Photosynthetic Responses to Light Intensity for Saplings of Some Tree Species Growing in the Shaded Undergrowth of a Quercus serrata Forest.

Abstract

Photosynthetic properties of leaves are compared among saplings of tree species. The interspecific difference is insignificant in maximal rate of net photosynthesis (Pmax) but is recognized in initial slope of light response curve (x) . Values of α are largest in C. controversa and smaller in M. kobus and Q. mongolica var. grosseserrata: P. verecunda and Q. serrata have intermediate values. Under exposure to an irradiance of 1, 400μmol quanta m-2 sec-1, the photosynthetic response (P*) declines rapidly for Q. serrata and Q. mongolica, whereas the other tree species show no rapid decreases at least for 5 min, also followed by relatively gentle decreases. The photosynthetic reduction of Pmax by the 60-min exposure to high light ranges from 16% of M. kobus to 35% of P. verecunda and that of a from 28% of Q. mongolica to 55% of P. verecunda, significantly differing due to species. However, the extent of photosynthetic reduction of Pmax or α is not directly correlated with the decrease in P*. It is saplings of C. controversa that is presumably able to utilize most efficiently both weak and strong light under the actual light regime of the forest floor. Saplings of Q. serrata and Q. mongolica, by contrast, have no particularly advantageous photosynthetic properties to either use of weak light or that of strong light.