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International audience; Interactions among plants have been long recognized as a major force driving plant community dynamics and crop yield. Surprisingly, our knowledge of the ecological genetics associated with variation of plant-plant interactions remains limited. In this opinion article by scientists from complementary disciplines, the international PLANTCOM network identified four timely questions to foster a better understanding of the mechanisms mediating plant assemblages. We propose that by identifying the key relationships among phenotypic traits involved in plant-plant interactions and the underlying adaptive genetic and molecular pathways, while considering environmental fluctuations at diverse spatial and time scales, we can improve predictions of genotype-by-genotype-by-environment interactions and modeling of productive and stable plant assemblages in wild habitats and crop fields.

Plasticity of plant architecture is a promising lever to increase crop resilience to biotic and abiotic damage. Among the main drivers of its regulation are the spectral signals which occur via photomorphogenesis processes. In particular, branching, one of the yield components, is responsive to photosynthetic photon flux density (PPFD) and to red to far-red ratio (R:FR), both signals whose effects are tricky to decorrelate in the field. Here, we developed a device consisting of far-red light emitting diode (LED) rings. It can reduce the R:FR ratio to 0.14 in the vicinity of an organ without changing the PPFD in outdoor high irradiance fluctuating conditions, which is a breakthrough as LEDs have been mostly used in non-fluctuant controlled conditions at low irradiance over short periods of time. Applied at the base of rapeseed stems during the whole bolting-reproductive phase, LightCue induced an expected significant inhibitory effect on two basal targeted axillary buds and a strong unexpected stimulatory effect on the overall plant aerial architecture. It increased shoot/root ratio while not modifying the carbon balance. LightCue therefore represents a promising device for progress in the understanding of light signal regulation in the field.

International audience; Maintaining seed yield under low N inputs is a major issue for breeding, which requires thoroughly exploiting the genetic diversity of processes related to Nitrogen Use Efficiency (NUE). However, dynamic analysis of processes underlying genotypic variations in NUE in response to N availability from sowing to harvest are scarce, particularly at the whole-plant scale. This study aimed to dynamically decipher the contributions of Nitrogen Uptake Efficiency (NUpE) and Nitrogen Utilization Efficiency (NUtE) to NUE and to identify traits underlying NUpE genetic variability throughout the growth cycle of rapeseed. Three experiments were conducted under field-like conditions to evaluate seven genotypes under two N conditions. We developed NUE_DM (ratio of total plant biomass to the amount of N available) as a new proxy of NUE at harvest, valid to discriminate genotypes from the end of inflorescence emergence, and N conditions as early as the beginning of stem elongation. During autumn growth, NUpE explained up to 100% of variations in NUE_DM, validating the major role of NUpE in NUE shaping. During this period, under low N conditions, up to 53% of the plant nitrogen was absorbed and NUpE genetic variability resulted not from differences in Specific N Uptake but in fine-root growth. NUtE mainly contributed to NUE_DM genotypic variation during the reproductive phase under high-N conditions, but NUpE contribution still accounted for 50–75% after flowering. Our study highlights for the first time NUpE and fine-root growth as important processes to optimize NUE, which opens new prospects for breeding.

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Epigenetic variations are involved in the control of plant developmental processes and participate in shaping phenotypic plasticity to the environment. Intense breeding has eroded genetic diversity, and epigenetic diversity now emerge as a new source of phenotypic variations to improve adaptation to changing environments and ensure the yield and quality of crops. Here, we review how the characterization of the stability and heritability of epigenetic variations is required to drive breeding strategies, which can be assisted by process-based models. We propose future directions to hasten the elucidation of complex epigenetic regulatory networks that should help crop modelers to take epigenetic modifications into account and assist breeding strategies for specific agronomical traits.

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International audience; Plants 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.

