UC Irvine

Field plots of aspen and black spruce in the Alaskan boreal forest were fertilized repeatedly with nitrogen during the 1993 summer growing season, and weekly determinations of the influence of fertilization on atmospheric CH4 oxidation were made with static chambers. Repeated fertilization with (NH4)2SO4 solution or nutrient media used to culture methanotrophic or nitrifying bacteria gave a total addition of 140 or 580 kg N ha-1. Time-integrated CH4 oxidation was not significantly different in fertilized soils versus watered controls because CH4 oxidation was localized in a subsurface soil zone that was probably not penetrated by surface-applied aqueous phase fertilizer. Insensitivity of CH4 oxidation by these soils to a high rate of N fertilization and the low current rate of atmospheric N deposition suggest that future increases in atmospheric N deposition will not alter the sink strength of high latitude boreal forest soils in the atmospheric CH4 budget. (C) 2000 Elsevier Science Ltd.