Evaluation of methane oxidation in the rhizosphere of a Carex dominated fen in north central Alberta, Canada

Rhizospheric methane oxidation was evaluated at a Carex (spp.) dominated fen in Alberta, Canada over three growing seasons. Aerobic incubations of bulk peat and live roots in the laboratory show a clear association between active methane oxidizing bacteria and the rhizosphere. Aerobic incubations also show an oxidation potential that far exceeds methane production potential measured in the laboratory. Quantitative estimates of how this oxidation potential is expressed in situ depend strongly on which of two common approaches are used. (1) Subtracting in situ methane emission rates from methane production rates measured in the laboratory with anaerobic incubations suggest that methane oxidation may attenuate emissions by 58 to 92%. (2) Applying the inhibitor methyl fluoride (CH3F) to whole plants in situ suggest methane oxidation attenuates emissions by less than 20% seasonally. The production minus emission technique likely overestimates methane oxidation because methane production measured via anaerobic incubations in the laboratory are probably overestimates. Oxidation percentages measured by CH3F were greatest early in the growing season when emission rates were low and fell to almost nondetectable levels as emission rates peaked in late summer. Estimates provided by the CH3F technique were generally in better agreement with estimates of oxidation based on a stable isotope mass balance (0-34%) determined in a companion study (Popp et al. 1999).