Plasticité de l'architecture aérienne du blé en réponse à la compétition pour la lumière au sein de cultures pures ou d'associations variétales : caractérisation expérimentale et développement d'un modèle 3D

The understanding of the interactions between plants within heterogeneous crops could allow for a more efficient use of wheat varietal mixtures, as there is a gap of knowledge on the complementarity, synergy and competition that develop among varieties within these systems. Our study is focused on competition for light, and its impact on the above ground architecture of wheat, coupling experimental analysis and model development. We first characterized the plasticity of the aerial architecture in response to different sowing densities, for 20 contrasting genotypes of winter wheat. The number of axes per plant was shown to be the most plastic trait for all genotypes. We developed an individual-based model representing wheat growth, from the sowing to flowering. The model is composed of two parts: a descriptive part of the foliar development based on the ADEL-wheat model and a mechanistic part which accounts for the regulation of tillering by light. Tillering is regulated by two simple hypotheses: (1) tillering stops when a critical value of local Green Area Index (GAI) is reached, (2) a tiller dies if the amount of intercepted light falls below a critical threshold. A realistic tillering dynamics was simulated by our model over a wide range of sowing densities, with a good fit with experimental data. We also experimentally characterized the plasticity of plant architecture for eight wheat genotypes observed in various two-components varietal mixtures. Contrasted plastic responses were observed when compared to those expressed in pure stands, underlining the specificity of certain plant-plant interactions. These experiments confirmed that the cultivar mixtures generally contribute to an overyielding, particularly in low-input agriculture . Finally, our results revealed that variety mixtures including genotypes with different heights may provide an advantage to the taller genotype with limited tradeoff on the short genotype. This work contributed to the development of a simplified formalism for tillering process, allowing to explore and optimize complementarities / competitions between plants within variety mixtures. Ultimately, the model could be coupled with a genetic model, in order to better describe the impact of plant-to-plant interactions in the selective value of individuals in heterogeneous populations.L’étude des interactions entre les plantes au sein de couverts hétérogènes pourrait permettre une meilleure utilisation des associations variétales de blé, car nous manquons de connaissances sur la manière dont les complémentarités, synergies et compétitions entre variétés affectent leurs performances dans ces conditions. Notre étude s'est focalisée sur la compréhension de l'impact de la compétition pour la lumière sur l'architecture aérienne du blé, en couplant une analyse expérimentale et une approche par modélisation. Nous avons dans un premier temps, caractérisé la plasticité de l’architecture aérienne en réponse à la modification de la densité de semis, pour 20 génotypes contrastés de blé tendre. Ainsi, nous avons déterminé que le nombre d’axes par plante était le trait le plus plastique pour tous les génotypes. Nous avons ensuite développé un modèle individu-centré représentant le développement du blé du semis à la floraison. Ce modèle est composé de deux parties : une partie descriptive du développement foliaire basée sur un modèle existant (ADEL-blé) et une partie plus mécaniste où nous avons intégré une régulation du tallage par la ressource lumineuse. Cette régulation du tallage se fait selon deux hypothèses simples : (1) la plante arrête d'émettre des talles dès que le Green Area Index (GAI) de son voisinage atteint une valeur seuil et (2) une talle meurt si la quantité de lumière qu'elle intercepte est inférieure à un seuil critique. La dynamique de tallage simulée par le modèle sur une large gamme de densité de semis est proche de la dynamique de tallage observée expérimentalement. Nous avons également caractérisé expérimentalement la plasticité de l’architecture aérienne de huit génotypes de blé en réponse à la compétition dans différentes associations variétales binaires. Ces analyses ont révélé des réponses assez différentes de celles mesurées en culture pure, soulignant la spécificité de certaines interactions entre plantes de génotypes différents. Ces essais ont confirmé que les associations contribuaient généralement à une augmentation de la production, en particulier dans des itinéraires techniques économes en intrants. Nous avons montré que des associations variétales comprenant des génotypes avec des hauteurs différentes permettaient d’avantager fortement le génotype haut sans trop pénaliser le génotype court. Ce travail a permis de développer un formalisme simplifié des processus régulant le tallage, qui va permettre d'explorer et optimiser les complémentarités/compétitions entre variétés dans des peuplements multi-variétaux. A terme le modèle pourra être couplé à des modèles génétiques pour mieux décrire l'impact de l'interaction plate-plante dans la valeur sélective des individus dans des populations hétérogènes

Modelling in agronomy: Model calibration : how to estimate model parameters

MasterThis modelling course is focused on parameter estimations. We first remind important notions such as what is a model, what is a parameters et how do we need to calibrate models.Then we use a simple calibration method (least square method) in two situations: first to calibrate a fimple function et then to calibrate au whole model

Plasticity of the aerial architecture of wheat in response to light competition within pure crops or variety mixtures : experimental characterization and 3D model development

