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High-throughput sequencing (HTS), combined with bioinformatics forde novodiscovery and assembly of plant virus or viroid genome reads, has promoted the discovery of abundant novel DNA and RNA viruses and viroids. However, the elucidation of a viral population in a single plant is rarely reported. In five birch trees of German and Finnish origin exhibiting symptoms of birch leaf-roll disease (BRLD), we identified in total five viruses, among which three are novel. The number of identified virus variants in each transcriptome ranged from one to five. The novel species are genetically - fully or partially - characterized, they belong to the generaCarlavirus, IdaeovirusandCapillovirusand they are tentatively namedbirch carlavirus,birch idaeovirus, andbirch capillovirus, respectively. The only virus systematically detected by HTS in symptomatic trees affected by the BRLD was the recently discovered birch leafroll-associated virus. The role of the new carlavirus in BLRD etiology seems at best weak, as it was detected only in one of three symptomatic trees. Continuing studies have to clarify the impact of the carlavirus to the BLRD. The role of theCapillovirusand theIdaeoviruswithin the BLRD complex and whether they influence plant vitality need to be investigated. Our study reveals the viral population in single birch trees and provides a comprehensive overview for the diversities of the viral communities they harbor.

My thesis subject includes one of the global projects of the UMR UFC/CNRS 6249 Chrono-Environnement entitled "phytoremediation strategies based on the use of trees and associated microorganisms", which is based, among other things, on 2 research projects:•the PROLIPHYT project (Eco-Industry programme, 2013-2018, ADEME) entitled "Production of woody phytoremediants",•the PHYTOCHEM project (ANR CD2i, 2013-2018) entitled "Development of eco-innovative chemical processes to exploit biomasses from phytotechnologies".The general objectives are to improve the phytoremediation potential of a panel of woody species and to develop the microbial potential for assisted phytoremediation on contaminated soil. In addition to limiting the impact of pollutants, this strategy aims to promote the production of biomass on land abandoned and not exploitable by agriculture, while ensuring the biodiversity needed to restore an anthropogenic ecosystem.My thesis work is financed through a ministerial doctoral contract for disability (dyslexia). It is based on the rehabilitation of two industrial sediment storage areas, used until the 2000s. These two experimental sites (INOVYN site of Saint-Symphorien-sur-Saône in Côte-d'Or, CRISTAL site of Ochsenfeld in Alsace) present very particular physico-chemical characteristics which make them privileged places of study. The first is a former settling lagoon whose sediments enriched in Hg, Ba and As come from the treatment of wastewater from SOLVAY's Hg electrolysis process. The second is a lagoon consisting of a backfill in which the titanium dioxide extraction residues from the CRISTAL Thann Plant have been stored since the 1930s. In contrast to the first experimental site, there is a low abundance of flora which results in heterogeneous development of a main woody species, the birch.The natural and spontaneous recolonisation of plants, more particularly woody species on both sites, is undoubtedly the result of close collaboration with telluric microorganisms located near their root systems. We have thus chosen to work on 3 pioneer species that have naturally relocated to the two study sites: willow and poplar for the industrial wasteland of Tavaux and birch for the effluent treatment unit at the Ochsenfeld site.; Mon sujet de thèse intègre l’un des projets globaux de l’UMR UFC/CNRS 6249 Chrono-Environnement intitule « stratégies de phytoremédiation basées sur l’utilisation d’arbres et de microorganismes associés », qui s’appuie, entre autre, sur 2 projets de recherche :•le projet PROLIPHYT (programme Eco-Industrie, 2013-2018, ADEME) intitulé « PROduction de LIgneux PHYtoremédiants»,•le projet PHYTOCHEM (ANR CD2i, 2013-2018) intitulé « Développement de procédés chimiques éco-innovants pour valoriser les biomasses issues des phytotechnologies ».Les objectifs généraux sont d’améliorer le potentiel de phytoremédiation d’un panel d’espèces ligneuses et de développer le potentiel microbien pour une phytoremédiation aidée sur sol contaminé. En plus de limiter l’impact des polluants, cette stratégie vise à promouvoir la production de biomasse sur sols délaissés et non exploitables par l’agriculture, tout en assurant la biodiversité nécessaire à la restauration d’un écosystème anthropogénique.Mon travail de thèse est financé au travers un contrat doctoral ministériel handicap (dyslexie). Il s’appuie sur la réhabilitation de deux zones de stockage de sédiments industriels, utilisés jusque dans les années 2000. Ces deux sites expérimentaux (site INOVYN de St Symphorien-sur-Saône en Côte d’Or, site CRISTAL de l’Ochsenfeld en Alsace) présentent des caractéristiques physico-chimiques très particulières qui en font des lieux d’étude privilégiés. Le premier est une ancienne lagune de décantation dont les sédiments enrichis en Hg, Ba et As proviennent du traitement des eaux usées issues du procédé d’électrolyse à Hg de l’entreprise SOLVAY. Le second est une lagune constituée d’un remblai dans lequel ont été stockés depuis les années 1930, les résidus d’extraction du dioxyde de titane de l’Usine CRISTAL de Thann. A l’inverse du premier site expérimental, on observe une flore peu abondante qui se traduit par un développement hétérogène d’une espèce ligneuse principale, le bouleau.La recolonisation naturelle et spontanée de végétaux, plus particulièrement d’espèces ligneuses sur les deux sites est sans doute le résultat d’étroites collaborations avec des microorganismes telluriques situés aux abords de leur système racinaire. Nous avons ainsi choisi de travailler sur 3 espèces pionnières qui se sont naturellement réimplantées sur les deux sites d’études : le saule et le peuplier pour la friche industrielle de Tavaux et le bouleau pour l’unité de traitement des effluents du site de l’Ochsenfeld.

