SUNLAB: a Functional-Structral Model for Genotypic and Phenotypic Characterization of the Sunflower Crop

International audienceA new functional-structural model SUNLAB for the crop sunflower (Helianthus annuus L.) is developed. It is dedicated to simulate the organogenesis, morphogenesis, biomass accumulation and biomass partitioning to organs in sunflower growth. It is adapted to model phenotypic response to diverse environment factors including temperature stress and water deficiency, and adapted to different genotypic variants. The model is confronted to experimental data and estimated parameter values of two genotypes "Melody" and "Prodisol" are presented. SUNLAB parameters seem to show genotypic variability, which potentially makes the model an interesting intermediate to discriminate between genotypes. Statistical tests on estimated parameter values suggest that some parameters are common between genotypes and others are genotypic specific. Since SUNLAB simulate individual leaf area and biomass as two state variables, an interesting corollary is that it also simulates dynamically the specific leaf area (SLA) variable. Further studies are performed to evaluate model performances with more genotypes and more discriminating environments to test and expand model's adaptability and usabilit

A stochastic growth model of grapevine with full interaction between environment, trophic competition and plant development.

International audienceGrapevine development is mainly determined by environmental factors whose effects are modulated by its complex topological structure. The trophic relationships between all the organs of the different axes appear to be the main underlying process which drive axis organogenesis in fluctuating environment. A new modelling approach is proposed based on GreenLab formalism in which axis organogenesis is controlled by stochastic processes according to trophic competition between the different axes. In this model, a water budget was also implemented to account for the effects of water depletion. The model was validated at organ and axis scales on a large range of environmental conditions in terms of photosynthetic active radiation, temperature and soil water supply. The efficiency of the model to simulate plant development at a detailed scale proved its ability to further analyse of the retroactions between plant development and the different environmental variables in order to improve crop management

Effect of topological and phenological changes on biomass partitioning in Arabidopsis thaliana inflorescence: a preliminary model-based study

International audienceAlthough the existence of phenological impact on biomass partitioning in the plant is known for many species, it is difficult to quantify this effect and to unravel it from the complex functional processes that interact during plant growth. This work explores the variations of biomass allocated to fruits according to simple changes in the topological and phenological development of Arabidopsis thaliana plants. Four plants of the same genotype (ecotype Columbia) were grown in controlled conditions in growth chamber. Their topological differences were studied using the functional-structural model GreenLab. It showed that when fitting the four plants with a single set of parameters, but each plant being given its own topological structure, half of the biomass variability can be reproduced

3D virtual plants to phenotype differences among genotypes: Taking into account plant-environment interactions to better understand genetic variability in leaf development response to light

Incident light affects orgnaogenesis and morphogenesis processes involved in leaf development through the amount of radiation absorbed by the plant (Chenu et al., 2005). The genetic variability of these responses was investigated on Arabidopsis thaliana ecotypes (Col, Di-m, Ler, Ws) and mutants (se-1, rot3-1, ron2-2, p70S-KOR) displaying contrasted architectures and radiation use efficiencies (Fig. 1). Plants were grown under various levels of incident light, with a stable light quality. The local plantenvironment interactions were estimated for each genotype, from plant emergence to the end of rosette expansion, using an architectural model (Barczi et al., 1997) coupled with a radiative model (Dauzat and Eroy, 1997). Leaf development was assessed in terms of the date of leaf initiation, the relative leaf expansion rate and the duration of leaf expansion. A reduction in light intensity affected with different extents the final leaf area of the genotypes, through modifications in the leaf development processes. For each genotype, stable relationships were found for (i) leaf initiation and (ii) initial leaf expansion rate with the amount of absorbed radiation, and for (iii) the duration of leaf expansion with the level of radiation intensity. Genotypes displayed different sensitivities in their responses of leaf initiation rate (Fig. 2) and duration of leaf expansion, whereas they all had a similar response in terms of initial relative expansion rate. Using a 3D virtual plant approach allowed us to take into account the genotype-environment interactions through the estimation of the amount of light absorption, and thus to better understand the genotypic differences in physiological responses to light. For example, an unexpected phenotype was revealed in the se-1 mutant. The SERRATE gene (SE) recently shown to determine early leaf development via leaf organogenesis and morphogenesis patterning (Grigg et al., 2005) was demonstrated here to also affect late leaf development and their responses to incident light (Chenu et al., 2007). Furthermore, contrary to its wild-type (Col) and the other studied genotypes, the se-1 mutant displayed a leaf initiation that was totally insensitive to the amount of absorbed radiation (Fig. 1) suggestion a role of carbon metabolism in SE functioning. The consistent relationships found between plant and light variables had genotype-specific parameters that were independent from the environment. Such parameters can therefore be considered as genotypic characteristics and could be used to identify associated QTL (Reymond et al., 2003). The method developed in this study comprises a new phenotypic tool that allows genotype characterisation for leaf development response to light, for a wide range of radiative environments. This approach was sufficiently precise to characterise the effect of monogenetic mutations and could be applied on a wider range of genotypes to focus on genes and pathways involved in leaf expansion responses to light. The presented results could also be used to integrate the knowledge collected among genotypes in order to predict their behaviour in various light environments

