Effects of temperature during light and dark periods on CO2 absorption of Phalaenopsis plants

Carbon dioxide absorption rate or net photosynthesis rate of Phalaenopsis, a CAM species, was precisely measured using a chamber built in this study. Environmental controls of the chamber including irradiance, air temperature, and CO2 concentration, were proved to be accurate. CO2 absorption rate was calculated from changes in CO2 concentration inside the airtight chamber. A metal-halide high pressure discharge lamp(400W) was used as a light source. Data acquisition and C02 control were done by a programmable data logger. With 32 plants, CO2 absorption rate was measured at 20, 25, and 30 deg C either during the dark period(12h) or during the light period(12h). When air temperature during the dark period was 25 deg C, CO2 absorption rate during the light period was highest at 20 deg C and decreased as temperature increased to 25 and 30 deg C. When the temperature during the light period was fixed to 25 deg C, CO2 absorption rate was higher when the temperature was lower, although the rate was the same during the light period. Since, both in light and dark periods, we did not observe differences in CO2 absorption rates when temperature was the same regardless of the temperature treatments, daily total of CO2 absorption was also higher when treatment temperature was lower. While the results showed that the CO2 absorption was largest at 20 deg C, growth rate of Phalaenopsis has been considered to have a peak at a considerably higher temperature than 20 deg C. We thought that this was because of higher leaf expansion rate at higher temperature than at 20 deg C, resulting a higher CO2 absorption rate per plant.