Fig. 3.

A comparison of modelled rates of the CO₂ assimilation rate as functions of partial pressures of CO₂ for C₃ (A) and C₄ photosynthesis (B). (A) Modelled rate of CO₂ assimilation as a function of chloroplast CO₂ partial pressure for the C₃ photosynthetic pathway at 25 °C. The Rubisco-limited (RuBP-saturated) rate of CO₂ assimilation has a dashed line extension at high CO₂. The electron transport-limited (RuBP regeneration) rate of CO₂ assimilation has a dotted line extension at low CO₂. The solid curve represents the minimum rate that is the actual rate of CO₂ assimilation. A possible triose phosphate limitation at high CO₂ is not shown. (after von Caemmerer, 2000). (B) Modelled rate of CO₂ assimilation as a function of mesophyll cytosolic CO₂ partial pressure for the C₄ photosynthetic pathway at 25 °C and an irradiance of 2000 µmol m^–2 s^–1. The enzyme-limited CO₂ assimilation rate (PEPC limitation at low CO₂ and Rubisco limitation at high CO₂ shows the Rubisco limited rate as a dashed line extension. The electron transport-limited (RuBP and PEP regeneration) rate of CO₂ assimilation has a dotted line extension at low CO₂. The solid curve represents the minimum rate that is the actual rate of CO₂ assimilation. Parameters used are given in Table 1.