Fig. 1.

Daily gas-exchange of plants with different modes of CAM: (A) Obligate CAM in watered plants of Opuntia ficus-indica (Nobel and Hartsock, 1983); (B) C₃ CO₂-uptake in well-watered plants of the inducible-CAM species, Talinum triangulare (Herrera et al., 1991); (C) small dark CO₂ fixation in plants of T. triangulare drought-stressed for 10 d (Herrera et al., 1991); (D) CAM-cycling in watered plants of Talinum calycinum (Martin et al., 1988); (E) CAM-idling in plants of Talinum calycinum drought-stressed for 3 d (Martin et al., 1988). The broken line indicates no net CO₂-exchange; the dark bar on the abscissa indicates the duration of the dark period. The corresponding values of nocturnal acid accumulation were: (A) 85 µmol H⁺ cm⁻² (droughted plants had a value of 16 µmol H⁺ cm⁻²); (B) 8 µmol H⁺ g⁻¹ FM (0·2 µmol H⁺ cm⁻²); (C) 100 µmol H⁺ g⁻¹ FM (2·0 µmol H⁺ cm⁻²); (D, E) 56 µmol H⁺ g⁻¹ FM. Redrawn with permission from the authors.