General Phenomena of CO2 Exchange

Thomas (1949) and Wolf (1949) named this anomalous CO2 fixation oeeurring during the dark period, in honor of its diseoverer, the De Saussure effeet. The term De Saussure effeet should not be used synonymously with CAM, but be reserved to eharaeterize the phenomenon of dark CO2 fixation, or, more preeise-ly, the phenomenon of net CO2 uptake from the atmosphere during the night by plants. 

It was not before 1949 that Thomas (1949), and Wolf (1949), stimulated by the discovery of nonphotosynthetic CO2 fixation in propionic bacteria by Wood and Werkmann (1938), recognized dark CO2 fixation as a missing link in the causal chain leading to dark malic acid accumulation during CAM. 

Further evidence for the concept that dark CO2 fixation is involved in CAM was provided by Thurlow and Bonner (1948) who demonstrated the appearance of radiocarbon in malic acid when C02 was supplied in the dark (see Chap. 3). 

A standard diurnal pattern of CO2 exchange during an experimental dark/ light regime of 12 12h and under constant temperatures of 20° C can be described. Such curves have been extensively discussed by Nuernbergk (1961,1962), 

In the following sections, the gas exchange involved in CAM and the factors affecting it will be considered in more detail. 

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