Hahn 1987, Ann. Bot.

The Hahn 1987 model is a kinetic model of C₃ leaf carbon metabolism that couples the Calvin-Benson-Bassham (CBB) cycle to the glycolate and glycerate pathways of photorespiration, formulated as a system of non-linear ordinary differential equations. It extends Hahn's earlier Calvin-cycle models (1984, 1986) by adding the competitive inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) by oxygen, which is the entry point of photorespiration: the same enzyme that fixes CO₂ also reacts with O₂, diverting carbon into the photorespiratory pathway. By representing both processes in one connected network, the model can describe the competition between carboxylation and oxygenation that governs net assimilation in C₃ plants.

The model reaches an effectively stable steady state and behaves realistically when the external CO₂ and O₂ concentrations are varied: photosynthesis is inhibited by higher oxygen levels, while photorespiration is inhibited by higher carbon dioxide levels, reproducing the well-known reciprocal sensitivity of the two pathways to gas composition. As one of the earlier mechanistic treatments of photorespiration, it is included in GreenSloth mainly as a historical and conceptual reference point — a compact example of how the carbon-fixing dark reactions and their photorespiratory by-pass can be modelled together, complementing the more abstract CBB-only treatment of the Zhu 2009 model.

Scheme

Model definition