Factors Affecting CO2 Exchange During the Light Period

2 Factors Affecting CO2 Exchange During the Light Period a) CO2 Fixation and Malic Acid Accumulation of the Preceding Night 

Photoperiods unfavorable for dark CO2 fixation or photoperiods in combination with unfavorable night temperatures will also reduce dark CO2 fixation and malic acid synthesis, thus enhancing CO2 uptake during the following day (Quei-roz, 1965 Allaway et al., 1974b). CAM plants cultivated under such conditions show 5 C values (see Chap. 3) tending in the direction of a C3 pattern rather than of C4 (Crews et al., 1976 Osmond et al., 1973). This reflects a high proportion of atmospheric CO2 fixed directly by C3-photosynthesis. 

There are a few reports in the literature on the effect of different light intensities on the day CO2 exchange of CAM plants. In Kalanchoe daigremontiana and Ananas commosus, high light intensity reduces the midday temporal extension of 

CO2 production from malic acid is also stimulated by high temperatures. Hence, the higher the day temperature, the higher the light that would be needed to fix the CO2 produced from malic acid. It can be expected that CAM species from different habitats will differ significantly in this behavior. 

Gregory et al. (1954) observed in Kalanchoe blossfeldiana that both dark CO2 fixation and CO2 uptake in the light period are affected by photoperiod. Plants precultivated under long-day conditions take up external CO2 throughout the day with little depression. With increasing numbers of short days, a depression of daytime CO2 fixation occurs, and finally even massive output of CO2 may be observed (Fig. 5.11). Since short-day treatments increase the nocturnal CO2 

---