Methyl fluoride, an inhibitor of methane oxidation and methane production

Abstract

Methyl fluoride (CH 3F) has been reported to inhibit effectively aerobic CH 4 oxidation, while not affecting methanogenesis. Currently it is applied in a variety of ecosystems, where oxidation and production of CH 4 take place simultaneously. We tested the effects of CH 3F on both processes in a flooded soil, in wetland plants (rice, Oryza sativa, and cottontail, Typha latifolia), and in a microbial mat. CH 4 emission from rice microcosms increased after treatment with up to 1.9% CH 3F, but decreased to less than the initial rate after 3.3% CH 3F had been added. In anoxic incubations of rice roots and Typha we observed in vitro an instantaneous methanogenesis that in rice was inhibited by CH 3F. Cottontail-associated methanogenesis was not affected by CH 3F. In anoxic slurries of ricefield soil CH 4 production was inhibited by CH 3F. Even at concentrations as low as 1000 ppmv CH 3F (≈ 40 μM) methanogenesis was reduced by about 75% as compared to the control without the inhibitor. Methanogenesis could be recovered partly when CH 3F was flushed out with N 2. In soil slurries with CH 3F methanogenesis could be stimulated by addition of formate, but not by acetate. Acetate accumulated in soil slurries with CH 3F to about the same amount as did CH 4 in the control experiment without inhibitor. Methanogenesis in the hypersaline microbial mat is probably driven by methylated amines; it was not affected by CH 3F. Hence, measurements of aerobic CH 4 oxidation may be biased if acetoclastic methanogenesis plays a significant role, and if CH 4 production and oxidation zones are closely coupled. This is to be expected especially in freshwater sediments, wetlands and ricefields.