Технология моделирования штормовых нагонов и ветрового волнения в Азовском море на неструктурированных сетках

Представлена технология численного моделирования штормовых нагонов и ветровых волн в Азовском море, объединяющая модель циркуляции вод ADCIRC и модель ветрового волнения SWAN. Обе модели реализованы на неструктурированной сетке и адаптированы для параллельных вычислений. Приведены результаты верификации численного алгоритма и анализ его чувствительности к вариациям входных параметров.Представлена технологія чисельного моделювання штормових нагонів і вітрових хвиль в Азовському морі, що об'єднує модель циркуляції вод ADCIRC і модель вітрового хвилювання SWAN. Обидві моделі реалізовані на неструктурованій сітці і адаптовані для паралельних обчислень. Наведено результати верифікації чисельного алгоритму і аналіз його чутливості до варіацій вхідних параметрів.The technology of numerical modeling of storm surge and wind waves in the Sea of Azov, unifying model of the ADCIRC ocean circulation model and SWAN wind waves model. Both models are implemented on unstructured mesh and adapted for parallel computing. The results numerical algorithm verification and analysis of its sensitivity to variations in input parameters are given

Etude de la signature isotopique du carbone (delta13C) du CO2 respiré et du cerne en relation avec le fonctionnement de l arbre

Dans le contexte actuel de l augmentation de la concentration en CO2 dans l atmosphère, l étude du fonctionnement des forêts tempérées comme puits ou sources de C est essentielle. Les études fonctionnelles à des échelles plus fines, comme celle de l arbre, permettent d améliorer les estimations des flux de C dans les écosystèmes forestiers. Ce travail de thèse examine principalement les signaux isotopiques (quantité de 13C par rapport au 12C, delta13C) de deux composantes du bilan carboné à l échelle de l arbre : 1) Le delta13C du CO2 respire par l arbre avec en particulier la caractérisation des variations temporelles du delta13C du CO2 respiré par le tronc en relation avec le fonctionnement de l arbre. Nos résultats montrent une forte variabilité du delta13C du CO2 respiré par le tronc due à des changements à la fois de delta13C des substrats respiratoires et de l intensité d utilisation de ces substrats. 2) Le delta13C du cerne comme indicateur du fonctionnement de l arbre en réponse au climat. Ce travail a montré que lors de la formation du bois final, les variations du delta13C des sucres assimilées par les feuilles sont transmises et enregistrées dans le delta13C du cerne. Ces résultats valident par une approche fonctionnelle l utilisation du delta13C du cerne comme archive des réponses fonctionnelles de l arbre au climat. En améliorant la compréhension des signaux isotopiques, ce travail de thèse permet d avancer dans leur interprétation à des échelles spatio-temporelles plus grandes, comme dans l étude des composantes du bilan de C à l échelle de l écosystème ou des réponses des forêts aux variations inter-annuelles du climat.Because of the current atmospheric CO2 increase, study of temperate forest functioning as C source or sink becomes essential. Functional studies at smaller scales, like tree scale, allow to improve C flux estimates at the forest level. This thesis work mainly examines isotopic signals (13C quantity compared to 12C, delta13C) of two components of tree-C balance : 1) delta13C of CO2 respired by tree and characterization of its temporal variations, in relation to tree functioning. Our results showed a high variability of respired CO2 delta13C due to changes either in respiratory substrate delta13C or in intensity of substrate use. 2) Ring delta13C as an indicator of tree functioning in response to climate changes. This work showed that during latewood formation, variations of delta13C of new assimilated sugars were transmitted and recorder in the ring delta13C. These results validate, by a functional approach, the use of ring delta13C as an archive of tree functional responses to climatic conditions. These studies improve the understanding the tree isotopic signals and their interpretation at larger spatial and temporal scales, like in the study of ecosystem C balance or in the study of forest responses to inter-annual climate changes.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Field study of leaf photosynthetic performance by a Mediterranean deciduous oak tree {Quercus pubescens) during a severe summer drought

