LEAF AND CANOPY PHOTOSYNTHESIS OF C-3 PLANTS AT ELEVATED CO2 IN RELATION TO OPTIMAL PARTITIONING OF NITROGEN AMONG PHOTOSYNTHETIC COMPONENTS - THEORETICAL PREDICTION

Effects of changes in the organization of photosynthetic components on leaf photosynthesis under contrasting atmospheric CO2 conditions (35 and 70 Pa) are evaluated using an optimization model, in which the pho tosynthetic rate is limited either by the capacity of ribulose bisphos phate carboxylase (RuBPCase) to consume ribulose bisphosphate (RuBP) o r by the capacity of RuBP regeneration. The nitrogen cost of photosynt hetic components to carry out each process is calculated for the optim al partitioning of nitrogen among the components. The model predicts t hat nitrogen allocation to the components carrying out RuBP regenerati on should be increased with reduction in allocation to RuBPCase to max imize daily photosynthesis at 70 Pa CO2. Al a temperature of 25 degree s C, doubling the current CO2 level increases daily photosynthesis by 60% with optimal reallocation of the nitrogen partitioning while the i ncrease without reallocation of nitrogen is 40%. However, at lower gro wth irradiance, the advantage in daily photosynthesis due to the reall ocation decreases with increasing nitrogen content. The ratio of photo synthesis at 70 Pa to that at 35 Pa increases with increasing temperat ure. The effects of CO2 levels on photosynthesis of a canopy in which nitrogen is optimally allocated among leaf layers are also examined. A t 25 degrees C, canopy photosynthesis at the doubled CO2 level is pred icted to increase 60 and 40% with and without the optimization of nitr ogen partitioning among photosynthetic components, respectively. Doubl ing the CO2 level does not affect the optimal nitrogen distribution am ong leaf layers in the canopy irrespective of optimization of nitrogen partitioning among photosynthetic components. (C) 1998 Elsevier Scien ce B.V. All rights reserved.