Effects of microplastics on plant growth and arbuscular mycorrhizal fungal communities in a soil spiked with ZnO nanoparticles

Emerging contaminants such as microplastics and engineered nanoparticles (NPs) have become an environmental issue of global concern, but little is known about their joint effects in soil–plant systems. We studied the effects of two microplastics, conventional non-degradable high–density polyethylene (HDPE) and biodegradable polylactic acid (PLA), on maize growth and arbuscular mycorrhizal (AM) fungal communities in a soil spiked with or without ZnO NPs. HDPE and low–dose PLA promoted plant growth, while high–dose PLA significantly decreased maize shoot (by 16%–40%) and root biomass (by 28%–50%), indicating high-dose PLA may have strong phytotoxicity. ZnO NPs displayed non-significant effects on plant growth, but caused greater Zn accumulation in plants. Both HDPE and PLA further increased Zn concentrations in roots, while decreasing Zn translocation to aerial parts. High–throughput sequencing showed that microplastics and ZnO NPs singly and jointly influenced AM fungal community composition and diversity, particularly the relative abundance of dominant genera. The presence of ZnO NPs and microplastics generally increased soil pH. Overall, our findings imply increasing contamination by microplastics and NPs can have profound ecological impacts on plant fitness, plant quality, and soil microbial community composition and diversity, resulting in uncertain consequences for agroecosystems. •Interactions of microplastics and nanoparticles on mycorrhizae were first studied.•Polylactic acid had low-dose stimulation and high-dose inhibition effects on plants.•Polyethylene antagonistically interacted with ZnO nanoparticles on plant growth.•Microplastics altered Zn accumulation and translocation in plants exposed to ZnO.•Microplastics and ZnO nanoparticles altered AMF community structure and diversity.