Les allergies sont classées au quatrième rang mondial des pathologies selon l’organisation mondiale de la santé. Parmi elles, les allergies respiratoires constituent un véritable problème de santé publique, la proportion de sujets allergiques ne cessant de progresser depuis ces trois dernières décennies. Les pollens, et notamment les pollens des Fagales, sont l’une des causes de ces allergies. Difficilement évitables, les patients allergiques sont alors sujets aux conjonctivites et/ ou rhinites allergiques, avec une possible évolution vers un asthme allergique. Outre les facteurs génétiques, la maitrise des facteurs environnementaux occupe une place importante dans la prise en charge de ces patients. Des informations concernant la qualité de l’air ainsi que les dates des saisons polliniques sont fournies aux patients, et aux professionnels de santé, par les réseaux de surveillance de la qualité de l’air répartis sur le territoire français. L’étude du mécanisme de l’hypersensibilité de type I, mécanisme immunitaire intervenant lors des allergies aux pollens, a permis de concevoir différents outils de diagnostics, ainsi que de mettre en évidence plusieurs cibles pharmacologiques à l’origine du panel thérapeutique actuellement disponible. Ces traitements font l’objet de conseils pharmaceutiques associés, de par leurs précautions d’emplois, leurs effets indésirables ou leurs contre-indications, lors de leur délivrance dans le but de lutter contre le mésusage des médicaments et donc d’améliorer l’observance et l’efficacité de ces derniers. En parallèle des traitements allopathiques, le pharmacien peut conseiller des traitements complémentaires, tels que l’homéopathie, la phytothérapie ou l’oligothérapie. Enfin, il est important de rappeler régulièrement certains conseils à appliquer lors de départs en voyage, ou même au quotidien, afin de limiter les risques d’exposition aux allergènes ou d’irritation des voies respiratoires.

International audience; Les systèmes d'exploitation de l'écorce de bouleau à la fin de la Préhistoire dans le nord-ouest méditerranéen révélés par une approche interdisciplinaire à la croisée de la chimie, de l'archéobotanique et de l'archéologie spatiale

