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A model for simulating the spatial distribution of Radiation Absorption, Transpiration and Photosynthesis within canopies

Overview

The model RATP (Radiation Absorption, Transpiration and Photosynthesis) 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 3D representation of the canopy (i.e. an array of 3D voxels, each one being characterised by a leaf area density) and allows several vegetation types (e.g. foliage of several plants) to be input at voxel scale (Figure 1). 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 30 min time step. Theoretical background and main equations of the RATP model are given in Sinoquet et al., 2001, Plant Cell and Environment.

(a)	(b)

Figure 1 : Schematic view of a 3D tree mock-up in an array of 3D voxels.

(a) Original 3D tree

(b) 3D voxels colored by radiation absorption

Implementation

The RATP is basically implemented as a set of Fortran90 modules which can be used as a standalone code or as a Python library in the OpenAlea platform (http://openalea.gforge.inria.fr/dokuwiki/doku.php). A Fortran90 module includes public variables and subroutines, which are all accessible in the OpenAlea environment.

Figure 2 : A RATP simulation in the OpenAlea platform

Applications

The RATP model has been applied to several tree species to assess the effect of tree foliage structure (distribution, type of shoots, leaf physiology) on tree physiology (transpiration, photosynthesis) and pest development

(a)	(b)

Figure 3 : Illustration of RATP applications on :

(a) the within tree crown variability in leaf photosynthesis and transpiration

(b) the within tree crown variability in insect development

Contacts :  marc.saudreau@clermont.inrae.fr and jerome.ngao@clermont.inrae.fr

References

Sinoquet H, Le Roux X, Adam B, Améglio T, Daudet FA, 2001. RATP, a model for simulating the spatial distribution of radiation absorption, transpiration and photosynthesis within canopies: application to an isolated tree crown. Plant Cell and Environment, 24, 395-406.

Massonnet C., J. L. Regnard, Lauri P. E, Costes, E. and Sinoquet H., 2008. Contributions of foliage distribution and leaf functions to light interception, transpiration and photosynthetic capacities in two apple cultivars at branch and tree scales. Tree Physiology 28(6): 665-678.

Pincebourde S., H. Sinoquet, Combes D. and Casas J. 2007. Regional climate modulates the canopy mosaic of favourable and risky microclimates for insects. Journal of Animal Ecology 76(3): 424-438.

Saudreau, M., S. Pincebourde, Dassot M., Adam B., Loxdale H. D. and Biron D. G. 2013. On the canopy structure manipulation to buffer climate change effects on insect herbivore development. Trees-Structure and Function 27(1): 239-248.

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