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National audience; Être capable de caractériser la diversité génétique du système racinaire est un enjeu réelpour la sélection, et notamment pour proposer des variétés multi-performantes, adaptées auxnouveaux agro-écosystèmes au sein desquels les interactions plante-sol jouent un rôle majeur, du faitdes multiples fonctions du système racinaire. Cependant les méthodes directes de phénotypage auchamp du système racinaire sont rarement compatibles avec la caractérisation d’un grand nombred’accessions. De ce fait, le système racinaire est souvent caractérisé à des stades précoces et dans desconditions contrôlées, ne permettant pas toujours une bonne prédiction des phénotypes en conditionsagronomiques. Ici nous présentons une méthode complémentaire, le phénotypage assisté par modèle,basée sur le phénotypage de variables “processus”, estimées à partir du modèle ARCHISIMPLE etpermettant d’accéder aux mécanismes contrôlant la mise en place de l’architecture racinaire. La miseen oeuvre de cette approche novatrice pour la caractérisation des systèmes racinaires est ensuiteillustrée à travers l’analyse de la diversité génétique de l’architecture racinaire du colza. Nousmontrons comment ces paramètres du modèle constituent des traits de sélection efficaces,permettant de proposer des idéotypes adaptés à des systèmes de culture à faibles niveaux d’intrantsazotés, qui optimisent l’exploration du sol et l’absorption de l’azote.

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

SPEEAGESTADGEAPSI; A new method to estimate the nitrogen status of individual plants in canopies. 14. ESA Congress ESA14

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In addition to their putative role in nitrogen storage, some vegetative storage proteins (VSPs) support further roles in biotic and abiotic stress responses. Functions of the 17 kDa VSP from witloof chicory (CiVSP) in N storage and plant resistance to pathogens and its regulation by nitrogen were investigated. The N-terminal end of this protein was sequenced and the corresponding full-length cDNA was obtained. The expression of the CiVsp gene was studied in various organs of chicory grown under replete or limited nitrogen supply. A strong expression of CiVsp was observed in both taproot and fine roots of mature plants and seedlings. CiVsp transcripts were also detected in mature leaves, especially in veins. In senescing leaves CiVsp transcripts accumulated concomitantly to a decrease in RbcS transcript abundance and Rubisco small-subunit degradation. CiVSP protein accumulated significantly only in the subterranean part of the plant during late stages of development. Nitrate limitation caused a reduction in CiVsp mRNA accumulation and a delay in CiVSP storage in the taproot. It is concluded that CiVSP accumulation is regulated at the transcriptional level by N external supply and that the protein is involved in long and short-term N storage. In silico analysis indicated that CiVSP is highly homologous with several allergens and PR-10 proteins. Moreover, CiVsp transcript and protein expression were significantly higher in Erwinia carotovora-resistant chicory inbred lines compared with susceptible lines, suggesting its involvement in chicory resistance to pathogens attack.

Vers une stabilisation de la production de colza sous contrainte : valorisation de la plasticité de la morphologie aérienne et de sa variabilité génotypique

The increase of environmental pressures and EEC control regulations lead to the development of low input cropping systems. To face this new context, breeding cultivars more efficient for N and able to sustain N limitation becomes a real issue. The identification of the key traits determining nitrogen use efficiency remains difficult because plant response to N limitation is a set of interacting processes, displaying a wide genetic and environmental variability and leading to a wide range of plant phenotypes. To cope with this plasticity and integrate processes at the whole plant scale, our strategy was to develop a simple compartmental model of C and N absorption and partitioning during vegetative growth of A. thaliana. The ARNICA (ARabidopsis NItrogen CArbon) model is based on interactions between C and N fluxes in shoot and root compartments. It combines integrative variables and parameters defined as efficiencies of plant CN functioning and morphogenesis. This mechanistic model was designed sufficiently simple to be compatible with a medium throughput phenotyping of all of the 11 parameters. By using the model on a core-collection of ecotypes representing 100% of allelic diversity and on Arabidopsis mutants, we were able to identify N uptake efficiency as the main parameter explaining the strong GxE variability of plant response to N supply. As NupE results from N uptake capacities and root system size, the next step was to evaluate the involvement of root morphogenesis on plant adaptation to N supply. More precisely, our question was to evaluate to what extend the modifications of root architecture in response to N supply derived from the modification of C flux arriving from shoot. This lead to the development of MINI-ROOT, an object oriented model connected to ARNICA, which simulates root morphogenesis during vegetative growth and was designed to account for the effect of endogenous C availability on root architecture. Only 12 parameters were needed to simulate contrasted responses of root system architecture under various CxN culture conditions. Root length and branching, as well as time of emergence of lateral roots were well predicted, suggesting that most of the modifications of root system architecture in response to limiting N supply were driven by modifications of aerial C fluxes. This work illustrated the interest of a model-assisted selection approach to screen the pertinent selection traits among the numerous one involved in a complex plant response. This is a joint work with François Brun, Loïc Pagès and Bertrand Ney.

