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International audience; Cross-species analyses of plant functional traits have shed light on factors contributing to differences in performance and distribution, but to date most studies have focused on either leaves or stems. We extend these tissue-specific analyses of functional strategy towards a whole-plant approach by integrating data on functional traits for 13 448 leaves and wood tissues from 4672 trees representing 668 species of Neotropical trees. Strong correlations amongst traits previously defined as the leaf economics spectrum reflect a tradeoff between investments in productive leaves with rapid turnover vs. costly physical leaf structure with a long revenue stream. A second axis of variation, the 'stem economics spectrum', defines a similar tradeoff at the stem level: dense wood vs. high wood water content and thick bark. Most importantly, these two axes are orthogonal, suggesting that tradeoffs operate independently at the leaf and at the stem levels. By simplifying the multivariate ecological strategies of tropical trees into positions along these two spectra, our results provide a basis to improve global vegetation models predicting responses of tropical forests to global change.

International audience; Chlorophyll meters such as the SPAD-502 offer a simple, inexpensive and rapid method to estimate foliar chlorophyll content. However, values provided by SPAD-502 are unitless and require empirical calibrations between SPAD units and extracted chlorophyll values. * Leaves of 13 tree species from the tropical rain forest in French Guiana were sampled to select the most appropriate calibration model among the often-used linear, polynomial and exponential models, in addition to a novel homographic model that has a natural asymptote.* The homographic model best accurately predicted total chlorophyll content (μg cm−2) from SPAD units (R2 = 0.89). Interspecific differences in the homographic model parameters explain less than 7% of the variation in chlorophyll content in our data set. * The utility of the general homographic model for a variety of research and management applications clearly outweighs the slight loss of model accuracy due to the abandon of the species' effect.

The use of cultured epithelial autografts (CEA) for the treatment of large burn wounds has gained popularity in recent years. This technique may circumvent the restrictions of limited donor site availability and hasten permanent wound coverage for large TBSA burns. The availability of a large amount of skin from a small donor site with the promise of permanent wound coverage suggests its use in other conditions such as giant congenital nevi (GCN) as well. The risk of malignant transformation of GCN to melanoma although somewhat controversial is significant enough to warrant early excision in childhood. Cultured keratinocytes may provide one-stage coverage of these large wounds, lessening the number of surgeries and the inherent staging problems of tissue expansion or autografting. A retrospective single institution review of was done for 29 children (20 burns and 9 patients with GCN) who underwent coverage of their large surface area wounds with CEA over an 18-year period. Excellent take rates were noted; 76.4% for burn patients and 66% for patients with GCN. Several strategies in preoperative, perioperative, and postoperative care have been standardized and have helped improve outcome. The keys to success with the CEA technique have been aggressive control of wound sepsis, surgical technique, specific use of topical antimicrobials, dressings, and the standardization of nursing and physiotherapy care. Although the cost of CEA is high, the benefits to patient care make this technique an appealing choice for large wound coverage in the pediatric population.

