Papers by Alexandra Jullien
HAL (Le Centre pour la Communication Scientifique Directe), Mar 26, 2023
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
HAL (Le Centre pour la Communication Scientifique Directe), Mar 26, 2007
The dynamics of leaf and pod apparition and loss play a key role in rapeseed plant growth, as it ... more The dynamics of leaf and pod apparition and loss play a key role in rapeseed plant growth, as it controls the biomass production and repartition among organs. The source/sink ratio in turn influences appearance and disappearance of organs. Our objective is to investigate this interaction and its consequences on seed growth and development in order to better understand yield variability and seed quality (oil and protein content). In order to quantify the dynamics of C offer and demand, the functional-structural model GREENLAB is being used. It models the interactions between morphogenesis and growth. Biological processes are described according to needs. The mathematical form of GREENLAB allows estimating the ecophysiological parameters of the model (photosynthesis parameters, sink strengths, sink functions) from experimental data by using optimization procedures. The model is being calibrated for rapeseed plant and will be used to investigate the interactions between morphogenesis and biomass production by simulating plant development and growth in response to nitrogen (N) nutrition. In this study we present the calibration procedure for the vegetative phase over autumn and winter for two nitrogen nutrition levels.
Journal of Plant Nutrition and Soil Science, Oct 13, 2010
HAL (Le Centre pour la Communication Scientifique Directe), Jun 5, 2011
The observed decrease in oilseed rape conversion of intercepted radiation efficiency during repro... more The observed decrease in oilseed rape conversion of intercepted radiation efficiency during reproductive phase could be due to leaf falling off, pod senescence or to the specific energy cost of oil production. In reason of its interest in modelling, we tried to identify and quantify the processes really involved in this decrease, for different genotypes under contrasted nitrogen fertilisations.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 5, 2011
Classical yield components analysis can be highlighted for winter oilseed rape by an architectura... more Classical yield components analysis can be highlighted for winter oilseed rape by an architectural analysis of morphology and morphogenesis during the reproductive phase. For two conventional genotypes (Aviso and Montego) cultivated under usual agronomic practices and two nitrogen availability levels, the differences observed in grain yield mainly rely on branching and branches characteristics. The analyse of the dynamics of branching, pod setting and grain growth allows to decipher the different processes involved and to precise their dependence on genotype.
Journal of Horticultural Science & Biotechnology, 2008
ABSTRACT We aimed to define a more robust indicator for banana harvest date that ensures an optim... more ABSTRACT We aimed to define a more robust indicator for banana harvest date that ensures an optimal fruit green life (GL). Our hypothesis was that development rather than growth would account for
HAL (Le Centre pour la Communication Scientifique Directe), Oct 31, 2012
HAL (Le Centre pour la Communication Scientifique Directe), Jul 31, 2022
HAL (Le Centre pour la Communication Scientifique Directe), Oct 31, 2012
Use of a structural-functional plant model to assess the morphogenetical plasticity. How does var... more Use of a structural-functional plant model to assess the morphogenetical plasticity. How does variation in phyllochron impact plant growth and development of Brassica napus in the GreenLab model. 4. International Symposium PMA 12
HAL (Le Centre pour la Communication Scientifique Directe), Mar 26, 2007
Compared to other crops, oilseed rape is known to absorb nitrate in large amount when available. ... more Compared to other crops, oilseed rape is known to absorb nitrate in large amount when available. However, absorbed nitrogen is not optimised by oilseed rape in terms of yield and seed quality ; the latter remains weak in relation to nitrogen potentially remobilised towards the seeds, especially because of abscission of leaves with variable nitrogen content. Acquisition of knowledge on the processes involved in leaf falling off would then contribute to reduce nitrate leaching and to improve yield and seed quality. The general objective of our work was to evaluate the behaviour of different oilseed rape genotypes in response to nitrogen fertilisation, and to provide a grid for selection of genotypes with respect to a better remobilisation of absorbed nitrogen and a reduction of leaf abscission. In this aim, our experimental design consisted in analysing the different kinetics of green leaf area components of three genotypes, contrasted according to their size (dwarf and semi-dwarf) and architecture, grown in different conditions of nitrogen supply during two cycles. Experimental results concerning leaves falling off in different conditions (genotype, nitrogen availability, position on main stem), indicate a great variability in nitrogen content. Moreover large differences of transmitted radiation at the bottom of the canopy were observed. The objective of this paper is, concerning rapeseed bottom leaves, i) to test if the different couples of values of both bottom leaf nitrogen content and transmitted Photosynthetic Active Radiation (PARt) observed just before leaf falling off, are consistent with the hypothesis of leaf falling off linked to a single low net photosynthesis level, ii) to analyse the genotypic variation on this process.
