Figure 3.

Oxygen isotope discrimination (Δ¹⁸O) as a function of the ratio of mesophyll cytosolic to ambient CO₂ partial pressure (p_m/p_a). Where p_m was calculated with g_w = 10 mol m⁻² s⁻¹ Pa⁻¹ for the C₄ plants and 5 mol m⁻² s⁻¹ Pa⁻¹ for tobacco. 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. 4) and the CO₂ supplied to the leaf had a δ¹⁸O of 24‰ relative to VSMOW. Each point represents a measurement made on a different plant grown under ambient conditions in a glass house or at 0.96 kPa CO₂ in growth chambers. Measurement conditions are as in Table II and Figure 1. Each point represents a measurement made on a different plant or different light level: wild-type F. bidentis (□); anti-CA F. bidentis (▪); anti-SSU F. bidentis (▴); wild-type Z. mays (⋄); and wild-type tobacco (▵). Plants grown in ambient and 0.96 kPa CO₂ were grouped together in this figure.