EFFECTS OF DAY LENGTH ON GAS-EXCHANGE CHA RACTERISTICS IN CRASSULACEAN ACID METABOLISM PLANT, DENDROBIUM-EKAPOL CV PANDA

Effects of growth day length on gas exchange characteristics were inve stigated in a crassulacean acid metabolism (CAM) plant, Dendrobium Eka pol cv. Panda. Long (16h) and short (10h) day lengths were treated for 57 to 60 days in a growth chamber set at day/night temperatures of 30 /25 degrees C. As a control, plants were grown under natural condition s (light period was 12h). The data showed that the diurnal CO2 exchang e of D. Ekapol was classified as typical crassulacean acid metabolism type, an obligate CAM. The CO2 balance of each phase was affected by t he day length treatments. The CO2 balances of short-day-length grown p lants were increased in phase 1, whereas those of long-day-length grow n plants were increased in phases 2 and 4. The CO2 balance of whole da y and diurnal malate fluctuation was increased in natural and short-da y-length grown plants. The activity of phosphoenolpyruvate carboxylase did not response to the day length treatments. However, susceptibilit y of phosphoenolpyruvate carboxylase to malate was detected dearly in phase 4 and at the beginning of phase 1 under different day length. It was suggested that the difference between treatments was related to t he changes in the CO2 exchange rate in those phases.