International audience; Vibration welding of wood that has been preheated according to an industrial two-step process indicates that such wood can be welded and can yield welded joints of good strength. The joint strength is, however, markedly lower than obtained when welding non-heat-treated timber. In general, weld strength of the timber is poor if welding is done on hydrothermolyzed wood. The strength results are instead much better if welding is done at the end of the complete heat treatment process, i.e., after the dry heat step. The weld lines of heat-treated wood show entangled cells where there is none or very little of the molten matrix intercellular material usually observed in welded timber. Furthermore, in weldlines obtained after hydrothermolysis an increase in rigidity and brittleness of the wood cells is observed. Hence, the wood cells are not entangled at all or very little. Both observations indicate that heat treatment has affected the main melting region of the wood, namely the intercellular material. As most of this material is already either lost or heavily cross-linked during heat treatment, only little of it is now available to melt and bind the wood surfaces during vibrational wood welding

The aim of the present work was to provide a synopsis of the scientific literature concerning the effects of different tree spe- cies on soil and to quantify the effect of common European temperate forest species on soil fertility. The scientific literature dealing with the tree species effect on soil has been reviewed. The composition of forest overstory has an impact on the chemical, physical and biolo- gical characteristics of soil. This impact was highest in the topsoil. Different tree species had significantly different effects on water ba- lance and microclimate. The physical characteristics of soils also were modified depending on the overstory species, probably through modifications of the soil fauna. The rates of organic matter mineralization and nitrification seem to be dependent on tree species. A coni- ferous species, Picea abies, had negative input-output budgets for some nutrients, such as Ca and Mg. This species promoted a higher soil acidification and a decrease in pH. Thus, it should not be planted in very poor soils in areas affected by acidic atmospheric deposi- tions. Nevertheless, the effect of the canopy species on soil fertility was rarely significant enough to promote forest decline. The impact of a tree species on soil fertility varied depending on the type of bedrock, climate and forest management. forest soils / tree species / fertility / sustainability / resiliency

International audience

La fabrication du brai de bouleau : données expérimentales, sources historiques et ethnographiques

National audience; To better understand the interactions between the ecosystems and the climate, it is necessary to understand how global hanges affect Green House Gas (GHG) fluxes. In natural environment, and especially in peatlands, spatio-temporal variability are very important and still remains to be studied in detail. Furthermore, these fluxes, closely related to the vegetation and hydrological conditions, occur through different pathways: diffusion, transport through plants, ebullition. This last form of emission, because it is abrupt and occasional, is difficult to grasp and quantify with traditional Gas Chromatography techniques. Here we report the observations and quantification of CH4 emission through bubbles with a new high frequency infra-red spectrometer.; Afin de mieux comprendre les interactions entre les écosystèmes et le climat, il est nécessaire de comprendre comment les changements globaux affectent les flux de gaz à effet de serre (GES). Dans les milieux naturels, et particulièrement dans les tourbières, la variation spatio-temporelle des flux GES est très importante et reste encore à déterminer avec précision. De plus, ces flux, fortement dépendant du couvert végétal et des conditions hydriques, peuvent se produire selon différents modes : diffusion, transport par les végétaux vasculaires, émission de bulles. Cette dernière forme d'émission étant de nature abrupte et ponctuelle dans le temps, les techniques traditionnelles de chromatographie en phase gazeuse ne permettent pas facilement de la mettre en évidence et encore moins de la quantifier. Grâce à des développements technologiques récents, nous rapportons ici l'observation et la quantification d'émission de bulles de CH4 dans une tourbière de Sologne.

he reliability of a double-ended pressure sleeve technique was evaluated on three woody angiosperm species with contrasting maximum vessel lengths. Vulnerability curves (VCs) were constructed by varying sample length and the size of the pressure sleeves. VCs were compared against curves obtained with reference techniques. For the two diffuse-porous species, Betula pendula and Prunus persica, VCs built with shoot segments shorter than maximum vessel length strongly overestimated species vulnerability. Furthermore, increasing the size of the pressure sleeve also tended to lead to overestimated VCs. For the ring-porous species Quercus robur, the technique strongly overestimated vulnerability to embolism, whatever the sample length or chamber tested. In conclusion, the double-ended pressure sleeve technique only gives reliable VCs on diffuse-porous angiosperms with short pressure sleeves, only when segments are longer than maximum vessel length.

