Mise en évidence et caractérisation de protéines de réserve (VSP) chez la chicorée (Cichorium intybus L.). Effet de la nutrition au nitrate et comportement au forçage

* INRA Métabolisme et Nutrition des Plantes, centre de Versailles Diffusion du document : INRA Métabolisme et Nutrition des Plantes, centre de Versailles Diplôme : DEALicenc

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

International audienc

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

Effet de la diversité fonctionnelle dans le sol sur les interactions interspécifiques dans un système de cultures associées

National audienc

How does earthworm functional diversity affect rapeseed-weeds interactions ?

How does earthworm functional diversity affect rapeseed-weeds interactions ? . International Conference on Ecological Science

Les processus de rhizodéposition, un levier majeur pour la séquestration du carbone dans les sols

International audiencePlants represent the main source of organic carbon in soils. While inputs of carbon from the aerial parts are easy to measure, the difficulty in quantifying inputs from roots has prevented us to estimate the actual potential of soil carbon sequestration associated to each type of organic matters released by the roots. Besides the decay of root tissues, root systems have been shown to release organic carbon by various mechanisms, e.g. exudation of soluble compounds, mucilage secretion, and cells sloughing. Such rhizodeposition processes may consume 5% to 15% of the total amount of carbon photosynthetically fixed by the plant, and can generate an input of carbon to the soil ranging from 0.5 to 5 tC ha-1 yr-1. Because of this large range and the uncertainties associated to rhizodeposition mechanisms, current models of soil organic matter dynamics poorly assess the actual sequestration potential offered by plants. We performed a meta-analysis of the literature data generated over the last 60 years in order to assess which rhizodeposition processes quantitatively prevail, and what is the maximal amount of carbon inputs that can be expected from an entire growing root system, depending on plant species, growth stage, soil properties, and environmental conditions. According to our current dataset, the exudation of soluble sugars represents the major flow of organic carbon into the rhizosphere in most conditions, but other rhizodeposition processes such as mucilage secretion and cells sloughing can locally become as important in terms of carbon release. Following the presentation of these results, the consequences of these emissions on the actual soil carbon sequestration potential will be discussed based on our current understanding of carbon use efficiency and priming effect

Les processus de rhizodéposition, un levier majeur pour la séquestration du carbone dans les sols

International audiencePlants represent the main source of organic carbon in soils. While inputs of carbon from the aerial parts are easy to measure, the difficulty in quantifying inputs from roots has prevented us to estimate the actual potential of soil carbon sequestration associated to each type of organic matters released by the roots. Besides the decay of root tissues, root systems have been shown to release organic carbon by various mechanisms, e.g. exudation of soluble compounds, mucilage secretion, and cells sloughing. Such rhizodeposition processes may consume 5% to 15% of the total amount of carbon photosynthetically fixed by the plant, and can generate an input of carbon to the soil ranging from 0.5 to 5 tC ha-1 yr-1. Because of this large range and the uncertainties associated to rhizodeposition mechanisms, current models of soil organic matter dynamics poorly assess the actual sequestration potential offered by plants. We performed a meta-analysis of the literature data generated over the last 60 years in order to assess which rhizodeposition processes quantitatively prevail, and what is the maximal amount of carbon inputs that can be expected from an entire growing root system, depending on plant species, growth stage, soil properties, and environmental conditions. According to our current dataset, the exudation of soluble sugars represents the major flow of organic carbon into the rhizosphere in most conditions, but other rhizodeposition processes such as mucilage secretion and cells sloughing can locally become as important in terms of carbon release. Following the presentation of these results, the consequences of these emissions on the actual soil carbon sequestration potential will be discussed based on our current understanding of carbon use efficiency and priming effect

Modelling rhizodeposition with functional-structural plant models

Plants are the main source of organic carbon in soils. Besides litter incorporation, most of plant carbon fluxes to soil occur belowground, through the release of organic compounds by roots and the decay of root tissues. Despite the importance of these processes for soil carbon sequestration and for soil biological functions, our understanding of such fluxes has been hampered by the difficulties associated to their measurement in actual soil environments and their integration to plant growth models. Our aim is to develop new modelling approaches in order to accurately describe trophic fluxes from roots to soil and their spatial and temporal evolution. Functional-structural plant models (FSPM), which take into account both plant physiology and plant architecture, may be well adapted to such a modelling strategy, but also bring new challenges in terms of processes coupling. This work will present our current strategy to simulate and integrate root exudation, mucilage emissions, root cells desquamation and root senescence into a common model, and will highlight some of the main knowledge gaps associated to the simulation of these processes

Effet de la diversité fonctionnelle dans le sol sur les interactions interspécifiques dans un système de cultures associées

National audienc