Low-density polyethylene microplastics and biochar interactively affect greenhouse gas emissions and microbial...

Paddy soils are susceptible to microplastics (MPs) contamination. As a common soil amendment, biochar (BC) has been extensively applied in paddy fields. The co-occurrence of MPs and BC may cause interactive effects on soil biogeochemical processes, which has yet been well studied. In this study, a 41-days of microcosm experiment was conducted using paddy soil added with 0.5-1.5 wt% of low-density polyethylene (LDPE) and 5 wt% of BC individually or jointly. Application of BC, LDPE, or their mixture into soil significantly increased the emission of methane (CH₄), but suppressed the emission of carbon dioxide (CO₂). LDPE addition lowered soil nitrous oxide (N₂O) emissions, while BC exerted an opposite effect. Proteobacteria was the most dominant phylum with a relative abundance range of 35.1-51.0%, followed by Actinobacteria (19.3-30.9%) and Acidobacteria (7.5-23.5%). The abundances of the mcrA gene and pH values were increased in soils added with BC or/and LDPE, which were the possible reasons for the higher CH₄ emissions in these treatments. The emission of N₂O was positively related to the abundances of norB and narG genes, suggesting denitrification was a major pathway to produce N₂O. Results of structural equation modeling demonstrated that addition of BC or/and LDPE MPs could affect greenhouse gas emissions from paddy soil by altering soil chemical properties, microbial community structure, and functional gene abundances.