A Perspective: A Biochemical Model of Photosynthetic CO2 Assimilation in Leaves of C3 Species (planta 149, 78–90)

The model of C3 photosynthesis of Farquhar et al. (1980) integrated knowledge of the functioning of the biochemical components of photosynthetic carbon assimilation in C3 plants. The model linked equations describing activated Rubisco kinetics with those on the stoichiometry of the photosynthetic carbon reduction cycle and the photorespiratory carbon oxidation cycle, particularly on their energetic (electron transport, ATP synthesis and NADPH) requirements. It included temperature dependencies of these processes and combined them with a semi-empirical equation for the dependence of potential electron transport rate on absorbed irradiance. The model aimed to match generalized observations of photosynthetic gas exchange of leaves with predictions from this mathematical summary of photosynthesis. In this model, we introduced the hypothesis that the rate of Rubisco carboxylation could not exceed the capacity for RuP2 regeneration or the enzymatic capacity to consume RuP2, and that the system behaved as a teeter-totter (see-saw) with a sharp transition from one limiting state to the other. We suggested that to model genotypic and phenotypic variations amongst leaves most parameters could be assigned a priori and only the maximum Rubisco activity (Vcmax) and the maximal electron transport rate, Jmax, needed to be varied. This simplicity of use led to the wider spread application and success of the model.