Microbial oxidation of methane,ammonium and carbon monoxide,and turnover of nitrous oxide and nitric oxide in soils

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, NH ₄ ⁺ 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 NH ₄ ⁺ 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 NH ₄ ⁺ and CO. Analogously, oxidation of NH ₄ ⁺ 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 NH ₄ ⁺ , 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.