A model for photosynthesis and photorespiration in C₃ plants based on the biochemistry and stoichiometry of the pathways

A model is developed for photosynthesis and photorespiration in C 3 plants, using an equation for the multisubslrate ordered reaction of ribulose 1,5‐bisphosphalc carboxylase‐oxygenase (Farazdaghi & Edwards, 1988). The model examines net CO 2 fixation with O 2 inhibition, and mutual inhibition when equilibrium exists between carboxylation and oxygenation (at the CO 2 compensation point). It is based on the stoichiometry of energy requirements and O 2 , and CO 2 exchange in the cycles, the quantum efficiency for RuBP generation, the maximum capacity for RuBP generation, the carboxylation efficiency with respect to [CO 2 ], and the oxygenation efficiency with respect to [O 2 ]. With increasing concentrations of CO 2 above the CO 2 compensation point, decreasing quantum flux density, or decreasing O 2 , simulations show that the rate of photorespiration progressively decreases. The two components of O 2 inhibition of photosynthesis change disproportionately with increasing CO 2 concentration. According to the model, the energy utilized during photosynthesis at the CO 2 compensation point is about half that under atmospheric conditions.