Nitrogen is known to modulate plant development and resistance to pathogens. Four selected lines (Alg, NS1, NR1 and NR2) of chicory (Cichorium intybus L.) were grown on low (0.6 mM) and high (3 mM) NO(-)(3) nutrition in order to study the effect of N on the expression of three traits, namely, shoot/root ratio, chicon morphology and resistance to soft rot caused by Erwinia sp. For all genotypes, increasing N supply led to a higher shoot/root ratio, resulting from an increased shoot biomass but with no effect on root growth. In contrast, the effect of N on chicon morphology and resistance to bacteria was genotype-dependent and we distinguished two groups of lines according to their phenotypic characteristics. In the group consisting of NR1 and NR2, increasing NO(-)(3) supply during the vegetative phase made the chicon morphology switch from an opened to a closed type while resistance to bacteria was not affected by N supply. In the NS1 and Alg group, the effect of N on chicon morphology was the opposite to that observed in the NR1-NR2 group while NS1 and Alg exhibited a partial resistance to Erwinia sp. , only expressing soft-rot disease when the N supply reached 3 mM. Characterization by DNA amplification fingerprinting (DAF) allowed the generation of 110 polymorphic bands and confirmed that the lines NR1 and NR2, on the one hand, and NS1 and Alg, on the other hand, belong to two distinct genetic groups. The DAF results indicate that chicon morphology and partial resistance to Erwinia sp. are complex traits which would be amenable to quantitative trait loci analysis. The split growth phase of chicory means that any changes in chicon related to N supply during vegetative growth were mediated by a root-originating signal. No variation in root carbon content among genotypes and NO(-)(3) treatments was observed. In contrast, differences in root N content revealed the same grouping of the chicory lines, NR1 and NR2 being systematically richer in amino acids and NO(-)(3) than NS1 and Alg. However, no correlation existed between N compounds and chicon morphology or pathology if all genotypes were considered together. Thus, the effect of N on plant development and pathology as well as putative identified signals might be specific for a genotype. Our study indicates that it is necessary to consider the genetic variability within a species in any signalling-pathway research.

