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Abstract

The effect of soil microbial processes on production and/or consumption of atmospheric trace gases was studied in four different soils which were preincubated in the presence of elevated concentrations of CH4, NH4+ or CO, to simulate the growth of the resident populations of methanotrophic, nitrifying, or carboxydotrophic bacteria, respectively. Oxidation of CH4, both at atmospheric (1.8 ppmv) and at elevated (3500 ppmv) CH4 mixing ratios, was stimulated after preincubation with CH4, but not with NH4+ or CO, indicating that CH4 was oxidized by methanotrophic, but not by nitrifying or carboxydotrophic bacteria. However, the oxidation of CH4 was partially inhibited by addition of NH4+ and CO. Analogously, oxidation of NH4+ was partially inhibited by addition of CH4. Oxidation of CO at elevated mixing ratios (2300 ppmv) was stimulated after preincubation with CO, indicating oxidation by carboxydotrophs, but was also stimulated at a small extent after preincubation with CH4, suggesting the involvement of methanotrophs. At atmospheric CO mixing ratios (0.13 ppmv), on the other hand, oxidation of CO was stimulated after preincubation with NH4+, indicating that the activity was due to nitrifiers. NO uptake was stimulated in soils preincubated with CH4, indicating the involvement of methanotrophs. However, production of N2O was only stimulated, if CH4 was added as a substrate. The results indicate that especially the methanotrophic and nitrifying populations in soil not only oxidize their specific substrates, but are also involved in the metabolism of other compounds.