| Methane oxidation in aerobic upland soils is an important sink for annually increasing atmospheric methane. The methane oxidation capacity of soil may be declining due to the conversion of natural forest to other uses. I investigate methane oxidation along a gradient of soil disturbance from mature old-growth forest to agricultural fields. I found that soils in the mature deciduous forest oxidize substantially more CH4 than mid-successional forest and no-till agricultural fields.; A single application of 100 kg N fertilizer per hectare significantly decreased CH4 oxidation rates in both mature deciduous forest and mid-successional communities but had no effects in agricultural fields, which already had low oxidation rates. In contrast, a 10 cm depth plowing did not show a significant detectable effect on soil CH4 consumption in any soils. Additionally, lower levels of N fertilization (30 kg N ha -1) significantly affected CH4 oxidation in coniferous forest, but not in deciduous forest nor in mid-successional communities.; Methane oxidation significantly differed among soil depths. In deciduous forest soil cores incubated in the laboratory, CH4 uptake was highest at 5--10 cm depth whereas there were no significant differences with depth (0--5, 5--10, 10--20, and 20--30 cm) in coniferous forest, in a mid-successional community, nor in no-till agricultural soils. Organic and conventional corn-corn-soybean-wheat management systems also had similar average soil CH4 uptake rates. Nevertheless, CH4 oxidation significantly differed among crops, such that organic corn had the highest rates of oxidation while organic soybean and wheat had the lowest rates. Rates in conventionally managed corn, soybean, and wheat crops were similar and intermediate.; Soil methane oxidation was not significantly correlated with CO 2 emission. Soil nitrate and ammonium were weak indicators of changes of CH4 oxidation among land use types and soil depths. Nitrification potential was also a good indicator of CH4 oxidation rates.; Results suggest a major effect of agricultural management on CH 4 oxidation in terrestrial ecosystems, with reductions in oxidation capacity related more to changes in nitrogen availability than physical soil disturbance itself. Low-level nitrogen additions (10 kg N ha-1 ), similar to rates of N-deposition, however, were not sufficient to reduce oxidation in undisturbed forests or mid-successional communities. |
