Effect of tree distance on N2O and CH4-fluxes from soils in temperate forest ecosystems

Abstract

Complete annual cycles of N2O and CH4 flux in forest soils at a beech and at a spruce site at the Hoglwald Forest were followed in 1997 by use of fully automatic measuring systems. In order to test if on a microsite scale differences in the magnitude of trace gas exchange between e.g. areas in direct vicinity of stems and areas in the interstem region at both sites exist, tree chambers and gradient chambers were installed in addition to the already existing interstem chambers at our sites. N2O fluxes were in a range of −4.6–473.3 μg N2O-N m−2 h−1 at the beech site and in a range of −3.7–167.2 μg N2O-N m−2 h−1 at the spruce site, respectively. Highest N2O emissions were observed during and at the end of a prolonged frost period, thereby further supporting previous findings that frost periods are of crucial importance for controlling annual N2O losses from temperate forests. Fluxes of CH4 were in a range of +10.4–−194.0 μg CH4 m−2 h−1 at the beech site and in a range of −4.4–−83.5 μg CH4 m−2 h−1 at the spruce site. In general, both N2O-fluxes as well as CH4-fluxes were higher at the beech site. On a microsite scale, N2O and CH4 fluxes at the beech site were highest within the stem area (annual mean: 49.6±3.3 μg N2O-N m−2 h−1; −77.2±3.1 μg CH4 m−2 h−1), and significantly lower within interstem areas (18.5±1.4 μg N2O-N m−2 h−1; −60.2±1.8 μg CH4 m−2 h−1). Significantly higher values of total N, C and pH in the organic layer, as well as increased soil moisture, especially in spring, in the stem areas, are likely to contribute to the higher N2O fluxes within the stem area of the beech. Also for the spruce site, such differences in trace gas fluxes could be demonstrated to exist (mean annual N2O emission within (a) stem areas: 9.7±0.9 μg N2O-N m−2 h−1 and (b) interstem areas: 6.2±0.6 μg N2O-N m−2 h−1; mean annual CH4 uptake within (a) stem areas: −26.1±0.6 μg CH4 m−2 h−1 and (b) interstem areas: −38.4±0.8 μg CH4 m−2 h−1), though they were not as pronounced as at the beech site.