Irradiance elicits a large plasticity in leaf traits, but little is known about the modulation of this plasticity by ontogeny. Interactive effects of relative irradiance and ontogeny were assessed on leaf traits for two tropical rainforest tree species: Dicorynia guianensis Amshoff and Tachigali melinonii (Harms) Barneby (Fabaceae, Caesalpinioideae). Eleven morphological and physiological leaf traits, relative to photosynthetic performance, were measured on saplings at three different architectural development stages (ASD 1, 2 and 3) and used to derive composite traits like photosynthetic N-use efficiency. Measurements were made along a natural irradiance gradient. The effect of ASD was very visible and differed between the two species. For Dicorynia guianensis, only leaf mass-per-area (LMA) significantly increased with ASDs whereas for Tachigali melinonii, almost all traits were affected by ASD: LMA, leaf N content and photosynthetic capacity increased from ASD 1 to ASD 3. Photosynthetic N-use-efficiency was not affected by ASD in any species. Leaf traits were severely modulated by irradiance, whereas the degree of plasticity was very similar among ASDs. Only few interactions were detected between irradiance and ASD, for leaf thickness, carbon content, and the ratio Chl/N in T. melinonii and for photosynthetic capacity in D. guianensis. We conclude that ontogenic development and irradiance-elicited plasticity modulated leaf traits, with almost no interaction, i.e., the degree of irradiance-elicited plasticity was stable across development stages and independent of ontogeny in these two species, at least in the early stages of development assessed here., Les traits foliaires varient fortement avec l'éclairement mais également avec l'ontogenèse. Cependant, l'impact de l'ontogenèse sur la plasticité induite par l'éclairement reste mal connu. Les interactions entre ontogenèse et éclairement relatif ont ainsi été étudiées pour des traits fonctionnels foliaires de deux espèces de forêt tropicale humide de Guyane française : Dicorynia guianensis Amshoff et Tachigali melinonii (Harms) Barneby (Fabaceae, Caesalpinioideae). • Onze traits morphologiques et physiologiques foliaires, relatifs aux capacités photosynthétiques, ont été mesurés sur de jeunes arbres ayant atteint trois stades architecturaux de développement successifs (ASD 1, 2 et 3) et utilisés pour en déduire des traits composites. Les mesures ont été réalisées le long d'un gradient naturel d'éclairement en forêt. • L'impact de stades successifs de développement différait entre espèces. Pour D. guianensis, seule la masse surfacique (LMA) a augmenté significativement avec les stades de développement tandis que pour T. melinonii, presque tous les traits foliaires étaient modulés. Pour cette espèce, LMA, teneur en N et capacité photosynthétique ont augmenté de ASD 1 à ASD 3. Par contre, l'efficience d'utilisation de N par la photosynthèse est restée stable entre ASDs. • Les traits foliaires ont été fortement modifiés par l'éclairement mais le degré de plasticité était similaire entre les ASDs. Des interactions entre ASD et éclairement n'ont été observées que pour l'épaisseur, la teneur en C et le rapport Chl/N de T. melinonii ainsi que pour la capacité photosynthétique de D. guianensis. • En dépit de l'effet significatif de l'ontogénèse sur les traits foliaires, seules de très faibles interactions ont pu être détectées avec l'éclairement pour les deux espèces. On peut en conclure que les stades successifs de développement ne modifient pas le degré de plasticité foliaire en réponse à l'éclairement tout au moins dans le cas des stades jeunes pris en compte ici.

We characterised the among species variability in leaf gas exchange and morphological traits under controlled conditions of seedlings of 22 tropical rainforest canopy species to understand the origin of the variability in leaf carbon isotope discrimination (Delta) among species with different growth and dynamic characteristics (successional gradient). Our results first suggest that these species pursue a consistent strategy in terms of (Delta) throughout their ontogeny (juveniles grown here versus canopy adult trees from the natural forest). Second, leaf (Delta) was negatively correlated with WUE and N, and positively correlated with gs, but among species differences in (Delta) were mainly explained by differences in WUE. Finally, species belonging to different successional groups display distinct leaf functional and morphological traits. We confirmed that fast growing early successional species maximise carbon assimilation with high stomatal conductance. In contrast, fast and slow growing late successional species are both characterised by low carbon assimilation values, but by distinct stomatal conductance and leaf morphological features. Along the successional gradient, these differences result in much lower (Delta) for the intermediate species (i.e. fast growing late successional) as compared to the two other groups., Nous avons caractérisé la variabilité interspécifique des échanges gazeux et des traits morphologiques foliaires en conditions environnementales contrôlées de jeunes plants de 22 espèces d'arbres de la canopée en forêt tropicale humide afin de comprendre l'origine de la variabilité de la discrimination isotopique du carbone foliaire (Delta) observée entre ces espèces présentant des caractéristiques de croissance et de dynamique distinctes (groupes successionnels). Nous montrons premièrement que les espèces tropicales possèdent une stratégie très conservée de (Delta) au cours de leur ontogénie (juvéniles élevés ici versus arbres adultes de la canopée en forêt naturelle). Deuxièmement,(Delta) était négativement corrélée à WUE et N, et positivement à gs_, mais les différences de (Delta) entre espèces sont principalement expliquées par des différences de WUE. Enfin, nous montrons que les espèces appartenant à des groupes successionnels distincts présentent des traits fonctionnels et morphologiques foliaires distincts. Nous confirmons que les espèces à croissance rapide qui s'installent en premier au cours de la succession écologique (FE) maximisent A avec de fortes conductances stomatiques. Les espèces climax (qui s'installent en second dans la succession écologique), à croissance rapide (FL) ou à croissance faible (SL), présentent des valeurs de A identiques, mais des valeurs de gs, ainsi que des caractéristiques morphologiques foliaires distinctes. Dans la succession écologique, ces différences se traduisent par des valeurs de(Delta)nettement plus faibles pour les espèces intermédiaires (c'est-à-dire les espèces climax à croissance rapide) par rapport aux deux autres groupes.