In chicory, we examined how NO3 − supply affected NO3 − uptake, N partitioning between shoot and root and N accumulation in the tuberized root throughout the vegetative period. Plants were grown at two NO3 − concentrations: 0.6 and 3 mM. We used 15N-labelling/chase experiments for the quantification of N fluxes between shoot and root and for determining whether N stored in the tuberized root originates from N remobilized from the shoot or from recently absorbed NO3 −. The rate of 15NO3 − uptake was decreased by low NO3 − availability at all stages of growth. In young plants (10–55 days after sowing; DAS), in both NO3 − treatments the leaves were the strongest sink for 15N. In mature (tuberizing) plants, (55–115 DAS), the rate of 15NO3 − uptake increased as well as the amount of exogenous N allocated to the root. In N-limited plants, N allocation to the tuberized root relied essentially on recent N absorption, while in N-replete plants, N remobilized from the shoot contributed more to N-reserve accumulation in the root. In senescing plants (115–170 DAS) the rate of 15NO3 − uptake decreased mainly in N-replete plants whereas it remained almost unchanged in N-limited plants. In both NO3 − treatments the tuberized root was the strongest sink for recently absorbed N. Remobilization of previously absorbed N from shoot to tuberized root increased greatly in N-limited plants, whereas it increased slightly in N-replete plants. As a consequence, accumulation of the N-storage compounds vegetative storage protein (VSP) and arginine was delayed until later in the vegetative period in N-limited plants. Our results show that although the dynamics of N storage was affected by NO3 − supply, the final content of total N, VSP and arginine in roots was almost the same in N-limited and N-replete plants. This indicates that chicory is able to build up a store of available N-reserves, even when plants are grown on low N. We also suggest that in tuberized roots there is a maximal capacity for N accumulation, which was reached earlier (soon after 100 DAS) in N-replete plants. This hypothesis is supported by the fact that in N-replete plants despite NO3 − availability, N accumulation ceased and significant amounts of N were lost due to N efflux.

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

A functional-structural model of winter oilseed rape (WOSR) has been developed to study plant morphogenetic plasticity, i.e. how processes of morphogenesis are adapted in response to environmental constraints. The phyllochron (time between emergence of two successive leaves) is one of the variables sensitive to environment. The aim of this article is to use model sensitivity analysis to quantify the impact of an increase or a reduction in phyllochron on plant growth and source/sink functioning.

actes sur CDROMactes sur CDROM; International audience; 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.

Actes sur CDROMActes sur CDROM; International audience; 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.

International audience; Root system architecture adapts to low nitrogen (N) nutrition. Some adaptations may be mediated by modifications of carbon (C) fluxes. The objective of this study was to test the hypothesis that changes in root system architecture under different N regimes may be accounted for by using simple hypotheses of C allocation within the root system of Arabidopsis thaliana. With that purpose, a model during vegetative growth was developed that predicted the main traits of root system architecture (total root length, lateral root number, and specific root length). Different experimental data sets crossing three C levels and two N homogenous nutrition levels were generated. Parameters were estimated from an experiment carried out under medium C and high N conditions. They were then checked under other CxN conditions. It was found that the model was able to simulate correctly C effects on root architecture in both high and low N nutrition conditions, with the same parameter values. It was concluded that C flux modifications explained the major part of root system adaptation to N supply, even if they were not sufficient to simulate some changes, such as specific root length.

International audience

International audience

International audience; In a low-input agricultural context, plants facing temporal nutrient deficiencies need to be efficient. By comparing the effects of NOFormula-starvation in two lines of Arabidopsis thaliana (RIL282 and 432 from the Bay-0xShahdara population), this study aimed to screen the physiological mechanisms allowing one genotype to withstand NOFormula-deprivation better than another and to rate the relative importance of processes such as nitrate uptake, storage, and recycling. These two lines, chosen because of their contrasted shoot N contents for identical shoot biomass under N-replete conditions, underwent a 10 d nitrate starvation after 28 d of culture at 5 mM NOFormula. It was demonstrated that line 432 coped better with NOFormula-starvation, producing higher shoot and root biomass and sustaining maximal growth for a longer time. However, both lines exhibited similar features under NOFormula-starvation conditions. In particular, the nitrate pool underwent the same drastic and early depletion, whereas the protein pool was increased to a similar extent. Nitrate remobilization rate was identical too. It was proportional to nitrate content in both shoots and roots, but it was higher in roots. One difference emerged: line 432 had a higher nitrate content at the beginning of the starvation phase. This suggests that to overcome NOFormula-starvation, line 432 did not directly rely on the N pool composition, nor on nitrate remobilization efficiency, but on higher nitrate storage capacities prior to NOFormula-starvation. Moreover, the higher resistance of 432 corresponded to a higher nitrate uptake capacity and a 2–9-fold higher expression of AtNRT1.1, AtNRT2.1, and AtNRT2.4 genes, suggesting that the corresponding nitrate transporters may be preferentially involved under fluctuating N supply conditions.

