ASPECTS OF CO₂ UPTAKE IN THE CRASSULACEAN ACID METABOLISM ORCHID PHALAENOPSIS

Phalaenopsis and its hybrids are the most important orchid pot plant com¬mercially in the world now.
Research on photosynthesis gives us practical and useful information for improving cultivation.
Although conventional gas-exchange technique has some limitations in the research of a crassulacean acid metabolism plant (CAM), we investigated CO₂ uptake in Phalaenopsis. CO₂ uptake at night (Phase 1) changed with temperature.
Maximum CO₂ uptake was observed around 20°C. CO₂ absorption at night increased in proportion to CO₂ concentration.
Rate of CO₂ absorption was higher at 20°C than at 25°C. CO₂ uptake in the late afternoon (Phase 4) showed a maximum around 20°C. CO₂ absorption in Phase 4 increased in proportion to CO₂ concentration but stomata conductance decreased under high CO₂ levels.
CO₂ absorption response curve to light intensity in Phase 4 was not saturated till 500 µmol.m^-2.s^-1 PPFD when CO₂ level was 2000 ppm, and then the stomata conductance showed very low values.
Under various water and humidity condition when Phalaenopsis was irrigated weekly, CO₂ uptake in Phase 1 was the largest at one day before watering, but that of Phase 4 was the largest at one day after watering.
Total CO₂ uptake in all Phases was stimulated the most at 70% relative humidity and suppressed drastically at 30% relative humidity.
These results indicated that higher relative humidity was likely the most important factor for high CO₂ absorption in Phalaenopsis.

XXVII International Horticultural Congress – IHC2006: International Symposium on Ornamentals, Now!

S. Ichihashi, T. Higuchi, H. Shibayama, Y. Tesima, Y. Nishiwaki, K. Ota

photosynthesis, CAM, relative humidity, temperature, light, irrigation

https://doi.org/10.17660/ActaHortic.2008.766.33