Previous studies in lowland tropical rainforests of French Guiana showed that, among non-N 2 -fixing trees, two groups of late successional species contrasting in their leaf 15 N natural abundance coexist, suggesting two different main ways of nitrogen acquisition. Two abundant late-successional species typically co-occurring in rainforests in French Guiana, namely Eperua falcata and Dicorynia guianensis, were chosen as representative of each group. Stable isotope techniques and measurements of potentials of microbial N transformation were performed to assess to what extent leaf 15 N natural abundance of these species could be related to (i) δ 15 N signatures of soil mineral N sources and (ii) the capacity of soil to express nitrification and denitrification (both processes being directly involved in the balance between NH 4 + and NO 3 – ). Soil δ 15 N-NH 4 + was roughly similar to leaf δ 15 N of D. guianensis (around 3.5‰), suggesting a preferential use of NH 4 + , whereas in E. falcata, leaf δ 15 N values were closer to root δ 15 N-NO 3 − values (0.2 and −2.0‰, respectively), suggesting a preferential use of NO 3 − . These differences in N source utilization were not accompanied by differences in availability in soil NO 3 − or in intensity of microbial functions responsible for soil N mineral evolution. However, (i) under both tree species, these functions showed clear spatial partitioning, with denitrification occurring potentially in soil and nitrification in the litter layer, and (ii) E. falcata fine roots colonized the litter layer much more strongly than D. guianensis fine roots. This strongly suggests that (i) the contrasted leaf δ 15 N values found in the two late-successional species reveal distinct N acquisition strategies and (ii) the ability of roots to predominantly exploit the litter layer ( E. falcata ) or the soil ( D. guianensis ) may constitute an important explanation of the observed differences. A complementarity between tree species, based on mineral N resource partitioning (itself resulting from a spatially structured location of the microbial functions responsible for the balance between NH 4 + and NO 3 – ), can thus be supposed.

Microbial-based indicators, such as C and N contents or microbial functions involved in C and N cycles, are currently used to describe the status of soils in disturbed areas. Microbial functions are more accurate indicators but their measurement for studies at the ecosystem level remains problematical because of the huge spatial variability of these processes and, consequently, of the large number of soil samples which must be analyzed. Our goal was to test the capacity of near-infrared reflectance spectroscopy (NIRS) to predict respiration and denitrification but also carbon and nitrogen contents of soils submitted to various procedures of restoration. To achieve this objective, we took advantage of an experiment conducted on a reforestation system established after open-cast gold mining in French Guiana. In this experimental station, plantations of various ages and various soil textures were at our disposal. Our results showed that both plantations and soil texture had a strong impact on the recovery of soil functioning: carbon and nitrogen contents, respiration and denitrification increased with age of plantation and clay content. Calibrations were performed between spectral data and microbial-based indicators using partial least squares regression (PLS). The results showed that C and N contents were accurately predicted. Microbial functions were less precisely predicted with results more accurate on clayey soils than on sandy soils. In clayey soils, perturbed or restored soils and the year of plantation were discriminated very efficiently through principal component analyses of spectral signatures (over 80% of variance explained on the first two axes). Near-infrared spectroscopy may thus be extended to the prediction of functional soil parameters, but the capacity of this method must be strengthened by expending the databases with other soils in other contexts. The possibility of using NIRS provides many opportunities for understanding both the temporal dynamics and the spatial variability of the recovery of key microbial functions during soil restoration.

