Within-individual variation of trunk and branch xylem density in tropical trees

Premise of the study: Wood density correlates with mechanical and physiological strategies of trees and is important for estimating global carbon stocks. Nonetheless, the relationship between branch and trunk xylem density has been poorly explored in neotropical trees. Here, we examine this relationship in trees from French Guiana and its variation among different families and sites, to improve the understanding of wood density in neotropical forests. Methods: Trunk and branch xylem densities were measured for 1909 trees in seven sites across French Guiana. A major-axis fit was performed to explore their general allometric relationship and its variation among different families and sites. Key results: Trunk xylem and branch xylem densities were significantly positively correlated, and their relationship explained 47% of the total variance. Trunk xylem was on average 9% denser than branch xylem. Family-level differences and interactions between family and site accounted for more than 40% of the total variance, whereas differences among sites explained little variation. Conclusions: Variation in xylem density within individual trees can be substantial, and the relationship between branch xylem and trunk xylem densities varies considerably among families and sites. As such, whole-tree biomass estimates based on non- destructive branch sampling should correct for both taxonomic and environmental factors. Furthermore, detailed estimates of the vertical distribution of wood density within individual trees are needed to determine the extent to which relying solely upon measures of trunk wood density may cause carbon stocks in tropical forests to be overestimated

Comparative Analysis of Three Different Methods Used to Determine the Elastic Modulus for a Choice of Tropical Guianese Wood Species

This study compares variability in the longitudinal Modulus of Elasticity (MOE) values, measured by three different methods, for eight tropical wood species covering a wide range of densities, a property that has been little described in the literature for some of the species studied. The modulus of elasticity in wood species is one of the main mechanical properties measured to characterize wood materials. However, this property is seldom described for the tropical wood species studied here, and the method used is often variable. The aim is to answer the following questions. In the methods used, what are the main variability factors which influence modulus measurement? Is the modulus different with regard to the solicitation direction (radial or tangential)? Which relationship exists between modulus and density for these species? The samples were subjected to the four-point bending test, then to the free vibration test and to the forced-vibration test (which allows tests on small samples).The samples were subjected to stress in radial and tangential directions. The modulus values obtained by the different methods were well correlated for most of the species. The relationship between modulus and density was very good at inter-specific level because sampling covered a wide range of densities. But this relationship was not so good for each of the species sampled. This kind of test was not appropriate for detecting differences in behavior between the two directions of solicitation for these species. The main features of the three methods were summarized, highlighting the advantages of each for the species studied

Comparison of physical and mechanical properties of tension and opposite wood from ten tropical rainforest trees from different species

On 10 trees from 10 species of French Guyana tropical rainforest in a clear active process of restoring verticality growth strains were measured in situ in order to determine the occurrence of tension wood within samples. Wood specimens were cut in the vicinity of the growth strains measurements in order to measure some mechanical and physical properties. As suspected, tensile growth strains was very much higher in tension wood zone, because longitudinal modulus of elasticity was slightly higher. Longitudinal shrinkage was also much higher in tension wood than in opposite wood.Des mesures de contraintes de croissance ont été réalisées sur 10 arbres en cours de redressement actif appartenant à 10 espèces de la forêt tropicale humide de Guyane Française afin de s'assurer de la présence de bois de tension. Des échantillons de bois, prélevés au voisinage des mesures de contraintes de croissance, ont permis de mesurer un certains nombres de propriétés physiques et mécaniques. Comme présumé les contraintes de croissance sont beaucoup plus élevées au niveau du secteur de bois de tension, car le module d'élasticité est légèrement plus élevé. Le retrait longitudinal est aussi plus élevé dans le bois de tension que dans le bois opposé

Wood quality in French Guiana

Les bois tropicaux, et en particulier les bois de Guyane, témoignent de la biodiversité des forêts denses humides. Les atouts et contraintes liés à cette diversité sont présentés ainsi que la façon objective de classer les espèces ou essences par rapport à des critères de qualité. La variabilité de la qualité des bois est illustrée à travers quelques exemples : la qualité des arbres sur pied, la qualité non constante de l'Angélique (Dicorynia guianensis), les troncs cannelés du Wacapou (Vouacapoua americana), les différences entre deux espèces d'Eperua spp.. La conclusion porte sur la petite filière-bois guyanaise, ses difficultés et les enjeux à relever

ArchiRac : Caractérisation de la diversité génétique de l’architecture racinaire chez le blé tendre et le blé dur

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

Within-individual variation of trunk and branch xylem density in tropical trees

Premise of the study: Wood density correlates with mechanical and physiological strategies of trees and is important for estimating global carbon stocks. Nonetheless, the relationship between branch and trunk xylem density has been poorly explored in neotropical trees. Here, we examine this relationship in trees from French Guiana and its variation among different families and sites, to improve the understanding of wood density in neotropical forests. Methods: Trunk and branch xylem densities were measured for 1909 trees in seven sites across French Guiana. A major-axis fit was performed to explore their general allometric relationship and its variation among different families and sites. Key results: Trunk xylem and branch xylem densities were significantly positively correlated, and their relationship explained 47% of the total variance. Trunk xylem was on average 9% denser than branch xylem. Family-level differences and interactions between family and site accounted for more than 40% of the total variance, whereas differences among sites explained little variation. Conclusions: Variation in xylem density within individual trees can be substantial, and the relationship between branch xylem and trunk xylem densities varies considerably among families and sites. As such, whole-tree biomass estimates based on nondestructive branch sampling should correct for both taxonomic and environmental factors. Furthermore, detailed estimates of the vertical distribution of wood density within individual trees are needed to determine the extent to which relying solely upon measures of trunk wood density may cause carbon stocks in tropical forests to be overestimated

Improving nitrogen use efficiency in wheat by genome wide and candidate genes targeted association studies

Book of abstracts, ISBN: 978-3-900932-48-0Abstract p. 73Improving nitrogen use efficiency in wheat by genome wide and candidate genes targeted association studies. 13. IWG

Natural durability of 8 tropical species suitable for round wood building: fungal and termites laboratory screening tests

Knowledge of the wood properties of tropical tree species is still relatively limited, making that timber exploitation focuses on a few abundant, large-diameter species. Very few is known about small diameter trees although they may be used, directly as round wood, in construction timber building. The aim of this work was to determine the wood natural durability of 8 candidate species for roundwood building in French Guiana ; Oxandra askeckii, Goupia glabra, Lecythis persistens, Hymenopus heteromorphus, Pouteria bangii, Licania alba, Tachigali melinonii, Simarouba amara and Virola surinamensis wood samples were exposed to white rots (European and tropical), brown rot (European) and European subterranean termites (using non-choice and multi-choice tests), in laboratory conditions by screening tests adapted from European standards. Only two species were classified as durable against both fungi and termites: Licania alba and Pouteria bangii, meaning they can be used without treatment as building material under tropical or temperate climate. The other tested species were classified (1) as durable but with important difference observed between fungal and termite durability (Goupia, Lecythis, Oxandra), (2) moderately durable (Hymenopus), (3) or slightly durable to sensible (Tachigali, Simarouba, Virola), meaning actual European standards would not let use these last species in outdoor structure without protection, despite their vernacular use. However, they could be used in structure with appropriate protection systems (including wood protection and design protection systems). The results obtained on wood decay resistance bring crucial information to assess the valorization of these 8 tree species in the Guyanese construction market