RHIZOSPHERIC METHANE OXIDATION DETERMINED VIA THE METHYL-FLUORIDE INHIBITION TECHNIQUE

Methane oxidation rates in the rhizosphere of aquatic macrophytes were quantified by development of a technique employing a recently describ ed inhibitor of methane oxidation, methyl fluoride. Unlike other inhib itors, methyl fluoride appears to be nontoxic to the plants, allowing them to act as natural conduits, transporting the inhibitor from the h eadspace to the rhizosphere. Increases in methane emissions were recor ded after closed chamber methyl fluoride incubations, primarily in gre enhouse (Pontederia cordata and Sagittaria lancifolia) experiments wit h some preliminary outdoor and field (Oryza sativa and Typha latifolia ) data. Comparison of emissions before and after incubation indicated oxidation of 23 to 90% of the methane produced (defined as CH4 emissio n in the absence of oxidation) in greenhouse studies and 10 to 47% in field and outdoor studies. A comparison of 1.5 and 3.0% methyl fluorid e chamber headspace incubations as well as initial dose-response data indicated that the lower concentration was sufficient to obtain inhibi tion of methane oxidation in the greenhouse studies without significan tly affecting methanogenesis. Inhibition was possible with one 16- to 18-hour incubation period. Methyl fluoride within the rhizosphere disa ppeared after approximately 1 week due to plant ventilation and possib le bacterial uptake.