Search

International audience

The impact of a heterogeneous within-crown light environment on carbon allocation was investigated on young walnut trees trained on two branches: one left in full sunlight, the other shaded until leaf fall resulting in 67% reduction in photosynthetically active radiation. In September, the two branches were separately labelled with 14CO2 and 13CO2, respectively, so that the photosynthates from each branch could be traced independently at the same time. Although some carbon movements could be detected within 5 d in both directions (including from the shaded branch to the sun branch), between-branch carbon movements were very limited: approximately 1% of the diurnal net assimilation of a branch. At this time of the year branch autonomy was nearly total, leading to increased relative respiratory losses and a moderate growth deficit in the shaded branch. The ratio of growth to reserve storage rate was only slightly affected, indicating that reserves acted not as a mere buffer for excess C but as an active sink for assimilates. In winter, branch autonomy was more questionable, as significant amounts of carbon were imported into both branches, possibly representing up to 10% of total branch reserves. Further within-plant carbon transfers occurred in spring, which totally abolished plant autonomy, as new shoots sprouted on each branch received significantly more C mobilized from tree-wide reserves than from local, mother-branch located reserves. This allowed great flexibility of tree response to environment changes at the yearly time scale. As phloem is considered not functional in winter, it is suggested that xylem is involved as the pathway for carbohydrate movements at this time of the year. This is in agreement with other results regarding sugar exchanges between the xylem vessels and the neighbouring reserve parenchyma tissues.

absent

A model of within-plant carbon allocation is proposed which makes a generalized use of the Münch mechanism to integrate carbon and water functions and their involvement in growth limitations. The plant is envisioned as a branched network of resistive pathways (phloem and xylem) with nodal organs acting as sources and sinks for sucrose. Four elementary organs (leaf, stem, fruit, root) are described with their particular sink functions and hydraulic attributes. Given the rates of photosynthesis and transpiration and the hydraulic properties of the network as inputs, the model calculates the internal fluxes of water and sucrose. Xylem water potential (Psi), phloem sucrose concentration (C) and turgor pressure (P) are calculated everywhere in the network accounting for osmotic equilibrium between apoplasm and symplasm and coupled functioning of xylem and phloem. The fluxes of phloem and xylem saps are driven by the gradients of P and Psi, respectively. The fruit growth rate is assumed as turgor pressure dependent. To demonstrate its ability to address within-plant competition, the model is run with a simple-branched structure gathering three leaves, eight stem segments, three competing growing fruits and one root. The model was programmed with P-Spice, a software specifically designed for simulating electrical circuits but easily adaptable to physiology. Simulations of internal water fluxes, sucrose concentrations and fruit growth rates are given for different conditions of soil water availability and hydraulic resistances (sensitivity analysis). The discussion focuses on the potential interest of this approach in functional--structural plant models to address water stress-induced effects.

In south-central France, Walnut exhibited freezing tolerance by acclimation in the fall and deacclimation in the spring. This involved a sequence of active processes that result in well-defined changes in cellular composition (starch level in particular). At the same time, the response to freezing by dehydration of cells showed that Walnut trees present also freezing avoidance. We developed a new simple tool for testing cold hardiness and compared it with the classical LT 50 test (electrical leakage conductivity). The new test gave similar results. We observed also similar results for both tests when applied to colddeprived trees (in greenhouse >15°C). Frost hardiness was correlated with carbohydrate reserve status in the both cases (cold-deprived trees and orchard trees).

