Microplastics as drivers of carbon and nitrogen cycling alterations in aquatic ecosystems: A meta-analysis

Microplastics (MPs) have been increasingly recognized as an emerging contaminant in aquatic ecosystems, with growing evidence of their impact on biogeochemical cycles. This study synthesizes the effects of MPs on nitrogen and carbon cycling in aquatic environments by performing a network meta-analysis. Our findings suggest that MPs enhance dissolved organic carbon and total organic carbon concentrations, promote anaerobic processes, and stimulate greenhouse gas emissions, including N₂O and CH₄. In seawater sediments, MPs significantly enhance denitrification, as evidenced by increased abundances of narG, nirS, nirK, and nosZ genes, elevated N₂O production, and reduced NO₃⁻ concentrations. In contrast, MP addition exhibit weaker denitrification but heightened N₂O production in freshwater sediments, likely driven by enhanced dissimilatory nitrate reduction to ammonium processes. Furthermore, biodegradable MPs exhibit stronger effects on carbon and nitrogen metabolism compared to non-biodegradable MPs. These findings highlight the complex and medium-dependent role of MPs in biogeochemical cycles, emphasizing the need for interdisciplinary research to fully elucidate their environmental impacts.