Johnson 2021, Photosynth. Res.

The Johnson & Berry (2021) model is a mechanistic, steady-state framework designed to extend the classical Farquhar, von Caemmerer, and Berry (FvCB) model of C3​ leaf photosynthesis. It integrates the light reactions (Photosynthetic Electron Transport, or PET) with the dark reactions (Calvin-Benson-Bassham cycle, or CBBC) to explore how steady-state photosynthesis is controlled under varying environments. While conventional models assume control abruptly switches between Rubisco-limited and RuBP-regeneration-limited states, Johnson & Berry demonstrate that control is shared continuously. The Cytochrome b6​f (Cyt b6​f) complex serves as a primary kinetic regulatory bottleneck—acting as a metabolic switch that balances energy capture with carbon assimilation. The model introduces a mechanistic formulation for how the transthylakoid proton gradient acts via feedback loop to down-regulate plastoquinol oxidation at the Cyt b6​f complex. This process occurs rapidly to protect Photosystem I (PSI) from over-reduction and photoinhibition.
Unlike traditional dynamic frameworks that rely on systems of Ordinary Differential Equations (ODEs), the Johnson & Berry model operates purely under steady-state assumptions. The model translates four primary environmental input variables (Temperature, Light, CO2​, and O2​) into functional photosynthetic metrics.

Scheme

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Model definition