Variability of leaf traits related to photosynthesis was assessed in seedlings from 14 tree species growing in the tropical rain forest of French Guiana. Leaf photosynthetic capacity (maximum rate of carboxylation and maximum rate of electron transport) was estimated by fitting a biochemical model of photosynthesis to response curves of net CO2 assimilation rate versus intercellular CO2 mole fraction. Leaf morphology described by leaf mass per unit leaf area (LMA), density and thickness, as well as area- and mass-based nitrogen (N) and carbon (C) concentrations, were recorded on the same leaves. Large interspecific variability was detected in photosynthetic capacity as well as in leaf structure and leaf N and C concentrations. No correlation was found between leaf thickness and density. The correlations between area- and mass-based leaf N concentration and photosynthetic capacity were poor. Conversely, the species differed greatly in relative N allocation to carboxylation and bioenergetics. Principal component analysis (PCA) revealed that, of the recorded traits, only the computed fraction of total leaf N invested in photosynthesis was tightly correlated to photosynthetic capacity. We also used PCA to test to what extent species with similar shade tolerances displayed converging leaf traits related to photosynthesis. No clear-cut ranking could be detected among the shade-tolerant groups, as confirmed by a one-way ANOVA. We conclude that the large interspecific diversity in photosynthetic capacity was mostly explained by differences in the relative allocation of N to photosynthesis and not by leaf N concentration, and that leaf traits related to photosynthetic capacity did not discriminate shade-tolerance ranking of these tropical tree species.

International audience; Two methods of N transfer between plants—by litter decomposition and root-to-root exchange—were examined in mixed plantations of N-fixing and non-fixing trees. Nitrogen transfers from decaying litters were measured by placing 15N-labelled litters from four actinorhizal tree species around shoots of containerized Prunus avium. Nitrogen transfers by root-to-root exchanges were measured after foliar NO3-15N fertilization of Alnus subcordata and Elaeagnus angustifolia growing in containers in association with P. avium. During the first 2 years of litter decomposition, from 5–20% of the N, depending on the litter identity, was released and taken up by P. avium. N availability in the different litters was strongly correlated with the amount of water-soluble N, which was highest in leaves of E. angustifolia. In the association between fixing and non-fixing plants, 7.5% of the A. subcordata N and 25% of E. angustifolia N was transferred to P. avium by root exchange. These results showed that the magnitude of N transfers by root exchange depended on the associated N2-fixing species. Among the species investigated, E. angustifolia displayed the highest capacity for exudating N from roots as well as for releasing N from litters. These qualities make this tree a promising species for enhancing wood yields in mixed stands.

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Les forêts hétérogènes guyanaises sont des milieux complexes dont la gestion passe par la compréhension de leur organisation (structure spatiale, horizontale et verticale et diversité spécifique) et de leur dynamique. Dans ce contexte, l'étude des stratégies de développement et d'occupation de l'espace des arbres permet de mieux comprendre comment les différentes espèces exploitent et structurent l'hétérogénéité du milieu. Depuis une trentaine d'années, les travaux menés en architecture végétale ont permis d'établir un contexte méthodologique et conceptuel pour étudier la structure globale de l'arbre et pour comprendre les mécanismes morphologiques qui lui ont donné naissance. Après une présentation de concepts majeurs d'architecture végétale, cet article expose les méthodes employées pour quantifier la structure des arbres et les approches permettant d'intégrer les critères architecturaux dans un diagnostic à l'échelle du peuplement.