Quercus pubescens Willd. is a winter deciduous oak species which co-occurs in the Mediterranean area with an evergreen oak, Q. ilex. As the knowledge of Q. pubescens assimilation patterns is poorly documented, we monitored leaf physiological parameters throughout a growing season. In summer, drought was particularly severe, and sotne trees experienced pre-dawn water potentials (fp^) as low as-4'5 MPa. Diurnal courses of net photosynthesis, stomatal conductance and I photochemical efficiency of photosystem 11 (PS II) were recorded on four trees in the field. Maximum assimilation rates (10-16-5 //mol m"^ s'\ depending on sampled trees) occurred in spring. Leaf carbon gain recovered in autumn even after water potential fell to-34 MPa. During progressive drought, Y^d ecreased substantially, leaf gas exchange was reduced and showed an important diurnal depression. At-2 MPa (f.,a), net photosynthesis and stomatal conductance were still about 5 /tmo! m"^ s"' and 50 mmol m"^ s"^, respectively. Pre-dawn maximal PS 11 photochemical efficiency was stabJe to-4 MPa. The diurnal decrease in photochemical efficiency of PS II (Fv/Fm), measured after 30 min of dark adaptation, was enhanced during drought but maxima] values always recovered at sunset, i.e. leaves only experienced short-term reversible PS II inhibition induced by high light and temperature. In conclusion, Q. pubescens displays a strategy of tolerance to drought and an efficient protection against high irradiance

Etude de l'assimilation de carbone par le compartiment ligneux aérien de l'arbre

L'assimilation de carbone des plantes est principalement assurée par la photosynthèse foliaire mais d'autres organes tels que les tiges des espèces ligneuses sont capables de photosynthétiser. L'objectif principal de cette thèse a été d examiner chez les arbres, les processus écophysiologiques et biochimiques, encore très peu étudiés, de la photosynthèse des jeunes tiges. L étude s est focalisée sur le hêtre (Fagus sylvatica L.) et d'autres espèces tempérées. Les résultats montrent une variabilité interspécifique et saisonnière de l'assimilation de carbone. La photosynthèse brute mesurée à éclairement saturant est positivement corrélée aux contenus en chlorophylle et en azote des tiges, aussi bien en interspécifique qu en intraspécifique. L'activité totale Rubisco est très faible, comparée aux feuilles, alors que l'activité PEPC montre une activité jusqu'à 13 fois supérieure chez la tige. Ajoutée à la configuration concentrique des tissus et aux observations de distribution de la chlorophylle dans la tige, la forte activité PEPC mesurée chez la jeune tige de hêtre a soulevé l'hypothèse d'un métabolisme de type C4 dans la tige. Nous montrons qu'il n'y a pas de distribution radiale préférentielle ni de la Rubisco, ni de la PEPC dans les tiges et que les caractéristiques biochimiques de la PEPC sont typiques de plantes en C3. En terme de fonctionnement, la photosynthèse des tiges est similaire à celles des feuilles et la PEPC semble jouer un rôle relativement important dans la refixation de carbone dans la tige. Ce travail ouvre plusieurs perspectives notamment sur le devenir des assimilats des tiges et l importance de la photosynthèse des tiges dans le bilan de carbone.Plant carbon assimilation is mainly provided by leaf photosynthesis. However, other plant organs, like woody stems are able to photosynthesize. The main goal of this thesis was to investigate the little-studied ecophysiological and biochemical processes of photosynthesis in the young stems of trees. The study particularly focused on the European beech (Fagus sylvatica L.) and some other temperate tree species. Gas exchange, chlorophyll fluorescence, enzyme activities, chlorophyll and nitrogen content measurements were achieved. Results show an interspecific and a seasonal variability of stem carbon assimilation. Light-saturated gross photosynthesis is positively correlated to the chlorophyll and nitrogen contents. In comparison with leaves, the Rubisco total activity measured in young stems is very low while PEPC activity is up to 13 times higher. Coupled with the concentrically organized tissues of tree stem and the observations of chlorophyll distribution shown by epifluorescence microscopy, the high stem PEPC activity suggested the possibility of a C4-type metabolism in young stems of beech. Immunogold labelling does not reveal any differential localization of PEPC and Rubisco and leaf and stem PEPCs exhibit classical biochemical characteristics of C3 PEPCs. All these results allow us to conclude that the stem photosynthesis functioning is similar to the one of the tree leaves and that PEPC seems to play a relatively important role in stem carbon refixation. This work opens several prospects on stem carbon assimilation, especially on the stem photoassimilates allocation and the importance of stem photosynthesis in tree carbon balance.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Effect of soil nitrogen supply on carbon assimilation by tree stems