17 ref.; absent

23 ref. Annexes 3 p.; absent

International audience; Carbon assimilates flow from "source" areas such as leaves to "sink" areas where they are taken up and used. The assimilate fluxes from sources to sinks are mainly dependent on the source-sink distances and on the respective abilities of the different sinks to take up and use the assimilates that are available to them. The widely accepted, basic mechanism of assimilate movement by mass-flow, although conceptually simple, has so far proved too complex for practical modeling purposes in whole tree systems. Four main modeling approaches can be found in current models: (i) models involving empirically determined allocation coefficients; (ii) models based on growth rules, including functional balance or "goal-seeking" principles; (iii) transport-resistance models; (iv) models based on relative sink strength, with two main sub-classes: "hierarchical" and "proportional" models. These different model classes can be conceptually closer to each other than is readily apparent. They are presented in relation to their generality and ability to account for complex architectures or responses to environmental changes. The feedback relationship of allocation to growth is pointed out.; La répartition du carbone entre organes chez les arbres : processus de base et représentation dans les modèles "structure-fonction". Les assimilats carbonés circulent de zones "sources" telles les feuilles, vers des "puits" où ils sont prélevés et utilisés. Ces flux d'assimilats dépendent principalement des distances entre sources et puits ainsi que des capacités respectives des différents puits à prélever et utiliser les assimilats disponibles. Il est largement admis aujourd'hui que le mécanisme de base de la translocation est un flux de masse. Mais malgré sa simplicité conceptuelle, la simulation de ce processus implique des calculs trop complexes pour une modélisation pratique. On trouve actuellement quatre approches modélisatrices principales : (i) l'utilisation de coefficients d'allocation empiriques ; (ii) la mise en œuvre de règles de croissance, notamment des équilibres fonctionnels et autres principes téléonomiques ; (iii) l'analogie électrique avec des résistances ; (iv) des règles de répartition basées sur les "forces" relatives des différents puits (modèles hiérarchiques et modèles proportionnels). Ces diverses classes de modèles sont parfois conceptuellement moins éloignées les unes des autres qu'il n'y paraît. Elles sont présentées en relation avec leur généralité et leur capacité à rendre compte d'une architecture complexe ou des influences de l'environnement. On souligne l'importance des rétroactions entre allocation et croissance.

International audience

International audience; An ecophysiological growth process model, called INCA, for simulating the growth and development of a young walnut tree (Juglans regia L.) during three or four years, is presented. This tool, currently under development, aims at integrating architectural and physiological knowledge of the processes involved, in order to give a more rational understanding of the pruning operation. The model describes a simple three-dimensional representation of tree crown, solar radiation interception, photosynthesis, respiration, growth and partitioning of assimilates to leaves, stems, branches and roots. It supports the hypothesis that the tree grows as a collection of semiautonomous, interacting organs that compete for resources, based on daily sink strengths and proximity to sources. The actual growth rate of organs is not predetermined by empirical data, but reflects the pattern of available resources. The major driving variables are solar radiation, temperature, topological, geometrical and physiological factors. Outputs are hourly and daily photosynthate production and respiration, daily dimensional growth, starch sorage, biomass production and total number of different types of organ. The user can interact or override any or all of the input variables to examine the effects of such changes on photosynthate production and growth. Within INCA, the tree entities and the surrounding environment are structured in a frame-based representation whereas the processes are coded in a rule-based language. The simulation mechanism is primarilybased on the rule chaining capabilities of an inference engine.; L'article présente un modèle écophysiologique de croissance et développement du noyer. INCA vise à intégrer les connaissances architecturales et physiologiques que l'on a sur le sujet, de manière à optimiser les opérations de taille.

Summary Daily fluxes of photoassimilates into young, branched walnut trees were investigated over the whole season through gas exchange measurements. Their partitioning among the different plant organs and functions was assessed by quantitative 14 C labelling in August and October. At harvest, 7 hours or 5 days after labelling, the labelled compounds were partitioned among 4 fractions: starch, sugars, lipids, and the «residue» fraction containing all other compounds, mainly cell walls and proteins. It took ca. five days for the bulk of exportable photoassimilates to be actually exported and metabolized in sink areas. Daily fluxes of recent photoassimilates were derived from applying the 5-day partitioning pattern of the 14 C recovered in the evening of the labelling day to the total C gained over the whole day by net assimilation (daily 43g CO 2 in August, and 10g in October, for a leaf surface area of 3.8 m 2 ). The translocation pattern, which was already highly basipetal in August, became even more so in October; in the same time, the daily fluxes of recent photoassimilates incorporated into all biochemical fractions decreased significantly at the whole plant level. Furthermore, the relative part of sugars in the total exported C doubled, which indicated a slower metabolic rate. However, whereas some organs like the tap-root apparently just slowed down but did not qualitatively change their activity — growth vs. reserve storage, as indicated by the starch : residue labelling ratio —, others like the fine roots exhibited a considerable shift from quasi-exclusive growth to a much more balanced activity. In contrast to the fluxes of recent assimilates incorporated into the plant dry matter, the fluxes allocated to respiration in October were only slightly lower than in August; expressed relative to the total incoming C, they appeared much greater. However, in both situations the part of recent (i.e., up to 5 days old) photoassimilates in the total plant respiration did not exceed 25 %, which stressed the importance of older carbon remobilization.

be a transient sink for the end products of the degradation of lipid reserves. During germination, tap root elongation was preferential over stem growth (fig 3). The tap root accounted for most of the seedling dry matter increase and carbohydrate accumulation mainly as starch (table I). The other organs accumulated essentially soluble carbohydrates. At the end of the experiment, only 26.7% of the carbohydrates (starch + soluble carbohydrates) from lipid conversion were recovered in the seedling and the nut. A similar discrepancy was found in the energy budget. The energy loss from the nut (76.391 kJ) and the total energy recovered in the seedling (30.985 kJ) differed markedly at the end of the experiment (fig 4); this difference of 59% can be attributed to the metabolic lipid conversion, respiration (growth and maintenance) and translocation (table II).

