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Mechanistic insights into microplastic-mediated shifts in nitrogen metabolism and sensory quality across emergent and submerged-plant wetlands: Evidence from metagenomics and physiological indicators
Summary
Researchers exposed surface-flow constructed wetlands planted with emergent and submerged macrophytes to polystyrene microplastics and found a 12.64% reduction in total nitrogen removal in the emergent plant system, driven by shifts in nitrogen-cycling microbial communities. PS-MPs also altered sensory water quality indicators, with effects varying by plant type.
Polystyrene microplastics (PS-MPs), increasingly present in aquatic environments, pose potential threats to constructed wetlands (CWs) potentially altering both nitrogen removal and sensory water quality. This study investigated the response of PS-MPs on surface flow constructed wetlands (SFCWs) planted with emergent (Iris pseudacorus) and submerged (Vallisneria natans) macrophytes. The results showed that PS-MPs significantly reduced total nitrogen removal by 12.64 % in emergent macrophyte systems (EM-CW) compared to the control, mainly due to a 45.23 % decrease in NO₃⁻-N removal. Conversely, submerged macrophyte systems (SM-CW) showed a 29.98 % increase in denitrification efficiency but experienced a 7.16 % reduction in NH₄⁺-N removal compared to controls (SU-CW). Sensory indicators, including surface chroma and turbidity, increased by 18.88 % and 20.60 %, respectively, in SM-CW, while EM-CW maintained stable sensory indicators, suggesting different tolerance based on macrophyte life form. Metagenomic analysis revealed a 45.6-70.7 % decline in denitrification genes (e.g., norC, nosZ) in EM-CW, whereas the nitrification gene hao was suppressed by 79.8 % in SM-CW. These findings demonstrate that macrophytes life form governs the impacts of PS-MPs on nitrogen removal and sensory quality, highlighting a life-form-dependent tolerance mechanism. This study also emphasizes the need to consider types of macrophytes when designing CWs under PS-MPs stress.
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