Pascal IMBERT - Academia.edu (original) (raw)

Papers by Pascal IMBERT

Research paper thumbnail of Phenoxy-substituted dextrans as emulsifying agent::: role of the substitution ratio on O/W emulsion stability and interfacial activity

Colloids and Surfaces A: …, 2002

Oil-in-water emulsions were prepared using dextran, a natural polysaccharide, hydrophobically mod... more Oil-in-water emulsions were prepared using dextran, a natural polysaccharide, hydrophobically modified with phenoxy groups. Emulsions were prepared by two different processes which were sonication and microfluidization. The average diameter of oil droplets and the stability with time of the resulting emulsions were investigated as a function of polymer concentration (Cp0/0.1 Á/1% w/w in water phase) and the degree of polymer grafting (t0/4.2 Á/15.7%). The microfluidization process allowed to realize emulsions with lower initial particle size than the sonication method. For the highest degrees of grafting and for Cp values ]/0.2% w/w, submicronic emulsions were obtained, which were stable for more than 4 months at room temperature. Interfacial measurements at the n-dodecane/water interface clearly showed a better efficiency of the most substituted polymers to lower the surface tension.

Research paper thumbnail of Croissance et assimilation nette foliaire de jeunes plants de dix arbres de la forêt guyanaise, cultivés à cinq niveaux d'éclairement

Annales des Sciences Forestières, 1998

Growth and net assimilation rate of seedlings of ten Guianan tree species grown under five light ... more Growth and net assimilation rate of seedlings of ten Guianan tree species grown under five light regimes. Seedlings of ten species of tropical rainforest trees (occurring in successional phases were grown in shade tunnels under five relative light levels (65 %, 45 %, 25 %, 10 % and 4 % of full sunshine). The study was designed to assess the behaviour of the species in juvenile stages versus different light growth conditions. Mainly net assimilation and growth rates were recorded. For seedlings growing under 65 % of full sunlight, maximum net assimilation rates were fairly variable between the species and ranged from 3.0 to 7 μmol m -2 s -1 and the total dry matter production ranged from 8 to 286 g per plant for plants grown for 20 months. The net assimilation rate of Carapa guianensis decreased by almost 40 % between 45 % and 65 % of full sunlight. The growth performance was substantially reduced at the lowest irradiance, but the pattern varied highly between species with increasing light intensity. The light level for optimal growth for most species ranged between 25 % and 45 % of full sunlight. Nevertheless, Bocoa prouacensis, a late successional species, had a higher growth performance under the highest light intensity tested (65 %) than in lower light environments (< 45 %).(© Inra/Elsevier, Paris.) tropical rainforest / net assimilation rate / growth rate / stem volume index Résumé -Des plantules de dix espèces d'arbres tropicaux (Bocoa prouacensis, Carapa guianensis, Carapa procera, Jacaranda copaia, Platonia insignis, Qualea rosea, Recordoxylon speciosum, Sterculia excelsa, Virola surinamensis, Vouacapoua americana) ont été élevées dans des serres tunnels sous différents régimes lumineux (65 %, 45 %, 25 %, 10 % et 4 % du plein découvert). L'objectif est de préciser le comportement des espèces au stade juvénile vis-à-vis de différentes conditions d'éclairement. L'assimilation nette foliaire et la croissance des plantules de ces espèces ont été plus particulièrement étudiées. Les valeurs maximales d'assimilation nette foliaire mesurées sur les plantules soumises à 65 % du plein éclairement étaient différentes d'une espèce à l'autre et étaient comprises entre 3,0 et 7,2 μmol m -2 s -1 tandis que la matière sèche totale produite par ces plantes âgées de vingt mois était comprise entre 8 et 286 g par plante. L'assimilation nette foliaire a été plus faible dans les conditions de faible éclairement. Chez l'espèce Carapa guianensis, une réduction d'environ 40 % du taux d'assimilation nette foliaire a été observée pour des niveaux d'éclairement compris entre 45 % et 65 % du plein découvert. La croissance maximale a sensiblement diminuée dans les conditions de faible éclairement et les taux de croissance étaient différents d'une espèce à l'autre lorsque les plantules étaient cultivées sous un régime lumineux plus fort. L'optimum de croissance, dans les conditions d'expérience, était compris entre 25 % et 45 % du plein découvert. Cependant, Bocoa prouacensis, espèce des stades tardifs de la succession, a présenté une croissance plus élevée pour l'intensité lumineuse la plus forte (65 %) que pour de plus faibles valeurs d'éclairement (< 45 %). (© Inra/Elsevier, Paris.) forêt tropicale humide / assimilation nette foliaire / vitesse de croissance / indice de volume

