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 agmecosystems.

Automated summary

The study found that different types of microplastics have varying effects on maize growth, with high doses of PLA potentially causing strong phytotoxicity and reducing biomass. ZnO nanoparticles had minimal effects on plant growth, but led to zinc accumulation in plants and an increase in soil pH. Both microplastics and ZnO nanoparticles influenced the composition and diversity of AM fungal communities.