Uptake of Ammonium and Nitrate in Forest Trees

BITÖK-N 5

From 01/1995 to 12/1997

Principal Investigator: Ernst-Detlef Schulze
Staff: Gerhard Gebauer, Christoph May, Gisela Schmidt
Grant: 0339476 B Vorhersage und Erklärung des Verhaltens und der Belastbarkeit von Ökosystemen unter veränderten Umweltbedingungen

In May 1996, a ¹⁵N tracer pulse study was established in beech stands (Fagus sylvatica L.) to investigate the effects of continuous atmospheric nitrogen (N) inputs to deciduous forest ecosystems. The study is based on tracer pulse experiments carried out in Norway spruce stands, under the framework of previous BITÖK projects and on a preliminary study carried out in 1995 in a mixed stand of 30-year-old beech and oak. The study presented here investigates: (1) the uptake of mineral nitrogen by beech and understorey species; (2) the fluxes and transformations of N in the beech forest ecosystem; (3) the effect of the growing season on N uptake and N distribution pattern and (4) the effect of stand age on N uptake and N distribution pattern, including quantification of N fluxes into the plant cover. Beech stands of five different ages, ranging between 10 and 140 years were selected for investigation.
Results obtained so far show:(1) Beech uses ammonium and nitrate throughout the entire growing season. This is consistent with the findings in coniferous forests.(2) The investigated beech stands have a very sparse cover of understorey vegetation. It has been demonstrated that in spruce forests, the understorey vegetation is a strong competitor for both mineral N compounds particularly for nitrate. Thus, the understorey vegetation plays an important role in compensating N inputs in spruce forests. The lack in ground cover in the beech stands might have impacts on the nitrate outputs.(3) In contrast to spruce, beech preferentially uses nitrate over ammonium. There are good indications that the total N use by beech exceeds that of spruce. Higher use of N and preferential use of nitrate by deciduous trees may at least partially compensate higher nitrification rates in deciduous forest soils and the low contribution of understorey vegetation to N uptake compared to coniferous forest ecosystems. An important factor for an effective compensation of N inputs on stand level may be the density of the stand, the living biomass per area. Thus, in future deciduous trees may be important with regard to a sustainable forest management. (final report 1998)

List of publications of this Project

Gebauer, G; Zeller, B; Schmidt, G; May, C; Buchmann, N; Colin-Belgrand, M; Dambrine, E; Martin, F; Schulze, ED; Bottner, P: The fate of 15N-labelled nitrogen inputs to coniferous and broadleaf forests. in E.-D. Schulze: Ecological Studies No. 142, Carbon and Nitrogen Cycling in European Forest Ecosystems, Springer, 144-170 (2000)

Gebauer, G: The use of stable isotopes to study the fate of nitrogen inputs to forest ecosystems. in M.A. Martins-Loucao, S.H. Lips: Nitrogen in a Sustainable Ecosystem - From the Cell to the Plant, Backhuys Publishers, Leiden, 317-327 (2000)

May, C; Schmidt, G; Gebauer, G; Schulze, ED: The fate of 15N-ammonium and 15N-nitrate in the soil of a 140-year-old spruce (Picea abies) stand in the Fichtelgebirge (NE-Bavaria), Isotopes Environm. Health Studies, 32, 149-158 (1996), doi:10.1080/10256019608036306 -- Details

Schmidt, G; May, C; Gebauer, G; Schulze, ED: Uptake of [15N]ammonium and [15N]nitrate in a 140-year-old spruce stand (Picea abies) in the Fichtelgebirge (NE-Bavaria), Isotopes Environm. Health Studies, 32, 141-148 (1996), doi:10.1080/10256019608036305 -- Details