title: Phosphorus affects growth and partitioning of nitrogen to Rubisco in Pinus pinaster.
abstract: We tested the hypothesis that photosynthetic and growth responses to phosphorus (P) are functions of differences in the partitioning of nitrogen (N) among different compounds, particularly ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). We tested this hypothesis in: (a) a greenhouse experiment with mycorrhizal seedlings of Pinus pinaster Ait. grown in sand culture for 4 months with six factorial combinations of N (0.125 and 2.0 mM) and P (0.02, 0.08 and 0.34 mM); and (b) a field study in which P was applied at five rates (up to 175 kg ha-1) to 2-year-old P. pinaster growing on P-deficient siliceous sand. After 4 months of nutrient addition or 2 years after fertilizer application, we measured light-saturated rates of photosynthesis, growth, and N and P allocation in needles. Growth of P. pinaster increased significantly with increasing concentrations of P, as did the concentration of P in needles. Concentrations of P and Rubisco were positively related, whereas those of N and Rubisco were unrelated. At low-P supply, the Rubisco/Chl ratio varied between 8.5 and 12 mmol mol-1. With P supply in excess of requirement (needle N:P ratio = 2-12) the Rubisco/Chl ratio increased to between 24 and 26 mmol mol-1. Rates of light-saturated photosynthesis were unaffected by P supply because adequate concentrations of P were maintained in plants in all treatments. Orthophosphate accumulated in needles of plants receiving a high P supply, which may allow growth to continue for periods under P deficiency, provided that other nutrients also accumulate. In the case of N, Rubisco may fill this role.
authors.affiliation: Department of Botany, University of Western Australia, Crawley, WA 6009, Australia. crwarren@uvic.ca
authors.forename: Charles R
authors.initials: CR
authors.lastname: Warren
authors.forename: Mark A
authors.initials: MA
authors.lastname: Adams
mesh_terms: D000596:Amino Acids / Q000032:analysis; D009584:Nitrogen / Q000502:physiology; D010758:Phosphorus / Q000502:physiology; D010788:Photosynthesis / Q000502:physiology; D028223:Pinus / Q000254:growth & development* / Q000502:physiology; D018515:Plant Leaves / Q000737:chemistry / Q000502:physiology; D000644:Quaternary Ammonium Compounds / Q000032:analysis; D012273:Ribulose-Bisphosphate Carboxylase / Q000502:physiology*; D014197:Trees / Q000254:growth & development* / Q000502:physiology
chemical_list: D000596:Amino Acids; D000644:Quaternary Ammonium Compounds; D010758:Phosphorus; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen