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Made available in DSpace on 2021-06-25T10:21:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-03-01 Aims: Belowground interactions are still poorly understood in mixed-species forests. We investigated the effects of soil fertility on belowground processes in mixed planted forests. Methods: The dynamics and traits of Eucalyptus and Acacia mangium fine roots (diameter < 2 mm) in plantations with 50% of each species were studied in a randomized block design established in a nutrient depleted soil. Stands with NPK fertilization applied at planting (F+) were compared to unfertilized stands (F-). Results: In the 0–15 cm soil layer, Eucalyptus root mass density (RMD) was higher than Acacia RMD by 50% in F+ and 10% in F-, considering both ages. At 34 months of age, Eucalyptus RMD was 94% higher near Acacia trees than near Eucalyptus trees in F-. In this layer, Eucalyptus specific root length (SRL) was 21% higher than Acacia SRL at 16 months of age and was 10% higher in F- than in F+ at 34 months of age. The cumulative Eucalyptus fine root length production between 16 and 34 months was 66% higher in F- than in F+ in the 0–1 m soil layer. Conclusions: Fertilization increased the competition between species and led to a partial exclusion of Acacia fine roots from the nutrient-rich topsoil. Soil exploration by Eucalyptus roots in the vicinity of Acacia trees was higher in F- than in F+, which suggests that unfertilized trees benefited from facilitation through higher soil N availability and direct N transfer from Acacia trees. ESALQ Forest Science Department Escola Superior de Agricultura Luiz de Queiroz Universidade de São Paulo Université de Lorraine AgroParisTech INRAE UMR Silva School of Agriculture São Paulo State University (UNESP) Eco&Sols CIRAD INRA IRD Montpellier SupAgro Univ Montpellier CIRAD UMR Eco&Sols ESALQ Soil Science Department Escola Superior de Agricultura Luiz de Queiroz Universidade de São Paulo UFES Centro de Ciências Agrárias e Engenharias Alto Universitário, S/N Guararema School of Agriculture São Paulo State University (UNESP)

The mapping of tree root systems within inhomogeneous dispersive subsoils is investigated by means of a non-destructive technique: Ground-Penetrating Radar (GPR). This work is motivated by the growing need for tree health and stability control, as well as the negative impact of roots on urban infrastructure, which could seriously compromise the safety of people and properties. A state of the art has allowed us to determine the limiting factors of coarse root (diameter > 0.5 cm) detection and resolution by GPR. Then, the focus is put on a novel processing procedure to reconstruct 3-D root architectures from GPR data with no a priori information on the soils involved. Viability is studied from comprehensive numerical simulations (via gprMax) on realistic root models in 3-D heterogeneous dispersive environments; this in particular means a number of simulations involving a variety of soils. Controlled laboratory measurements are conducted on root prototypes using a bi-static GPR system operating at 300 MHz – 3.3 GHz frequency range. This is extended to field studies on real root systems with the use of a commercial GPR (MALA). The good performance and high potential of the proposed approach are illustrated accordingly., La cartographie de systèmes racinaires dans des sols dispersifs et inhomogènes est mise en œuvre au moyen d’une technique non-destructive : le radar à pénétration de sol (dit GPR). Ce travail est motivé par les besoins croissants en termes de contrôle de santé et de stabilité des arbres, ainsi que l’impact négatif des racines sur les infrastructures urbaines pouvant parfois compromettre la sécurité des personnes et des biens. Un état de l'art a permis de déterminer les facteurs limitant la détection et la résolution des racines ligneuses (diamètre > 0,5 cm) par GPR. Puis l'accent est mis sur une nouvelle procédure de traitement pour reconstruire les architectures 3-D des racines à partir de données GPR sans information a priori sur les sols impliqués. La viabilité de la méthode proposée est étudiée à partir de simulations numériques (via gprMax) pour des modèles de racines réalistes en environnements hétérogènes dispersifs; cela implique un nombre de configurations pour une variété de sols. Des mesures contrôlées en laboratoire sont conduites sur des prototypes de racines en utilisant un système bi-statique dans la gamme fréquentielle 300 MHz – 3,3 GHz. Ceci est étendu à des études terrain de systèmes racinaires d’arbres réels avec l'utilisation d'un GPR commercial (MALA). Les bonnes performances et la pertinence de l'approche proposée sont illustrées par de multiples exemples.

The mapping of tree root systems within inhomogeneous dispersive subsoils is investigated by means of a non-destructive technique: Ground-Penetrating Radar (GPR). This work is motivated by the growing need for tree health and stability control, as well as the negative impact of roots on urban infrastructure, which could seriously compromise the safety of people and properties. A state of the art has allowed us to determine the limiting factors of coarse root (diameter > 0.5 cm) detection and resolution by GPR. Then, the focus is put on a novel processing procedure to reconstruct 3-D root architectures from GPR data with no a priori information on the soils involved. Viability is studied from comprehensive numerical simulations (via gprMax) on realistic root models in 3-D heterogeneous dispersive environments; this in particular means a number of simulations involving a variety of soils. Controlled laboratory measurements are conducted on root prototypes using a bi-static GPR system operating at 300 MHz – 3.3 GHz frequency range. This is extended to field studies on real root systems with the use of a commercial GPR (MALA). The good performance and high potential of the proposed approach are illustrated accordingly.; La cartographie de systèmes racinaires dans des sols dispersifs et inhomogènes est mise en œuvre au moyen d’une technique non-destructive : le radar à pénétration de sol (dit GPR). Ce travail est motivé par les besoins croissants en termes de contrôle de santé et de stabilité des arbres, ainsi que l’impact négatif des racines sur les infrastructures urbaines pouvant parfois compromettre la sécurité des personnes et des biens. Un état de l'art a permis de déterminer les facteurs limitant la détection et la résolution des racines ligneuses (diamètre > 0,5 cm) par GPR. Puis l'accent est mis sur une nouvelle procédure de traitement pour reconstruire les architectures 3-D des racines à partir de données GPR sans information a priori sur les sols impliqués. La viabilité de la méthode proposée est étudiée à partir de simulations numériques (via gprMax) pour des modèles de racines réalistes en environnements hétérogènes dispersifs; cela implique un nombre de configurations pour une variété de sols. Des mesures contrôlées en laboratoire sont conduites sur des prototypes de racines en utilisant un système bi-statique dans la gamme fréquentielle 300 MHz – 3,3 GHz. Ceci est étendu à des études terrain de systèmes racinaires d’arbres réels avec l'utilisation d'un GPR commercial (MALA). Les bonnes performances et la pertinence de l'approche proposée sont illustrées par de multiples exemples.

The model legume Medicago truncatula possesses a single outward Shaker K+ channel, whereas Arabidopsis thaliana possesses two channels of this type, named AtSKOR and AtGORK, with AtSKOR having been shown to play a major role in K+ secretion into the xylem sap in the root vasculature and with AtGORK being shown to mediate the efflux of K+ across the guard cell membrane, leading to stomatal closure. Here we show that the expression pattern of the single M. truncatula outward Shaker channel, which has been named MtGORK, includes the root vasculature, guard cells and root hairs. As shown by patch-clamp experiments on root hair protoplasts, besides the Shaker-type slowly activating outwardly rectifying K+ conductance encoded by MtGORK, a second K+ -permeable conductance, displaying fast activation and weak rectification, can be expressed by M. truncatula. A knock-out (KO) mutation resulting in an absence of MtGORK activity is shown to weakly reduce K+ translocation to shoots, and only in plants engaged in rhizobial symbiosis, but to strongly affect the control of stomatal aperture and transpirational water loss. In legumes, the early electrical signaling pathway triggered by Nod-factor perception is known to comprise a short transient depolarization of the root hair plasma membrane. In the absence of the functional expression of MtGORK, the rate of the membrane repolarization is found to be decreased by a factor of approximately two. This defect was without any consequence on infection thread development and nodule production in plants grown in vitro, but a decrease in nodule production was observed in plants grown in soil.

QTLs were identified for traits assessed on field-grown grafted grapevines. Root number and section had the largest phenotypic variance explained. Genetic control of root and aerial traits was independent. Breeding new rootstocks for perennial crops remains challenging, mainly because of the number of desirable traits which have to be combined, these traits include good rooting ability and root development. Consequently, the present study analyzes the genetic architecture of root traits in grapevine. A segregating progeny of 138 F1 genotypes issued from an inter-specific cross between Vitis vinifera cv. Cabernet-Sauvignon × V. riparia cv. Gloire de Montpellier, used as rootstock, was phenotyped in grafted plants grown for 2 years in the field. Seven traits, related to aerial and root development, were quantified. Heritability ranged between 0.44 for aerial biomass to 0.7 for root number. Total root number was related to the number of fine roots, while root biomass was related to the number of coarse roots. Significant quantitative trait loci (QTLs) were identified for all the traits studied with some of them explaining approximately 20% of phenotypic variance. Only a single QTL co-localized for root and aerial biomass. Identified QTLs for aerial-to-root biomass ratio suggest that aerial and root traits are controlled independently. Genes known to be involved in auxin signaling pathways and phosphorus nutrition, whose orthologues were previously shown to regulate root development in Arabidopsis, were located in the confidence intervals of several QTLs. This study opens new perspectives for breeding rootstocks with improved root development capacities.

Fine roots: when anisotropy matters

Plus de la moitié des pertes de bois dans les forêts européennes sont dues aux tempêtes. Une connaissance des mécanismes impliqués dans la stabilité mécanique des arbres est alors capitale. L’ancrage de l’arbre dans le sol constitue l’une des composantes principales du maintien mécanique de l’arbre. Il est principalement déterminé par l’architecture du système racinaire et son interaction mécanique avec le sol. Au cours de son développement, l’arbre modifie ses dimensions et se complexifie. Plus particulièrement, le système racinaire semble s’acclimater (ex : croissance en diamètre plus importante) aux déformations engendrées par le vent. L’ensemble de ces modifications conduit à une évolution des mécanismes à l’origine de l’ancrage au cours du développement de l’arbre. L’étude expérimentale de cette fonction est compliquée car les racines sont difficilement mesurables en continu dans le sol. Nous avons alors mis au point une approche numérique pour décrire la croissance du système racinaire et la distribution des déformations dues au vent. Une grande base de données structurée en chronoséquence de systèmes racinaires numérisés (Pinus pinaster) a été mobilisée. Comme l’étude de la structure et des fonctions des racines est plus efficiente quand la différentiation entre racines est prise en compte, nous avons d’abord formalisé les types racinaires du système racinaire du pin maritime à partir d’une technique de classification (« k-means clustering ») réalisée avec quatre variables. La classification des racines latérales du pin maritime nous a permis d’identifier 5 types racinaires au cours du développement du pin maritime. Ce regroupement explique 70% de la variabilité de notre base de données. Chaque système racinaire est caractérisé par trois grosses racines horizontales émises par la souche. Les racines montrent une forte différentiation pour leur tropisme, avec une direction de croissance soit horizontale soit verticale. La structure de la partie centrale du système racinaire est pratiquement complète dès l'âge de 4 ans. Sur la base des types racinaires identifiés, nous avons calibré un modèle architectural (RootTyp ; Pagès et al. 2004) pour le pin maritime. Treize paramètres pour chaque type racinaire ont été estimés par l’intermédiaire de la base de données, d’informations issues de la littérature et d’une procédure d'optimisation. Une modélisation réaliste du système racinaire jusqu'à 50 ans n’a pu être obtenue qu'en implémentant au modèle RootTyp de nouveaux processus biologiques : la diminution de la ramification avec la croissance de la racine et la diminution de la vigueur des racines avec l'ordre de ramification. Malgré ces améliorations, les systèmes racinaires de la base de données présentent des diamètres plus importants à proximité de la souche par rapport aux systèmes racinaires simulés. Ce biais systématique est principalement attribué à l’acclimatation des racines au vent dominant. Les altérations de croissance dues aux contraintes pédologiques ont également été implémentées grâce à l’amélioration du module de sol du modèle architectural.Enfin, pour comprendre les mécanismes à l’origine de l’acclimatation des racines nous avons combiné plusieurs modèles pour prédire la distribution spatiale des déformations dans des maquettes simplifiées de systèmes racinaires à 4, 6 et 13 ans, pour trois régimes de vent spécifiques à la région étudiée. D’après les simulations, les déformations des racines sous l'effet du vent diminuent avec l’âge, en raison de l’augmentation de la rigidité des racines. Cela suggère une plus forte réponse thigmomorphogénétique aux stades jeunes. Les modifications structurelles et anatomiques du système racinaire par acclimatation au vent s’expliquent principalement par les distributions des déformations et des contraintes dans les racines., Storms cause more than 50% of the timber loss in European forests. However, forest tree anchorage mechanisms throughout their lifespan are not fully understood, especially the strong acclimation of root systems to common winds. This lack of knowledge is mainly due to technical difficulties: neither the root structure nor the mechanical contribution of the roots could be characterized continually. Thus we set up a numerical approach to model the development of the root system and to describe the strains resulting from common winds. This generic approach has been developed using Pinus pinaster grown in sandy soils as model species.Seven datasets of excavated root systems from 0 to 50 years were employed. The assessment of root structure and functions is more powerful if the differentiation of root system in several root types is considered. We first proposed an automatic classification of roots with the k-means clustering algorithm. Four root traits were chosen as classifiers, including three geometric architectural traits, which can be precisely assessed whatever the tree/root age. Clustering yielded similar five groups of laterals roots at all ages, explaining 70% of the variability. The three largest lateral roots per tree were all horizontal roots branching from stump and the other lateral roots show a large differentiation for tropism: nearly all the roots were horizontal or vertical roots. The framework of the central part of the root system can be almost completed in 4-year-old trees (3.5 cm collar diameter). We then calibrated the existing RootTyp (Pagès et al. 2004) architectural model for P. pinaster for each of the root types defined by the cluster analysis. We used the database combined with a literature review and an optimization method to get accurate values for 13 parameters by root types. We devoted effort to validate our model calibration. In order to model architecture of the root system, damping properties had to be implemented to yield realistic outputs up to the mature stage. Branching varied as a function of distance from the root base, and growth capacity decreased with branching order. Nevertheless, the root diameters of simulated root systems were generally underestimated. This was certainly due to root growth plasticity to the prevailing wind, an acclimation facet not taken into account at this calibration step. Growth alterations due to a cemented horizon were reproduced using the new calibrated soil module. Then, the wind acclimation of roots was numerically investigated by examining the root mechanical stimuli due to wind. A chain of biomechanical models was used to predict the spatial distribution of stress and strain in simplified root systems at 4, 6 and 13-year-old as a result of three levels of usual winds. According to simulations, the strain amplitude decreased with tree growth due to the increasing root system stiffness. This suggests larger thigmomorphogenetic responses at young stages. The modifications of the structural and wood root properties related to wind acclimation were largely explained by the stress and strain distribution in the root system.

National audience; Le système racinaire constitue la partie invisible des plantes mais il joue néanmoins un rôleprimordial dans leur développement. C’est par le système racinaire que la plante va prélever deséléments qui sont indispensables à sa survie, et c’est donc, au moins en partie, les caractéristiques dece système racinaire qui vont lui permettre de résister à des stress abiotiques. Il a été notammentmontré que des caractères liés à l’architecture racinaire pouvaient être responsables d’une meilleuretolérance à des stress hydriques. Le projet FSOV ArchiRac vise à caractériser un grand nombre devariétés élites et de diversité de blé tendre et de blé dur pour leur architecture racinaire grâce à desexpérimentations en plateforme de phénotypage haut-débit 4PMI (Jeudy et al., 2016). Les mesuresréalisées sur cette plateforme seront confrontées à des mesures d’architecture racinaire réalisées auchamp dans des conditions optimales ou de stress hydriques, et à des mesures de caractèresagronomiques dans le réseau d’essais du projet BreedWheat. Des analyses de génétique d’associationet de prédiction génomique seront réalisées pour détecter des QTLs d’intérêt et calibrer des équationsde prédiction de manière à valoriser ces résultats en sélection. Les premiers résultats sont prometteurset illustrent la grande variabilité phénotypique disponible sur ce matériel.

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.

Prod 2019-83f BAP EA SPE GEAPSI SERRES GESTAD INRA; National audience; De nombreuses innovations ont été développées afin de caractériser le fonctionnement des plantes modèles ou cultivées. Ces innovations comprennent de nouvelles méthodes et équipements dédiés à l’analyse des plantes et la gestion des données associées. Ils permettent d’analyser dans des conditions climatiques variées la morphologie, la phénologie et le fonctionnement physiologique des plantes résultant de l’expression de leurs gènes, ce que l’on appelle le « phénotype » d’une plante. Ceci est réalisé à « haut débit » par le biais de la caractérisation non destructive, dynamique et automatisée des phénotypes de milliers de plantes et l’acquisition des données microclimatiques permettant de caractériser l’environnement des plantes. Le phénotypage haut débit des parties racinaires ainsi que celui de leurs interactions avec les microorganismes telluriques attirent de plus en plus l’attention des chercheurs. Considérant leur impact majeur sur la santé et la croissance des plantes, en particulier en conditions de stress, il y a là de gros enjeux méthodologiques et scientifiques pouvant conduire à des avancées majeures en sélection variétale.

Background Recently developed genetic and pharmacological approaches have been used to explore NO3- /ethylene signalling interactions and how the modifications in root architecture by pharmacological modulation of ethylene biosynthesis affect nitrate uptake. Key Results Structure-function studies combined with recent approaches to chemical genomics highlight the non-specificity of commonly used inhibitors of ethylene biosynthesis such as AVG (L-aminoethoxyvinylglycine). Indeed, AVG inhibits aminotransferases such as ACC synthase (ACS) and tryptophan aminotransferase (TAA) involved in ethylene and auxin biosynthesis but also some aminotransferases implied in nitrogen (N) metabolism. In this framework, it can be assumed that the products of nitrate assimilation and hormones may interact through a hub in carbon (C) and N metabolism to drive the root morphogenetic programme (RMP). Although ethylene/auxin interactions play a major role in cell division and elongation in root meristems, shaping of the root system depends also on energetic considerations. Based on this finding, the analysis is extended to nutrient ion-hormone interactions assuming a fractal or constructal model for root development. Conclusion Therefore, the tight control of root structure-function in the RMP may explain why over-expressing nitrate transporter genes to decouple structure-function relationships and improve nitrogen use efficiency (NUE) has been unsuccessful.

Plant response and adaptation to metallic stress are involving numerous mechanisms limiting the toxic effect of metals. Although a large number of these mechanisms are well characterized, many processes are in need to be identified in order to have a better understanding of strategies involved in plant response to toxic elements.In first instance, we investigated the role of two post-translational modifications, phosphorylation and methylation of non-histone proteins in response to stress induced by two toxic metals, cadmium and uranium. We analyzed the dynamic of these modifications in three species of Arabidopsis: A. thaliana, A. lyrata two species sensitive to cadmium and A. halleri, a species which naturally tolerate and hyperaccumulate toxic metals in her leaves. By using Western blots and mass spectrometry in parallel, we showed that lysine methylation pattern were changing during metallic stresses. Next, we analyzed the gene expression of enzymes involved in phosphorylation and lysine methylation processes in plants exposed to different adverse conditions. These analyses showed that numerous kinases expressions were differentially regulated in response to metallic stress. Concerning protein lysine methyltransferases, only a few enzymes were differentially regulated. Finally, through a mutant genetic screening we identified two genes coding for protein lysine methyltransferases involved in tolerance to a stress induced by cadmium.Secondly, we studied the physiological and cellular processes involved in the response of A. thaliana root system to uranium. Through the utilization of several reporters and the measure of physiological parameters, we demonstrated that the root architecture was strongly modulated in response to a stress induced by uranium and that in a dose dependent manner. These effects are linked to a cell cycle inhibition and the synthesis and accumulation of reactive oxygen species and nitric oxyde wich participated in the root apex cell death. These changes were associated with perturbation in auxin transport and distribution at the root apex and were temporally correlated to the deposition of defense polymers (callose and lignin) involved in cell proofing and cell wall stiffness. This study is confirming the fact that uranium induced stress is intimately linked to a disruption of phosphate and iron homeostasis. Furthermore, uranium-signaling cascade are sharing a part of the phosphate starvation-signaling cascade.Together, these two studies are revealing mechanisms involved in plant response and adaptation to metallic trace elements through the thin tuning of non-histone methylation and the identification of cellular process involved in the toxicity of uranium in roots., La réponse et l’adaptation des plantes à un stress métallique mettent en jeu de nombreux mécanismes afin de limiter les effets néfastes des éléments toxiques. Bien que certains de ces mécanismes soient bien caractérisés, de nombreux acteurs cellulaires et moléculaires restent à identifier pour mieux comprendre la diversité des stratégies mises en œuvre dans ces processus complexes et vitaux pour les plantes.Dans un premier temps, nous nous sommes intéressés au rôle de deux modifications post-traductionnelles, la phosphorylation et la méthylation des protéines non-histone dans la réponse à un stress induit par deux éléments non essentiels et toxiques, le cadmium (Cd) et l’uranium (U). Nous avons analysé la dynamique de ces modifications chez trois espèces du genre Arabidopsis : A. thaliana et A. lyrata, deux espèces sensibles au Cd, et A. halleri, espèce naturellement capable de tolérer et d’hyper-accumuler ce métal toxique dans ses feuilles. En utilisant une combinaison d’analyses par Western blot et par spectrométrie de masse nous avons montré que les patterns de méthylation des protéines changent au cours de stress métalliques. Puis, nous avons analysé l’expression des gènes codant les enzymes impliquées dans les réactions de phosphorylation et méthylation des protéines dans différentes conditions de stress. Ces analyses ont montré qu’un grand nombre de protéines kinases sont régulés au niveau transcriptionnel par un stress métallique tandis que seules quelques une en ce qui concerne la méthylation. Pour finir, nous avons mis en place un criblage génétique de mutants d’A. thaliana et identifié deux gènes codant des protéines lysine méthyltransférases impliqués dans la tolérance au Cd.Dans un deuxième temps, nous avons étudié les mécanismes cellulaires de la réponse du système racinaire d’A. thaliana lors d’une exposition à l’U. L’utilisation de différents systèmes rapporteurs et la mesure de différents paramètres physiologiques nous ont permis de mettre en évidence que l’architecture racinaire est fortement modulée en réponse à l’U et ceci de façon dose dépendante. Cet effet est lié à l’inhibition du cycle cellulaire et à la synthèse d’espèces réactives de l’oxygène et d’oxyde nitrique dont l’accumulation provoque la mort cellulaire. Ces changements sont associés à une perturbation du transport et de la distribution de l’auxine dans les racines. Ces événements sont temporellement corrélés avec l’accumulation de polymères de défense (callose et lignine) impliqués dans l’imperméabilisation des cellules et des parois. Cette étude confirme enfin que le stress induit par l’U est intimement lié à une perturbation de l’homéostasie de certains macronutriments (phosphate et fer) et partage les cascades de signalisation d’une carence en phosphate.Ce travail met en évidence des mécanismes de réponse et d’adaptation aux métaux toxiques à travers la régulation fine des phénomènes de méthylation des protéines non-histone et l’identification de processus cellulaires impliqués dans la réponse à la toxicité de l’U dans le système racinaire.

