CO2 Exchange Under Continuous Illumination

Because general metabolic activity is strongly inhibited by either low temperature or anaerobiosis, it is not surprising that these treatments inhibit the CO2 output rhythms (Wilkins, 1962 a, 1967). The application of low temperature or anaerobiosis for a limited interval causes phase shifts. Similarly to light (see Fig. 5.17), the effect depends on the time of the cycle when the treatments are applied (Wilkins, 1962a, b, 1967). 

It is not known if the CO2 output rhythms described above are accompanied by corresponding oscillations in malic acid concentrations. Clearly, such acid changes would occur if the rhythmic phenomena were CAM-related. Since CO2-free air inhibits malic acid accumulation even in normal day/night cycles (Wolf, 1960 Kluge, 1968 b), the rhythmic phenomena described by Wilkins may not be CAM-related. However, Queiroz (1975) reported a circadian CO2 output rhythm by Kalanchoe blossfeldiana in normal air in darkness as did Wilkins (1959) with B.fedtschenkoi. Hence, the rhythms are probably not the result of the C02-free air, but since we do not know more about corresponding malic acid fluctuations, we cannot determine the extent to which the rhythmic CO2 output is CAM related. 

In Kalanchoe tubiflora, the light CO2 uptake can be shifted to CO2 output by high temperature (35° C). After resetting the lower, normal temperature (20° C), the circadian rhythm phase of CO2 uptake remains shifted 180° with respect to the control (Fig. 5.18). Furthermore, under constant light and temperature, the phase shifts slowly, such that the maximum CO2 uptake occurs during the normal day period. 

In Kalanchoe tubiflora, during the first cycle the CO2 uptake rhythm in continuous light and normal air is accompanied by a predictable oscillation in malic acid (Kluge, 1969 c). The malic acid concentration increases with CO2 uptake and decreases during the low CO2 uptake period. In Bryophyllum calycinum, Kress in Kluge s laboratory (unpublished) showed that the rhythm of CO2 uptake and 

Such speculation presumes, however, that the rhythm is a general feature of CAM plants. Despite the fact that Kalanchoe blossfeldiana, K, daigremontiana, and Bryophyllum fedtschenkoi are typical CAM plants, only a few species have 

---