L’étude des interactions entre les plantes au sein de couverts hétérogènes pourrait permettre une meilleure utilisation des associations variétales de blé, car nous manquons de connaissances sur la manière dont les complémentarités, synergies et compétitions entre variétés affectent leurs performances dans ces conditions. Notre étude s'est focalisée sur la compréhension de l'impact de la compétition pour la lumière sur l'architecture aérienne du blé, en couplant une analyse expérimentale et une approche par modélisation. Nous avons dans un premier temps, caractérisé la plasticité de l’architecture aérienne en réponse à la modification de la densité de semis, pour 20 génotypes contrastés de blé tendre. Ainsi, nous avons déterminé que le nombre d’axes par plante était le trait le plus plastique pour tous les génotypes. Nous avons ensuite développé un modèle individu-centré représentant le développement du blé du semis à la floraison. Ce modèle est composé de deux parties : une partie descriptive du développement foliaire basée sur un modèle existant (ADEL-blé) et une partie plus mécaniste où nous avons intégré une régulation du tallage par la ressource lumineuse. Cette régulation du tallage se fait selon deux hypothèses simples : (1) la plante arrête d'émettre des talles dès que le Green Area Index (GAI) de son voisinage atteint une valeur seuil et (2) une talle meurt si la quantité de lumière qu'elle intercepte est inférieure à un seuil critique. La dynamique de tallage simulée par le modèle sur une large gamme de densité de semis est proche de la dynamique de tallage observée expérimentalement. Nous avons également caractérisé expérimentalement la plasticité de l’architecture aérienne de huit génotypes de blé en réponse à la compétition dans différentes associations variétales binaires. Ces analyses ont révélé des réponses assez différentes de celles mesurées en culture pure, soulignant la spécificité de certaines interactions entre plantes de génotypes différents. Ces essais ont confirmé que les associations contribuaient généralement à une augmentation de la production, en particulier dans des itinéraires techniques économes en intrants. Nous avons montré que des associations variétales comprenant des génotypes avec des hauteurs différentes permettaient d’avantager fortement le génotype haut sans trop pénaliser le génotype court. Ce travail a permis de développer un formalisme simplifié des processus régulant le tallage, qui va permettre d'explorer et optimiser les complémentarités/compétitions entre variétés dans des peuplements multi-variétaux. A terme le modèle pourra être couplé à des modèles génétiques pour mieux décrire l'impact de l'interaction plate-plante dans la valeur sélective des individus dans des populations hétérogènes.The understanding of the interactions between plants within heterogeneous crops could allow for a more efficient use of wheat varietal mixtures, as there is a gap of knowledge on the complementarity, synergy and competition that develop among varieties within these systems. Our study is focused on competition for light, and its impact on the above ground architecture of wheat, coupling experimental analysis and model development. We first characterized the plasticity of the aerial architecture in response to different sowing densities, for 20 contrasting genotypes of winter wheat. The number of axes per plant was shown to be the most plastic trait for all genotypes. We developed an individual-based model representing wheat growth, from the sowing to flowering. The model is composed of two parts: a descriptive part of the foliar development based on the ADEL-wheat model and a mechanistic part which accounts for the regulation of tillering by light. Tillering is regulated by two simple hypotheses: (1) tillering stops when a critical value of local Green Area Index (GAI) is reached, (2) a tiller dies if the amount of intercepted light falls below a critical threshold. A realistic tillering dynamics was simulated by our model over a wide range of sowing densities, with a good fit with experimental data. We also experimentally characterized the plasticity of plant architecture for eight wheat genotypes observed in various two-components varietal mixtures. Contrasted plastic responses were observed when compared to those expressed in pure stands, underlining the specificity of certain plant-plant interactions. These experiments confirmed that the cultivar mixtures generally contribute to an overyielding, particularly in low-input agriculture . Finally, our results revealed that variety mixtures including genotypes with different heights may provide an advantage to the taller genotype with limited tradeoff on the short genotype. This work contributed to the development of a simplified formalism for tillering process, allowing to explore and optimize complementarities / competitions between plants within variety mixtures. Ultimately, the model could be coupled with a genetic model, in order to better describe the impact of plant-to-plant interactions in the selective value of individuals in heterogeneous populations

Modelling root system growth with ArchiSimple

MasterThis course review some basics of root biology and developpement (elongation, branching, radial growth, root emission, root death) and explaines how these processes are simplified to be integrated in the ArchiSimple model that simulates root architecture and development through tim

Genotypic diversity and plasticity of root system architecture to nitrogen availability in oilseed rape.

