Potential fluxes of N2O and CH4 from soils of three forest types in Eastern Canada

We conducted laboratory incubation experiments to elucidate the influence of forest type and topographic position on emission and/or consumption potentials of nitrous oxide (N2O) and methane (CH4) 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 NH4NO3 amendment and an elevated headspace CH4 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 N2O and CH4 fluxes than did white pine forest soils. Mineral N addition resulted in significant increases in N2O emissions from wetland forest soils compared to the unamended soils, whereas well-drained soils exhibited no significant increase in N2O emissions in-response to mineral N additions. Soils in deciduous, boreal and white pine forests consumed CH4 when incubated under an elevated headspace CH4 concentration, except the poorly drained soils in the deciduous forest, which emitted CH4. CH4 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 N2O 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 CH4 unlike the well-drained soils, which are net sinks of atmospheric CH4. Because wetland soils can produce a substantial amount of CH4 and N2O, 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.