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

Abstract

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 (CH 3F) inhibition and anoxic/oxic flux chamber techniques. The similarity of rhizospheric CH 4 oxidation rates determined with the two techniques and the absence of an adverse effect of CH 3F on plant metabolism indicated that the CH 3F inhibition flux chamber technique was a useful tool for measuring rhizospheric CH 4 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 CH 4 oxidation. When averaged over the growing season, CH 4 oxidation in the rhizosphere of bulrush and reed reduced the potential CH 4 flux by 34.7%±20.3 and 16.1%±7.86, respectively. Highest CH 4 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 CH 4 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 CH 4 oxidation as a function of depth in sediment.