Microplastic diversity stimulates N₂O emission during NO₃^--N transformation by altering microbial interaction and...

Microplastic mixtures, consisting of various types, are widespread in aquatic ecosystems. However, the role of microplastic diversity in influencing N₂O emission during NO₃^--N transformation remains unclear, particularly in eutrophic water bodies. To address this, we established 10 microcosms with microplastic diversity of 0, 1, 3, and 5 and explored the effects of microplastic diversity on NO₃^--N transformation, N₂O emission, microbial communities, co-occurrence networks, and electron transfer. Results showed that microplastic diversity slightly impacted NO₃^--N transformation rates, but remarkably enhanced N₂O emission. Although elevated microplastic diversity caused notable variations in microbial community, bacterial abundance had insignificant correlations with NO₃^--N transformation or N₂O emission rates. Notably, the increased microplastic diversity made microbial networks more complex and stable, indirectly promoting N₂O emission by altering electron transfer and consumption during NO₃^--N transformation. Especially, electron consumption had the most direct effect on N₂O emission. Furthermore, the increasing microplastic diversity slightly affected NOR activity, while significantly decreasing NOS activity and raising (nirK+nirS)/nosZ ratio, which suggested that microplastic diversity primarily enhanced N₂O emission by inhibiting its further reduction. Our findings provide deeper insight into the nitrogen transformation and greenhouse gas emission influenced by microplastic mixtures in eutrophic aquatic environments.