Soil texture modulates the impact of biodegradable microplastics on N₂O emissions in agroecosystems

With the increasing usage of biodegradable plastics, the biodegradable microplastics (MPs) released will inevitably interact with soil microbiota and disturb biogeochemical processes. Though they are reported to influence greenhouse gas N₂O emissions, conflicting results were obtained in previous studies, rendering their risks still in dispute. Here, we evaluated the effects of poly (butylene adipate-co-terephthalate) (PBAT) MPs at environmentally relevant concentrations (0.2-0.5%) on N₂O emission in eight agricultural soils. The results for the first time demonstrated that, the effect of biodegradable MPs on N₂O was largely dependent on soil texture. PBAT MPs showed a negative effect in soils with high clay content (26.2-29.3%) (p < 0.05), a positive effect in soils with low clay content (7.7-15.1%) (p < 0.05), and insignificant effect in soils with moderate clay content (19.9%) (p > 0.05). The observed positive effect can be attributed to the labile carbon released during PBAT MPs degradation, which stimulated heterotrophic denitrifiers as evidenced by the increased nirK gene abundance and elevated denitrification rates relative to the control. Conversely, the negative effect may stem from the formation of stricter anaerobic micro-environments induced by PBAT MPs degradation in high-clay soils, promoting more complete denitrification. This is supported by the most significant increase in nosZ gene abundance and the enrichment of Bradyrhizobium, a denitrifier capable of both producing and reducing N₂O. This study greatly advances our understanding of how biodegradable MPs (i.e., PBAT) modify soil denitrifiers and N₂O emissions under different soil conditions, and underscore the importance of soil texture in regulating their effects.