The effect of leaf age on leaf resistance and CO2 exchange of the CAM plant Bryophyllum fedtschenkoi.

Leaves of different ages from the CAM (Crassulacean acid metabolism) plant Bryophyllum fedtschenkoi Hamet et Per. differ in their ability to accumulate titratable actidity during the night. Measurements of leaf resistance to water vapour diffusion and net CO2 exchange during the day and night show differing patterns of behaviour dependent upon leaf age. Young leaves do not exhibit CAM; they behave like typical mesophytes with low resistances and a net uptake of CO2 during the day and a net output of CO2 at night. Mature leaves exhibit CAM and have high leaf resistances during the day and lower resistances at night but their pattern of CO2 exchange is complex, with a net output early in their day followed by a net uptake which continues at a reduced rate through the night. Intermediate, leaves are intermediate in their behaviour The presence of CAM in older leaves may simply be the result of increased cell vacuole size.Leaf resistance measurements are discussed in relation to the possible control of stomatal opening by substomatal CO2 concentrations.