• Nitrogen (N) is one of the most important resources for plants, generally enhancing leaf photosynthesis because a large part of it is allocated to Rubisco and thylakoïds. This is well known in leaves where photosynthesis (i.e. gas exchange, Rubisco activity, chlorophyll content) is positively correlated to leaf N content. • In order to test this hypothesis in stems, N concentration, CO2 exchange and also Rubisco and PEP carboxylase activities were measured in summer on current-year stems of young European beeches (Fagus sylvatica L.) growing on soils of different N content. • The CO2 refixation rate of stems increased from 58.5% to 74.3% when stem N concentration increased from 5.7 to 10.1 mg g−1 DW. A hyperbolic relationship was obtained between stem gross photosynthesis and N concentration, with an x-intercept of 0.3 mmol N g−1 DW. Stem PEP carboxylase activity was higher in stems than in leaves and increased with stem N concentration whereas Rubisco activity did not change between treatments in both tissues. • In spite of a low nitrogen investment in stem photosynthesis (low PNUE), these results suggest that (1) stems invest more N in CO2 refixation when more N is widely available, (2) stem photosynthesis is able to operate at low N concentration and (3) stem PEP carboxylase is involved in stem carbon refixation, but also simultaneously supplies carbon skeletons for N assimilation

Croissance et 13C des cernes de trois essences forestières tempérées (Fagus sylvatica, Quercus petraea et Pinus sylvestris) face aux variations climatiques à l'échelle interannuelle et saisonnière

