Estimation of the amount of light intercepted by a plant in natural and artificial environments: Contribution of 3D virtual plants in sunflower and Arabidopsis thaliana

Light interception is a major contributor to biomass accumulation of crops. Beer's law has beenextensively used to estimate the amount of light intercepted by a plant at canopy level. Thismethod, based on the use of the leaf area index (LAI), is designed for well-developed crops wherethe canopy is assumed to be a turbid medium (Jones, 1992). However this assumption is seldomverified and in most situations canopies are strongly heterogeneous, as for example in perennialcrops such as vineyards and orchards (e.g. Louarn et al., 2007) or in row crops during the firstdevelopmental stages or when leaf senescence occurs. We propose here to test a method based on3D modelling to quantify the local light environment of plants in different situations, includingartificial conditions.3D virtual plants built from architectural measurements (Barczi JF et al., 1997) were used with aradiative balance model (Dauzat and Eroy, 1997) to characterise plant-environment interactions. Amulti-directional approach was chosen to take into account direct and diffuse photosyntheticallyactive radiations (PAR) which have a major influence on the plant radiative balance. Under naturalconditions, when there was no obstacle to light, the direct-diffuse PAR ratio was derived from asingle measurement of solar radiation above the canopy. In artificial conditions such as growthchambers or greenhouses, because of the presence of various occulting and reflecting materials andartificial light supplies, this ratio is more difficult to estimate. PAR sensors were specificallydesigned to measure the directional radiations received by plants in such environments. Theeffective radiation climate was mimicked by different virtual light sources whose characteristicswere estimated from the directional measurements.The method was tested in sunflower and in the rosette of Arabidopsis thaliana, in canopy orisolated plants, from plant germination to the end of the vegetative period (Fig. 1). Experimentswere carried out in natural (field), semi-controlled (greenhouse) and totally artificial (growthchamber) light environments. Various light levels were imposed and different genotypes were usedto test the model relevance to environmental and genetic variations in the plant architecture.This approach was evaluated using measurements on light interception efficiency (Fig. 2) and itwas compared to classical approaches (Beer's law for sunflower; leaf area x incident PAR forArabidopsis) in the different situations. The model was particularly relevant to quantify lightinterception for crops in early growth stages, isolated plants or artificial environments. It was alsoable to characterise the local environment of different genotypes and to quantify the impact ofarchitectural modifications on light interception. This 3D virtual plant approach is proposed as atool to analyse the genotype-environment interactions and identify new selection criteria to improvelight interception which is directly related to biomass production and yield.