Balancing carboxylation and regeneration of ribulose‐1,5‐ bisphosphate in leaf photosynthesis: temperature acclimation of an evergreen tree, Quercus myrsinaefolia
Changes in the temperature dependence of the photosynthetic rate depending on growth temperature were investigated for a temperate evergreen tree, Quercus myrsinaefolia. Plants were grown at 250 μmol quanta m–2 s–1 under two temperature conditions, 15 and 30 °C. The optimal temperature that maximizes the light-saturated rate of photosynthesis at 350 μL L–1 CO2 was found to be 20–25 and 30–35 °C for leaves grown at 15 and 30 °C, respectively. We focused on two processes, carboxylation and regeneration of ribulose-1,5-bisphosphate (RuBP), which potentially limit photosynthetic rates. Because the former process is known to limit photosynthesis at lower CO2 concentrations while the latter limits it at higher CO2 concentrations, we determined the temperature dependence of the photosynthetic rate at 200 and 1000 μL L–1 CO2 under saturated light. It was revealed that the temperature dependence of both processes varied depending on the growth temperature. Using a biochemical model, we estimated the capacity of the two processes at various temperatures under ambient CO2 concentration. It was suggested that, in leaves grown at low temperature (15 °C), the photosynthetic rate was limited solely by RuBP carboxylation under any temperature. On the other hand, it was suggested that, in leaves grown at high temperature (30 °C), the photosynthetic rate was limited by RuBP regeneration below 22 °C, but limited by RuBP carboxylation above 22 °C. We concluded that: (1) the changes in the temperature dependence of carboxylation and regeneration of RuBP and (2) the changes in the balance of these two processes altered the temperature dependence of the photosynthetic rate.