Exchange of N-gases at the Höglwald Forest – A summary

Abstract

During 4 years continuous measurements of N-trace gas exchange were carried out at the forest floor-atmosphere interface at the Hoglwald Forest that is highly affected by atmospheric N-deposition. The measurements included spruce control, spruce limed and beech sites. Based on these field measurements and on intensive laboratory measurements of N2-emissions from the soils of the beech and spruce control sites, a total balance of N-gas emissions was calculated. NO2-deposition was in a range of −1.6 −2.9 kg N ha−1 yr−1 and no huge differences between the different sites could be demonstrated. In contrast to NO2-deposition, NO- and N2O-emissions showed a huge variability among the different sites. NO emissions were highest at the spruce control site (6.4–9.1 kg N ha−1 yr−1), lowest at the beech site (2.3–3.5 kg N ha−1 yr−1) and intermediate at the limed spruce site (3.4–5.4 kg N ha−1 yr−1). With regard to N2O-emissions, the following ranking between the sites was found: beech (1.6–6.6 kg N ha−1 yr−1) >> spruce limed (0.7–4.0 kg N ha−1 yr−1) > spruce control (0.4–3.1 kg N ha−1 yr−1). Average N-trace gas emissions (NO, NO2, N2O) for the years 1994–1997 were 6.8 kg N ha−1 yr−1 at the spruce control site, 3.6 kg N ha−1 yr−1 at the limed spruce site and 4.5 kg N ha−1 yr−1 at the beech site. Considering N2-losses, which were significantly higher at the beech (12.4 kg N ha−1 yr−1) than at the spruce control site (7.2 kg N ha−1 yr−1), the magnitude of total gaseous N losses, i.e. N2-N + NO-N + NO2-N + N2O-N, could be calculated for the first time for a forest ecosystem. Total gaseous N-losses were 14.0 kg N ha−1 yr−1 at the spruce control site and 15.5 kg N ha−1 yr−1 at the beech site, respectively. In view of the huge interannual variability of N-trace gas fluxes and the pronounced site differences in N-gas emissions it is concluded that more research is needed in order to fully understand patterns of microbial N-cycling and N-gas production/emission in forest ecosystems and mechanisms of reactions of forest ecosystems to the ecological stress factor of atmospheric N-input.