Greenhouse gas fluxes from boreal forest soils during the snow-free period in Quebec, Canada

This paper presents soil fluxes of methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) from 12 sites located in four major forest types, black spruce (Picea mariana (Mill.) BSP), jack pine (Pinus banksiana Lamb.), aspen (Populus spp.), and alder (Alnus spp.) stands, in the Eastmain and Chibougamau regions of Quebec. Fluxes were determined with closed chambers during the snow-free period from May to October 2007. Well-drained black spruce, jack pine, and aspen forest soils were net sinks of atmospheric CH4 (-0.33 +/- 0.11 mg.m(-2).day(-1)), while alder-dominated wetland soils were sources of CH4 (0.45 +/- 0.12 mg.m(-2).day(-1)). The cut-over alder wetland soil produced 131 times more CH4 than the undisturbed wetland soil. Soil moisture and temperature mainly regulated CH4 fluxes. N2O fluxes from these forest soils were highly variable and smaller (1.6 +/- 0.33 mu g N.m(-2).h(-1)) than those from deciduous forest soils. N2O emission from the cut-over black spruce forest soil was 2.7 times greater than that from the mature black spruce forest soil. Large C/N ratios (27 to 78) and slow soil N mineralization and nitrification rates in these forest soils may have led to small N2O fluxes. CO2 emissions from these forest soils, ranging from 0.20 to 2.7 g.m(-2).day(-1), were mainly controlled by soil temperature.