Environmental influences on light and dark CO2 fixation by Kalanchoe daigremontiana

The influence of day length, light quality, temperature, drought, and oxygen concentration on gas exchange of Kalanchoe daigremontiana was investigated. The ratio of photosynthesis to dark CO 2 fixation with plants under a long-day and short-warm-night regime was 2.0 and under a short-day and long-cool-night regime, 0.2. With drought conditions this value may be less than 0.02. Under low oxygen concentrations high photosynthetic rates of about 20 mg CO 2 dm −2 h −1 were observed with a compensation point of about 20 ppm. Restricting CO 2 supply to dark periods produced plants with a δ 13 C value of −10.6‰. Restricting CO 2 supply to light periods gave a δ 13 C value of −25.9‰, whereas no control of CO 2 gave δ 13 C values of −15‰. The data obtained suggest that variations in δ 13 C values in Kalanchoe result from changes in the proportion of light and dark CO 2 fixation.Far-red light and oxygen promoted the release of CO 2 from Kalanchoe after the plants had undergone a period of dark CO 2 fixation. Maximum release occurred within about 1 h. The effect could be reversed by removal of either far-red light or oxygen. Decreases in the acidity of the plants accompanied CO 2 release, which indicated that decarboxylation of a C 4 acid was the source of the CO 2 .