Soil nitrogen content and key functional microorganisms influence the response of wetland anaerobic oxidation of methane to trivalent iron input.

Trivalent iron (Fe)-dependent anaerobic oxidation of methane (Fe-AOM), which is mediated by metal-reducing bacteria, is widely recognized as a major sink for the greenhouse gas methane (CH), and is a key driver of the carbon (C) biogeochemical cycle. However, the effect of Fe addition on AOM in the present investigation is still ambiguous, and the mechanism is vague. In this study, we investigated the mechanism of changes in AOM response to Fe input at different wetlands by using laboratory incubation methods combined with molecular biology techniques. Results indicated that Fe input did not always lead to promoted AOM rates, which may be mediated by complex environmental factors, while lower soil total nitrogen (TN) had a positive effect on the response of AOM subjected to Fe input. Notably, the promoted response of AOM was regulated by higher soil microbial diversity, of which the Shannon index was a key indicator leading to variation in the AOM response. Additionally, several biomarkers, including Planctomycetota and Burkholderiaceae, were key microorganisms responsible for alterations in AOM response. Our results suggest that the capacity of Fe cycling-mediated AOM may gradually decrease in light of increasing anthropogenic N and Fe inputs to global estuarine wetlands, while its reaction processes will become more complex and more strongly coupled with multiple environmental factors. This finding contributes to the enhanced understanding and prediction of the wetland CH-related C with Fe cycles, as well as provides theoretical support for the underlying mechanisms.