Effects of light intensity and temperature on growth, flowering, and single-leaf CO2 assimilation in Odontioda orchid

Abstract

We investigated the effects of light intensity and temperature on growth, flowering, and single-leaf CO2 assimilation of Odontioda orchid. CO2 assimilation in final leaves of back and current shoots was depressed significantly at a leaf temperature of about 30°C, in association with decreased stomatal conductance, although the light saturation point differed somewhat between back shoots and current shoots. A photosynthetic photon flux density (PPFD) of about 400 μmol· m -2·s-1 was optimum for CO2 assimilation. Large quantities of sugar and starch were reserved in pseudobulbs of back shoots under high light intensity, but they contents decreased while the current shoot was developing new leaves. When growth stopped, the amount of reserve assimilates increased again. Thus, there appears to be a dynamic translocation of assimilates between the pseudobulbs of back shoots and current shoots. All plants cultivated under a 28/18°C (day/night) died within 2 months after the beginning of the experiment confirmed that this species has low heat tolerance. Growth and flowering were stimulated at 23/13°C and a PPFD ranging between 300 and 500 μmol·m-2·s-1. These conditions seem to approximate the optimum conditions for CO2 assimilation.