Several techniques have been developed to quantify the degree of embolism of the xylem using hydraulic conductance. Although there have been several improvements to these techniques, their reliability is still questionable and many technical pitfalls persist. We are proposing here a manometric approach to improve the accuracy of xylem cavitation measurement by the original air-injection technique which uses twigs exposed to pressurized air to cause cavitation. The measured parameter is air bubble production (P (b)) caused by xylem cavitation in birch (Betula pendula Roth) twigs from which the percent increase in bubble production is calculated to quantify xylem cavitation. Data produced by three different methods (bench-drying, air-injection, and manometric approach) are compared. Xylem vulnerability curves (VCs) constructed by the reference and reliable bench-drying technique and the manometric approach show similar sigmoid "S" shape, but a small anomaly appeared in the VC constructed by the original air-injection technique. The xylem pressure inducing 50% of embolism (P (50)) was the same with the three techniques. Furthermore, there was a strong positive correlation between the estimators of xylem cavitation measured by the three different methods. For its reliability, precision and ease we recommend the manometric technique as an improved version of the original hydraulic air-injection method.

International audience; An increasing body of evidence indicates that the association between different plant species may lead to a reduction in insect herbivory, i.e. associational resistance. This might be due to a top–down regulation of herbivores by increased numbers of natural enemies or to a disruptive bottom–up influence of lower host plant accessibility. In particular, the richer plant communities release more diverse plant odours that may disturb olfactory-guided host choice and mating behaviour of insect herbivores, i.e. the “semiochemical diversity hypothesis”. However, this hypothesis has been rarely tested experimentally in natural habitats, notably forest ecosystems. We tested the effects of non-host volatiles (NHV) on mate and host location by the pine processionary moth (PPM) at the scale of individual pine trees with branches of non-host tree (birch) at their base. Pheromone trap catches and the numbers of larval nests were both reduced by non-host presence under treated pine trees, confirming an associational resistance mediated by NHV. In both males and females, the antenna could detect several birch volatiles, including methyl salicylate (MeSa). MeSa inhibited the attraction of the PPM male to pheromone traps, as did bark and leaf chips from birch trees. Our test of three doses of MeSa at the habitat scale (50 m forest edges) showed that the reduction in the numbers of male PPM captured in traps and in larval nests was MeSa dose-dependent. These results show that odours released by deciduous non-host trees can reduce herbivory by a forest defoliator in conifers, providing support to the “semiochemical diversity hypothesis” as a mechanism of associational resistance.

Processes involved in leaf photosynthetic acclimation to light and throughout the growing season were investigated in two hardwood species (Acer saccharum and Betula alleghaniensis), which differed in their level of shade-tolerance. For both species, variation in traits related to (i) leaf morphology (LMA, leaf mass:area ratio), (ii) leaf N content (N(A), leaf nitrogen content on an area basis and N(M), N concentration in leaf dry mass), (iii) leaf N partitioning among photosynthetic functions (P(r), N allocated to Rubisco, and P(b), N allocated to bioenergetics), and (iv) leaf photosynthetic capacity (V(cmax), maximal carboxylation rates, and J(max), maximal light-driven electron flow) were assessed at three different times during the growing season (early, mid- and late summer) and under four contrasting light regimes (40, 17,6 and 2% of full sunlight). For both species, light-driven variation in most traits was greater than their seasonally driven variation. Furthermore, results showed for both species the pre-eminence of LMA changes in the light-driven acclimation of N(A). Importance of N(M) to variation in N(A) was restricted to seasonal acclimation, especially for the less shade-tolerant species, B. alleghaniensis. Similarly, for both species, light-driven acclimation of leaf photosynthetic capacities was tightly related to variation in N(A), which was related to LMA changes. However, variation in P(r) and P(b) better explained seasonally driven variation in V(cmax) and J(max), specifically under lower light levels, where N(A) was low. Thus, the great variability observed for leaf activity in response to contrasting light environments was related to efficient morphological adjustments, regardless of species level of shade-tolerance. Finally, physiological adjustments were mainly involved in fine-scale changes observed during seasonally driven acclimation of leaves, when LMA was constrained to a slight range of variation.

