Application of sewage sludge containing environmentally-relevant silver sulfide nanoparticles increases emissions of...

Silver (Ag) is released from a range of products and accumulates in agricultural soils as silver sulfide (Ag₂S) through the application of Ag-containing biosolids as a soil amendment. Although Ag₂S is comparatively stable, its solubility increases with salinity, potentially altering its impacts on microbial communities due to the anti-microbial properties of Ag. In this study, we investigated the impacts of Ag on the microbially mediated N cycle in saline soils by examining the relationship between the (bio)availability of Ag₂S and microbial functioning following the application of Ag₂S-containing sludge. Synchrotron-based X-ray absorption spectroscopy (XAS) revealed that the Ag₂S was stable within the soil, although extractable Ag concentrations increased up to 18-fold in soils with higher salinity. However, the extractable Ag accounted for <0.05% of the total Ag in all soils and had no impact on plant biomass or soil bacterial biomass. Interestingly, at high soil salinity, Ag₂S significantly increased cumulative N₂O emissions from 80.9 to 229.2 mg kg^-1 dry soil (by 180%) compared to the corresponding control sludge treatment, which was ascribed to the increased abundance of nitrification and denitrification-related genes (amoA, nxrB, narG, napA, nirS, and nosZ) and increased relative abundance of denitrifiers (Rhodanobacter, Salinimicrobium, and Zunongwangia). Together, our findings show that the application of Ag₂S-containing sludge to a saline soil can disrupt the N cycle and increase N₂O emissions from agroecosystems.