Figure 1.

A diagram showing the major factors that determine Δ¹³C during CO₂ exchange in CAM species during the four phases of the CAM cycle according to Equations 5 and 12. The terms p_a, p_i, and p_m are the partial pressures of CO₂ in the atmosphere, the intercellular airspace, and in the mesophyll cells. PCR and PCO refer to the photosynthetic carbon reduction and oxygenation cycles, respectively. The associated fractionation factors are shown by lowercase letters and are described in the “Theory” section.