The accumulation of Ag2S in agricultural soil via application of Ag-containing sludge potentially affects the functioning of soil microorganisms and earthworms due to the strong antimicrobial properties of Ag. This study examined the effects of Ag2S nanoparticles (Ag2S-NPs) on the earthworm-mediated (Eisenia fetida and Pontoscolex corethrurus) soil N cycle. We used 16S rRNA gene based sequencing and quantitative polymerase chain reaction (qPCR) to examine the bacterial community and nitrification/denitrification-related gene abundances. The presence of either earthworms or Ag significantly increased denitrification and N2O emissions. However, the addition of Ag2S to earthworm-inhabited soil reduced N2O emissions by 14-33%. Furthermore, Ag2S caused a low-dose stimulation but a high dose inhibition to N2O flux from the earthworm gut itself. Accordingly, an increase in Ag in the earthworm gut caused a decrease in the relative abundance of denitrifiers in both the soil and the gut, especially for the dominant genus Bacillus. The Ag2S also decreased the copy numbers of nitrification gene (nxrB) and denitrification genes (napA, nirS and nosZ) in earthworm gut, leading to the observed decrease in N2O emissions. Collectively, applying Ag2S-containing sludge disturbs the denitrification function of the earthworm gut microbiota and the cycling of N in soil-based systems.
Jingtao Wu, Yunfei Bai, Bingkun Lu
Environmental science & technology