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We investigated morphological and photosynthetic responses of current-year seedlings of oak ( Quercus crispula  Blume) under high-light conditions.  Quercus crispula  seedlings were grown from seed in a relative photosynthetically active photon flux density (RPPFD) of 100, 10 or 2%. There was no difference in total dry mass between 100 and 10% RPPFD. At the end of the growing season, plants grown in 2% RPPFD had a lower total dry mass than those grown in 100 or 10% RPPFD. Seedlings grown in 100% RPPFD showed morphological acclimation, i.e., high root/shoot ratios and high leaf mass per area. De-epoxidation level in the xanthophyll cycle and activity of an antioxidant enzyme were highest in 100% RPPFD, but total chlorophyll concentration and photosynthetic rate were highest in 10% RPPFD. These results indicate that excess photons were generated in 100% RPPFD, leading to increased capacities for dissipation of received light energy through the xanthophyll cycle and for scavenging of reactive oxygen species through the water–water cycle. Nevertheless, a midday decrease in dark-adapted quantum yield of photosystem II ( F  v / F  m ) indicated that seedlings grown in 100% RPPFD were suffering from photoinhibition. We conclude that  Q. crispula  current-year seedlings have high morphological acclimation to high light but that photosynthetic efficiency cannot be maintained under high-light conditions even with a photoprotection system.

Morphological and photosynthetic responses of Quercus crispula seedlings to high-light conditions