Figure 1.

Light period of the day/night CAM cycle with JCO₂ (——) and φ_PSII (—○—) of an attached leaf of K. daigremontiana measured simultaneously in a climate-regulated cuvette. The average of φ_PSII (a) is obtained by integrating over the leaf area imaged and shown in Fig. 2. A–P: Quantitative estimation of spatial heterogeneity (b) of φ_PSII is calculated according to ref. 24. The four phases of net CO₂ exchange in CAM (JCO₂) are: (I) nocturnal CO₂ fixation via PEPCase leading to vacuolar malate accumulation; (II) transition between PEPCase and RUBISCO dominated CO₂ fixation; (III) malic acid decarboxylation leading to high internal CO₂ concentration and CO₂ fixation by RUBISCO behind closed stomata; (IV) stomatal opening and CO₂ fixation via RUBISCO. Experimental conditions were 28°C and 257 μmol photons m⁻²·s⁻¹ (λ = 400–660 nm). Black and white bars indicate dark and light periods, respectively. Gas exchange was measured as in ref. 13.