Regulation of coastal methane sinks by a structured gradient of microbial methane oxidizers.

Abstract Coastal wetlands are widely recognized as atmospheric methane sources. However, recent field studies suggest that some coastal wetlands could also act as methane sinks, but the mechanism is not yet clear. Here, we investigated methane oxidation with different electron acceptors (i.e., oxygen, nitrate/nitrite, sulfate, Fe(III) and Mn(IV)) in four coastal wetlands in China using a combination of molecular biology methods and isotopic tracing technologies. The geochemical profiles and in situ Gibbs free energies suggest that there was significant nitrite-dependent anaerobic oxidation of methane (nitrite-AOM) in the sub-surface sediments; this was subsequently experimentally verified by both the microbial abundance and activity. Remarkably, the methanotrophic communities seemed to exist in the sediments as layered structures, and the surface aerobic methane-oxidizing bacteria were able to take up atmospheric methane at a rate of 0.10–0.18 nmol CH 4 day⁻¹ cm⁻², while most, if not all, sedimentary methane was being completely consumed by anaerobic methanotrophs (23–58% by methane oxidizers in phylum NC10). These results suggest that coastal methane sinks might be governed by diverse microbial communities where NC10 methane oxidizers contributed significantly. This finding helps to better understand and predict the coastal methane cycle and reduce uncertainties in the estimations of the global methane flux. Graphical abstract Image 1 Highlights • Methane oxidation with different electron acceptors were investigated in four coasts. • A structured gradient of microbial methane oxidizers was found in coastal sediments. • Sub-surface NC10 bacteria were the dominant sink of coastal sedimentary methane. • Coastal sediments are weak atmospheric methane sinks in some nitrogen-rich areas. A structured gradient of microbial methane oxidizers was discovered in coastal sediments, and sub-surface NC10 methane oxidizers were the dominant methane sink. [ABSTRACT FROM AUTHOR]