Source: After Grif ths et al. (1986)

Source: After Grif ths et al. (1986)

enough in pineapple foliage to account for aH+ assuming that pyrophos-phate-dependent phosphofructokinase, not ATP-dependent phosphofruc-tokinase, catalyzed the phosphorylation of fructose-6-phosphate. Glucan contributed modestly to acidi cation in A. comosus. Foliar sucrose also diminished at night, but probably through export rather than metabolism.

Tillandsia usneoides monitored in a North Carolina forest illustrates how one CAM bromeliad behaves under a strongly seasonal climate. Subjects gained dry weight and consumed CO2 most vigorously from mid-spring through mid-fall (Martin et al. 1981). Acid uctuations and net CO2 uptake almost ceased in midwinter. Consistent with the situation in many other CAM types, carbon gain varied with temperature, aH+ peaking in late spring as daytime highs approximated 25 30 °C. If night air was programmed in a growth chamber to remain at 20 °C, diurnal maxima up to 35 °C had no dampening effect on CO2 consumption; however, as the nights grew warmer, net CO2 uptake fell, beginning with the disappearance of phase four. If the daytime maximum reached 20 °C, phase one could be sustained to a nocturnal low of about 5 °C. Net xation ceased below 5 °C, or if day/night temperatures uctuated by less than 5 °C.

Ecological correlates of the carbon fixation syndromes

Textbook treatments often imply that vascular ora segregate into clearly de ned CAM, C3 and C4 types. Likewise, these authors tend to assign

Table 4.4. Night-time gas exchange and related phenomena in CAM and C3-CAM bromeliads in Trinidad

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