Above ground uptake of nitrogen

BITÖK-N 4

From 01/1995 to 12/1997

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

Forest trees in anthropogenic influenced Central Europe can use nitrogen from different sources: a) NO₃^- and NH₄⁺ from the soil solution and b) nitrogen containing compounds with mostly anthropogenic origin from the atmosphere. The nitrogen containing substances in the atmosphere are oxidized compounds (NO, NO₂, HNO₃, NO₃^-) and reduced compounds (NH₃, NH₄⁺). The oxidized compounds mainly originate from the combustion of fossil fuel. The reduced compounds originat to more than 90 % from agriculture. Uptake of these nitrogen compounds from the atmosphere may be quantified from a change of the natural nitrogen isotope abundance in the plant tissue depending on the time of exposition to atmospheric depostion and from the concentration and nitrogen isotope abundance of the various atmospheric nitrogen containing compounds. The nitrogen isotope abundance of plant tissue, soil borne nitrogen and NH₃ in the atmosphere in the Fichtelgebirge is already known. For a fast and reliable on-line nitrogen isotope abundance determination of NH₃, NO and NO₂ on natural abundance level new analytical methods had to be developed. For the measurement by isotope ratio mass spectrometry the trace gases always must be converted to N₂. The following conversion techniques were developed: (1) Oxidation of NH₃ to N₂ on an NiO surface at 1150 °C and re-oxidation with O₂ before each analysis (11.7 to 58.8 nmol NH₃, ± 0.20 ‰) (2) Reduction of NO to N₂ on a Ni surface. (16.7 to 133.3 nmol NO, ± 0.30 ‰) (3) NO₂ was reduced to NO on a Mo surface and subsequently was handled as NO. (26.0 to 129.9 nmol NO₂, ± 1.15 ‰) With ambient air concentrations of NH₃, NO and NO₂ about 100 l are required for the nitrogen isotope abundance determination of these gases on natural abundance level. Trapping techniques for the trace gases on the basis of molecular sieves and cryofocussing techniques are currently under development. The absorption characteristics under ambient air conditions and the thermal desorption characteristics of NH₃, NO and NO₂ have to be determined. Subsequently the nitrogen isotope composition of NH₃, NO and NO₂ in ambient air will be determinded for the Waldstein site in the Fichtelgebirge.
(final report 1998)

List of publications of this Project

Harrison, AF; Schulze, ED; Gebauer, G; Bruckner, G: Canopy uptake and utilisation of atmospheric pollutant N. in E.-D. Schulze: Ecological Studies No. 142, Carbon and Nitrogen Cycling in European Forest Ecosystems, Springer, 171-188 (2000)

Lauf, J; Gebauer, G: On-line analysis of stable isotopes of nitrogen in NH₃, NO and NO₂ at natural abundance levels, Analytical Chemistry, 70, 2750-2756 (1998), doi:10.1021/ac9800053 -- Details