© 2003 Heron Publishing—Victoria, Canada
Morphological and photosynthetic responses of Quercus crispula seedlings to high-light conditions
Sawako Matsuki (1, 2, 3), Ken'ichi Ogawa (4), Ayumi Tanaka (1) and Toshihiko Hara (1)
1. The Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan / 2. Laboratory of Boreal Forest Conservation, Graduate School of Agriculture, Hokkaido University, Sapporo 060-0809, Japan / 3. Author to whom correspondence should be addressed (s-matsuk@exfor.agr.hokudai.ac.jp) / 4. Research Institute for Biological Sciences, Okayama (RIBS), 7549-1 Yoshikawa, Okayama 716-1241, Japan / Received June 14, 2002; accepted February 9, 2003; published online July 1, 2003
Summary
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 (Fv/Fm) 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.
Keywords:
biomass allocation, chlorophyll concentration, chlorophyll fluorescence, high light stress, membrane-bound ascorbate peroxidase
(EC 1.11.1.11), photoinhibition, photosynthetic rate, xanthophylls.
