| Recently, atmospheric CH{dollar}sb4{dollar} concentration has risen dramatically, apparently due to human activities. Since is CH{dollar}sb4{dollar} is involved in several atmospheric processes that regulate Earth's climate, it is important that we understand the factors that control its atmospheric concentration. One such factor is biological CH{dollar}sb4{dollar} consumption in well-drained soils. Although this sink may comprise nearly one-tenth of the annual destruction of atmospheric CH{dollar}sb4{dollar}, We know relatively little about it. I conducted a research project to investigate the influences of CH{dollar}sb4{dollar} supply, soil moisture, dissolved salts, and NH{dollar}sb4sp+{dollar}-fertilizer on the activity of soil CH{dollar}sb4{dollar} oxidizers.; When starved of CH{dollar}sb4{dollar}, two upland taiga soils gradually lost their capacities to oxidize CH{dollar}sb4{dollar}, indicating that the process was not merely fortuitous, and that the organisms involved were truly methanotrophic. The relationship between soil moisture and CH{dollar}sb4{dollar} consumption was parabolic, with maximum oxidation occurring at a moisture level that achieved the maximum possible CH{dollar}sb4{dollar} diffusion rate, while minimizing water stress on the methanotrophs. Optimal soil moisture occurred in a relatively narrow range among an array of physically dissimilar soils, providing that moisture content was expressed as a percentage of the water holding capacity fo a particular soil, rather than as absolute water content.; In recent years, one of the most intensely investigated controls on soil CH{dollar}sb4{dollar} consumption has been its inhibition by NH{dollar}sb4sp+{dollar}-fertilizer. In addition to NH{dollar}sb4sp+,{dollar} however, I found that other ions inhibited CH{dollar}sb4{dollar} oxidation. In some soils non-NH{dollar}sb4sp+{dollar} ions were so toxic that they completely masked the NH{dollar}sb4sp+{dollar} effect. It is crucial, therefore, to control for salt effects when investigating NH{dollar}sb4sp+{dollar}-inhibition. In both field and laboratory experiments, CH{dollar}sb4{dollar} consumption in a birch soil was sensitive to NH{dollar}sb4sp+{dollar}, whereas a spruce soil was unaffected. In the birch soil, NH{dollar}sb4sp+{dollar} apparently inhibited methanotroph growth, rather than enzymatic CH{dollar}sb4{dollar} oxidation, whereas methanotrophs in the spruce soil were apparently insensitive to NH{dollar}sb4sp+{dollar}. These results suggest that the primary landscape-level control over the response of soil CH{dollar}sb4{dollar} consumption to NH{dollar}sb4sp+{dollar}-fertilization is the cross-site distribution of physiologically distinct CH{dollar}sb4{dollar} oxidizers. |
