SENSITIVITY ANALYSIS OF LIGHT INTERCEPTION TO GEOMETRICAL TRAITS OF APPLE TREES: AN IN SILICO STUDY BASED ON MAPPLET MODEL

Abstract

The efficiency of light interception is a driving factor for plant transpiration and photosynthesis, and contributes greatly to plant growth. For a fruit tree, the efficiency of light interception is also a key factor to improve yield quality. Such efficiency is highly dependent on the tree geometrical and topological organisation which may vary between genotypes, or as a result of agronomic practices such as pruning. The purpose of this study was to use a functional-structural plant model, in order to find out the major geometrical traits that influence the efficiency of light interception in apple trees. MAppleT, an architectural model of apple tree, and VPlants, a software library that includes functionalities to simulate light environment, provided the basis for this work. The STAR, namely the silhouette to total area ratio of leaves, was used to evaluate the light interception efficiency. The general methodology contained three steps: (1) manipulation of a set of geometrical parameters in MAppleT, such as those related to internode elongation, leaf area expansion, and branching angle; (2) integration of the resulting tree architecture within the simulated light environment for calculation of STAR values at the whole tree scale; (3) analysis of the influence of the variation of each geometrical trait on the variance of STAR outputs. As expected, leaf area manipulation had the highest impact on STAR values. Interactions between input parameters were also found, and are illustrated in the case of leaf area versus internode length. This suggests that optimal combination(s) of the corresponding traits could be found, setting a target for genetic improvement, as well as physiological studies on real apple trees.