Photosynthetic responses to light intensity of deciduous broad-leaved tree seedlings raised under various artificial shade.

The light-photosynthesis curve of the seedlings of two species of Betura, Quercus, Acer, and two kinds of Fraxinus grown under three light levels was compared in relation to their specific leaf area (SLA) . With deeper shade, the SLA showed a increase, the largest in both Fraxinus, and the smallest in two kinds of Betula. The half-saturation of photosynthesis of all tree species occurred in a low photosynthetic photon flux density (PPFD), with deeper shade, especially in Quercus. With a reduction of PPFD, the initial slope of the light-photosynthesis curves of two species of Betula showed a slight steepness, whereas that of the other tree species showed a great steepness. The dark respiration rate of leaves of all tree species decreased with a deepening of shade. The photosynthetic acclimation of both Fraxinus was the greatest; this may be advantageous to surviving under a gap created in forest canopy. Two species of Betula had the smallest photosynthetic acclimation to shade, and this characteristic may imply that they can not survive under shaded conditions. The acclimation to shade of Quercus and Acer was observed not in the SLA, but in the photosynthesis; this might be an advantage for conserving photosynthates for expanding leaf area in shaded environments.