Polyethylene microplastic and biochar interactively affect the global warming potential of soil greenhouse gas emissions

Emerging microplastic pollution and biochar application result in their coexistence in the soil. In this study, a polyethylene microplastic, a straw biochar, and a manure biochar were applied alone or in combination to an agricultural soil to explore their interactive effects on microbial biomass carbon and nitrogen, bacterial community composition, structure and function, and the resultant greenhouse gas emissions in a 45-day laboratory incubation. At the end of incubation, the co-application of microplastic and biochar suppressed the global warming potential of cumulative greenhouse gas emissions compared with the sum of their application alone. Specifically, coexisting with microplastics increased N2O emissions by 37.5% but decreased CH4 emissions by 35.8% in the straw biochar added soil, and decreased N2O, CO2 and CH4 emissions by 24.8, 6.2, and 65.2%, respectively, in the manure biochar added soil. A correlation network analysis illustrated that the increased global warming potential was related to the changed bacterial function and microbial biomass carbon and nitrogen in the treatments with straw biochar and/or polyethylene microplastic added, and by the changed bacterial community structure and function in the treatments with manure biochar and/or polyethylene microplastic added. Bacterial functions associated with tricarboxylic acid cycle contributed to CO2 emissions. Bacterial functions associated with the nitrogen cycle such as nosZ and AOBamoABC were negatively and positively correlated with N2O emissions, respectively. The interaction between different types of microplastics and soil amendments and the resultant effects on ecosystem function deserve further research.