UC Irvine

SUMMARY: Orchid aerial roots contained chlorophylls and were shown to be capable of photosynthesis. 14CO2 feeding in the light showed that the C3 pathway was operating during the day. Aerial roots also exhibited diurnal acidity fluctuations typical of crassulacean acid metabolism (CAM) and malate was the only labelled compound isolated after night 14CO2 feeding. CO2 exchange patterns in aerial roots were consistent with CAM CO., fixation during the night hours. The rate of photosynthetic CO., fixation in the light was much greater than the rate of CAM CO2 fixation in the night. Measurements of CO2 exchange, however, showed little or no net uptake indicating that these roots were not completely autotrophic.