Il est probable que les changements climatiques futurs diminuent la croissance forestière en région tempérée. Cette vulnérabilité des espèces face aux contraintes du climat peut être étudiée via les cernes des arbres. Ces derniers sont en effet des archives du carbone utilisé par les arbres pour leur croissance, en lien avec les caractéristiques spécifiques de gestion du carbone et de réponse au climat. L objectif principal de cette thèse est de déterminer, à partir des cernes, les réponses fonctionnelles de trois essences forestières tempérées (Fagus sylvatica, Quercus petraea et Pinus sylvestris) aux variations climatiques. Pour cela, nous avons réalisé une approche expérimentale en étudiant deux proxys (ou indices climatiques) : la croissance et la composition isotopique en 13C ( 13C) des cernes, à deux échelles temporelles : interannuelle et saisonnière. A l échelle interannuelle, sur la période 1960-2007, une étude dendrochronologique a été réalisée sur les trois essences et a été complétée par l analyse du 13C des cernes (en relation avec le climat). A l échelle saisonnière, nous avons déterminé précisément, sur une année (2009), les dynamiques de croissance du cerne et les variations de 13C intra-cerne. Nos résultats mettent en évidence une sensibilité de la croissance et du 13C des cernes des trois essences aux sécheresses estivales. Grâce à la complémentarité des proxys et des échelles temporelles, nous avons également trouvé des réponses climatiques contrastées entre espèces. La croissance du Hêtre est la plus réactive au climat d une année à l autre. Cette croissance ainsi que le 13C des cernes sont fortement sensibles aux températures de juillet, en plus des précipitations printanières et estivales. Cette réponse immédiate au climat peut être expliquée par une forte dépendance de la croissance au fonctionnement foliaire et une faible utilisation des réserves carbonées pour assurer le début de la croissance. Le Chêne présente lui des arrières-effets climatiques sur sa croissance, via une forte sensibilité aux sécheresses de l automne précédent, contrairement aux deux autres espèces. Ce résultat est à mettre en relation avec l utilisation importante de réserves carbonées par rapport aux assimilats pour la croissance du bois initial, cette dernière étant très rapide, comme nous l avons observé grâce à l analyse saisonnière de la croissance. Concernant le Pin, la croissance, parce qu elle dure plus longtemps que celle des décidues, est influencée par les températures et les précipitations de juin jusqu'à août. Le 13C des cernes de pins est celui qui enregistre le plus la réponse au VPD, aussi bien à l échelle saisonnière qu'interannuelle, probablement du fait d une forte sensibilité de la conductance stomatique à ce paramètre. Les informations fournies par les cernes permettent d appréhender la survie des espèces face aux changements climatiques futurs et peuvent être utilisées pour comprendre le dépérissement lié à ces changements.Climate change will probably alter the tree growth in temperate forests. The species vulnerability to climatic constraints can be studied using tree rings. The latter's are natural archives of carbon used for tree growth and are linked to species carbon transfer and response to climate. The main thesis objective was to determine the functional response of three temperate species (Fagus sylvatica, Quercus petraea et Pinus sylvestris) under climatic variations using tree rings. For this, an experimental approach was conducted using two proxies (or climatic indices): the radial growth and the carbon isotope composition in 13C ( 13C) of rings at two time scales: interannual and intra-annual (or seasonal). At interannual scale, over the period 1960-2007, a dendrological study was done for three species and was completed by analysis of ring 13C (in relation to climate). Over one year (2009) at seasonal scale, we precisely determined the radial growth dynamics and the variations in intra-ring 13C. Our results highlighted growth and ring 13C sensitivities to summer droughts. Because of proxy and time-scale complementarities, we have also found contrasted climatic responses among species. The beech growth is the most year-to-year responsive to climate. This growth and ring 13C were highly sensitive to temperature in July in addition to spring and summer precipitation. This quick response of beech growth to climate could be explained by strong growth dependence to leaf functioning and low carbon reserve use to ensure the growth beginning. Contrary to the two others species, long-term consequences of climate on oak growth were found, via a high sensitivity to previous autumnal droughts. This result could be related to the high use of carbon reserves compared to assimilates for earlywood growth, which was very quick as observed by seasonal growth analysis. Concerning pine, the growth was influenced by temperatures and precipitation from June to August because the growth lasted longer for pine than that of the deciduous species. At both seasonal and interannual scales, the ring 13C of pine trees was the best recorder of the VPD response, probably because of strong sensitivity of stomatal conductance to VPD. The information provided by tree rings allow to anticipate the species survival under future climate change and could be used to understand the declining due to these changes.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Evidence of a seasonal trade-off between growth and starch storage in declining beeches: Assessment through stem radial increment, non-structural carbohydrates and intra-ring δ13C

Forest decline is reported in recent decades all over the world. However, developing a clear vision of the associated tree dysfunctioning is still a challenge for plant physiologists. In this study, our aim was to examine the seasonal carbon adjustments of beech trees in the case of a long-term drought-induced decline. We compared healthy and declining trees in terms of stem radial growth, phloem sugar content and δ13C, together with xylem carbohydrates and intra-ring δ13C patterns. The radial growth of declining trees was clearly reduced by lower growth rates and shorter growing season length (44 days compared with healthy trees). The soluble sugar content was higher in the xylem of declining trees compared with the healthy ones, but similar in the phloem except at the end of their growth. Declining trees increased their levels of xylem starch content from budburst until the date of maximal growth rate. These reserve dynamics revealed an early trade-off between radial growth and starch storage that might be the result of an active or passive process. For declining trees, the slight decrease of intra-ring cellulose δ13C pattern during the early growing season was attributed to the synthesis of 13C enriched starch. For healthy trees, δ13C patterns were characterized by a progressive 13C increase along the ring, attributed to increased water-use efficiency (WUE) in response to decreased water availability. Individual variations of the crown area were negatively correlated to the intra-ring δ13C amplitude, which was ascribed to variations in canopy WUE and resource competition for healthy trees and partly to variations in the amount of reserves accumulated during spring for declining ones. Our study highlights the carbon physiological adjustment of declining trees towards reducing spring growth while storing starch, which can be reflected in the individual intra-ring cellulose δ13C patterns

