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

de Fury and Farquhar [de Fury, D.G.G., Farquhar, G.D. Simple scaling of pho tosynthesis from leaves to canopies without the errors of big-leaf models. Plant, Cell Environ. 20 (1997) 537-557] published a paper that integrated n itrogen and light profiles separately for sun and shade leaves in a canopy, and combined these with a current biochemically based model of leaf photos ynthesis. It was shown that this gave good agreement with the output of a m ulti-layered model with the same biochemical properties. Wang and Leuning [ Wang, Y.-P., Leuning, R. A two-leaf model for canopy conductance, photosynt hesis and partitioning of available energy. I. Model description and compar ison with a multi-layered model. Agric, For. Meteor. 91 (1998) 89-111] repe ated the comparison of the sun/shade model and a multi-layered model, but r eported that the agreement was poor, and developed what was reported to be an alternative treatment, with a more robust approach. We show here that th eir 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 dis cussed. (C) 1999 Elsevier Science B.V. All rights reserved.