Fig. 1. Responses of transpiration efficiency (TE) to CO2 concentration in C3 and C4 plants: (A) relative increases in TE with increasing CO2 concentration (normalized to 350 µmol mol-1 CO2), and (B) possible absolute responses of TE to CO2. Transpiration efficiency was calculated assuming a ratio of intercellular to atmospheric CO2 concentration of 0.7 for C3 plants and 0.4 for C4 species and a mole fraction water vapor gradient from the leaf to bulk air of 12 x 10-3 mole mole-1 across CO2 concentrations.
