Methane is a powerful greenhouse gas whose atmospheric concentration continues to rise due to human activities. Current models include only temperature and water content as the primary drivers of methane emissions from terrestrial ecosystems, however there are other factors that may act to significantly alter the net production of methane from natural ecosystems. Methanogenesis is a thermodynamically marginal process, and so the presence of alternative electron acceptors can lead to the competitive inhibition of methane production in anaerobic, carbon-rich environments that would otherwise produce high quantities of methane. Secondly, recently discovered mechanisms of anaerobic methane oxidation can reduce net methane production despite low levels of oxygen. We have several lines of evidence for the significance of both of these phenomena in tundra of the Arctic Coastal Plain of northern Alaska: (1) The presence of the alternative electron acceptors, ferric iron (Fe(III)) and humic acids, is associated with reduced methane fluxes and concentrations in soil pore water; (2) experimental additions of these electron acceptors reduced methane fluxes in field experiments; (3) genetic surveys (metagenomic and 16S rRNA) show the predominance of alternative anaerobic respiratory pathways in these soils; (4) laboratory incubations using stable isotope techniques show the potential for anaerobic methane oxidation in these soils; (5) genetic surveys reveal DNA sequences closely related to known anaerobic methane oxidizing microorganisms. Our data are consistent with studies from other ecosystems that show that alternative electron acceptors are important modulators of methane release from ecosystems, and should be incorporated into modeling efforts. This raises challenges for the future, as the availability of alternative electron acceptors is likely to exhibit complex spatial patterns and is not easily remotely sensed.

Alternative electron acceptors regulate methane production and consumption in an Arctic ecosystem: Implications for global methane models

247th National Meeting (2014)

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