A commentary on the use of a sun/shade model to scale from the leaf to a canopy

De Pury and Farquhar [de Pury, D.G.G., Farquhar, G.D. Simple scaling of photosynthesis from leaves to canopies without the errors of big-leaf models. Plant, Cell Environ. 20 (1997) 537-557] published a paper that integrated nitrogen and light profiles separately for sun and shade leaves in a canopy, and combined these with a current biochemically based model of leaf photosynthesis. It was shown that this gave good agreement with the output of a multi-layered model with the same biochemical properties. Wang and Leuning [Wang, Y.-P., Leuning, R. A two-leaf model for canopy conductance, photosynthesis and partitioning of available energy. I. Model description and comparison with a multi-layered model. Agric. For. Meteor. 91 (1998) 89-111] repeated the comparison of the sun/shade model and a multi-layered model, but reported that the agreement was poor, and developed what was reported to be an alternative treatment, with a more robust approach. We show here that their alternative, while appearing to be more complicated, is mathematically identical with our sun/shade model, and that the discrepancy they reported was caused by their coding error. The issue of tuning of such models is discussed.