Regulatory Network Behind Systemic Nitrogen Signaling, in Arabidopsis. Gordon Research Conference :Plant Molecular Biology "Dynamic Plant Systems"

Gene Regulatory Network Dynamics: Lessons from Plants. Gordon Research Conference :Plant Molecular Biology "Dynamic Plant Systems"

International audience; Improving crop yields under rainfed environments is key to meeting the food security demands of an everincreasing population, but climate change-associated expansion of drought-affected arable land means that resilient crops and agronomic practices are critical. High-throughput plant phenomics and modern genetic approaches must be directed towards precise understanding of factors controlling crop yield. This special issue covers root dynamics, turgor management under desiccation, molecular responses to dehydration, impact of drought on plant development and seed abortion, and adjustment of traits to the most frequent patterns of drought. It also addresses interdisciplinary views for enhancing genetic gains and achieving a more sustainable climate-resilient agronomy.

International audience; Plant growth and development has to be continuously adjusted to the available resources. Their optimization requires the integration of signals conveying the plant metabolic status, its hormonal balance, and its developmental stage. Many investigations have recently been conducted to provide insights into sugar signaling and its interplay with hormones and nitrogen in the fine-tuning of plant growth, development, and survival. The present review emphasizes the diversity of sugar signaling integrators, the main molecular and biochemical mechanisms related to the sugar-signaling dependent regulations, and to the regulatory hubs acting in the interplay of the sugar-hormone and sugar-nitrogen networks. It also contributes to compiling evidence likely to fill a few knowledge gaps, and raises new questions for the future.

Roots provide basic functions to plants such as water/nutrient uptake and anchoring in soil. The growth and development of root systems contribute to colonizing the surrounding soil and optimizing the access to resources. It is usually admitted that the variability of plant root architecture results from the combination of genetic, physiological and environmental factors, in particular soil mechanical impedance. However this last factor has never been investigated at the soil grain scale. In this paper, we are interested in the effect of the disordered texture of granular soils on the evolution of external forces experienced by root cap. We introduce a numerical model in which the root is modeled as a flexible self-elongating tube that probes a soil composed of solid particles. By means of extensive simulations, we show that the forces exerted on the root cap during its growth reflect interparticle force chains. Our extensive simulations also show that the mean force declines exponentially with root flexibility, the highest force corresponding to the soil hardness. Furthermore, we find that this functional dependence is characterized by a single parameter that combines the granular structure and root bending stiffness. This finding will be useful to further address the biological issues of mechanosensing and thigmomorphogenesis in plant roots.

QTLs were identified for traits assessed on field-grown grafted grapevines. Root number and section had the largest phenotypic variance explained. Genetic control of root and aerial traits was independent. Breeding new rootstocks for perennial crops remains challenging, mainly because of the number of desirable traits which have to be combined, these traits include good rooting ability and root development. Consequently, the present study analyzes the genetic architecture of root traits in grapevine. A segregating progeny of 138 F1 genotypes issued from an inter-specific cross between Vitis vinifera cv. Cabernet-Sauvignon × V. riparia cv. Gloire de Montpellier, used as rootstock, was phenotyped in grafted plants grown for 2 years in the field. Seven traits, related to aerial and root development, were quantified. Heritability ranged between 0.44 for aerial biomass to 0.7 for root number. Total root number was related to the number of fine roots, while root biomass was related to the number of coarse roots. Significant quantitative trait loci (QTLs) were identified for all the traits studied with some of them explaining approximately 20% of phenotypic variance. Only a single QTL co-localized for root and aerial biomass. Identified QTLs for aerial-to-root biomass ratio suggest that aerial and root traits are controlled independently. Genes known to be involved in auxin signaling pathways and phosphorus nutrition, whose orthologues were previously shown to regulate root development in Arabidopsis, were located in the confidence intervals of several QTLs. This study opens new perspectives for breeding rootstocks with improved root development capacities.

Phénotypage des réponses racinaires du blé dur à l'inoculation par des bactéries diazotrophes. Interactions céréales micro-organismes bénéfiques du sol

Background In order to efficiently determine genotypic differences in rooting patterns of crops, novel hardware and software are needed simultaneously to characterize dynamics of root development. Results We describe a prototype robotic monitoring platform—the RhizoChamber-Monitor for analyzing growth patterns of plant roots automatically. The RhizoChamber-Monitor comprises an automatic imaging system for acquiring sequential images of roots which grow on a cloth substrate in custom rhizoboxes, an automatic irrigation system and a flexible shading arrangement. A customized image processing software was developed to analyze the spatio-temporal dynamics of root growth from time-course images of multiple plants. This software can quantify overall growth of roots and extract detailed growth traits (e.g. dynamics of length and diameter) of primary roots and of individual lateral roots automatically. It can also identify local growth traits of lateral roots (pseudo-mean-length and pseudo-maximum-length) semi-automatically. Two cotton genotypes were used to test both the physical platform and the analysis software. Conclusions The combination of hardware and software is expected to facilitate quantification of root geometry and its spatio-temporal growth patterns, and therefore to provide opportunities for high-throughput root phenotyping in support of crop breeding to optimize root architecture.

Lasso mutants link root gravitropic response and salt stress. 8th International Symposium on Root Development

EABAPGEAPSI DOCT INRA; Le pois (Pisum sativum) possède la capacité de fixer l’azote atmosphérique via une symbiose avec des bactéries du sol, permettant ainsi de s’affranchir d’engrais azotés. Cependant, ce processus est très sensible au stress hydrique, et reste affecté même lorsque les conditions hydriques redeviennent optimales. Or, la capacité d’une plante à récupérer après un stress hydrique peut être déterminante pour l’élaboration de son rendement. Pourtant, les mécanismes enclenchés lors de la phase de récupération restent peu connus. Le but de cette thèse est d’évaluer la capacité de la plante à récupérer après un stress hydrique et d’identifier les processus écophysiologiques et moléculaires ainsi que les signaux intra-plante sous-jacents à cette récupération. Pour cela, deux génotypes contrastés pour leur architecture racinaire et pour leur capacité à récupérer après un stress hydrique ont été sélectionnés. Les processus écophysiologiques impliqués dans la récupération après le stress seront analysés en utilisant un cadre d’analyse structure-fonction associé à une étude des flux d’eau, de carbone et d’azote au sein du continuum sol-plante-atmosphère. Les processus moléculaires seront étudiés via des analyses transcriptomiques et métabolomiques afin d’identifier respectivement les gènes clés et les principales voies métaboliques impliqués. Cette combinaison d’approches permettra de contribuer à la conception d’idéotypes de pois mieux adaptés à des conditions hydriques fluctuantes.

Pearl millet plays an important role for food security in arid regions. Improving its root system toward increased water uptake efficiency could improve pearl millet tolerance to drought and lead to a significant production rise under water-limiting conditions. The objective of this work was to provide an integrated description of root system development at early stages and to assess the consequences of these findings for water uptake. A precise description of pearl millet root system development evidenced large variability among lateral root growth profiles. To further analyze this diversity, the growth rates of many lateral roots were measured daily and a statistical model was designed to classify these roots on the basis of their growth profiles. Three categories of lateral roots were identified in this way: (i) roots with high growth rate that could keep on growing after the end of the experiment, (ii) roots with intermediate growth rates and (iii) roots with low growth rates that quickly stop growing. The different lateral root types were randomly distributed along the primary root and there was no influence of root types on the intervals between successive lateral roots. The proportions of these different types were variable between plants of the same genotype, suggesting that small environmental variations could control these proportions. Water movements between soil and roots is modeled with R-SWMS to assess (i) the benefits of the three-type structuring, (ii) the relative contribution of each type to water uptake and (iii) the impact of specific proportions on global water uptake.

