METHYL-FLUORIDE, AN INHIBITOR OF METHANE OXIDATION AND METHANE PRODUCTION

Methyl fluoride (CH3F) has been reported to inhibit effectively aerobi c CH4 oxidation, while not affecting methanogenesis. Currently it is a pplied in a variety of ecosystems, where oxidation and production of C H4 take place simultaneously. We tested the effects of CH3F on both pr ocesses in a flooded soil, in wetland plants (rice, Oryza sativa, and cottontail, Typha latifolia), and in a microbial mat. CH4 emission fro m rice microcosms increased after treatment with up to 1.9% CH3F, but decreased to less than the initial rate after 3.3% CH3F had been added . In anoxic incubations of rice roots and Typha we observed in vitro a n instantaneous methanogenesis that in rice was inhibited by CH3F. Cot tontail-associated methanogenesis was not affected by CH3F. In anoxic slurries of ricefield soil CH4 production was inhibited by CH3F. Even at concentrations as low as 1000 ppmv CH3F (approximate to 40 alpha M) methanogenesis was reduced by about 75% as compared to the control wi thout the inhibitor. Methanogenesis could be recovered partly when CH3 F was flushed out with N-2. In soil slurries with CH3F methanogenesis could be stimulated by addition of formate, but not by acetate. Acetat e accumulated in soil slurries with CH3F to about the same amount as d id CH4 in the control experiment without inhibitor. Methanogenesis in the hypersaline microbial mat is probably driven by methylated amines; it was not affected by CH3F. Hence, measurements of aerobic CH4 oxida tion may be biased if acetoclastic methanogenesis plays a significant role, and if CH4 production and oxidation zones are closely coupled. T his is to be expected especially in freshwater sediments, wetlands and ricefields.