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 fe n in Alberta, Canada over three growing seasons. Aerobic incubations of bul k peat and live roots in the laboratory show a clear association between ac tive methane oxidizing bacteria and the rhizosphere. Aerobic incubations al so show an oxidation potential that far exceeds methane production potentia l measured in the laboratory. Quantitative estimates of how this oxidation potential is expressed in situ depend strongly on which of two common appro aches are used. (1) Subtracting in situ methane emission rates from methane production rates measured in the laboratory with anaerobic incubations sug gest that methane oxidation may attenuate emissions by 58 to 92%. (2) Apply ing the inhibitor methyl fluoride (CH3F) to whole plants in situ suggest me thane oxidation attenuates emissions by less than 20% seasonally. The produ ction minus emission technique likely overestimates methane oxidation becau se methane production measured via anaerobic incubations in the laboratory are probably overestimates. Oxidation percentages measured by CH3F were gre atest early in the growing season when emission rates were low and fell to almost nondetectable levels as emission rates peaked in late summer. Estima tes provided by the CH3F technique were generally in better agreement with estimates of oxidation based on a stable isotope mass balance (0-34%) deter mined in a companion study (Popp et al. 1999).