La croissance du chene pedoncule cultive a 25 o C (±1 o C) en jour long, est parfaitement rythmique. La suppression des limbes dont la taille est inferieure a 10 mm, la transforme en croissance continue. La suppression des feuilles d'un etage n ayant atteint leur taille definitive, provoque une tres forte reduction en longueur de l'etage n+1 lorsque celui-ci se developpe. Au cours d'un flush, l'incorporation de la 14 C-DMO (5-5' dimethyloxazolidine 2-4 dione), acide faible lipophile, par le bourgeon terminal, les tissus de l'axe sous-jacent au bourgeon terminal et les feuilles en croissance varie au cours du temps chez une plante intacte (...)

Apres plantation a des dates echelonnees entre les mois de septembre et d'avril, de jeunes plantules de D. alata produites par culture in vitro, de morphologie comparable, ont ete cultivees en conditions irriguees. En plein champ, ces plantes different d'une plantation a l'autre par le developpement et la croissance des parties aeriennes (architecture et taille maximale) et par les rendements en poids de tubercules qui, pour les plantations des mois d'octobre a decembre, deviennent infimes par rapport aux plantations des mois de janvier a avril. [...]

La culture in vitro des ignames Dioscorea alata L. produit des plantes aptes à croître en plein champ après passage par 2 milieux d’adaptation intermédiaires. La morphogenèse initiale de ces vitroplants les distingue du matériel traditionnel obtenu par fragmentation des tubercules, et les apparente au contraire aux jeunes semis d’espèces voisines. Ultérieurement, ces particularités juvéniles sont masquées par l’émergence de grandes lianes semblables à celles du matériel usuel. Comme en culture traditionnelle, la partie aérienne est d’abord seule (avec les racines) à croître pendant plusieurs mois. La mise en réserve dans les tubercules, différenciés pourtant très précocement, ne devient significative qu’après diminution de l’intensité de croissance aérienne. Le nombre et la morphologie des tubercules en fin de cycle sont comparables à ce que l’on observe sur le matériel conventionnel ; mais, dans nos conditions expérimentales, leur poids est inférieur de moitié. On peut les récolter plusieurs semaines avant la disparition totale de l’appareil aérien sans conséquence sur le rendement ni sur le comportement ultérieur des tubercules. Les corrélations entre poids de matière sèche des tubercules et plusieurs paramètres caractérisant le développement de la partie aérienne sont utilisables pour une aide à la prévision des rendements et pour une évaluation de l’efficacité de la plante à convertir l’énergie lumineuse incidente en amidon stocké dans le tubercule., Plantlets of yam (Dioscorea alata L.) from in vitro culture were adapted to field conditions by culturing in two successive, transition media. After planting in April, the early growth pattern of these plantlets was different from that of traditional sets obtained by breaking up tubers, and resembled instead that of young seedlings of related yam species. Later, these juvenile-looking characteristics vanished with the emergence of long vines identical to those of normal yam plants. As observed in normal cultivation, tubers, though present soon after planting, did not grow significantly before August, when the growth rate of the aerial parts fell. At the end of the cycle, the number and shape of tubers was the same as for conventional plants, but their weight was halved (in our experimental conditions). Tubers could be harvested several weeks before vine drying without any consequences for yield or for the subsequent rest period. The correlations between tuber dry matter weight and several parameters which characterize development of the aerial parts could be used to forecast yield and to evaluate the plant’s efficiency in converting incident light into tuber starch.

We studied seasonal variation in xylem sap pH of Juglans regia L. Our main objectives were to (1) test the effect of temperature on seasonal changes in xylem sap pH and (2) study the involvement of plasma membrane H+-ATPase of vessel-associated cells in the control of sap pH. For this purpose, orchard-grown trees were compared with trees grown in a heated (> or = 15 degrees C) greenhouse. During autumn, sap pH was not directly influenced by temperature. A seasonal change in H+-ATPase activity resulting from seasonal variation in the amount of protein was measured in orchard-grown trees, whereas no significant seasonal changes were recorded in greenhouse-grown trees. Our data suggest that H+-ATPase does not regulate xylem sap pH directly by donating protons to the xylem, but by facilitating secondary active H+/sugar transport, among other mechanisms.

