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The model RATP (radiation absorption, transpiration and photosynthesis) is presented. The model was designed to simulate the spatial distribution of radiation and leaf-gas exchanges within vegetation canopies as a function of canopy structure, canopy microclimate within the canopy and physical and physiological leaf properties. The model uses a three-dimensional (3D) representation of the canopy (i.e. an array of 3D cells, each characterized by a leaf area density). Radiation transfer is computed by a turbid medium analogy, transpiration by the leaf energy budget approach, and photosynthesis by the Farquhar model, each applied for sunlit and shaded leaves at the individual 3D cell-scale. The model typically operates at a 20-30 min time step. The RATP model was applied to an isolated, 20-yearold walnut tree grown in the field. The spatial distribution of wind speed, stomatal response to environmental variables, and light acclimation of leaf photosynthetic properties were taken into account. Model outputs were compared with data acquired in the field. The model was shown to simulate satisfactorily the intracrown distribution of radiation regime, transpiration and photosynthetic rates, at shoot or branch scales.

strategies are influenced by topological constraints, namely hydraulics and biomechanics, and how plants regulate biomass investment in order to achieve multiple purpose optimisation. This illustrates the usefulness of FSPMs to understand interactions between multiple processes better. Plant as a networkThe plant structure provides the support for different forms of fluxes (water, sugars) and signals (mechanical constraints, hormones) that control the plant functioning and growth. Models of water transport have been developed in the past decade and rely on the application of Darcy's law to express the relationship between fluxes and water potential in porous media, (e.g. Früh & Kurth, 1999). More recently, the simulation of mechanical stress and strains in plants has been considered by several teams ( Jirasek et al ., 2000; Alméras et al ., 2002; Fourcaud & Lac, 2003) and is now considered to be a tractable issue. The problem of carbon transport and allocation is more complex because the underlying physiological processes are difficult to observe and are not yet well understood. Current modelling approaches use different variants of the concept of source and sink strength, reviewed in this issue by this issue). The authors suggest that a 'minimal Münch model' can provide a sound and general theoretical framework to model carbon transport, where allocation priorities are an emergent property of the model. this issue) illustrate this approach by describing a transport-resistance model based on the integration of similar assumptions for carbohydrate flow and allocation and  -systems for studying the growth of peach trees. Plant as a developing organismThe growth of the plant continuously modifies the network of components and space occupation, which in turn changes the general balance between organ demand and production. This dynamic feedback between structure and function is probably one key issue in the understanding of plant development which necessitates further theoretical and applied developments. Current work in this area consists of developing mechanistic models that integrate models of physiological processes and descriptive information where knowledge of the underlying mechanisms is lacking. Knowledge is usually expressed at the metamer or growth unit level, and the growth of the entire organism is considered as an emerging property of the locally defined interactions between plant components or between plant components and environmental factors. Two approaches in this issue were designed to study the effect of environmental factors (here, light) on plant growth. , this issue) adopted a detailed descriptive approach to model the growth of wheat. The variation of architectural variables throughout time (e.g. leaf dimensions, internode length, phyllochrone and leaf number) was estimated according to field measurements or bibliographic data. this issue) designed a model where each metamer can produce a flush of growth. Flushes are controlled by the product of probabilities, depending on their metamer...

The spatial variations in the stable carbon isotope composition ( and water-use efficiency resulted from the short-term response of leaf gas exchange to variations in local irradiance and, to a much lesser extent, from the long-term acclimation of leaf characteristics to the local light regime.

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