Factors Affecting CO2 Exchange During the Dark Period

2 Factors Affecting CO2 Exchange During the Dark Period a) Nocturnal Temperature 

There is overwhelming evidence that high night temperatures inhibit malic acid accumulation in CAM plants, whereas low night temperatures have the opposite effect (see reviews of Wolf, 1960 Ranson and Thomas, 1960 see Chap. 4.3.1). Because malic acid is the end product of the metabolic pathway of dark CO2 fixation, it is reasonable to predict that CO2 exchange during the night would also be affected by temperature. 

In most of the CAM plants investigated, substantial net CO2 fixation occurs if the night temperatures are 10° C or above. Optimal CO2 uptake is observed at nightly temperatures ranging from 15°-22°C (see Fig. 5.3, Kluge et al., 1973 Medina et al., 1977 Neales, 1975 for exceptions see Dinger and Patten, 1974 Lange et al., 1975). 

The mechanism by which temperature affects dark CO2 fixation in CAM plants cannot be entirely explained. Since net CO2 uptake from the atmosphere 

Brandon (1967) concluded from in vitro experiments that the thermal properties of the carboxylating and decarboxylating enzymes (PEP carboxylase, malic enzyme, see Chap.4.2.3.2) are such that lower temperatures would favor CO2 consumption (i.e., malic acid synthesis) higher temperatures, however, would increase CO2 production by malic acid decarboxylation. Hence, the thermal properties of the enzymic proteins could account partly for the observed temperature effects. 

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