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 consider complex canopy arrangements, and is used to simulate the photosynthesis of laterals, trees and orchards. Results showed that the photosynthesis varied from 5 to 15 μmol m−2 s−1 between laterals of different architectures. The photosynthesis per unit leaf area was sensitive to the orientation 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 leaves, 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 leaf 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 density. 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 important result of this study is that the variation of photosynthesis per unit leaf area, is mainly determined by the fraction of sunlit leaf area.