Home / Conferences / Frontiers of Potassium Science, Rome, 2017 Frontiers of Potassium Science Rome 2017 Frontiers of Potassium Science Conference Presentations - Sustainable Intensification Presentations - 4R Source Presentations - 4R Rate Presentations - 4R Time Presentations - 4R Place Presentations - Connecting Frontier Science to Frontier Practice Presentations - Conclusion and Next Steps Posters Conference Proceedings Contenu des liens YouTube Root traits and rhizosphere characteristics determining potassium acquisition from soils icon-email icon-facebook icon-linkedin icon-twitter 27 Jan 2017 4R Place - Root traits and rhizosphere characteristics determining potassium acquisition from soils Philippe Hinsinger, INRA Plants acquire K+ ions from the soil solution, and this small and dynamic pool needs to be quickly replenished by the other soil pools, either the exchangeable pool via desorption of K adsorbed onto clay minerals and organic matter, or the nonexchangeable pool via weathering of K-bearing silicates. Because of these chemical interactions with soil solid phases, K+ concentration is kept low, restricting its mobility. Mass-flow therefore only partly contributes to K+ transfer to the root surface, and K+ depletion occurs as a consequence of K+ uptake by roots, which is the driving force for the diffusion of K+ in the rhizosphere. Because of this restricted mobility of K in soils, plants have evolved efficient strategies of root foraging. Therefore, root traits related to root system architecture (root angle, branching, depth), root length and growth, as well as root hairs and mycorrhiza-related traits play an important role in determining the capacity of plants to cope with the poor mobility of soil K, as well as its distribution in the whole soil profile, with potential significant contribution of subsoil K in many soils. Another consequence of the root-induced depletion of K+ is a shift of the exchange equilibria, enhancing the desorption of exchangeable K, as well as the release of nonexchangeable, interlayer K from micaceous minerals in the rhizosphere. This means that both of these pools can be bioavailable, provided that plant roots can take up significant amounts of K at low K+ concentrations in the soil solution (in the micromolar range). This is thus an important physiological root trait determining the acquisition efficiency of plants. Besides, roots can significantly acidify their environment or release large amounts of exudates, these two processes ultimately promoting the dissolution of K-bearing silicates such as micas and feldspars in the rhizosphere, which contributes the mining strategy evolved by plants. There are thus a number of root or rhizosphere-related traits (either morphological or physiological) that determine the acquisition efficiency of crop species and genotypes. The aim of this paper is to provide a detailed overview of these.

Plant growth-promoting rhizobacteria (PGPR) of the genus Azospirillum are used commercially for their capacity to stimulate the growth and enhance the yield of cereal crops via an intricate, complex and poorly understood associative relationship. The aim of this study was to use modern metabolomics tools to decipher the biochemical mechanisms activated by A. lipoferum CRT1 in its maize host.The analysis of the phytochemical contents of roots, leaves and ascending sap revealed for the first time the importance of root-to-shoot communication and of simple sugars in the enhancement of growth and photochemical conversion potential of young plantlets by A. lipoferum CRT1. A transcriptomic analysis showed moderate impact on roots and a coordinate modulation of several regulatory nodes of cellular biological processes, including some mediated by auxins and abscissic acid. Agronomic field trials conducted two consecutive years in four sites correlated yield enhancement by A. lipoferum CRT1 to the securing of seed germination during environmental stresses. No correlation was found with modifications of plantlets metabolomes (including those linked to nitrogen and phosphorus nutrition), growth and photochemical conversion potential which were found to depend on additional soil and climate cues. Germination securing was due to a speeding of radicule emergence and of seed simple sugars consumption, Les bactéries rhizosphériques stimulatrices de croissance (PGPR) du genre Azospirillum sont utilisées commercialement pour leur capacité à stimuler la croissance et à augmenter le rendement des céréales via une relation associative complexe et peu comprise. L'objectif de cette étude a été d'utiliser les outils modernes de la métabolomique pour caractériser les mécanismes biochimiques activés par la souche A. lipoferum CRT1 chez son hôte, le maïs.L'analyse des contenus phytochimiques des racines, feuilles et sève ascendante a suggéré pour la première fois l'importance de la communication racine-feuille et des sucres simples dans l’augmentation de croissance et du potentiel de conversion photochimique de jeunes plantules par A. lipoferum CRT1. Une analyse transcriptomique a révélé un impact modéré au niveau des racines et des modifications de nombreux nœuds régulateurs des processus biologiques cellulaires des feuilles, dont ceux contrôlés par les auxines et l’acide abscissique. Des essais agronomiques conduits deux années consécutives sur quatre sites ont indiqué que l'augmentation de rendement par A. lipoferum CRT1 dérivait d’une sécurisation de la germination lors de stress environnementaux précoces et non de modifications des métabolomes (dont ceux liés à la nutrition azotée et phosphorée), de la croissance et du potentiel photosynthétique des plantules, des modifications qui étaient par contre liées aux contextes pédo-climatiques. La sécurisation de la germination était due à une accélération de la sortie de la radicule et de la consommation des sucres simples, et molécules apparentées, de la graine

Co-phytoremediation of both trace elements and polycyclic aromatic hydrocarbons (PAH) is an emerging technique to treat multi-contaminated soils. In this study, root morphological and structural features of the heavy metal hyperaccumulator Noccaea caerulescens, exposed to a model PAH phenanthrene (PHE) in combination with cadmium (Cd), were observed. In vitro cultivated seedlings were exposed to 2 mM of PHE and/or 5 mu M of Cd for 1 week. Co-phytoremediation effectiveness appeared restricted because of a serious inhibition (about 40%) of root and shoot biomass production in presence of PHE, while Cd had no significant adverse effect on these parameters. The most striking effects of PHE on roots were a decreased average root diameter, the inhibition of cell and root hair elongation and the promotion of lateral root formation. Moreover, endodermal cells with suberin lamellae appeared closer to the root apex when exposed to PHE compared to control and Cd treatments, possibly due to modified lateral root formation. The stage with well-developed suberin lamellae was not influenced by PHE whereas peri-endodermal layer development was impaired in PHE-treated plants. Many of these symptoms were similar to a water-deficit response. These morphological and structural root modifications in response to PHE exposition might in turn limit Cd phytoextraction by N. caerulescens in co-contaminated soils.

Contrôle de l’accumulation de cations toxiques chez le riz par modification des transporteurs, de l’architecture et de l’anatomie racinaires: application à une culture sur des sols contaminés par le césium 137. Rencontres Céréales

Better managing crop : weed competition in cropping systems while reducing both nitrogen and herbicide inputs is a real challenge that requires a better understanding of crop and weed root architecture in relation to soil-nitrogen availability. An original approach was used which considered the parameters of a simulation model of root architecture as traits to analyse (a) the interspecific diversity of root system architecture, and (b) its response to soil-nitrogen availability. Two greenhouse experiments were conducted using three crop and nine weed species grown at two contrasted concentrations of soil-nitrogen availability. Plant traits were measured to characterise both overall plant growth and root architecture, with a focus on primary root emergence, root elongation and branching. The studied root traits varied among species (from a twofold to a fourfold factor, depending on the trait), validating their use as indicators to analyse the interspecific variability of root architecture. The largest interspecies differences were for two traits: ‘maximal apical root diameter’ and ‘interbranch distance’ (distance between two successive laterals on the same root). Conversely, most of the studied root traits varied little with soil-nitrogen availability (from no variation to a 1.1-fold factor, depending on the trait) even though soil-nitrogen availability varied with a 17-fold factor and impacted the overall shoot and root biomass. So, the root traits used in this article are stable whatever soil-nitrogen availability. As they reflect processes underlying root system architecture, this low effect of nitrogen suggests that the rules governing root architecture are little affected by plant nitrogen status and soil-nitrogen availability. We propose that the determinants of differences in root system architecture between soils with contrasted nitrogen availability mainly originate from differences in the amount of carbon allocated to and within the root system. Characterising each plant species by a combination of root traits gave insights regarding the potential species competitive ability for soil resources in agroecosystems.

We use molecular dynamics simulations to investigate the effects of root bending stiffness and packing fraction on the path followed by a growing root in 2D packings of grains representing a soil. The root is modeled as a chain of elements that can grow in length and change their direction depending on the forces exerted by soil grains. We show that the root shape is mainly controlled by the bending stiffness of its apex. At low stiffness, the root randomly explores the pore space whereas at sufficiently high stiffness, of the order of soil hardness multiplied by mean grain size, the root follows a straight path across the soil. Between these two limits, the root shape can be characterized by the standard deviation of its re-directions at the scale of soil grains. We find that this shape parameter varies as a power-law function of the normalized bending stiffness.

