Coupling the functional-structural plant models MAppleT and QualiTree to simulate carbon allocation and growth variability of apple trees

Plant growth highly depends on the carbon allocation which results from combined effects of environment, horticultural practices and management. QualiTree has been demonstrated to be a useful model to simulate carbon allocation in peach trees. The objective of this study was to adapt QualiTree to apple trees to simulate carbon economy and organ growth dynamics as well as their within-tree variability. We used MappleT to generate tree architectures corresponding to the 'Fuji' cultivar and to account for the variability among individuals. Architectures were saved into a Multiscale Tree Graph(MTG) that included information on all shoot and fruit locations as well as their initial weights. This information was then used as input for QualiTree. Furthermore, based on the observed shoot polymorphism in apple trees, we modified QualiTree to take into account different classes of shoots (long, medium and short) that are characterized by different growth rates and duration. The light interception sub-model, based on a turbid medium hypothesis, was also modified to allow the usage of user-defined ellipsoids to represent the shape of apple trees. The simulations were compared to 3D digitized trees and measurements previously performed on 'Fuji' apple trees. The model was useful for simulating organ growth and their within tree variability. This modelling approach coupling MAppleT and QualiTree will help provide deeper understanding of complex interactions between growth, architecture and management practices. To reach this objective, further works are needed to integrate into MappleT retroaction loops between carbon allocation and plant architecture dynamics.