Rubber tree (Hevea brasiliensis Mull. Arg.) radial growth dynamics were monitored with displacement sensors, together with latex production, to investigate three aspects of the dual production of latex and wood: (1) the usefulness of fine-scale dendrometric measurements as a physiological tool to detect water shortage through radial growth; (2) the dynamic aspects, both at the seasonal and at the multi-year scale, of the competition between latex and wood production; and (3) the spatial distribution of radial growth rates around the tapping cut. Radial growth of untapped control trees started with the onset of the rainy season and lasted until the onset of the dry season, ceasing completely during the driest period. Displacement sensors provided a sensitive means of detecting water shortage, with a clear correlation between diameter variations and changes in water availability (both daily evapotranspiration and monthly rainfall) over the whole annual cycle. However, the correlation was significantly disturbed in tapped trees. After resumption of tapping, the radial growth rate dropped sharply within two weeks and the effect persisted throughout the whole season, so that the cumulative growth of tapped trees was about half that of untapped trees, with the cumulative growth deficit reaching 80% for the period from mid-June to November. This long-known negative impact of tapping on growth was much stronger in the second year of tapping than in the first, whereas latex production increased significantly between the first and second year of tapping. The increased latex production, which could not be ascribed to climatic conditions, shows that the establishment of an artificial latex sink is a progressive, long-term process likely involving many aspects of metabolism. As expected, ethylene significantly increased latex production in both years; however, ethylene had no effect on the growth rates of tapped trees. Radial growth was differentially affected at different locations around the tapping cut, with growth rates significantly lower in the tapped panel than in the untapped panel, and higher above the cut than below the cut. Thus, caution is needed when deriving whole stem wood production from girth measurements at one location on the stem, especially from girth measurements made close to the tapping cut. This also provides new evidence for the location of the latex regeneration area in the tapped panel, below the cut.

A deterministic and dynamic model of carbon allocation in walnut seedlings is described briefly. The plant is modelled as a network of nodal organs acting as net sources or sinks for carbohydrates. In a sink organ the demand for carbon is the sum of 4 elementary demands: maintenance respiration, structural growth, growth-associated respiration and carbon storage. The organs of the plant are assumed to be in potentially exponential growth phase. The supply of carbon readily accessible to the organs is the store of soluble sugars present in a local reservoir. Carbon flows through the network according to the source/sink activities of the organs. Two carbon sources of different C-13 isotopic ratio are used as known inputs: variable exportation of soluble sugars from the kernel, and gross photosynthesis. The outputs are the predicted fluxes of carbon within the seedling;: carbohydrate allocation to the growing organs, starch accumulation, respiration and C-13 composition of these different fractions. Data for the precise time course of the carbon content and chemical/isotopic composition of the kernel and growing organs (roots, stem, leaves), and gas exchange rates during the first 55 days after sowing were used to calibrate and validate the model. After optimisation of the parameter values, the model provided an accurate description of experimental observations in the seed-plant system during the critical transition from heterotrophy to autotrophy, especially C allocation and partitioning between storage, structural growth and respiration in each organ. The results suggest that the growth of the young plant is supply-limited, except at the earliest stages. As a consequence, intense competition for carbohydrates dominates the relations among organs at that time. It is suggested that similar principles could valuably be applied to describe carbon allocation within elder trees.

International audience

UMR AGAP - équipe AFEF - Architecture et fonctionnement des espèces fruitières; L’occurrence des événements phénologiques de printemps a avancé au cours des dernières décennies du fait du réchauffement climatique. Les modèles phénologiques basés sur les processus sont maintenant utilisés pour prévoir à quelles dates ces événements auront lieu dans les prochaines décennies. Dans ce travail, nous avons cherché à savoir dans quelles mesures ces projections pouvaient être fiables et notamment si les dates de levée de dormance qu’ils estiment sont correctes. En effet les ajustements de ces modèles se font sans information sur ce stade pourtant critique étant donné que la dormance nécessite du froid pour être levée. Nous avons utilisé des séries de dates de levée de dormance et de débourrement/floraison pour le noyer, le pêcher et l’abricotier. Nos résultats montrent que les modèles à deux phases ajustés sans information sur la date de levée de dormance ne donnent pas toujours des prédictions justes de cette date. Nous montrons également que ces modèles donnent des projections pour le futur qui peuvent être très différentes de modèles qui ont été ajustés avec des informations sur les dates de levée de dormance.

