Interactions of microplastics and cadmium on plant growth and arbuscular mycorrhizal fungal communities in an agricultural soil

Microplastics (MPs) as emerging contaminants have attracted attention worldwide, but little is known on their interactions with metallic contaminants in soil-plant systems. Here, we investigated the interactions between MPs, i.e., polyethylene (PE) and polylactic acid (PLA), and cadmium (Cd) on plant performance and arbuscular mycorrhizal fungal community in an agricultural soil. PE showed no noticeable phytotoxicity, while 10% PLA decreased maize biomass and chlorophyll content in leaves. A significant interaction on root biomass occurred between PE and Cd, but not between PLA and Cd. Both PE and PLA caused increase in soil pH and DTPA-extractable Cd concentrations, but no alterations in Cd accumulation in plant tissues. Different numbers of endemic and total OTUs were observed in various treatments. The relative abundance of arbuscular mycorrhizal fungi (AMF) genera highly varied with MPs and Cd. MPs altered AMF community structure and diversity, depending on their type and dose. Coexisting Cd produced slight but significant interactions with MPs on the dominant AMF genera. Overall, plant growth and AMF community varied with MPs type and dose, Cd, and their interactions, and the high dose of PLA produced stronger phytotoxicity. In conclusion, coexisting MPs and Cd can jointly drive shifts in plant performance and root symbiosis, thereby posing additional risks for agroecosystems and soil biodiversity.