International audience; Du brai de bouleau en Corse à l’Âge du Fer : nouvelles données chimiques, environnementales et archéologiques

Canopy closure and soil characteristics are commonly used to explain regeneration distribution at local and regional scales, although very few studies take both factors into account. The combination of environmental variables defined at broad and local scales is necessary to provide regeneration distribution models with a small resolution (tree scale) that are valid on a large spatial scale (regional scale). Our aim was to quantify how gap partitioning among tree species at the seedling stage varies across large soil and stand type gradients. Regeneration inventories performed 5 years after gap creation were used to analyse the combined effects of soil type, stand type, and position within canopy gaps on the regeneration development of eight western European broadleaved species: Acer campestre, Acer pseudoplatanus, Betula pendula, Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Quercus sp., and Salix caprea. A clear pattern of gap partitioning among the eight species was observed. All species had higher density at the gap edge except birch and willow showing the highest presence in gap centres. For all species, the probability of presence of tall seedlings (height > 0.5 m) increased from gap edge to gap centre. Small seedlings presented the opposite trend except birch and willow. Soil pH influenced probability of presence for each species, but did not affect the pattern of gap partitioning among species. Both local (location within the gap) and regional (soil pH and stand type) scale factors affect recruitment distribution and are thus necessary to predict seedling distribution. The models developed may be used to determine the optimal gap size in order to obtain a given species composition according to soil and stand type conditions.

National audience

International audience; This study was designed to examine saprophytic fungi diversity under different tree species situated in the same ecological context. Further, the link between the diversity and decomposition rate of two broadleaved, two coniferous and two mixed broadleaved-coniferous litter types was targeted. Litter material was decomposed in litter bags for 4 and 24 months to target both early and late stages of the decomposition. Fungal diversity of L and F layers were also investigated as a parallel to the litter bag method. Temperature gradient gel electrophoresis fingerprinting was used to assess fungal diversity in the samples. Mass loss values and organic and nutrient composition of the litter were also measured. The results showed that the species richness was not strongly affected by the change of the tree species. Nevertheless, the community compositions differed within tree species and decomposition stages. The most important shift was found in the mixed litters from the litter bag treatment for both variables. Both mixed litters displayed the highest species richness (13.3 species both) and the most different community composition as compared to pure litters (6.3–10.7 species) after 24 months. The mass loss after 24 months was similar or greater in the mixed litter (70.5% beech–spruce, 76.2% oak–Douglas-fir litter) than in both original pure litter types. This was probably due to higher niche variability and to the synergistic effect of nutrient transfer between litter types. Concerning pure litter, mass loss values were the highest in oak and beech litter (72.8% and 69.8%) compared to spruce and D. fir (59.4% and 66.5%, respectively). That was probably caused by a more favourable microclimate and litter composition in broadleaved than in coniferous plantations. These variables also seemed to be more important to pure litter decomposition rates than were fungal species richness or community structure.

International audience; The study of the fate of assimilated carbon in respiratory fluxes in the field is needed to resolve the residence and transfer times of carbon in the atmosphere– plant–soil system in forest ecosystems, but it requires high frequency measurements of the isotopic composition of evolved CO2.We developed a closed transparent chamber to label the whole crown of a tree and a labelling system capable of delivering a 3-h pulse of 99% 13CO2 in the field. The isotopic compositions of trunk and soil CO2 effluxes were recorded continuously on two labelled and one control trees by a tuneable diode laser absorption spectrometer during a 2-month chase period following the late summer labelling. The lag times for trunk CO2 effluxes are consistent with a phloem sap velocity of about 1 m h_1. The isotopic composition (d13C) of CO2 efflux from the trunk was maximal 2–3 days after labelling and declined thereafter following two exponential decays with a half-life of 2–8 days for the first and a half-life of 15– 16 days for the second. The isotopic composition of the soil CO2 efflux was maximal 3–4 days after labelling and the decline was also well fitted with a sum of two exponential functions with a half-life of 3–5 days for the first exponential and a half-life of 16–18 days for the second. The amount of label recovered in CO2 efflux was around 10–15% of the assimilated 13 CO2 for soil and 5–13% for trunks. As labelling occurred late in the growing season, substantial allocation to storage is expected.