Nodulated legume trees comprised 43% of the stand basal area in the low, most frequently flooded microsites, and 23% in higher, drier microsites in a tropical freshwater swamp forest in French Guiana. Dinitrogen fixation in Pterocarpus officinalis, Hydrochorea corymbosa and Inga pilosula was confirmed by acetylene reduction assay (ARA), presence of leghaemoglobin in nodules and the 15N natural abundance method. The results for Zygia cataractae were inconclusive but suggested N2 fixation in drier microsites. Nodulated Inga disticha had a 15N-to-14N ratio similar to non-N2-fixing trees, but ARA indicated nitrogenase activity and leghaemoglobin was present in nodules. All bacterial strains were identified as Bradyrhizobium spp. according to the partial 16S rDNA sequences, and they were infective in vitro in the model species Macroptilium atropurpureum. About 35-50% of N in the leaves of P. officinalis, H. corymbosa and I. pilosula was fixed from the atmosphere. Dinitrogen fixation was estimated to contribute at least 8-13% and 17-28% to whole-canopy N in high and low microsites, respectively. Symbiotic N2 fixation appears to provide both a competitive advantage to legume trees under N-limited, flooded conditions and an important N input to neotropical freshwater swamp forests.

International audience; Les forêts hétérogènes guyanaises sont des milieux complexes dont la gestion passe par la compréhension de leur organisation (structure spatiale, horizontale et verticale et diversité spécifique) et de leur dynamique. Dans ce contexte, l'étude des stratégies de développement et d'occupation de l'espace des arbres permet de mieux comprendre comment les différentes espèces exploitent et structurent l'hétérogénéité du milieu. Depuis une trentaine d'années, les travaux menés en architecture végétale ont permis d'établir un contexte méthodologique et conceptuel pour étudier la structure globale de l'arbre et pour comprendre les mécanismes morphologiques qui lui ont donné naissance. Après une présentation de concepts majeurs d'architecture végétale, cet article expose les méthodes employées pour quantifier la structure des arbres et les approches permettant d'intégrer les critères architecturaux dans un diagnostic à l'échelle du peuplement.

Architectural analyses of temperate tree species using a chronological approach suggest that the expression of epicormic branches is closely related to low growth rates in the axes that make up the branching system. Therefore, sole consideration of epicormic criteria may be sufficient to identify trees with low secondary growth levels or with both low primary and secondary growth levels. In a tropical tree such as Dicorynia guianensis (basralocus), where chronological studies are difficult, this relationship could be very useful as an easily accessible indicator of growth potentials. A simple method of architectural tree description was used to characterize the global structure of more than 1650 basralocus trees and to evaluate their growth level. Measurements of simple growth characters [height, basal diameter, internode length of submittal part (top of the main axis of the tree)] and the observation of four structural binary descriptors on the main stem (presence of sequential branches and young epicormic branches, state of the submittal part, global orientation), indicated that epicormic branch formation is clearly related to a decrease in length of the successive growth units of the main stem. Analysis of height vs. diameter ratios among different tree subgroups, with and without epicormic branching, suggested that trees with epicormic branches generally have a low level of secondary growth compared with primary growth.

International audience

The natural 15N abundance method for estimating symbiotic biological N2-fixation was tested on legume trees from two rain forests on contrasting soils (oxisols and spodosols) in French Guiana. When possible, the significance of N2-fixing species in the plant community was evaluated in terms of density, biomass and contribution of N2-fixation to the building up of the total nitrogen mass in the leaves. Of the two sites, the rain forest on spodosols was the less favourable for application of the [delta]15N method: the available soil nitrogen was isotopically similar to fixed-N2. Hence, the results showed that a reliable estimate of N2-fixation could not be obtained. A substantial contribution of fixed-N2 to the nitrogen nutrition of legumes was found on oxisols, with an average value of 54 % Ndfa (Nitrogen derived from the atmosphere). The contribution of the N2-fixing legumes to the biomass of the stand was estimated to be 2 t ha[minus sign]1 for the leaf biomass and 136 t ha[minus sign]1 for the total above-ground plant biomass. With 7.5 % of trees in the stand able to fix N2 (462 out of 6156), N2-fixation was estimated to be 7 kg ha[minus sign]1 y[minus sign]1. These results are the first use of the [delta]15N method to estimate nitrogen input by N2-fixing legumes to a natural rain forest. The inter-site variability observed in the [delta]15N of the non-fixing plants suggested different nitrogen-cycling processes in the two soils. The [delta]15N of the non-N2-fixing plants could be related to the soil nitrogen availability and be used as an indicator of efficient or non-efficient nitrogen-cycling rain forests. The spatial variability of the [delta]15N in the plant-available soil nitrogen pool and the nitrogen balance in tropical rain forests are discussed.