In the emerging new agricultural context, a drastic reduction in fertilizer usage is required. A promising way to maintain high crop yields while reducing fertilizer inputs is to breed new varieties with optimized root system architecture (RSA), designed to reach soil resources more efficiently. This relies on identifying key traits that underlie genotypic variability and plasticity of RSA in response to nutrient availability. The aim of our study was to characterize the RSA plasticity in response to nitrogen limitation of a set of contrasted oilseed rape genotypes, by using the ArchiSimple model parameters as screening traits. Eight accessions of Brassica napus were grown in long tubes in the greenhouse, under two contrasting levels of nitrogen availability. After plant excavation, roots were scanned at high resolution. Six RSA traits relative to root diameter, elongation rate and branching were measured, as well as nine growth and biomass allocation traits. The plasticity of each trait to nitrogen availability was estimated. Nitrogen-limited plants were characterized by a strong reduction in total biomass and leaf area. Even if the architecture traits were shown to be less plastic than allocation traits, significant nitrogen and genotype effects were highlighted on each RSA trait, except the root minimal diameter. Thus, the RSA of nitrogen-limited plants was primarily characterised by a reduced lateral root density, a smaller primary root diameter, associated with a stronger root dominance. Among the RSA traits measured, the inter-branch distance showed the highest plasticity with a level of 70%, in the same range as the most plastic allocation traits. This work suggests that lateral root density plays the key role in the adaptation of the root system to nitrogen availability and highlights inter-branch distance as a major target trait for breeding new varieties, better adapted to low input systems

Modeling as a tool for identifying root architecture traits defining root systems adapted to a nitrogen-limited environment

International audienceOptimization of the root system architecture (RSA) is a promising lever to increase nitrogen use efficiency, which is a major issue to preserve yields while reducing nitrogen (N) fertilizer inputs, as required by the emerging new agricultural context. This is particularly relevant for winter oilseed rape, that has high nitrogen requirements. Using a modelling approach, we aimed to (i) rank the impact of various traits describing root architecture on the root system development and (ii) define combinations of root architecture traits shaping root morphotypes more or less adapted to low nitrogen environment. Using the ArchiSimple model, we implemented and simulated five output variables, that were not accessible through experimentation, to describe root system development: root total biomass (g), length of the primary root (mm), volume of explored soil (mm2), proportion of thin roots, and colonization efficiency, considered as the ratio between volume of explored soil and total root biomass. A sensitivity analysis was performed to quantify the impact of nine of the ArchiSimple parameters, which have biological significance and correspond to root architecture traits. The range of variation was defined to represent the genetic diversity and plasticity to nitrogen availability observed in previous experimentations on rapeseed. Then, we simulated 20 000 genotypes differing in RSA, through the variation of five parameters emerging from the sensitivity analysis. The values of these parameters were randomly chosen within a range defined from previous experimentations. The five outputs variables were computed for each genotype and clusters were then generated to group genotypes in a three dimension space described by thin root proportion, volume of explored soil and colonization efficiency.The sensitivity analysis highlighted five of the nine parameters studied as having a significant impact on total biomass, length of primary root, volume of explored soil, colonization efficiency and the proportion of thin roots. Five clusters emerged from in silico genotype simulations, characterized by contrasting values of thin root proportion, volume of explored soil and colonization efficiency. For each cluster, we found close correlations between mean values of root architecture traits of the genotypes composing the cluster and the output variables characterizing the cluster. Thus, genotypes with the smallest colonization efficiency were characterized by the highest values of root elongation rate (EL), diameter ratio between mother versus daughter roots (DlDm) and maximal root diameter (Dmax), and by the lowest values of delay before root elongation (DelBEl) and inter-branching distance (IBD). Genotypes with RSA traits specific of N limited plants were mainly found in three of the five clusters and were characterized by small values of EL, DlDm, Dmax and high values of DelBEl, IBD.Our study shows that modelling is an integrated tool, useful to overcome experimental constraints and prospect a wide number of virtual combinations. It allowed us to identify the main RSA traits driving root system development and to suggest combination of RSA traits leading to root system architectures differentially adapted to contrasting soil nutritional environments. It opens promising perspectives for rapeseed breeding

In Sillico prospections to define rapeseed root system ideotypes adapted to low nitrogen environment

International audienc

Modelling competition for light in wheat mixtures

International audienc

Are dispersal behaviours of earthworms related to their functional group?

International audienceDispersal plays a key role in the dynamics of ecological communities as it strongly determines the potential of individuals to colonize new habitats. Understanding and predicting species dispersal behaviour is therefore central to any effort at managing or even understanding the formation of communities. In this context, it is essential to understand the influence of environmental and biotic determinants of dispersal. In this work, we assessed these questions using earthworms as model organisms. We assessed the dispersal behaviour of six earthworm species belonging to two different functional groups (i.e. three anecics and three endogeics) in response to three key environmental factors: habitat quality, intraspecific density, and environment homogeneity. We found that habitat quality significantly influenced the dispersal rates of all species. Intraspecific density increased the dispersal rate of the three anecic species but only of one endogeic species. In a homogeneous environment, anecics dispersed further and in greater proportion than the majority of endogeics. Moreover, few anecic species have shown a tendency to follow conspecifics. Overall, anecic species seemed to have a higher active dispersal inclination than most endogeic ones. We found a high variability of our results within each functional groups, which suggests that this classification cannot be used to explain or predict the dispersal behaviour of earthworms