A 3D peach canopy model used to evaluate the effect of tree architecture and density on photosynthesis at a range of scales

A 3D model of tree architecture is developed to simulate the photosynthesis of peach trees. The model uses a simple graphical procedure to compute the light interception and the corresponding photosynthesis. It allows to cons ider complex canopy arrangements, and is used to simulate the photosynthesi s of laterals, trees and orchards. Results showed that the photosynthesis v aried from 5 to 15 mu mol m(-2) s(-1) between laterals of different archite ctures. The photosynthesis per unit leaf area was sensitive to the orientat ion of the lateral, its size (number of leaves, length, number of shoots), to the angle between the stem and the shoots, the distance between the leav es, and the angle between the leaf and the shoot. When the isolated lateral is placed in the context of a single tree, its photosynthesis per unit lea f area decreases by a factor of two due to the shadowing. For orchards, the photosynthesis per unit leaf area decreases as a function of the tree dens ity. The photosynthesis per unit area of sunlit leaves at the lateral, tree or orchard levels, was found to be almost constant, because the leaf angle distribution of the illuminated leaves do not vary much. Therefore, one im portant result of this study is that the variation of photosynthesis per un it leaf area, is mainly determined by the fraction of sunlit leaf area. (C) 2000 Elsevier Science B.V. All rights reserved.