Summary Physiological and developmental analyses provide evidence that the highly branched root architecture of a mutant results from systemic regulation by its nitrogen status, possibly involving glutamine or asparagine signals., To complement N2 fixation through symbiosis, legumes can efficiently acquire soil mineral N through adapted root architecture. However, root architecture adaptation to mineral N availability has been little studied in legumes. Therefore, this study investigated the effect of nitrate availability on root architecture in Medicago truncatula and assessed the N-uptake potential of a new highly branched root mutant, TR185. The effects of varying nitrate supply on both root architecture and N uptake were characterized in the mutant and in the wild type. Surprisingly, the root architecture of the mutant was not modified by variation in nitrate supply. Moreover, despite its highly branched root architecture, TR185 had a permanently N-starved phenotype. A transcriptome analysis was performed to identify genes differentially expressed between the two genotypes. This analysis revealed differential responses related to the nitrate acquisition pathway and confirmed that N starvation occurred in TR185. Changes in amino acid content and expression of genes involved in the phenylpropanoid pathway were associated with differences in root architecture between the mutant and the wild type.

As plant roots forage the soil for food and water, they translate a multifactorial input of environmental stimuli into a multifactorial developmental output that manifests itself as root system architecture (RSA). Our current understanding of the underlying regulatory network is limited because root responses have traditionally been studied separately for individual nutrient deficiencies. In this study, we quantified 13 RSA parameters of Arabidopsis thaliana in 32 binary combinations of N, P, K, S, and light. Analysis of variance showed that each RSA parameter was determined by a typical pattern of environmental signals and their interactions. P caused the most important single-nutrient effects, while N-effects were strongly light dependent. Effects of K and S occurred mostly through nutrient interactions in paired or multiple combinations. Several RSA parameters were selected for further analysis through mutant phenotyping, which revealed combinations of transporters, receptors, and kinases acting as signaling modules in K–N interactions. Furthermore, nutrient response profiles of individual RSA features across NPK combinations could be assigned to transcriptionally coregulated clusters of nutrient-responsive genes in the roots and to ionome patterns in the shoots. The obtained data set provides a quantitative basis for understanding how plants integrate multiple nutritional stimuli into complex developmental programs.

Grain legume pulse crops are of great interest to allow a production of seeds high nutritional value without any contribution of nitrate fertilizer. The nitrogen nutrition of legumes depends indeed mainly on the fixation in nodules of atmospheric dinitrogen through the plant-rhizobium symbiosis, and to a lesser extent, absorption by roots of soil mineral nitrogen.A better understanding has been obtained on the genetic control of the development of roots and nodules and on their impact on nitrogen nutrition. High genetic variability of these characters has been detected, and the existence of genetic correlations between them demonstrated. A quantitative genetic approach has identified several genomic regions that may be involved in their variations. The two different ways to improve nitrogen nutrition were also studied: the improvement of nitrogen acquisition by roots through a detailed study of a root architecture mutant, and the improvement of symbiosis via the study of the ability of peas to promote symbiotic associations with the most effective rhizobia.The results provide interesting bases for the design of a pea nitrogen-nutrition ‘ideotype’. Beyond the essential complementarity between the two pathways of nitrogen acquisition, it is necessary to optimize the interaction between the two symbiotic partners, which is a complex mechanism involving nodules formation and functioning in connection with complex signaling and trophic interactions between the partners and intra-plant., La culture de Légumineuses présente le double intérêt de permettre une production de graines à haute valeur nutritionnelle sans nécessité d’un apport d’engrais azoté. La nutrition azotée des légumineuses dépend en effet majoritairement de la fixation symbiotique de l’azote atmosphérique réalisée par des bactéries du sol, les rhizobia, au sein des nodosités, et dans une moindre mesure, de l’assimilation de l’azote minéral du sol par les racines.Une meilleure compréhension a été acquise sur le contrôle génétique de la mise en place des racines et des nodosités et sur leur impact sur la nutrition azotée. Une grande variabilité génétique pour ces caractères a été mise en évidence, ainsi que l’existence de corrélations génétiques entre eux. Une approche de génétique quantitative a permis d’identifier des régions génomiques pouvant être impliquées dans leurs variations. Deux pistes d’amélioration de la nutrition azotée ont aussi été étudiées : l’amélioration de l’acquisition d’azote par les racines à partir d’une étude détaillée d’un mutant de développement racinaire, et l’amélioration de la symbiose via l’étude de la capacité des pois à favoriser les associations symbiotiques avec les rhizobia les plus performants.Les résultats obtenus apportent des bases de réflexion concernant la conception d’un idéotype de nutrition azotée. Au-delà de la complémentarité indispensable entre les deux voies d’acquisition d’azote, il convient d’optimiser l’interaction entre les deux partenaires symbiotiques, mécanisme complexe mettant en jeu la formation et le fonctionnement des nodosités, en lien avec une signalétique et des interactions trophiques entre partenaires et intra-plante.

La culture de Légumineuses présente le double intérêt de permettre une production de graines à haute valeur nutritionnelle sans nécessité d’un apport d’engrais azoté. La nutrition azotée des légumineuses dépend en effet majoritairement de la fixation symbiotique de l’azote atmosphérique réalisée par des bactéries du sol, les rhizobia, au sein des nodosités, et dans une moindre mesure, de l’assimilation de l’azote minéral du sol par les racines. Une meilleure compréhension a été acquise, par ce travail de thèse, sur le contrôle génétique de la mise en place des racines et des nodosités et sur leur impact sur la nutrition azotée. Une grande variabilité génétique pour ces caractères a été mise en évidence, ainsi que l’existence de corrélations génétiques entre eux. Une approche de génétique quantitative a permis d’identifier des régions génomiques pouvant être impliquées dans leurs variations. Deux pistes d’amélioration de la nutrition azotée ont aussi été étudiées : l’amélioration de l’acquisition d’azote par les racines à partir d’une étude détaillée d’un mutant de développement racinaire, et l’amélioration de la symbiose via l’étude de la capacité des pois à favoriser les associations symbiotiques avec les rhizobia les plus performants. Les résultats obtenus apportent des bases de réflexion concernant la conception d’un idéotype de nutrition azotée. Au-delà de la complémentarité indispensable entre les deux voies d’acquisition d’azote, il convient d’optimiser l’interaction entre les deux partenaires, mécanisme complexe mettant en jeu la formation et le fonctionnement des nodosités, en lien avec une signalétique et des interactions trophiques complexes entre partenaires symbiotiques et intra-plante. ABSTRACT Grain legume pulse crops are of great interest to allow a production of seeds high nutritional value without any contribution of nitrate fertilizer. The nitrogen nutrition of legumes depends indeed mainly on the fixation in nodules of atmospheric dinitrogen through the plant-rhizobium symbiosis, and to a lesser extent, absorption by roots of soil mineral nitrogen. A better understanding has been obtained on the genetic control of the development of roots and nodules and on their impact on nitrogen nutrition. High genetic variability of these characters has been detected, and the existence of genetic correlations between them demonstrated. A quantitative genetic approach has identified several genomic regions that may be involved in their variations. The two different ways to improve nitrogen nutrition were also studied: the improvement of nitrogen acquisition by roots through a detailed study of a root architecture mutant, and the improvement of symbiosis via the study of the ability of peas to promote symbiotic associations with the most effective rhizobia. The results provide interesting bases for the design of a pea nitrogen-nutrition ‘ideotype’. Beyond the essential complementarity between the two pathways of nitrogen acquisition, it is necessary to optimize the interaction between the two symbiotic partners, which is a complex mechanism involving nodules formation and functioning in connection with complex signaling and trophic interactions between the partners and intraplant, Grain legume pulse crops are of great interest to allow a production of seeds high nutritional value without any contribution of nitrate fertilizer. The nitrogen nutrition of legumes depends indeed mainly on the fixation in nodules of atmospheric dinitrogen through the plant-rhizobium symbiosis, and to a lesser extent, absorption by roots of soil mineral nitrogen. A better understanding has been obtained on the genetic control of the development of roots and nodules and on their impact on nitrogen nutrition. High genetic variability of these characters has been detected, and the existence of genetic correlations between them demonstrated. A quantitative genetic approach has identified several genomic regions that may be involved in their variations. The two different ways to improve nitrogen nutrition were also studied: the improvement of nitrogen acquisition by roots through a detailed study of a root architecture mutant, and the improvement of symbiosis via the study of the ability of peas to promote symbiotic associations with the most effective rhizobia. The results provide interesting bases for the design of a pea nitrogen-nutrition ‘ideotype’. Beyond the essential complementarity between the two pathways of nitrogen acquisition, it is necessary to optimize the interaction between the two symbiotic partners, which is a complex mechanism involving nodules formation and functioning in connection with complex signaling and trophic interactions between the partners and intraplant.

