The relationship between the Rubisco reaction mechanism and models of photosynthesis*

Abstract. A new model of photosynthesis published recently in this journal (H. Farazdaghi & G. E. Edwards, Plant, Cell and Environment (1988) 11 , 789–798; 799–809) clams to have a more complete mechanistic basis than currently used models based on the paper of G. D. Farquhar, S. von Caemmerer & J. A. Berry (Planta (1980) 149 , 78–90). In this paper, we examine the validity of the new kinetic expression for the rate of CO₂ fixation by Rubisco, and the derivation of an equation for photosynthetic CO₂ assimilation as a function of light intensity and CO₂ concentration presented in the new model. In addition, we compare measured response curve of photosynthesis to CO₂ and light with simulated curves using alternative models. We conclude that the new model is mechanistically misleading and, empirically, overestimates the extent to which light and CO₂ co-limit the rate of photosynthesis under most physiological conditions.