International audience; The stolons of white clover (Trifolium repens L.) contain a predominant 17.3-kDa protein, previously characterized as a vegetative storage protein (VSP), which accumulates under autumn and winter conditions. Its full-length complementary DNA, TrVsp, was obtained and its 157 amino acid sequence deduced. This VSP has common characteristics to stress-responsive proteins (high neutral amino acid content and potential alpha helices in its secondary structure) and shows high homologies to abscisic acid-responsive and pathogenesis-related-10 proteins. The lack of any common amino acid sequence domains with known dehydrins or late embryogenesis abundant proteins suggests that clover VSP is not related to these proteins. Antibodies raised against the protein were produced and used in light and electron microscopic studies to show that it is localized to the cytosol of cortical parenchyma cells. This is in agreement with the VSP sequence, which does not contain any transit peptide signal. The accumulation of the transcript and the protein in roots is quickly induced by root chilling, suggesting a direct transcriptional regulation of TrVsp in response to low temperatures. Altogether, these results suggest that the 17.3-kDa protein may have an additional or alternative function to its role in nitrogen storage and may confer putative tolerance to chilling in white clover.

Studying Arabidopsis thaliana (L.) Heynh. root development in situ at the whole plant level without affecting shoot development has always been a challenge. Such studies are usually carried out on individual plants, neglecting competition of a plant population, using hydroponic systems or Agar-filled Petri dishes. Those both systems, however, present some limitations, such as difficulty to study precisely root morphogenesis or time-limited culture period, respectively. In this paper, we present a method of Arabidopsis thaliana (L.) Heynh. cultivation in soil medium, named “Ara-rhizotron”. It allows the non-destructive study of shoot and root development simultaneously during the entire period of vegetative growth. In this system, roots are grown in 2D conditions, comparable to other soil cultures. Moreover, grouping several Ara-rhizotrons in a box enables the establishment of 3D shoot competition as for plants grown in a population. In comparison to a control culture grown in pots in the same environmental conditions, the Ara-rhizotron resulted in comparable shoot development in terms of dry mass, leaf area, number of leaves and nitrogen content. We used this new culture system to study the effect of irrigation modalities on plant development. We found that irrigation frequency only affected root partitioning in the soil and shoot nitrogen content, but not shoot or root growth. These effects appeared at the end of the vegetative growth period. This experiment highlights the opportunity offered by the Ara-rhizotron to point out tardy effects, affecting simultaneously shoot development and root architecture of plants grown in a population. We discuss its advantages in relation to root development and physiology, as well as its possible applications.

International audience

International audience

International audience

Summary In the present work we evaluate the accumulation and further remobilization of vegetative storage proteins (VSP) in chicory. A protein with molecular weight of 17kDa, corresponding to 7 isoforms with pi ranging between 5 and 7, accumulated dramatically over the vegetative phase from spring to autumn and was extensively depleted during the flowering period in the following summer, a pattern typical for a VSP. When mature tuberized roots of chicory are harvested in autumn and forced in darkness, an etiolated bud (chicon) grows: this is the salad known as Belgian endive. In our experiments plants were fed, during the forcing process, nutrient solutions containing 1.5 or 18 mmol/L 15 NO 3 (1.79 % atom excess 15 N) or with demineralized water (control). We determined the cycling of endogenous nitrogen ( 14 N), protein (VSP) and amino acids, and the movement of concurrently absorbed nitrogen ( 15 N). Soluble proteins were remobilized at the onset of forcing as a primary response of nitrogen cycling in chicory root. Amino acid remobilization took place only when the chicon growth began with arginine remobilized first. Although 14 N flux into the chicon was similar in all three treatments, indicating that NO 3 supply did not effect endogenous N remobilization, VSP use was effected by NO 3 supply. SDS-PAGE and 2-D gel electrophoresis analyses showed an extensive depletion of VSP (especially five isoforms) only in the control. We suggested that extensive and specific depletion of VSP was delayed by NO 3 supply; with higher NO 3 availability, there was lower VSP remobilization. Furthermore, neo-synthesis of VSP could occur during the forcing process. The finding that 15 N was incorporated into the protein pool during this period supports this hypothesis. The chicon constituted a very strong sink for absorbed nitrogen. Either in high or low NO 3 supply, 15 N was translocated to the chicon almost without mixing with the bulk nitrogen of the root.