Communication atthe National Day, impact of climate change on the functioning of ecosystems. FST, Fes, Morocco

La pratique du «sans labour» (NT) se développe dans le cadre de l’agriculture de conservation des sols. Cette pratique modifie nombre de propriétés du sol comme, par exemple, la répartition du phosphore (P) dans le profil du sol. L’objectif de cette thèse est d’analyser les impacts après plusieurs décennies du NT sur le cycle biogéochimique du P et d’intégrer ces effets dans un modèle de fonctionnement. Nous avons utilisé un essai au champ de longue durée sous maïs-soja (L’Acadie, Québec, Canada) implanté sur un sol argilo-limoneux. Le dispositif était un split-plot à 4 blocs avec mouldboard plough (MP) et sans labour (NT), subdivisés par 3 doses de fertilisation en P minéral [0 (0P), 17.5 (0.5P), 35 (1P) kg P ha-1] apportées sur le maïs et localisées à 5 cm de profondeur et à 5 cm du rang de maïs. La concentration des ions phosphates du sol (Cp) test était relativement uniforme dans la couche labourée (0-20 cm) (0.08 mg P L-1), puis baissait légèrement dans 20-30 cm (0.05 mg P L-1) et davantage au-delà (0.01 mg P L-1). Sous les traitements [NT, 0.5P] et [NT, 1P] traitements, le Cp était plus élevé dans la couche 0-10 cm (0.28 et 0.19 mg P L-1) que dans la couche labourée mais baissait rapidement avec la profondeur. Cette stratification verticale sous NT était également observée pour les teneurs en P-Olsen, P-M3 et autres nutriments comme C, N et K. Après 23 et 24 années d’essai, il y avait tendanciellement moins de racines du maïs sous NT (-14%) que sous MP, probablement à cause de la présence plus importante d’adventices sous NT. Pour le soja, il y avait beaucoup plus de racines dans la couche 0-10 cm sous NT (44% de longueur total) que sous MP (21%) et inversement dans la couche 10-20 cm. Ces différences de distribution des racines sous NT et MP correspondent à la stratification de N, P, et K. Cet ensemble de données sur la distribution des racines et du phosphore a été utilisé pour i) évaluer un modèle 1D décrivant la dynamique du P sur plusieurs décennies dans la couche labourée du sol, ii) proposer un mode d’estimation de la distribution du prélèvement dans le profil de sol, et iii) développer un modèle spatialisé 2D décrivant la dynamique du P pour le traitement sans labour. Ce modèle permet de simuler l’évolution de la disponibilité en P du sol sur le long terme quels que soient les modes de préparation du sol et le régime de fertilisation P. Même si le modèle surestime parfois la disponibilité en P à proximité de la zone fertilisée, il permet de prédire la stratification du P du sol en NT et ses conséquences sur le prélèvement de P en relation avec les propriétés du sol et le développement du système racinaire. Il pourra contribuer à améliorer le raisonnement de la fertilisation phosphatée dans le contexte du sans-labour.

The relation between a growing root and the soil movement has often been under-estimated. The present work aims to determine how grains in granular soils are reorganized by the action of growing roots, and in turn how the resulting forces acting on root tips modify their development. For this purpose, we have developed a 2D Discrete Element Model (DEM) able to compute a numerical growth of a single root inside a granular medium, taking into account the grain-grain and the root-grain contact forces during the growth. First in silico simulations were carried out in order to : 1-quantify the influence of the granular structure (grain diameter distribution and gaps) and root mechanical properties (root bending stiffness) on the evolution of reaction forces applied to a single root during its growth; 2-highlight “group effects”, e.g. how the reorganization of grains and their interaction forces due to a given growing root can affect the mechanical signal perceived by its near neighbours; 3-investigate how the presence of initial channels within the granular medium can effect the growth trajectory and minimize the resistance to penetration. All simulations were carried out assuming that root growth direction was only driven by external forces. Simlation results allowed the extraction of general physical laws that will be used further to provide mechanoperceptive indicators and analyze experimental data provided by phenotyping platforms. The final objective will be to quantify the response of plants to mechanical stresses in terms of root elongation rate, root straightness and ramification.

Phosphorus (P) is one of the essential nutrients for plants, and is indispensable for plant growth and development. P deficiency severely limits crop yield, and regular fertilizer applications are required to obtain high yields and to prevent soil degradation. To access P from the soil, plants have evolved high- and low-affinity Pi transporters and the ability to induce root architectural changes to forage P. Also, adjustments of numerous cellular processes are triggered by the P starvation response, a tightly regulated process in plants. With the increasing demand for food as a result of a growing population, the demand for P fertilizer is steadily increasing. Given the high costs of fertilizers and in light of the fact that phosphate rock, the source of P fertilizer, is a finite natural resource, there is a need to enhance P fertilizer use efficiency in agricultural systems and to develop plants with enhanced Pi uptake and internal P-use efficiency (PUE). In this review we will provide an overview of continuing relevant research and highlight different approaches towards developing crops with enhanced PUE. In this context, we will summarize our current understanding of root responses to low phosphorus conditions and will emphasize the importance of combining PUE with tolerance of other stresses, such as aluminum toxicity. Of the many genes associated with Pi deficiency, this review will focus on those that hold promise or are already at an advanced stage of testing (OsPSTOL1, AVP1, PHO1 and OsPHT1;6). Finally, an update is provided on the progress made exploring alternative technologies, such as phosphite fertilizer.

Background and Aims Little quantitative information is available on the protective role of tropical species on slope sites prone to erosive phenomena. One of the key parameters to evaluate of species’ capabilities in erosion mitigation is root individual scale mechanical traits. We explored, for the first time, the variability of root mechanics of several dominant species in tropical ecosystems. Methods We carried out ex situ experimental tests on roots of four common tropical tree species, i.e. Barringtonia fusicarpa Hu, Pometia pinnata J.R. Forst. & G. Forst., Baccaurea ramiflora Lour. and Pittosporopsis kerrii Craib as model species in Xishuangbanna forests, Yunnan, China. Tensile strength and modulus of elasticity, as two of the most important root mechanic traits were estimated. Results and Conclusions Root mechanics vary greatly depending on root size and tree species. And root size the primordial factor determining the variability of root mechanics, especially for very fine roots. The significant disparity of root mechanics between the four tree species suggests that the use of generic equations in soil stability modelling procedures may not be relevant in tropical ecosystems that possess a high species richness level. General discussions are provided concerning the disparity of geomorphological modelling between temperate and tropical forests.