How relevant are instantaneous measurements for assessing resource depletion under plant cover? A test on light and soil water availability in 18 herbaceous communities

International audience1. Quantifying the amount of resources remaining under plant cover is essential for assessing plant–plant interactions or biological invasions. Although resource levels fluctuate in time, their quantification is performed mainly by instantaneous measurements. We investigated how instantaneous measurements are related to the amount of resources cumulated throughout one growing season, measuring parameters of both light and soil water depletion. 2. During a growing season, we measured regularly light and soil water levels under the cover of 18 plant species grown as monocultures in a common garden. The temporal dynamics of light and soil water depletion were assessed within each monoculture using mechanistic modelling approaches. 3. The total amounts of resources remaining over the year under the range of communities were best predicted by instantaneous measurements performed at critical periods, differing among resources. The significance of prediction decreased dramatically for other dates, including the period of peak production, but without changing the ranking of communities according to ability to deplete resources. We therefore recommend that such measurements should be limited to qualitative studies, and that mechanistic modelling for quantitative assessments should be developed

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

International audienceLight interception is a major contributor to biomass accumulation of crops. Beer's law has been extensively used to estimate the amount of light intercepted by a plant at canopy level. This method, based on the use of the leaf area index (LAI), is designed for well-developed crops where the canopy is assumed to be a turbid medium (Jones, 1992). However this assumption is seldom verified and in most situations canopies are strongly heterogeneous, as for example in perennial crops such as vineyards and orchards (e.g. Louarn et al., 2007) or in row crops during the first developmental stages or when leaf senescence occurs. We propose here to test a method based on 3D modelling to quantify the local light environment of plants in different situations, including artificial conditions. 3D virtual plants built from architectural measurements (Barczi JF et al., 1997) were used with a radiative balance model (Dauzat and Eroy, 1997) to characterise plant-environment interactions. A multi-directional approach was chosen to take into account direct and diffuse photosynthetically active radiations (PAR) which have a major influence on the plant radiative balance. Under natural conditions, when there was no obstacle to light, the direct-diffuse PAR ratio was derived from a single measurement of solar radiation above the canopy. In artificial conditions such as growth chambers or greenhouses, because of the presence of various occulting and reflecting materials and artificial light supplies, this ratio is more difficult to estimate. PAR sensors were specifically designed to measure the directional radiations received by plants in such environments. The effective radiation climate was mimicked by different virtual light sources whose characteristics were estimated from the directional measurements. The method was tested in sunflower and in the rosette of Arabidopsis thaliana, in canopy or isolated plants, from plant germination to the end of the vegetative period (Fig. 1). Experiments were carried out in natural (field), semi-controlled (greenhouse) and totally artificial (growth chamber) light environments. Various light levels were imposed and different genotypes were used to 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 it was compared to classical approaches (Beer's law for sunflower; leaf area x incident PAR for Arabidopsis) in the different situations. The model was particularly relevant to quantify light interception for crops in early growth stages, isolated plants or artificial environments. It was also able to characterise the local environment of different genotypes and to quantify the impact of architectural modifications on light interception. This 3D virtual plant approach is proposed as a tool to analyse the genotype-environment interactions and identify new selection criteria to improve light interception which is directly related to biomass production and yield