Seasonal variation in methane oxidation by the rhizosphere of Phragmites australis and Scirpus lacustris

Methane oxidation in the rhizosphere of two common wetland plants, reed (Phragmites australis (Cav.) Trin. Ex Steud.) and bulrush (Scirpus lacustris L.), was quantified using the methylfluoride (CH3F) inhibition and anoxic/oxic flux chamber techniques. The similarity of rhizospheric CH4 oxidation rates determined with the two techniques and the absence of an adverse effect of CH3F on plant metabolism indicated that the CH3F inhibition flux chamber technique was a useful tool for measuring rhizospheric CH4 oxidation in freshwater wetlands. A significant seasonal pattern for both plant species as well as a significant difference between the plant species were observed. Light or dark conditions had no significant effect on rhizospheric CH4 oxidation. When averaged over the growing season, CH4 oxidation in the rhizosphere of bulrush and reed reduced the potential CH4 flux by 34.7%+/-20.3 and 16.1%+/-7.86, respectively. Highest CH4 oxidation rates were noted early in the plant growth cycle with more than 55% of the generated methane being oxidised in the bulrush system, Methane oxidation rates were lowest after plants matured. The difference in rhizospheric CH4 oxidation capacity between reed and bulrush and the seasonal variation for reed were confirmed by a series of slurry incubations. Slurry incubations also showed a significant decrease of potential CH4 oxidation as a function of depth in sediment. (C) 1998 Elsevier Science B.V.