The presence of Betula in Turkey over the last 15,000 years has been studied on the basis of the pollen record. It seems that modem birch pollen merely is “background noise”, mostly noticeable in the north, where wind-borne pollen from Europe may be precipitated by rainfall. Subfossil evidence demonstrates that a shift in the distribution of birch took place from the west to the east, probably connected with an upward shift in the upper tree-line during the Holocene. Conditions for birch growth around this limit are nowadays found only on the high mountains in eastern Turkey., La présence de Betula en Turquie au cours des derniers 15.000 ans a été envisagée sur la base des données pollenanalytiques. Il semble que les occurrences modernes de pollen de bouleau correspondent plutôt à un «bruit de fond», relevé principalement dans le nord, où le pollen transporté par le vent en provenance d’Europe peut précipiter sous l’effet de la pluie. Les séquences plus anciennes montrent un glissement de la distribution de bouleau d’ouest en est probablement lié un déplacement vers le haut de la limité supérieure des forêts au cours de l’Holocène. Les conditions permettant le développement du bouleau au voisinage de cette limite ne se rencontrent aujourd’hui que dans les hautes montagnes de Turquie Orientale., Bottema Sytse. Notes on the history of the genus Betula in Turkey during the Late Quaternary. In: Ecologia mediterranea, tome 16,1990. pp. 145-150.

Diplôme : Master; Water transport in plants occurs under a negative pressure. Edaphic drought can cause sap cavitation. Cavitation leads a vessel to embolism, that is to say a total loss of conductivity. In order to study water stress acclimatation, we put two variety of trees beech and silver birch under three levels of water stress. The result was a significant drop in water potential, evaporative rate, hydraulic conductivity and growth rate. Pits are structures of the xylem wall involved in the seeding of cavitation. Pit’s stucture is composed only of the primary, pectin-rich, porous cell wall. Pectin structure is shaped and modified by enzymes in response to various stimuli, including stresses. In order to know if these CAZy play a role in water stress response we cloned three of them.; En condition de sécheresse édaphique, la tension exercée devient telle que les colonnes d’eau des vaisseaux du xylème peuvent se rompre (caviter). Les vaisseaux deviennent incapables de conduire la sève, on parle alors d’embolie. Afin d’étudier les possibilités d’adaptation au stress hydrique de deux arbres, le hêtre et le bouleau, nous les avons soumis à trois niveaux de contraintes hydriques et avons mesuré l’impact de notre traitement sur la croissance et quelques caractères hydrauliques de ces arbres. La contrainte hydrique a eut pour effet une réduction notable de la transpiration, du potentiel hydrique, de la croissance et de la conductivité hydraulique. Des éléments de la paroi des vaisseaux du xylem appelés ponctuations permettent le passage de l’eau d’un conduit à l’autre et seraient impliquées dans l’apparition de la cavitation. La structure de ces ponctuations, très riche en pectine, est soumise à de nombreuses régulations enzymatiques en réponses à de nombreux stimuli et stress. Nous avons clonés trois gènes codant pour ces CAZy dans le but d’étudier leur rôle éventuel dans la réponse au stress hydrique.

International audience

International audience; Chlorophyll (Chl) and epidermal polyphenol (EPhen) contents were estimated in vivo using two optical leaf-clips, SPAD-502 and Dualex, respectively. The area-based measurements were transformed into mass-based data by taking into account the leaf dry mass per area (LMA). Measurements were performed on forest trees and on saplings grown under controlled conditions. While LMA increased with irradiance along a vertical transect in a beech canopy or in saplings grown under different and increasing irradiance levels, mass-based EPhen (EPhenm) increased, whereas mass-based Chl (Chlm) decreased. This was a signature of a gradual switch of investment from protein into polyphenol production. A similar signature was obtained in saplings grown on nitrogen-deficient soil with respect to fertilized controls. However, nitrogen effects remained moderate compared to irradiance-induced effects. EPhenm and Chlm both declined with plant ageing-induced increases in LMA, under all tested growth conditions. This was a signature of an accumulation of dry matter that diluted Chl and EPhen. The described competition between Chl and EPhen in leaves fits well with the predictions of the Protein Competition Model (PCM), that is, that the total leaf mass-based polyphenols content (Phent) is controlled by the competition between protein and polyphenol biosynthetic pathways and its metabolic regulation

