A 2-LEAF MODEL FOR CANOPY CONDUCTANCE, PHOTOSYNTHESIS AND PARTITIONING OF AVAILABLE ENERGY - II - COMPARISON WITH MEASUREMENTS

A new two-leaf canopy model for predicting fluxes of net radiation, se nsible heat, latent heat and CO2 between plant canopies and the atmosp here was tested against 228 half-hourly micrometeorological flux measu rements spanning over two months during the vegetative growth of two w heat crops. During that period green area index ranged from 1.8 to 4.5 for the fertilised crop and from 1.0 to 2.7 for the control crop. Exc ellent agreement was obtained between simulations and measurements for fluxes of net radiation, latent heat and CO2, although sensible hear fluxes were less satisfactory, Uncertainties in estimates for fluxes o f water vapour and CO2 from the underlying soil contributed to discrep ancies between measurements and simulations. Modelled canopy fluxes of both CO2 and latent heat are highly sensitive to the quantum yield of photosynthesis (mu mol CO2 mol(-l) quanta). Fluxes of latent heat are more sensitive than CO2 to parameters describing stomatal function, w hile CO2 flux was more sensitive than transpiration to maximum carboxy lation rates.The two-leaf model requires only a few parameters that ma y vary with plant species. It is computationally 10 times more efficie nt than an earlier described multilayered model and is suited for inco rporation into regional- or global-scale climate models. (C) 1998 Publ ished by Elsevier Science B.V. All rights reserved.