The Correlation between CO2 Uptake of CAM Dendrobium Hybrid and Environmental Factors under Shade Net House Conditions

Abstract

The diurnal net CO2 uptake in Dendrobium ‘Khao Sanan’ leaves was measured year-round (June 2010 to April 2011) and integrated to obtain total CO2 uptake under commercial shade net house conditions. Seasonal changes varied between 20−40 °C air temperature, 42−94% relative humidity (RH) and 667 μmol m-2 s-1 maximum light intensity, while Den. ‘Khao Sanan’ leaves performed typical CAM photosynthesis and reached their highest net CO2 uptake rate of 4 μmol m-2 s-1 after midnight and in the early morning under a 12 ± 0.5 hours photoperiod. Total CO2 uptake during the nighttime, daytime and in a total of 24 hours (daily) increased significantly and had a maximal value of more than 2 to 2.5 folds in December and February compared with the other months. The net CO2 uptake values were correlated with temperature (r2 = 0.41), RH (r2 = 0.25) and light intensity (r2 = 0.06). The net CO2 uptake were positive between 22−29°C, 60−90% RH and less than 200 μmol m-2 s-1 light intensity conditions. CO2 uptake during the nighttime and daytime was most affected by temperature, while total CO2 uptake had a higher correlation with temperature and RH. The results of this study contribute to improve the ability to efficiently design and manipulate a semi-controlled greenhouse for Dendrobium orchids for commercial scale production in Thailand.