A preliminary study on the photosynthetic induction response of Quercus serrata seedlings

To understand the sunfleck utilization of leaves in heliophilic trees within grass canopies, we studied the photosynthetic induction response of Quercus serrata seedlings grown for 5 months in different microsites in a Miscanthus sinensis canopy. Two phases, a rapid increase in CO₂ uptake and a following slow increase, were recognizabie in the time course of CO₂ uptake in response to an increase of photon flux densities (PFD). When the preceding period of low light became shorter, the period of the two phases became shorter. The capacity of response to a sudden light increase was evaluated by the relative photosynthetic induction efficiency (RPIE) defined as the ratio of integrated carbon gain measured to that calculated by assuming that a steady-state assimilation would be achieved instantaneously after the light increase. RPIEs estimated were negatively related to potential sunfleck PFD of microsite. The leaves of the seedlings grown in the microsite with a lower sunfleck PFD and a shorter sunfleck duration showed a more rapid response to a sudden increase of light. These findings suggest that the leaves of Q. serrata seedlings growing under a lower sunfleck PFD are able to increase the photosynthetic capacity more rapidly to an increase of PFD.