CO2 supply and acclimation effects on photosynthetic induction response under high CO2 in Populus plants
The photosynthetic utilization of dynamic photon flux density (PFD) strongly affects leaf photosynthetic carbon gain. Photosynthetic induction response, i.e., the increasing process of photosynthetic rate in response to a sudden increase in PFD, plays a major role in the photosynthetic utilization of dynamic PFD. To predict carbon fixation under dynamic light in future high-CO2 world, it is necessary to characterize the photosynthetic induction response under high CO2 environments. We found that Populus grown in high-CO2 environments generally exhibit a fast photosynthetic induction response. However, it remains unclear whether the enhanced induction speed is due to “short-term CO2 response” (CO2 supply effect) and/or to “long-term CO2 growth effect” (plant acclimation effect). Following previous study, we examined the above two effects on photosynthetic induction response in two poplar species, Populus euramericana cv. I-55 with normal stomatal response to PFD and P. koreana × trichocarpa cv. Peace with little response to PFD, under two CO2 environments, 380 and 1,020 μmol CO2 mol-1 in air.
Photosynthetic induction response, i.e., induction time required for the photosynthetic rate to reach 50% of steady-state photosynthesis under high PFD, was significantly faster in cv. I-55 plants grown under high compared to low CO2 when measured at the same CO2 concentration. This suggests that the enhanced induction response was caused by the acclimation effect in the species with normal stomatal response to PFD. However, in plants of cv. Peace, in which stomata are insensitive to PFD changes, growth CO2 did not affect the induction response, but the induction response was faster in the high measuring CO2 in plants from the same growing CO2 environment. This suggests that in cv. Peace CO2 supply effect enhanced induction speed under high CO2 environment. Since the acclimation effect was only significant in cv. I-55 plants with normal stomatal response, we concluded that the enhanced induction speed under high CO2 is mainly due to the stomatal acclimation to high growth CO2 environment.