Gross N2O emission and gross N2O uptake in soils under temperate spruce and beech forests

Abstract

Soils are not only a major source but also a potential sink of atmospheric nitrous oxide (N2O), a potent greenhouse gas and the most important substance causing stratospheric ozone depletion. Net N2O flux at the soil surface is a result of two concurrent processes: gross N2O emission and gross N2O uptake. Little is known about these processes and their controlling factors because it is only in the last five years that the 15N2O pool dilution method was developed to measure these processes in the field. Here, we used this method to quantify gross N2O emission and gross N2O uptake in adjacent spruce and beech forests on a Cambisol soil in central Germany. Our results showed that the beech stand had higher soil gross and net N2O emissions (P < 0.01–0.04) than the spruce stand. Seasonal variations in gross N2O emission and gross N2O uptake were influenced mainly by soil NO3− concentration and soil extractable organic C, respectively. The strong correlation between gross N2O emission and net N2O fluxes suggests that gross N2O emission rather than gross N2O uptake drove the net N2O flux from the soil. Our study showed the underlying mechanisms and controls of gross N2O fluxes, which until now were not quantified in actual field conditions across seasons.