Figure 3.

Assuming a fixed number of Rubisco active sites per unit leaf area and the dependence of catalytic rate per active site on specificity described for different photosynthetic organisms by Zhu et al. [116], the line shows, for any given atmospheric [CO₂], the specificity (τ) that will give the highest light-saturated rate of leaf photosynthetic CO₂ uptake (A_sat). The average τ for terrestrial C₃ crop plants (92.5) is indicated (τ₁) together with the interpolated atmospheric [CO₂] at which it would yield the maximum A_sat (C₁). Point τ₂ is the specificity that would yield the highest A_sat at the current [CO₂] of the atmosphere (C₂). At C₂, decrease in τ from present average (τ₁) to the optimum for current [CO₂] (τ₂) can increase light-saturated leaf photosynthetic carbon uptake by 12%. Reproduced with permission from Zhu et al. [116].