Plant roots play a key role in reinforcing soils against erosion and shallow landslides through different chemical (formation of soil aggregate) and physical processes (mechanical reinforcement, water infiltration and water suction). Managing vegetated slopes on a longterm perspective to avoid soil loss necessitates understanding and quantifying the dynamics of root-soil interaction. Soil resistance to penetration is a major component that can significantly affect root growth. The impact of soil properties on root growth has been largely studied at the root, plant and vegetation scales, mainly reducing soil properties to a single input variable representing soil impedance. However the mechanical feedback between growing roots and a deformable soil, is still largely unknown. The underlying questions are how the grains are reorganizing under the action of growing roots, and in return how the resulting forces acting on the growing root tips modify its development, including root elongation rate, root shape and ramification. We started answering these questions in a theoretical way, developing a numerical model of root growth in a granular medium. The model is based on the discrete-element method (DEM). Single roots are modelled using chains of connected spheroline elements. The growth is initiated from a circular element placed at the free surface of a granular bed prepared by random pluviation. This circle plays the role of a meristem, which is constantly replicated at a given rate and pushed forward under the action of elastic forces, generating a line of fixed thickness equal to the diameter of the circle and with prescribed stiffness and bending moment. The orientation of the meristem at every growth step is driven by the dynamics of the whole root under the action of its internal elastic forces and reaction forces exerted by the grains. The preliminary model is two-dimensional, which not allows the pore space to be opened as in a 3D situation, consequently limiting root the penetration. To overcome this limitation, we introduce two different diameters for the grains, i.e. a “real” diameter that is considered to calculate grain-grain mechanical interactions, and a smaller “virtual” diameter to take into account root-grains interactions. The difference between the two diameters corresponds to the width of a gap at contact points through which the roots can pass. The ratio of this gap to the root diameter is considered as a model parameter. Parametric studies showed the influence of granular structure and root mechanical properties on root trajectories. The analysis of the evolution of reaction forces exerted by grains on the root tip exhibited a broad distribution of the forces experienced by the root apex during a given growth period. This distribution has the same functional form for each root stiffness when forces are normalized by the mean force. It is characterized by a decreasing power law for forces below the mean force, and by an exponential fall-off for forces above the mean force, thus reflecting the broad distribution of forces inside the granular material. (Texte intégral)

The stabilization of roadside embankments is a major challenge for land managers worldwide. While most studies focused on the short-term influence of revegetation measures (such as planting or hydroseeding) on soil stabilization, little is known about the long-term effect of successional dynamics occurring along roadsides. Our aim is to explore the influence of a vegetation successional dynamic on the stabilization of soil aggregates, a proxy for soil stability, along a 70-years roadside chronosequence. We selected 24 plots (16 x 4 m) on embankments along roadsides in the Mediterranean region (South France), spread into 5 age-classes (0-10; 11-20; 21-30; 31-40 and >40 years-old, Fig.1).[br/] We measured soil aggregate stability and several soil (soil organic carbon, soil nitrogen, soil texture, pH, CEC) and vegetation (root morphology, root mass density, plant community composition) characteristics. We found that soil aggregate stability varied significantly along the successional gradient, from unstable in early-successional plots (0-10 years-old) to very stable in late-successional plots (>40 years-old). More precisely, soil aggregates first appeared stable in the 31-40 years-old age class, reflecting that efficient stabilization of soil embankments by vegetation dynamics required about 3 decades (Fig.2). We notice that the most critical period for embankment stability is restricted to the 0-10 years-old class, characterized by unstable aggregates and thus high erosive risk, while moderate stability is reached from 11-20 years-old class. This highlights the importance to invest in revegetation measures in the first decade after roadside construction. Along the gradient, the accumulation of soil organic carbon related to plant community dynamics appeared as the major factor driving the stabilization of soil aggregates. The increase in root density also enhanced soil aggregate stability. Remarkably, the replacement of herbs species by shrubs and tree species as the succession proceeded was not related to any destabilization of the soils, even though the direct soil coverage is usually reduced by encroachment. To conclude, vegetation successional dynamics are responsible for the long-term stabilization soil aggregates on roadside embankments.

National audience; Dans un contexte de changements climatiques, la fréquence et l’intensité des évènements de sécheresse ne cessent d’augmenter. Une compréhension des mécanismes physiologiques à l’origine d’une meilleure tolérance à la sécheresse est donc nécessaire afin de pouvoir sélectionner des plantes de culture mieux adaptées à cet environnement fluctuant. L’objectif de cette étude est de déterminer si des différences de perception précoce du stress, notamment au niveau membranaire, peuvent expliquer les variations de tolérance au stress hydrique observées entre différents génotypes de la légumineuse modèle Medicago truncatula. Pour ce faire, une core-collection de 16 génotypes de Medicago à laquelle sont ajoutés trois génotypes, le génotype de référence Jemalong A17 et deux génotypes identifiés dans la littérature comme étant tolérants au stress hydrique, ont été étudiés. Ils ont été phénotypés pour leur réponse au PolyEthylène Glycol (PEG) dont le rôle est de mimer le manque d’eau. Les plantes ont été cultivées 15 jours dans des poches en plastique transparent contenant un papier filtre imbibé d’une solution nutritive, laissant ainsi le système racinaire apparent. Au bout d’une semaine, la moitié des plantes a reçu la solution nutritive seule (condition contrôle), tandis que l’autre moitié a reçu la solution nutritive additionnée de PEG (condition stress). Elles ont ensuite été scannées quotidiennement afin de pouvoir suivre le développement du système racinaire : vitesse de croissance, longueur du pivot, apparition des racines latérales, etc. A l’issue des 15 jours de culture, le contenu relatif en eau des feuilles, la surface foliaire et la biomasse des parties aériennes et racinaires ont été mesurées. Ces données ont permis d’identifier des génotypes contrastés pour leur réponse au PEG. En parallèle, trois types de signalisation précoce au niveau membranaire ont été étudiés sur le génotype de référence Jemalong A17 via l’utilisation de sondes fluorescentes en microscopie confocale : le taux d’endocytose avec la sonde FM4-64, le degré d’ordre avec la sonde di-4-ANEPPDHQ et la production de formes actives de l’oxygène (FAO) avec la sonde H2DCFDA. Une augmentation de l’endocytose et du degré d’ordre a été observée mais aucune production de FAO n’a pu être détectée. La prochaine étape de ce projet consistera à étendre ces analyses aux génotypes contrastés pour leur réponse au stress, afin de tester l’hypothèse selon laquelle il existerait un lien entre perception précoce et meilleure tolérance au stress hydrique.

Background In order to maintain high yields while saving water and preserving non-renewable resources and thus limiting the use of chemical fertilizer, it is crucial to select plants with more efficient root systems. This could be achieved through an optimization of both root architecture and root uptake ability and/or through the improvement of positive plant interactions with microorganisms in the rhizosphere. The development of devices suitable for high-throughput phenotyping of root structures remains a major bottleneck. Results Rhizotrons suitable for plant growth in controlled conditions and non-invasive image acquisition of plant shoot and root systems (RhizoTubes) are described. These RhizoTubes allow growing one to six plants simultaneously, having a maximum height of 1.1 m, up to 8 weeks, depending on plant species. Both shoot and root compartment can be imaged automatically and non-destructively throughout the experiment thanks to an imaging cabin (RhizoCab). RhizoCab contains robots and imaging equipment for obtaining high-resolution pictures of plant roots. Using this versatile experimental setup, we illustrate how some morphometric root traits can be determined for various species including model (Medicago truncatula), crops (Pisum sativum, Brassica napus, Vitis vinifera, Triticum aestivum) and weed (Vulpia myuros) species grown under non-limiting conditions or submitted to various abiotic and biotic constraints. The measurement of the root phenotypic traits using this system was compared to that obtained using “classic” growth conditions in pots. Conclusions This integrated system, to include 1200 Rhizotubes, will allow high-throughput phenotyping of plant shoots and roots under various abiotic and biotic environmental conditions. Our system allows an easy visualization or extraction of roots and measurement of root traits for high-throughput or kinetic analyses. The utility of this system for studying root system architecture will greatly facilitate the identification of genetic and environmental determinants of key root traits involved in crop responses to stresses, including interactions with soil microorganisms.