Regulation of N2O and NOx emission patterns in six acid temperate beech forest soils by soil gas diffusivity, N turnover, and atmospheric NOx concentrations

Abstract

Low gas diffusivity of the litter layer is held responsible for high seasonal nitrous oxide (N2O) and low nitric oxide (NO) emissions from acid beech forest soils with moder type humus. The objectives were (i) to evaluate whether these beech forest soils generally exhibit high seasonal N2O emissions and (ii) to assess the influence of gas diffusivity and nitrogen (N) mineralisation on N oxide fluxes. We measured N2O and NOx (NO + NO2) fluxes in six German beech stands and determined net N turnover rates and gas diffusivity of soil samples taken at each chamber. High N2O emissions (up to 113 μg N m−2 h−1) were only observed at one beech stand. Net nitrification of the organic layer and soil gas diffusivity explained 77 % of the variation in N2O fluxes (P = 0.001). Fluxes of NOx were low (−6.3 to 12.3 μg N m−2 h−1) and appeared to be controlled by NOx concentrations in the forest air. Low soil gas diffusivity and high N turnover rates promoted high N2O losses in times of high soil respiration but were not necessarily associated with moder type humus. High seasonal emissions are probably less common in German beech forests than previously assumed.