Methane oxidation in forest, successional, and no-till agricultural ecosystems: Effects of nitrogen and soil disturbance

Methane oxidation in well-aerated soils is a significant global sink for atmospheric methane. We examined the effects of soil disturbance (simulated tillage) and N-fertilizer additions on methane oxidation in old-growth forest, mid-successional, and no-till maize ecosystems in southwest Michigan, USA. We found highest oxidation rates in forest sites (about 30 mu g CH4-C m(-2) h(-1) on average), with average rates in successional and agricultural sites about 75 and 12% of this, respectively. In the forest and successional sites a one-time N-fertilizer addition (100 kg NH4NO3-N ha(-1)) significantly suppressed oxidation for the several weeks that inorganic N pools were elevated. There was no effect of fertilizer addition in the agricultural site, where available N was already high and oxidation rates low. Soil disturbance by itself had no detectable effect on fluxes in any of the sites. Results confirm the overriding importance of elevated N for suppressing CH4 oxidation in managed and unmanaged ecosystems, and suggest further that recovery of CH4 suppression following agriculture is related to slow-changing soil properties such as soil organic matter composition or microbial community structure.