Evaluation of methane oxidation in therhizosphere of a Carex dominated fen in northcentral Alberta, Canada

Rhizospheric methane oxidation was evaluated at a Carex (spp.) dominated fen in Alberta, Canada overthree growing seasons. Aerobic incubations of bulkpeat and live roots in the laboratory show a clearassociation between active methane oxidizing bacteriaand the rhizosphere. Aerobic incubations also show anoxidation potential that far exceeds methaneproduction potential measured in the laboratory. Quantitative estimates of how this oxidation potentialis expressed in situ depend strongly on which of twocommon approaches are used. (1) Subtracting in situmethane emission rates from methane production ratesmeasured in the laboratory with anaerobic incubationssuggest that methane oxidation may attenuate emissionsby 58 to 92%. (2) Applying the inhibitor methylfluoride (CH₃F) to whole plants in situ suggestmethane oxidation attenuates emissions by less than20% seasonally. The production minus emissiontechnique likely overestimates methane oxidationbecause methane production measured via anaerobicincubations in the laboratory are probablyoverestimates. Oxidation percentages measured byCH₃F were greatest early in the growing seasonwhen emission rates were low and fell to almostnondetectable levels as emission rates peaked in latesummer. Estimates provided by the CH₃F techniquewere generally in better agreement with estimates ofoxidation based on a stable isotope mass balance(0–34%) determined in a companion study (Popp et al. 1999).