International audience

Comment la diversité fonctionnelle des vers de terre modifie les interactions entre plantes dans un couvert associé ?. TEBIS V, Traits écologiques et biologiques des invertébrés du sol

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http://dx.doi.org/10.1111/j.1399-3054.2004.00366.x; International audience

International audience

International audience

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

Improving rapeseed yields in a low-Nitrogen (N) agricultural context is a major issue for breeding. It requires a thorough knowledge of the genotypic variation of the processes related to Nitrogen Use Efficiency (NUE, seed yield per unit of N available). This PhD aims at better understanding the ecophysiological processes determining the NUE and its components under low-N availability by identifying and hierarchizing the main traits supporting observed genotypic variation. Six winter oilseed rape genotypes were investigated throughout the crop cycle under semi-controlled conditions and contrasting N-conditions. We proposed NUE_DM (plant dry matter per unit of N available), as a new proxy of NUE at harvest, valid as early as the beginning of stem elongation. This proxy allowed us to dynamically characterize NUE, highlighting NUpE (plant N-amount per unit of N available) as a main contributor of NUE under low-N conditions, which explained up to 80% of the NUE_DM variations before flowering, and more than 30% after. Moreover, NUpE genotypic variability resulted from fine root growth rather than specific N-uptake differences. We developed a whole-plant conceptual modeling framework of carbon and nitrogen absorption and partitioning for winter oilseed rape. This framework, validated up to flowering, highlighted specific carbon assimilation, carbon partitioning between leaves and stems, and fine root ratio as critical traits explaining contrasting genotypic behavior to N-conditions. Our results suggest NUpE and fine root ratio as promising traits for screening larger sets of varieties for NUE breeding purposes., Améliorer le rendement du colza dans un contexte de bas intrants azotés (N) est un enjeu majeur de sélection. Ceci impose une connaissance approfondie de la variabilité génétique des processus sous-tendant l’efficacité d’utilisation de l’azote (NUE, rendement en graines par unité d’azote disponible). Cette thèse vise à mieux comprendre les processus écophysiologiques contribuant à la NUE et à ses composantes sous faible nutrition azotée, en identifiant et hiérarchisant les principaux traits sous-tendant leur variabilité génotypique. Six génotypes de colza d’hiver ont été étudiés en conditions semi-contrôlées sous des doses d’azote contrastées. Nous avons montré que la variable NUE_DM (biomasse totale produite par unité d’azote disponible) est un indicateur précoce de la NUE à la récolte valable dès la montaison, qui nous a permis de caractériser dynamiquement la NUE. L’efficience d'absorption d’azote (NUpE, N absorbé par unité d’azote disponible) s’est révélée être une composante majeure de la NUE sous contrainte azotée, expliquant 80 % des variations avant la floraison, et plus de 30 % après. De plus, sa variabilité génotypique dépend de la biomasse des racines fines et non de l’absorption spécifique d'azote. Grâce au développement d’un cadre conceptuel de modélisation du fonctionnement du colza décrivant les flux de carbone et d’azote dans la plante entière et valable jusqu’à floraison, nous avons fait ressortir l'assimilation spécifique de carbone, la part de carbone allouée aux tiges et la proportion de racines fines comme paramètres clés de la réponse génotypique à l’azote. Nos résultats suggèrent que la NUpE et la proportion de racines fines seraient des indicateurs de la NUE permettant de cribler précocement des variétés à haut débit.