Silver nanoparticles altered soil respiration, enzyme activity, carbon use efficiency and microbial community in an upland soil

Silver nanoparticles (AgNPs) are popular for their antimicrobial properties but their effects on soil carbon cycles remain unclear. This study explored AgNPs' impact on soil carbon dynamics and related microbial structures. Topsoil samples were treated with varying AgNPs concentrations (1, 10, 100, 500, and 1000 mg kg-1) over 56 days. Soil sampling was conducted at five time points (days 7, 14, 28, 42 and 56) to capture temporal changes. We assessed carbon mineralization, dissolved organic carbon (DOC), microbial biomass carbon (MBC), and enzymatic activities, along with 13C-labeled DOC and 13C-phospholipid fatty acid assays for tracing microbial carbon assimilation and evaluating carbon use efficiency (CUE). Following exposure to AgNPs in Ag100, Ag500, and Ag1000 treatments, cumulative CO2 emissions and DOC content increased by 40.3 %-170.0 % and 46.9 %- 74.9 %, respectively. However, MBC decreased in Ag500 (63.8 %) and Ag1000 (63.0 %) treatments. Enzyme activities declined: (3-glucosidase (43.7 %-48.4 %), (3-xylosidase (48.9 %-79.7 %), and Cellobiohydrolase (50.8 %-97.6 %). Additionally, microbial CUE increased 49.7 % in Ag1000 treatment. Soil microbial communities exhibited significant alterations in response to AgNPs in Ag100, Ag500, and Ag1000 treatments as well. By day 56, the relative abundance of Gram-positive bacteria and Actinomycetes decreased by 5.7 %-15.9 % and 9.7 %- 25.8 %, respectively, while Gram-negative bacteria increased significantly by 12.9 %-25.6 %. Meanwhile, the proportion of 13C-DOC derived C attributed to Gram-negative bacteria increased by 56.8 %-184.1 %, whereas Gram-positive bacteria (70.8 %-99.5 %) and Actinomycetes (64.2 %-82.3 %) decreased. These findings reveal the substantial role of AgNPs in altering soil carbon processes and microbial communities.