Investigation of the Effects of Polyethylene Microplastics at Environmentally Relevant Concentrations on the Plant-Soil-microbiota System: A Two-Year Field Trial

Microplastics are a potential threat to agricultural sustainability. However, the effects of microplastics at environmentally relevant concentrations on the plant-soil-microbiota system in realistic field conditions are largely unknown. Herein, we conducted a two-year field trial to study the effects of polyethylene (PE) microplastics at 0, 100, and 600 mg/kg on crop growth, soil properties, and the composition and function of microbial communities in a farmland with rice-wheat rotation. PE did not affect wheat growth but it increased the rice grain weight by 42.5 % at 600 mg/kg, and enhanced rice height by 35.4 % and 30.2 % at 100 and 600 mg/kg, respectively. The presence of PE significantly decreased soil available phosphorus during the wheat season, while it reduced soil total nitrogen, NH4+-N and available phosphorus during the rice season. There were five and sixteen bacterial orders identified changed by PE in wheat and rice soils, respectively. Specifically, PE at different concentrations differentially altered the abundances of sulfate-reducing bacteria Thermodesulfovibrionia, Thermoactinomycetales and Syntrophobacterales, and further modified soil sulfate respiration in wheat soils. During the rice season, PE (100 mg/kg) increased the abundance of Xanthomonadales by 98.0 % and enriched the functional groups of intracellular parasites, while PE (600 mg/kg) inhibited twelve cluster of orthologous group function classes and disturbed bacterial metabolism. This study suggests that PE exhibits a greater impact on the plant-soil-microbiota system during the rice season compared to the previous year's wheat season, highlighting the importance of crop type and cultivation practices in determining the environmental risks of microplastics in agroecosystems.