Anaerobic Methane Oxidation in High-Arctic Alaskan Peatlands as a Significant Control on Net CH4 Fluxes

Kimberley Miller,Chun-Ta Lai,Randy Dahlgren,David Lipson

doi:10.3390/soilsystems3010007

Kimberley Miller, Chun-Ta Lai + Show 2 more

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https://doi.org/10.3390/soilsystems3010007

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Abstract

Terrestrial consumption of the potent greenhouse gas methane (CH4) is a critical aspect of the future climate, as CH4 concentrations in the atmosphere are projected to play an increasingly important role in global climate forcing. Anaerobic oxidation of methane (AOM) has only recently been considered a relevant control on methane fluxes from terrestrial systems. We performed in vitro anoxic incubations of intact peat from Utqiaġvik (Barrow), Alaska using stable isotope tracers. Our results showed an average potential AOM rate of 15.0 nmol cm3 h−1, surpassing the average rate of gross CH4 production (6.0 nmol cm3 h−1). AOM and CH4 production rates were positively correlated. While CH4 production was insensitive to additions of Fe(III), there was a depth:Fe(III) interaction in the kinetic reaction rate constant for AOM, suggestive of stimulation by Fe(III), particularly in shallow soils (<10 cm). We estimate AOM would consume 25–34% of CH4 produced under ambient conditions. Soil genetic surveys showed phylogenetic links between soil microbes and known anaerobic methanotrophs in ANME groups 2 and 3. These results suggest a prevalent role of AOM to net CH4 fluxes from Arctic peatland ecosystems, and a probable link with Fe(III)-reduction.

Highlights

Anaerobic oxidation of methane (AOM) affects global climate, as it constrains the atmospheric release of the powerful greenhouse gas methane (CH4 )
Phylogenetic analysis of 16s rRNA showed the clustering of Utqiaġvik basin soil sequences with known methane-cycling archaea, including ANME groups 2 and 3 (Figure 1)
2027920) sequences were similar to nitrate-dependent methanotrophs belonging to the phyla NC10. Soils sequenced in this series were exclusively from old and ancient age class basins, and so they are not directly related to the soils incubated for AOM and methanogenesis rates

Summary

Introduction

Anaerobic oxidation of methane (AOM) affects global climate, as it constrains the atmospheric release of the powerful greenhouse gas methane (CH4 ). AOM linked to sulfate-reduction consumes approximately 90% of methane before it can be released into the atmosphere [1,2]. There is increasing evidence that AOM plays a similar role in controlling net CH4 fluxes from soils and freshwater systems [3,4,5]. Global climate change is disproportionately warming Arctic systems, enhancing the likelihood of changes in net greenhouse gas fluxes to the atmosphere from warming soils [7]. Northern peatlands traditionally act as sinks of carbon dioxide (CO2 ) and sources of CH4 to the atmosphere [8,9,10]. Estimates of the AOM pathway and its impact on net ecosystem CH4 balance within intact northern soils are limited [3,11,12,13,14,15], highlighting the need for additional studies to determine the role of AOM in CH4 cycling in northern peatlands

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