Silver Sulfide Nanoparticles Reduce Nitrous Oxide Emissions by Inhibiting Denitrification in the Earthworm Gut.

The accumulation of Ag2S in agricultural soil via application of Ag-containing sludge potentially affects the functioning of soil microorganisms and earthworms (EWs) due to the strong antimicrobial properties of Ag. This study examined the effects of Ag2S nanoparticles (Ag2S-NPs) on the EW-mediated (Eisenia fetida and Pontoscolex corethrurus) soil N cycle. We used 16S rRNA gene-based sequencing and quantitative polymerase chain reaction to examine the bacterial community and nitrification/denitrification-related gene abundance. The presence of either EWs or Ag significantly increased denitrification and N2O emissions. However, the addition of Ag2S to EW-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 EW gut itself. Accordingly, an increase in Ag in the EW gut caused a decrease in the relative abundance of denitrifiers in both the soil and the gut, especially for the dominant genus Bacillus. Ag2S also decreased the copy numbers of nitrification gene (nxrB) and denitrification genes (napA, nirS, and nosZ) in EW gut, leading to the observed decrease in N2O emissions. Collectively, applying Ag2S-containing sludge disturbs the denitrification function of the EW gut microbiota and the cycling of N in soil-based systems.

Application of sewage sludge containing environmentally-relevant silver sulfide nanoparticles increases emissions of nitrous oxide in saline soils.

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.

[Study on spatial-temporal variation of infected snail in bottomland areas after an integrated control strategy at village level in the marshland and lake regions based on geographic information system].

OBJECTIVE: To evaluate the effect of an integrated control strategy and to quantify the spatial-temporal variation of infected snails in the bottomland areas after the strategy was implemented. METHODS: Based on the geographic database of infected snail distribution at the village level during 2004 - 2010 in Anxiang county, Hunan province, spatial autocorrelation analysis and spatial scan statistics were applied to analyze the spatial-temporal characteristics on the distribution of infected snails. RESULTS: The number of embankments with infected snails in Anxiang county decreased from 23 in 2004 to 10 in 2010, while the rate of frame with infected snail in embankments decreased from 4.32‰ in 2004 to 0.12‰ in 2010. The spatial distribution of infected snails was nonrandom, only in 2004 and 2005 with Moran's I = 0.21 (P < 0.10) and Moran's I = 0.13 (P < 0.10) respectively. Data from the local spatial auto-correlation analysis showed that the number of villages with H-H types of auto-correlation model had been gradually decreasing. The results of SaTScan statistics appeared the same as from the local spatial auto-correlation analysis, showing that the number of areas with increased risk was decreasing. CONCLUSION: The comprehensive measures with emphasis on infectious source control seemed effective for schistosomiasis control program. The current distribution characteristics provided us with evidence that the resource assignment could be more reasonably implemented so as to control schistosomiasis in a more effective way.