Gas concentration driven fluxes of nitrous oxide and carbon dioxide in boreal forest soil

Abstract

Nitrous oxide (N₂O) and carbon dioxide (CO₂) fluxes were measured in a boreal forest during two growing seasons with soil gradient and chamber methods. N₂O fluxes obtained by these two techniques varied from small emission to small uptake. N₂O fluxes were of the same order of magnitude, however, the fluxes measured by the soil gradient method were higher and more variable than the fluxes measured with chambers. The highest soil gradient N₂O fluxes were measured in the late summer and the lowest in the autumn and spring. In the autumn, litter fall induced a peak in N₂O concentration in the organic O-horizon, whereas in the spring N₂O was consumed in the O-horizon. Overall, the uppermost soil layer was responsible for most of the N₂O production and consumption. Soil gradient and chamber methods agreed well with CO₂ fluxes. Due to the very small N₂O fluxes and the sensitivity of the flux to small concentration difference between the soil and the ambient air, the flux calculations from the O-horizon to the atmosphere were considered unreliable. N₂O fluxes calculated between the soil A- and O-horizons agreed relatively well with the chamber measurements.