title: Influence of tree internal nitrogen reserves on the response of beech (Fagus sylvatica) trees to elevated atmospheric carbon dioxide concentration.
abstract: We examined the influence of plant internal nitrogen (N) reserves on the response of 3-year-old beech (Fagus sylvatica L.) trees to elevated atmospheric CO2 concentration ([CO2]) in a dual 15N and 13C long-term labeling experiment. Trees were grown on sand and received either no N nutrition (-N treatment) or 4 mM N (+N treatment) for 1 year. The -N and +N pretreated trees were then placed in growth chambers and grown in 350 (ambient) or 700 ppm (elevated) of a 13CO2 atmosphere for 24 weeks. In all treatments, trees were supplied with 4 mM 15N during the experiment. Irrespective of tree N reserves, elevated [CO2] increased cumulative carbon (C) uptake by about 30% at Week 24 compared with that for trees in the ambient treatment. Elevated [CO2] also caused a shift in C allocation to belowground compartments, which was more pronounced in -N trees than in +N trees. In +N trees, belowground allocation of new C at Week 24 was 67% in ambient [CO2] compared with 70% in elevated [CO2]. The corresponding values for -N trees were 70 and 79%. The increase in C allocation in response to elevated [CO2] was most evident as an increase in belowground respiration; however, specific root respiration was unaffected by the CO2 or N treatments. Although elevated [CO2] increased root growth and belowground respiration, it had no effect on N uptake at Week 24. As a result of increased C uptake, N concentrations were decreased in trees in the elevated [CO2] treatment compared with trees in the ambient treatment in both N treatments. Partitioning of new N uptake was unaffected by elevated [CO2] in +N trees. In -N trees, however, N allocation to the stem decreased in response to elevated [CO2] and N allocation to fine roots increased, suggesting a reduction in the formation of N reserves in response to elevated [CO2]. We conclude that the response of beech trees to elevated [CO2] is affected by internal N status and that elevated [CO2] may influence the ability of the trees to form N reserves.
authors.affiliation: Institute of Soil Science and Forest Nutrition, University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany. jdyckma@gwdg.de
authors.forename: Jens
authors.initials: J
authors.lastname: Dyckmans
authors.forename: Heiner
authors.initials: H
authors.lastname: Flessa
mesh_terms: D002245:Carbon Dioxide / Q000502:physiology; D029964:Fagus / Q000502:physiology*; D009584:Nitrogen / Q000502:physiology; D018515:Plant Leaves / Q000502:physiology; D018517:Plant Roots / Q000502:physiology; D018520:Plant Shoots / Q000502:physiology; D014197:Trees / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide; D009584:Nitrogen