Functional Structural Plant models can help to understand plant plasticity. Such a model was deve... more Functional Structural Plant models can help to understand plant plasticity. Such a model was developed for winter oilseed rape, based on the GreenLab model. However, the model had a large number of parameters, which made its calibration difficult. In order to simplify the model, we applied sensitivity analysis method to select the most important parameters. Analyses were performed on the following outputs: biomasses of the whole plant, of leaves, internodes and pods. First, the model linearity was computed with the Standardized Regression Method, revealing two phases of high nonlinearity. Second, total sensitivity indices were computed for each parameter with the Sobol method. We deduced that five parameters out of 46 had a prevalent impact on model outputs, while the other had a limited influence and could be fixed to reference values.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 16, 2019
HAL (Le Centre pour la Communication Scientifique Directe), Jun 16, 2019
Annals of Botany, Jun 19, 2018
• Background and Aims Functional-structural plant models (FSPMs) describe explicitly the interact... more • Background and Aims Functional-structural plant models (FSPMs) describe explicitly the interactions between plants and their environment at organ to plant scale. However, the high level of description of the structure or model mechanisms makes this type of model very complex and hard to calibrate. A two-step methodology to facilitate the calibration process is proposed here. • Methods First, a global sensitivity analysis method was applied to the calibration loss function. It provided first-order and total-order sensitivity indexes that allow parameters to be ranked by importance in order to select the most influential ones. Second, the Akaike information criterion (AIC) was used to quantify the model's quality of fit after calibration with different combinations of selected parameters. The model with the lowest AIC gives the best combination of parameters to select. This methodology was validated by calibrating the model on an independent data set (same cultivar, another year) with the parameters selected in the second step. All the parameters were set to their nominal value; only the most influential ones were re-estimated. • Key Results Sensitivity analysis applied to the calibration loss function is a relevant method to underline the most significant parameters in the estimation process. For the studied winter oilseed rape model, 11 out of 26 estimated parameters were selected. Then, the model could be recalibrated for a different data set by re-estimating only three parameters selected with the model selection method. • Conclusions Fitting only a small number of parameters dramatically increases the efficiency of recalibration, increases the robustness of the model and helps identify the principal sources of variation in varying environmental conditions. This innovative method still needs to be more widely validated but already gives interesting avenues to improve the calibration of FSPMs.
HAL (Le Centre pour la Communication Scientifique Directe), 2015
Vers une stabilisation de la production de colza sous contrainte : valorisation de la plasticite ... more Vers une stabilisation de la production de colza sous contrainte : valorisation de la plasticite de la morphologie aerienne et de sa variabilite genotypique
Journal of Agricultural Biological and Environmental Statistics, Feb 20, 2018
Modeling inter-individual variability in plant populations is a key issue to understand crop hete... more Modeling inter-individual variability in plant populations is a key issue to understand crop heterogeneity and its variations in response to the environment. Being able to describe the interactions among plants and explain the variability observed in the population could provide useful information on how to control it and improve global plant growth. We propose here a method to model plant variability within a field, by extending the so-called GreenLab functional-structural plant model from the individual to the population scale via nonlinear mixed-effects modeling. Parameter estimation of the population model is achieved using the stochastic approximation expectation maximization algorithm, implemented in the platform for plant growth modeling and analysis PyGMAlion. The method is first applied on a set of simulated data and then on a real dataset from a population of 34 winter oilseed rape plants at the rosette stage. Results show that our method allows for a good characterization of the variability in the population with only a limited number of parameters, which is a key point for plant models. Results on simulated data show that parameters associated with a low sensitivity index are inaccurately estimated by the algorithm when considered as random effects, but a good stability of the results can be obtained by considering them as fixed effects. These results open new ways for the analysis of inter-plant variability within a population and the study of plant-plant competition. Supplementary materials accompanying this paper appear online.
HAL (Le Centre pour la Communication Scientifique Directe), 2007
HAL (Le Centre pour la Communication Scientifique Directe), 2010
National audienc
Functional Structural Plant models can help to understand plant plasticity. Such a model was deve... more Functional Structural Plant models can help to understand plant plasticity. Such a model was developed for winter oilseed rape, based on the GreenLab model. However, the model had a large number of parameters, which made its calibration difficult. In order to simplify the model, we applied sensitivity analysis method to select the most important parameters. Analyses were performed on the following outputs: biomasses of the whole plant, of leaves, internodes and pods. First, the model linearity was computed with the Standardized Regression Method, revealing two phases of high nonlinearity. Second, total sensitivity indices were computed for each parameter with the Sobol method. We deduced that five parameters out of 46 had a prevalent impact on model outputs, while the other had a limited influence and could be fixed to reference values.
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Papers by Alexandra Jullien