Short-term effects of high CO₂ accelerate photosynthetic induction in Populus koreana × trichocarpa with always-open stomata regardless of phenotypic changes in high CO₂ growth conditions

Long-term high CO₂ exposure accelerates photosynthetic induction response due to rapid light increase. However, it is unclear whether the acceleration is caused by acclimation of photosynthetic components (long-term CO₂ effect) and/or by the sufficient substrate under high CO₂ at the measurement (short-term CO₂ effect). Populus koreana × trichocarpa cv. Peace has wide-open stomata almost not responding to changes of photon flux density. Using this species, we examined the long- and short-term CO₂ effects on photosynthetic induction by focusing on biochemical components. We grew the plants under [CO₂] of 380, 700 and 1020 μmol CO₂ mol⁻¹ air and measured the photosynthetic induction response under [CO₂] of 380 and 1020 μmol CO₂ mol⁻1 air. Despite significant reduction in Rubisco content and light-saturated photosynthetic rate in the leaves from the high growth CO₂, the photosynthetic induction time was similar in leaves from different growth CO₂ plants when measurement [CO₂] was the same. The induction, however, was significantly fast at the higher than at the lower measurement [CO₂], regardless of growth CO₂ of the plants. These results demonstrate that the acceleration of apparent photosynthetic induction under high CO₂ environment was mainly contributed by a short-term CO₂ effect rather than by a long-term acclimation effect when stomatal limitation is not the major factor.