Potential fluxes of N 2O and CH 4 from soils of three forest types in Eastern Canada

Abstract

We conducted laboratory incubation experiments to elucidate the influence of forest type and topographic position on emission and/or consumption potentials of nitrous oxide (N 2O) and methane (CH 4) from soils of three forest types in Eastern Canada. Soil samples collected from deciduous, black spruce and white pine forests were incubated under a control, an NH 4NO 3 amendment and an elevated headspace CH 4 concentration at 70% water-filled pore space (WFPS), except the poorly drained wetland soils which were incubated at 100% WFPS. Deciduous and boreal forest soils exhibited greater potential of N 2O and CH 4 fluxes than did white pine forest soils. Mineral N addition resulted in significant increases in N 2O emissions from wetland forest soils compared to the unamended soils, whereas well-drained soils exhibited no significant increase in N 2O emissions in-response to mineral N additions. Soils in deciduous, boreal and white pine forests consumed CH 4 when incubated under an elevated headspace CH 4 concentration, except the poorly drained soils in the deciduous forest, which emitted CH 4. CH 4 consumption rates in deciduous and boreal forest soils were twice the amount consumed by the white pine forest soils. The results suggest that an episodic increase in reactive N input in these forests is not likely to increase N 2O emissions, except from the poorly drained wetland soils; however, long-term in situ N fertilization studies are required to validate the observed results. Moreover, wetland soils in the deciduous forest are net sources of CH 4 unlike the well-drained soils, which are net sinks of atmospheric CH 4. Because wetland soils can produce a substantial amount of CH 4 and N 2O, the contribution of these wetlands to the total trace gas fluxes need to be accounted for when modeling fluxes from forest soils in Eastern Canada.