Natural chalcopyrite mitigates nitrous oxide emissions in sediment from coastal wetlands

Coastal wetlands are one of the most important natural sources of nitrous oxide (N₂O). Previous studies have shown that copper-containing chemicals are able to reduce N₂O emissions from these ecosystems. However, these chemicals may harm organisms present in coastal waters and sediment, and disturb the ecological balance of these areas. Here, we first investigated the physiological characteristics and genetic potential of denitrifying bacteria isolated from coastal wetlands. Based on an isolated denitrifier carrying a complete denitrification pathway, we tested the effect of the natural mineral chalcopyrite on N₂O production by the bacteria. The results demonstrated that chalcopyrite addition lowers N₂O emissions from the bacteria while increasing its N₂ production rate. Among the four denitrification genes of the isolate, only nosZ gene expression was significantly upregulated following the addition of 2 mg L^-1 chalcopyrite. Furthermore, chalcopyrite was applied to coastal wetland sediments. The N₂O flux was significantly reduced in 50-100 mg L^-1 chalcopyrite-amended sets relative to the controls. Notably, the dissolved Cu concentration in chalcopyrite-amended sediment remained within the limit set by the National Sewage Treatment Discharge Standard. qPCR and metagenomic analysis revealed that the abundance of N₂O-reducing bacteria with the nosZ or nirK + nosZ genotype increased significantly in the chalcopyrite-amended groups relative to the controls, suggesting their active involvement in the reduction of N₂O emissions. Our findings offer valuable insights for the use of natural chalcopyrite in large-scale field applications to reduce N₂O emissions.