Diffusion du document : INRA Antilles-Guyane, UMR ECOFOG, F97387 Kourou, Guyane (France) Diplôme : Dr. d'Université; On ignore l'importance des espèces arborées fixatrices d'azote en forêt tropicale Guyanaise, tant en nombre de taxons qu'en nombre d'individus ainsi qu'en terme de biomasse et de dominance. On ne connaît pas non plus la diversité et le niveau de spécificité des micro-organismes qui leur sont associés. L'objectif de ce travail était donc de répondre aux questions suivantes : - Quelles espèces contribuent à la fixation de l'azote moléculaire. Ce type de stratégie d'acquisition des ressources azotées peut-il rendre compte du schéma de régénération de ces espèces et de leur importance au sein du continuum «d'éco-unités» que constitue cet écosystème ? Quelle est la diversité des micro-organismes qui leur sont associés ? Outre les aspects phylogénétiques non encore étudiés dans cet écosystème, le niveau de diversité et de spécificité des endosymbiotes fixateurs d'azote peut-il apporter des arguments en faveur ou non d'une co-évolution linéaire entre macro et micro symbiotes ? Pour répondre à ces questions l'approche choisie a comporté trois phases principales : - L'identification sur un échantillon le plus large possible (espèces, type de sols) des espèces arborescentes fixatrices d'azote par mesure du ∂15N foliaire. Celui-ci a présenté une forte variabilité suggérant une capacité de fixation de l'azote atmosphérique inconnue chez certaines espèces. Deux nouvelles espèces végétales porteuses de nodules aériens ont été également identifiées. - L'estimation des taux de fixation (Ndfa) des différentes espèces ainsi que celle de leur phytomasse dans le peuplement. - L'étude de la diversité des endosymbiotes associés par amplification de L'ADN 16S et l'analyse de son polymorphisme par RFLP. Ces endosymbiotes sont très homogènes et se regroupent autour des genres Bradyrhizobium et Azorhizobium. Les fixateurs d'azote interviennent dans toutes les phases silvigénétiques et représentent environ 10% de la phytomasse totale du peuplement avec un Ndfa moyen de 50%.

A homolog of the endoplasmic reticulum (ER) hsp70 protein, binding protein (BiP), from the parasitic protozoan Trypanosoma brucei (Bangs, J. D., Uyetake, L., Brickman, M. J., Balber, A. E., and Boothroyd, J. C.(1993) J. Cell Sci. 105, 1101-1113) is further characterized. In co-precipitation experiments, BiP transiently associates with newly synthesized secretory proteins, including variant surface glycoprotein (VSG), confirming its role as a molecular chaperone. To study the molecular signals targeting BiP to the ER, we have developed soluble secretory reporters for expression in transformed procyclic trypanosomes. Deletion of the BiP C-terminal tetrapeptide (MDDL) and the glycosylphosphatidylinositol-anchor addition sequence of VSG converts these proteins to secreted forms. Attachment of MDDL to VSG results in intracellular retention confirming that MDDL is a trypanosomal ER localization signal. Secretion of both reporters is inefficient, but further truncation of the BiP C-terminal peptide-binding domain allows quantitative export ( t1/2 approximately 1 h) of the N-terminal ATPase domain (BiPN), consistent with the conserved domain structure of hsp70 proteins. This is the first demonstration of soluble protein secretion in African trypanosomes. Using the BiPN reporter, the sequence specificity of C-terminal tetrapeptide retention signals in trypanosomes is analyzed and found to be similar to higher eukaryotes. These results indicate that the basic signals mediating protein targeting to the ER lumen are conserved throughout the wide range of eukaryotic evolution.

"It was the best of times, it was the worst of times." This isn't a "tale of two cities." It's a tale of two Catholic health care systems in one city. For nearly a century, we were vigorous competitors. We were forced to consolidate our operations in 1987 as a result of the consolidation of our national Health Care sponsors. This is a detailed account of how that consolidation was achieved.