David Da Silva

Multiscale Framework for Modeling and Analyzing Light Interception by Trees

This paper presents a new framework for modeling light interception by isolated trees which makes it possible to analyze the influence of structural tree organization on light capture. The framework is based on a multiscale representation of the plant organization. Tree architecture is decomposed into a collection of components representing clusters of leaves at different scales in the tree crown. The components are represented by porous envelopes automatically generated as convex hulls containing components at a finer scale. The component opacity is defined as the interception probability of a light beam going through its envelope. The role of tree organization on light capture was assessed by running different scenarii where the components at any scale were either randomly distributed or localized to their actual three-dimensional (3D) position. The modeling framework was used with 3D digitized fruit trees, namely peach and mango trees. A sensitivity analysis was carried out to assess the effect of the ...

Linking water stress effects on carbon partitioning by introducing a xylem circuit into L-PEACH

BACKGROUND AND AIMS Many physiological processes such as photosynthesis, respiration and transpiration can be strongly influenced by the diurnal patterns of within-tree water potential. Despite numerous experiments showing the effect of water potential on fruit-tree development and growth, there are very few models combining carbohydrate allocation with water transport. The aim of this work was to include a xylem circuit into the functional-structural L-PEACH model. METHODS The xylem modelling was based on an electrical circuit analogy and the Hagen-Poisseuille law for hydraulic conductance. Sub-models for leaf transpiration, soil water potential and the soil-plant interface were also incorporated to provide the driving force and pathway for water flow. The model was assessed by comparing model outputs to field measurements and published knowledge. KEY RESULTS The model was able to simulate both the water uptake over a season and the effect of different irrigation treatments on tree development, growth and fruit yield. CONCLUSIONS This work opens the way to a new field of modelling where complex interactions between water transport, carbohydrate allocation and physiological functions can be simulated at the organ level and describe functioning and behaviour at the tree scale.

Influence of the variation of geometrical and topological traits on light interception efficiency of apple trees: sensitivity analysis and metamodelling for ideotype definition

Background and Aims The impact of a fruit trees architecture on its performance is still under debate, especially with regard to the definition of varietal ideotypes and the selection of architectural traits in breeding programmes. This study aimed at providing proof that a modelling approach can contribute to this debate, by using in silico exploration of different combinations of traits and their consequences on light interception, here considered as one of the key parameters to optimize fruit tree production. Methods The variability of organ geometrical traits, previously described in a bi-parental population, was used to simulate 1- to 5-year-old apple trees (Malus × domestica). Branching sequences along trunks observed during the first year of growth of the same hybrid trees were used to initiate the simulations, and hidden semi-Markov chains previously parameterized were used in subsequent years. Tree total leaf area (TLA) and silhouette to total area ratio (STAR) values were estimated, and a sensitivity analysis was performed, based on a metamodelling approach and a generalized additive model (GAM), to analyse the relative impact of organ geometry and lateral shoot types on STAR. Key Results A larger increase over years in TLA mean and variance was generated by varying branching along trunks than by varying organ geometry, whereas the inverse was observed for STAR, where mean values stabilized from year 3 to year 5. The internode length and leaf area had the highest impact on STAR, whereas long sylleptic shoots had a more significant effect than proleptic shoots. Although the GAM did not account for interactions, the additive effects of the geometrical factors explained >90% of STAR variation, but much less in the case of branching factors. Conclusions This study demonstrates that the proposed modelling approach could contribute to screening architectural traits and their relative impact on tree performance, here viewed through light interception. Even though trait combinations and antagonism will need further investigation, the approach opens up new perspectives for breeding and genetic selection to be assisted by varietal ideotype definition.

Modeling of light transmission under heterogeneous forest canopy: an appraisal of the effect of the precision level of crown description

Abstract• ContextLight availability in forest understory is essential for many processes; it is, therefore, a valuable information regarding forest management. However, its estimation is often difficult and direct measurements are tedious. Models can be used to compute understory light, but they often require a lot of field data to accurately predict light distribution, particularly in the case of heterogeneous canopies.• AimsThe influence of the precision level of crown description was studied with a model (MμSLIM) that can be used with both detailed and coarse parameterization with the aim of reducing field data requirements to a minimum.• MethodsWe analyzed the deterioration of the prediction quality of light distribution to the reduction of inputs by comparing simulations to transmitted light measurements in forests of increasing complexity in three different locations.• ResultsWith a full set of parameters to describe the tree crown (i.e., crown extension in at least eight directions, crown height and length), the model accurately simulated the light distribution. Simplifying crown description by a geometric shape with a mean radius of crown extension led to deteriorated but acceptable light distributions. Allometric relationships used to calculate crown extension from trunk diameter at breast height seriously reduced light distribution accuracy.

The phyllochron of well-watered and water deficit mature peach trees varies with shoot type and vigour

The addition of new nodes to shoots is an essential mechanism for understanding and modelling canopy growth but surprisingly, there is very little research on the factors that control the phyllochron in tree species. It is often assumed that the phyllochron is regulated by temperature and is consistent among all shoot types. This research clearly indicates that this is not the case. This study shows differences in the phyllochron between different shoot types and water treatments that appear to be associated with rank effect rather than temperature.