Silver Sulfide Nanoparticles Eliminate the Stimulative Effects of Earthworms on Nutrient Uptake by Soybeans in High Organic Matter Soils

A significant knowledge gap exists regarding the impact of soil organic matter on the bioavailability of AgS-NPs (environmentally relevant forms of Ag-NPs) in soil-earthworm-plant systems. This study used two soils with varying organic matter content, both with and without earthworms, to investigate the bioavailability of AgS-NPs. The findings revealed an 80 % increase in Ag bioaccessibility to soybeans in soils with high organic matter content compared to soils with low organic matter. Additionally, the presence of earthworms significantly increased Cl concentrations from 24.3-62.2 mg L to 80.1-147.2 mg L, triggering the elevated bioavailability of Ag. Interestingly, AgS-NPs eliminated the stimulative effects of earthworms on plant nutrient uptake. In the presence of earthworms, the high organic matter soil amended with AgS-NPs exhibited lower concentrations of essential elements (Ca, Cu, Fe, K, and P) in plant tissues compared to soils without earthworms. Our study presents evidence of the transformation of AgS-NPs into Ag-NPs across various soil solutions, resulting in the formation of Ag nanoparticle complexes. Particularly noteworthy is the significant reduction in particle sizes in soils incubated with earthworms and high organic matter content, from 85.0 nm to 40.2 nm. Notably, in the rhizosphere soil, a decrease in the relative abundance of nutrient cycling-related phyla was observed, with reductions of 18.5 % for Proteobacteria and 30.0 % for Actinobacteriota. These findings offer valuable insights into the biological and biochemical consequences of AgS-NP exposure on earthworm-mediated plant nutrient acquisition.