Analysis of Light Compensation Point for CO2 Gas Exchange of Thujopsis dolabrata var. hondae Young Growths Growing on the Forest Floor.

Abstract

The light compensation point for CO2 gas exchange is formulated as a function of 2 physiological factors, dark respiration and initial slope of the photosynthetic response curve to light intensity. The response surface curve of light compensation point given by the above model explains how the 2 physiological factors concern the change in light compensation point with temperature or the inter-specific difference. The increase in light compensation point for young growths of T. dolabyata var. hondae with increasing temperature is insignificant until the optimum temperature of photosynthesis. This is due to that initial slope of the photosynthetic response curve increases in parallel with the raise in dark respiration. In the higher temperature region the remarkable increase in light compensation point is seen mainly due to the increase in dark respiration. Light compensation points of young growths of T. dolabyata var. hondae are in the range of 4 to 6 μmol quanta m-2 sec-1 at the optimum temperature. Thus they do not have particularly lower compensation points but rather higher values compared with other woody species growing on the same forest floor. Lower light compensation points of the seed-lings of Q, mongolica var. grosseserrata and A. japonica var. borealis is attributed to the low respiration, and those of C. harringtonia var. nana to the effects of the low respiration and steep initial slope of the photosynthetic response curve.