Research paper thumbnail of Leaf photosynthetic traits of 14 tropical rain forest species in relation to leaf nitrogen concentration and shade tolerance

Tree Physiology, 2005

Variability of leaf traits related to photosynthesis was assessed in seedlings from 14 tree speci... more 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 CO 2 assimilation rate versus intercellular CO 2 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 massbased 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.

Research paper thumbnail of Links between tree structure and functional leaf traits in the tropical forest tree Dicorynia guianensis Amshoff (Caesalpiniaceae)

Annals of Forest Science, 2005

This study looked at the interactive effects of tree architectural stage of development (ASD) and... more This study looked at the interactive effects of tree architectural stage of development (ASD) and light availability on different plant traits (growth parameters, leaf morpho-anatomy and photosynthetic capacities) in the tropical species Dicorynia guianensis. A qualitative architectural analysis was used to categorize tree individuals sampled along a natural light gradient. The results show that some traits could have an ASD-dependence at the whole plant and leaf level without control of light. The changes observed relate to vigour thresholds the plant has to reach to shift from one ASD to another (i.e., the number of nodes and the internodes length per Growth Unit). Light conditions do not modify these thresholds but may modify the time they are crossed. Tree height was found strongly modulated by light conditions; hence, at a similar height, individuals may belong to different ASD. At the functional level, a decrease in N m , and A maxm was observed with increasing light availability, while N a increased and A maxa remained unaffected. An ASD effect was also observed on A maxa and LMA but not on A maxm . These results demonstrated a weak ability of photosynthetic plasticity in response to light conditions, and that variations of leaf photosynthetic variables according to ASD can be explained by modifications in leaf nitrogen and LMA. Questions on the reliability of a height-based sampling strategy for evaluating the phenotypic plasticity of trees in relation to light conditions are raised.

Research paper thumbnail of Leaf photosynthetic traits of 14 tropical rain forest species in relation to leaf nitrogen concentration and shade tolerance

Tree Physiology, 2005

Variability of leaf traits related to photosynthesis was assessed in seedlings from 14 tree speci... more 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 CO 2 assimilation rate versus intercellular CO 2 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 massbased 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.

Research paper thumbnail of Phenoxy-substituted dextrans as emulsifying agent::: role of the substitution ratio on O/W emulsion stability and interfacial activity

Colloids and Surfaces A: …, 2002

Oil-in-water emulsions were prepared using dextran, a natural polysaccharide, hydrophobically mod... more Oil-in-water emulsions were prepared using dextran, a natural polysaccharide, hydrophobically modified with phenoxy groups. Emulsions were prepared by two different processes which were sonication and microfluidization. The average diameter of oil droplets and the stability with time of the resulting emulsions were investigated as a function of polymer concentration (Cp0/0.1 Á/1% w/w in water phase) and the degree of polymer grafting (t0/4.2 Á/15.7%). The microfluidization process allowed to realize emulsions with lower initial particle size than the sonication method. For the highest degrees of grafting and for Cp values ]/0.2% w/w, submicronic emulsions were obtained, which were stable for more than 4 months at room temperature. Interfacial measurements at the n-dodecane/water interface clearly showed a better efficiency of the most substituted polymers to lower the surface tension.

