Using functional-structural modeling of carbon acquisition and utilization to understand fruit size distribution in tree canopies

Fruit size is an important parameter affecting both yield and quality. Fruit of multiple sizes can be found within a tree canopy and this has been correlated with factors involving carbon availability, e.g., crop load, light and temperature. However, the underlying mechanisms determining fruit size distribution seem complex and not easy to identify. It is very difficult to carry out multi-factor field experiments to increase our understanding in this area due to time, economic and technical constraints. Functional-structural models of carbon acquisition and utilization have been previously employed to simulate and understand the effects of date of thinning and irrigation regime on size of individual fruits and fruit size distribution in the tree canopy. These models used concepts of potential relative growth rates of individual organs and inter-organ competition for carbon. We built a functional-structural model of canopy growth at the individual organ scale, and used this model to simulate and study patterns of fruit size distribution in tree canopies with different training systems, crop loads, light and temperature regimes. The functional-structural tree model combines models of light interception, photosynthesis, potential relative growth rates of individual organs and inter-organ competition for carbon within each shoot. Canopy architectural data were employed to reconstruct and visualize our trees in the modeling platform. These virtual canopies were selected as inputs for simulating the growth of individual shoots and fruits in the canopy during one growing season. Our model showed that we can simulate multi-factor experiments, allowing us to increase our understanding and test concepts about the effects of carbon availability on fruit size distribution in trees growing in orchard systems.