In situ assessment of seasonal variation of assimilated carbon transfer to biochemical compounds by tracing 13C after pulse labelling on Quercus petraea

Allocation of assimilated carbon among organs and more specially to biochemical compounds is affected by theenvironment and affects tree growth, the contribution of each organ to autotrophic respiration, and, in fine, carbonsequestration in the ecosystem.The aim of this study (ANR CATS) was to assess the seasonal evolution of the contribution of assimilated carbonto leaf, stem and root biochemical compounds and the contribution of photo-assimilates to leaf exportation andautotrophic respiration. In situ 13C pulse labeling of 10–15 m tall trees was conducted in the field on six sessileoak (Quercus petraea) throughout the growing season (i.e. in May, July and September). Leaf, stem and root 13Ccontent of starch, soluble sugars, structural matter and total organic matter was analyzed during 30 days afterlabeling. 13C content in leaf respired CO2 was also determinedIn leaves, the proportion of 13C allocated to total organic matter decreased in average by 48% during the first3 days after the three labeling date. The proportion of leaf respired 13C stayed stable at 4% of total recovered13C all along the season. Leaves exported the main part of assimilated 13C to other compartments during the 3days after labeling with an hourly export rate comprised between 0.5 and 0.8 %. Whatever the labeling date, 6hours after labeling, in leaves, 60% of labeled organic matter corresponded to starch, soluble sugars and structuralmatter. In May, this proportion remained similar 30 days after labeling date. However partitioning between eachbiochemical fraction changed : during the 6 first days after labeling, starch corresponded to the most labeledcompound, thereafter structural matter became the more labeled : it reveals the use of starch for leaf growth at thisperiod. For July and September labeling, the proportion of labeling organic matter corresponding to starch, solublesugars and structural matter decrease to 50 and 40% respectively, until day 30 after labeling. In this fraction, theallocation to structural matter increase to 30% and 20 % respectively for July and September labeling. For thosedates, 13C also participated to construction of the leaves but in a lower extent: it progressively diminishes alongthe season.In stems and roots, the proportion of 13C allocated to starch, soluble sugars and structural matter increased from40 % to 80% whatever the season from the first day after labeling to day 30. For May and July labeling, theallocation to structural matter significantly increased: from 10 % the first day after labeling to 70 % the day 30after labeling. 13C assimilated in May and in July contribute to the structure of stems and roots. For Septemberlabeling, allocation of 13C to starch clearly increased from 5 % to 25 % during the month after labeling andshowed the priority to reserve accumulation at this period.This type of study allow determination of allocation to metabolites and exportation rates which are rarely studie

Retrieving leaf conductances from sap flows in a mixed Mediterranean woodland: a scaling exercise