Diplôme : Diplôme d'Ingénieur

We assessed the irradiance-related plasticity of hydraulic architecture in saplings of Betula pendula Roth., a pioneer species; Acer pseudoplatanus L., Fraxinus excelsior L., Quercus robur L., and Quercus petraea Matt. Liebl. which are post-pioneer light-requiring species; and the relatively shade-tolerant Fagus sylvatica L. Plants were grown in pots in 36%, 16% and 4% of full sunlight. Hydraulic conductance was measured with a high-pressure flow-meter in entire, in situ root systems and in excised shoots. Leaf-specific whole-plant conductance (LSC) increased with irradiance, due, in part, to an effect of irradiance on plant size. In addition, there was a size-independent effect of irradiance on LSC due, in part, to an increase in root hydraulic conductance paralleled by an increase in root biomass scaled to leaf area. Changes in shoot conductivity also contributed to the size-independent plasticity of LSC. Vulnerability to cavitation measured in current-year twigs was much larger in shade-grown plants. Betula pendula had the highest whole-plant, root and shoot conductances and also the greatest vulnerability to cavitation. The other species were similar in LSC, but showed some variation in root conductance scaled to biomass, with Q. robur, Q. petraea and E sylvatica having the lowest root conductance and susceptibility to cavitation. All species showed a similar irradiance-related plasticity in LSC.

International audience

International audience

The development of ectomycorrhizal symbiosis leads to drastic changes in gene expression in both partners. However, little is known about the spatial regulation of symbiosis-regulated genes. Using cDNA array profiling, we compared the levels of expression of fungal genes corresponding to approximately 1,200 expressed sequenced tags in the ectomycorrhizal root tips (ECM) and the connected extraradical mycelium (EM) for the Paxillus involutus - Betula pendula ectomycorrhizal association grown on peat in a microcosm system. Sixty-five unique genes were found to be differentially expressed in these two fungal compartments. In ECM, a gene coding for a putative phosphatidylserine decarboxylase (Psd) was up-regulated by 24-fold, while genes coding for urea (Dur3) and spermine (Tpo3) transporters were up-regulated 4.1- and 6.2-fold in EM. Moreover, urea was the major nitrogen compound found in EM by gas chromatography-mass spectrometry analysis. These results suggest that (i) there is a spatial difference in the patterns of fungal gene expression between ECM and EM, (ii) urea and polyamine transporters could facilitate the translocation of nitrogen compounds within the EM network, and (iii) fungal Psd may contribute to membrane remodeling during ectomycorrhiza formation.

Leaf or needle ozone uptake was estimated for young trees at seven experimental sites across Europe using a stomatal conductance simulation model. Dose–response relationships based on cumulative leaf uptake of ozone (CUO) were calculated using different hourly ozone flux thresholds and these were compared to dose–response relationships based on daylight AOT40, which is currently used within the UNECE Convention on Long-Range Transboundary Air Pollution (CLRTAP). Regression analysis showed that the CUO–biomass response relationships were highly significant for both coniferous and broadleaf trees, and independent of which ozone flux threshold was applied. On the basis of this regressions analysis, an hourly flux threshold of 1.6 nmol m −2 s −1 (CUO>1.6) is proposed as the most appropriate for all species categories in deriving dose–response relationships. The analysis indicated that the current critical level for ozone impacts on European forests of AOT40 10 ppm h may not protect the most sensitive receptors and that critical levels for AOT40 and CUO>1.6 of 5 ppm h and 4 mmol m −2 , respectively, are more appropriate. The research identified weaker dose–response relationships for the CUO exposure index compared with AOT40. Distinguishing between sensitive and less sensitive species substantially improved the CUO–biomass response relationships although, still, to a lesser extent than when exposure was expressed as AOT40.

International audience

La santé des forêts (France) en 2000 et 2001; National audience

INRA URM Physiologie intégrée de l'arbre fruitier et forestier Domaine de Crouelle 63039 Clermont-Ferrand (FRA) Diffusion du document : INRA URM Physiologie intégrée de l'arbre fruitier et forestier Domaine de Crouelle 63039 Clermont-Ferrand (FRA); absent

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