Silver nanoparticles and Fe(III) co-regulate microbial community and N2O emission in river sediments

The effects of environmental concentration silver nanoparticles (ecAgNPs) on microbial communities and the nitrogen cycling in river sediments remain largely uncharacterized. As a fundamental component of sediments, Fe (III) can interact with AgNPs and participate in nitrogen transformation processes. N2O is an important intemiediate in nitrogen transformation processes and can be a potent greenhouse gas with significant environmental effects. However, the impacts of the co-existence of AgNPs and Fe(III) on microbial communities and N2O emission in river sediments are still unclear. In the present study, mesocosm experiments were concluded to assess the changes of microbial communities and N2O emission in response to the co-existence of AgNPs and environmental concentration Fe(III). Our results revealed that the microbial community diversity and N2O emission in river sediments responded differently to ecAgNPs (0.05 mg/kg) and high-polluting concentration AgNPs (hcAgNPs, 5 mg/kg), which was further regulated by the environmental concentration Fe(III) (1 mg/g and 10 mg/g). After ecAgNPs treatments, a marked increase was observed in microbial diversity compared to hcAgNPs treatments, regardless of the Fe(III) concentration in the sediment. The beta-NTI index indicated that AgNPs had stronger impacts on phylogenetic distance of bacterial communities in sediments containing 1 mg/g Fe(III) than that containing 10 mg/g Fe(III). In sediments containing 1 mg/g Fe(III), ecAgNPs did not affect N2O emission, but hcAgNPs significantly inhibited the emission of N2O. However, in sediments containing 10 mg/g Fe(III), N2O emission was significantly stimulated upon exposure to ecAgNPs, but the inhibition effect of hcAgNPs was barely observed. Functional prediction and real-time PCR analyses indicated that AgNPs and Fe(III) predominantly affected N2O emissions by affecting the abundance of the nirK gene. Our results provide new insights into the ecological impacts of the co-existence of environmental concentration AgNPs and Fe(III) in altering microbial communities and nitrogen transformation functions in river sediments. (C) 2018 Elsevier B.V. All rights reserved.