ASPECTS OF CO2 UPTAKE IN THE CRASSULACEAN ACID METABOLISM ORCHID PHALAENOPSIS

Abstract

Phalaenopsis and i ts hybrids are the most important orchid pot plant commercial ly in the world now. Research on photosynthesi s gives us practical and useful information for improving cul t ivation. Although conventional gas-exchange technique has some l imitations in the research of a crassulacean acid metabol i sm 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 proport ion to CO2 concentration . Rate of CO2 absorption was higher at 20 C than at 25 C. CO2 uptake in the late af ternoon (Phase 4) showed a maximum around 20 C. CO2 absorption in Phase 4 increased in proportion to CO2 concentration but s tomata conductance decreased under high CO2 levels . CO2 absorption response curve to l ight intens ity in Phase 4 was not saturated t i l l 500 umol . m 2 . s 1 PPFD when CO 2 level was 2000 ppm, and then the s tomata conductance showed very low values . Under various water and humidity condit ion 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 af ter watering. Total CO 2 uptake in al l Phases was s t imulated the most at 70% relative humidity and suppressed drastical ly at 30% relat ive humidi ty. These resul ts indicated that higher relative humidi ty is l ikely the most important factor for high CO2 absorption in Phalaenopsis . INTRODUCTION Flower beauty, rap id growth, easy to cont ro l f lower ing, and other features make Phalaenopsis p roduct ion advantageous. Because of