title: Effects of elevated carbon dioxide concentration on growth and N2 fixation of young Robinia pseudoacacia.
abstract: Effects of elevated CO2 concentration ([CO2]) on carbon (C) and nitrogen (N) uptake and N source partitioning (N2 fixation versus mineral soil N uptake) of 1-year-old Robinia pseudoacacia were determined in a dual 13C and 15N continuous labeling experiment. Seedlings were grown for 16 weeks in ambient (350 ppm) or elevated [CO2] (700 ppm) with 15NH4 15NO3 as the only mineral nitrogen source. Elevated [CO2] increased the fraction of new C in total C, but it did not alter C partitioning among plant compartments. Elevated [CO2] also increased the fraction of new N in total N and this was coupled with a shift in N source partitioning toward N2 fixation. Soil N uptake was unaffected by elevated [CO2], whereas N2 fixation was markedly increased by the elevated [CO2] treatment, mainly because of increased specific fixation (mg N mg(-1) nodule). As a result of increased N2 fixation, the C/N ratio of tree biomass tended to decrease in the elevated [CO2] treatment. Partitioning of N uptake among plant compartments was unaffected by elevated [CO2]. Total dry mass of root nodules doubled in response to elevated [CO2], but this effect was not significant because of the great variability of root nodule formation. Our results show that, in the N2-fixing R. pseudoacacia, increased C uptake in response to increased [CO2] is matched by increased N2 fixation, indicating that enhanced growth in elevated [CO2] might not be restricted by N limitations.
authors.affiliation: Institute of Soil Science and Forest Nutrition, University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany.
authors.forename: Z
authors.initials: Z
authors.lastname: Feng
authors.forename: J
authors.initials: J
authors.lastname: Dyckmans
authors.forename: H
authors.initials: H
authors.lastname: Flessa
mesh_terms: D002245:Carbon Dioxide / Q000502:physiology; D009586:Nitrogen Fixation / Q000502:physiology*; D031301:Robinia / Q000254:growth & development* / Q000502:physiology; D036226:Seedlings / Q000254:growth & development / Q000502:physiology; D014197:Trees / Q000254:growth & development* / Q000502:physiology
chemical_list: D002245:Carbon Dioxide