Apples, which are the most cultivated fruit in France, are mainly endangered by the fungal pathogen Venturia inaequalis that cause apple scab disease on apple. This disease can be responsible of major products loss unless orchards are treated against apple scab. Nowadays in France, the phytopathological diseases management policies are encouraging growers to reduce considerably the use of pesticides, while keeping a high quality and yield level. In this context, one must understand better how the plant, the pathogen and their environment, interact with each other: for apple scab, the most important environmental parameter is leaf wetness duration. During this work, we studied leaf wetness duration to understand the interactions that occur between the tree microclimate and the wetness duration. To do that we divided our work in three major steps : the modeling of evaporation of a droplet at rest on a leaf, the experimental study of apple leaves wettability, and the experimental study of wetness duration spatial variability within an apple trees orchard. This study led us to clarify the strong intra-crown variability of leaf wetness duration through the consideration of tree structure and hourly dynamics of microclimate. The model we developed, beyond the known links between the evaporative flux intensity and the climatic parameters, showed a strong sensibility of the evaporation duration to the substrate wettability, highlighting the necessity to quantify at best this interaction, through the estimation of static and dynamic contact angles., La pomme, fruit le plus cultivé sur le sol français, est principalement menacée par le pathogène Venturia inaequalis, responsable de la maladie de la tavelure qui génère des pertes considérables si elle n'est pas traitée. La politique actuelle de gestions des risques phytopathologiques en France incite à une forte réduction des traitements phytosanitaires tout en maximisant le rendement et la qualité des productions. Dans ce contexte, il apparaît indispensable de mieux comprendre les interactions entre l'arbre, son pathogène, et leur environnement, qui s'articulent pour le cas de la tavelure du pommier autour de la durée d'humectation des feuilles. Au cours de ce travail nous nous sommes intéressés à ce paramètre pour essayer de mieux comprendre les interactions entre microclimat de l'arbre et durée d'humectation. L'étude s'est déroulée en trois étapes majeures : la modélisation de l'évaporation d'une goutte sur un support végétal, l'étude expérimentale de la mouillabilité des feuilles de pommier, et l'étude expérimentale de la variabilité spatiale de la durée d'humectation sous un couvert de pommiers. Ce travail a permis d’expliciter la forte variabilité intra-couronne de la durée d'humectation via la prise en compte de la structure de l’arbre et de la dynamique horaire du microclimat. Le modèle développé, au delà des liens déjà connus entre l’intensité du flux évaporatif et les variables climatiques, a montré la sensibilité importante du temps d’évaporation à la mouillabilité du support via la forme de la goutte d’eau, mettant en avant la nécessité de quantifier au mieux cette interaction goutte support via l’estimation des angles de contact statiques et dynamiques.

annexes Diplôme : Diplôme d'Ingénieur

Number : 43840065; This study was devoted to the evaluation of diurnal and seasonal carbon flux distribution between different functional sinks. The results showed that tapping activity has a huge physiological effect at the whole trunk scale in any aspect involved with carbon utilization. In comparison with untapped tree, tapping is confirmed to modify the whole physiological behavior of the trunk. A huge depletion of the latex sucrose concentration at whole trunk scale was obviously demonstrated, but the spatial extension of the regeneration area was shown to depend on quantitative rubber production. The latex diagnosis approach allowed a rather precise description of the shape and size of the metabolically active bark area. The multi-clonal linear relation between rubber production and the estimated latex regeneration area indicates that the regeneration of 1 g of dry rubber requires an average of 100 cm2 latex regeneration area. Tapping strongly affected radial growth. However, this effect seems to depend on the distance from the cut. Tapped tree exhibited a higher reserves deposition than untapped, suggesting that latex regeneration induces an extra demand for more reserves to be used for the future. This strong evidence indicates that reserves sink is not a mere passive buffer and the plant tends to keep reserves at a sufficient level, depending on the demand. Starch and sucrose are the main forms of reserved presented in wood tissue, with maximum deposition of reserves at defoliation and massive utilization occurred during annual leaf shedding – refoliation. The difference in pattern and amount of respiration activity due to tapping and ethephon stimulation was well addressed. Highly linear correlation between respiration activity and radius increment in untapped tree will allow establishing the growth coefficient and respiratory cost for wood production. No linear relationship between growth and respiration in tapped tree especially in tapped panel indicates that respiration is mainly devoted to latex production. This will allow estimating the total cost for rubber biosynthesis

annexes Diplôme : Master Professionnel