Figure 2.

Oxygen isotope discrimination (Δ¹⁸O) as a function of the ratio of mesophyll cytosolic to ambient CO₂ partial pressure (p_m/p_a). p_m was calculated with g_m = 1 mol m⁻² s⁻¹ bar⁻¹. The line represents the theoretical relationship of Δ¹⁸O and p_m/p_a at full isotopic equilibrium where a = 7.7‰ and Δ_ea = 33.7‰ (Eq. 8) and the CO₂ supplied to the leaf had a δ¹⁸O of 24‰ relative to VSMOW. Symbols are as in Figure 1 and measurement conditions are as in Table I. The inset shows the expanded scale of Δ¹⁸O for the wild-type and Pp plants.