© 2002 Heron Publishing—Victoria, Canada
Phosphorus affects growth and partitioning of nitrogen to Rubisco in Pinus pinaster
Charles R. Warren (1, 2, 3) and Mark A. Adams (1, 4)
1. Department of Botany, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia / 2. Centre for Forest Biology, University of Victoria, PO Box 3020 STN CSC, Victoria, B.C. V8W 3N5, Canada / 3. Author to whom correspondence should be addressed (crwarren@uvic.ca) / 4. Forest Science Centre, The University of Melbourne/Natural Resources and Environment, Water Street, Creswick, VIC 3363, Australia / Received March 29, 2001; accepted July 6, 2001; published online December 1, 2001
Summary
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.
Keywords:
fertilizer, nitrogen allocation, nitrogen storage, N:P ratio, orthophosphate, photosynthesis .
