Unveiling the effects of two distinct microplastics on the sediment microbial community and greenhouse gas emissions: a case study of the Nu River

Abstract

Microplastics (MPs) in river ecosystems significantly affect sediment microbial communities and biogeochemical cycling. However, the specific microbial responses to distinct MPs and their subsequent effects on greenhouse gas (GHG) emissions remain poorly understood. In this study, the effects of conventional polyvinyl chloride (PVC) and biodegradable polylactic acid (PLA) on sediment microbial communities and GHG emissions were compared. Both PVC and PLA increased sediment total organic carbon (STOC) by 31.3% and 36.7%, respectively, leading to an increase in sediment bacterial abundance. Notably, compared with PLA, PVC reduced bacterial richness more significantly. Community composition and FAPROTAX function prediction analysis revealed that PVC-enriched taxa involved in nitrate reduction (e.g., Desulfuromonas, Hydrogenophage, Azospira) resulted in a significant decrease in NO₃⁻ contents. In contrast, PLA increased the abundance of microorganisms associated with organic matter degradation (Chitinophagaceae, Comamonadaceae, and Caulobacteraceae). Both PVC and PLA significantly reduced the relative abundance of the mcrA gene, leading to decreased CH₄ fluxes, likely due to competition from enriched acetate-utilizing bacteria (Desulfuromonas, Pseudomonas, and Azospira). Additionally, PLA significantly reduced the abundance of the nirK gene. This study systematically elucidates the differential effects of PVC and PLA on microbial community structure and GHG emissions, providing new insights into the ecological impacts of MPs.

Graphical abstract

Keywords

Microplastics / Microbial community / Function predication / Greenhouse gas emissions

Highlight

	● PVC and PLA both significantly increased the sediment organic carbon content.
	● PVC had a more pronounced effect on the microbial community structure than PLA.
	● PVC enhanced the intensities of the sediment nitrate reduction and denitrification.
	● PLA enriched bacteria genera involved in complex organic matter degradation.
	● PVC & PLA decreased CH4 fluxes due to reduced abundances of methanotrophic bacteria.

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