Xylem sap-flux densities were monitored continuously using Granier-type sensors on five Quercus ilex, four Arbutus unedo and one Quercus pubescens from June 1993 to October 1994. Half-hourly measurements of incoming solar radiation, air temperature and humidity, horizontal wind speed and precipitation were carried out at the top of a tower at a height of 12 m, about 2 m above the canopy. Leaf physiological measurements (stomatal conductance, water potential) on individual sunlit leaves from each of the three tree species were obtained on seven complete or partial diurnal time courses. For these three species, to estimate leaf stomatal conductance, we used the big-leaf approach of Penman-Monteith. We have divided the leaves into sunlit and shaded. The model sums the individual-leaf model for only the sunlit fraction to produce the whole-canopy predictions. Transpiration was deduced from sap flux through a transfer function taking into account stem water storage. Stomatal conductance for a given species was evaluated half-hourly from transpiration and microclimate data inverting the Penman-Monteith equation. An empirical model was identified that related stomatal aperture to simultaneous variations of microclimate and plant water potential for the 1993 period. The predicted leaf conductances were validated against porometer data and those of the 1994 period. The diurnal patterns of predicted and measured transpiration indicated that stomatal conductance was accurately predicted. The leaf conductance models were also compared with already published literature values from the same tree species. In spite of the simplifications inherent to the big-leaf representation of the canopy, the model is useful for predicting interactions between Mediterranean mixed woodland and environment and for interpreting H2 O exchange measurements. (© Inra/Elsevier, Paris.)Estimation des conductances foliaires à partir des flux de sève dans une forêt mixte méditerranéenne : un exercice de changement d'échelle. La densité de flux de sève a été mesurée en continu à l'aide de capteur de type Granier sur cinq Quercus ilex, quatre Arburus unedo et un Quercus pubescens de juin 1993 à octobre 1994. Ces mesures ont été complétées par des mesures microclimatiques bihoraires de rayonnement global, de température et d'humidité de l'air, de vitesse du vent et de hauteur de précipitation. Ces mesures sont faites au sommet d'une tour de 12 m dominant le couvert forestier d'environ 2 m. Sept suivis journaliers complets ou partiels de conductance stomatique et de potentiel hydrique pour des feuilles exposées au soleil des trois espèces d'arbre ont été réalisés. Pour ces trois espèces, nous avons estimé la conductance stomatique à l'aide du modèle simple feuille de Penman-Monteith. Les feuilles sont subdivisées en feuilles de lumière et d'ombre. Seule les feuilles de lumière sont supposées contribuer à la transpiration totale. La transpiration est dérivée des mesures de flux de sève à l'aide d'une fonction de transfert qui tient compte du stockage de l'eau dans le tronc. La conductance stomatique est déduite de l'inversion du modèle de Penman-Monteith compte tenu de la transpiration et des conditions microclimatiques. Un modèle empirique multiplicatif de ces conductances a été ajusté sur les données acquises en 1993. Il les relie aux conditions microclimatiques et au potentiel hydrique foliaire. Ce modèle de conductance a été validé à l'aide des données acquises en 1994 et à des mesures de conductances réalisées au poromètre. Ce modèle a été comparé aux modèles de la littérature proposés pour ces espèces. En dépit des simplifications inhérentes à la représentation simple feuille du couvert, ce modèle est utile pour prédire les interactions entre les forêts mixtes méditerranéennes et leur environnement et pour interpréter les mesures de transpiration. (© Inra/Elsevier, Paris.

Comparing the intra-annual wood formation of three European species (Fagus sylvatica, Quercus petraea and Pinus sylvestris) as related to leaf phenology and non-structural carbohydrate dynamics

Monitoring cambial phenology and intra-annual growth dynamics is a useful approach for characterizing the tree growth response to climate change. However, there have been few reports concerning intra-annual wood formation in lowland temperate forests with high time resolution, especially for the comparison between deciduous and coniferous species. The main objective of this study was to determine how the timing, duration and rate of radial growth change between species as related to leaf phenology and the dynamics of non-structural carbohydrates (NSC) under the same climatic conditions. We studied two deciduous species, Fagus sylvatica L. and Quercus petraea (Matt.) Liebl., and an evergreen conifer, Pinus sylvestris L. During the 2009 growing season, we weekly monitored (i) the stem radial increment using dendrometers, (ii) the xylem growth using microcoring and (iii) the leaf phenology from direct observations of the tree crowns. The NSC content was also measured in the eight last rings of the stem cores in April, June and August 2009. The leaf phenology, NSC storage and intra-annual growth were clearly different between species, highlighting their contrasting carbon allocation. Beech growth began just after budburst, with a maximal growth rate when the leaves were mature and variations in the NSC content were low. Thus, beech radial growth seemed highly dependent on leaf photosynthesis. For oak, earlywood quickly developed before budburst, which probably led to the starch decrease quantified in the stem from April to June. For pine, growth began before the needles unfolding and the lack of NSC decrease during the growing season suggested that the substrates for radial growth were new assimilates of the needles from the previous year. Only for oak, the pattern determined from the intra-annual growth measured using microcoring differed from the pattern determined from dendrometer data. For all species, the ring width was significantly influenced by growth duration and not by growth rate, which differs from previous studies. The observed between-species difference at the intra-annual scale is key information for anticipating suitability of future species in temperate forests