Research paper thumbnail of Croissance et assimilation nette foliaire de jeunes plants de dix arbres de la forêt guyanaise, cultivés à cinq niveaux d'éclairement

Annales des Sciences Forestières, 1998

Growth and net assimilation rate of seedlings of ten Guianan tree species grown under five light ... more Growth and net assimilation rate of seedlings of ten Guianan tree species grown under five light regimes. Seedlings of ten species of tropical rainforest trees (occurring in successional phases were grown in shade tunnels under five relative light levels (65 %, 45 %, 25 %, 10 % and 4 % of full sunshine). The study was designed to assess the behaviour of the species in juvenile stages versus different light growth conditions. Mainly net assimilation and growth rates were recorded. For seedlings growing under 65 % of full sunlight, maximum net assimilation rates were fairly variable between the species and ranged from 3.0 to 7 μmol m -2 s -1 and the total dry matter production ranged from 8 to 286 g per plant for plants grown for 20 months. The net assimilation rate of Carapa guianensis decreased by almost 40 % between 45 % and 65 % of full sunlight. The growth performance was substantially reduced at the lowest irradiance, but the pattern varied highly between species with increasing light intensity. The light level for optimal growth for most species ranged between 25 % and 45 % of full sunlight. Nevertheless, Bocoa prouacensis, a late successional species, had a higher growth performance under the highest light intensity tested (65 %) than in lower light environments (< 45 %).(© Inra/Elsevier, Paris.) tropical rainforest / net assimilation rate / growth rate / stem volume index Résumé -Des plantules de dix espèces d'arbres tropicaux (Bocoa prouacensis, Carapa guianensis, Carapa procera, Jacaranda copaia, Platonia insignis, Qualea rosea, Recordoxylon speciosum, Sterculia excelsa, Virola surinamensis, Vouacapoua americana) ont été élevées dans des serres tunnels sous différents régimes lumineux (65 %, 45 %, 25 %, 10 % et 4 % du plein découvert). L'objectif est de préciser le comportement des espèces au stade juvénile vis-à-vis de différentes conditions d'éclairement. L'assimilation nette foliaire et la croissance des plantules de ces espèces ont été plus particulièrement étudiées. Les valeurs maximales d'assimilation nette foliaire mesurées sur les plantules soumises à 65 % du plein éclairement étaient différentes d'une espèce à l'autre et étaient comprises entre 3,0 et 7,2 μmol m -2 s -1 tandis que la matière sèche totale produite par ces plantes âgées de vingt mois était comprise entre 8 et 286 g par plante. L'assimilation nette foliaire a été plus faible dans les conditions de faible éclairement. Chez l'espèce Carapa guianensis, une réduction d'environ 40 % du taux d'assimilation nette foliaire a été observée pour des niveaux d'éclairement compris entre 45 % et 65 % du plein découvert. La croissance maximale a sensiblement diminuée dans les conditions de faible éclairement et les taux de croissance étaient différents d'une espèce à l'autre lorsque les plantules étaient cultivées sous un régime lumineux plus fort. L'optimum de croissance, dans les conditions d'expérience, était compris entre 25 % et 45 % du plein découvert. Cependant, Bocoa prouacensis, espèce des stades tardifs de la succession, a présenté une croissance plus élevée pour l'intensité lumineuse la plus forte (65 %) que pour de plus faibles valeurs d'éclairement (< 45 %). (© Inra/Elsevier, Paris.) forêt tropicale humide / assimilation nette foliaire / vitesse de croissance / indice de volume

Research paper thumbnail of Leaf photosynthetic traits of 14 tropical rain forest species in relation to leaf nitrogen concentration and shade tolerance

Tree Physiology, 2005

Variability of leaf traits related to photosynthesis was assessed in seedlings from 14 tree speci... more 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 CO 2 assimilation rate versus intercellular CO 2 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 massbased 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.

Research paper thumbnail of Links between tree structure and functional leaf traits in the tropical forest tree Dicorynia guianensis Amshoff (Caesalpiniaceae)

Annals of Forest Science, 2005

This study looked at the interactive effects of tree architectural stage of development (ASD) and... more This study looked at the interactive effects of tree architectural stage of development (ASD) and light availability on different plant traits (growth parameters, leaf morpho-anatomy and photosynthetic capacities) in the tropical species Dicorynia guianensis. A qualitative architectural analysis was used to categorize tree individuals sampled along a natural light gradient. The results show that some traits could have an ASD-dependence at the whole plant and leaf level without control of light. The changes observed relate to vigour thresholds the plant has to reach to shift from one ASD to another (i.e., the number of nodes and the internodes length per Growth Unit). Light conditions do not modify these thresholds but may modify the time they are crossed. Tree height was found strongly modulated by light conditions; hence, at a similar height, individuals may belong to different ASD. At the functional level, a decrease in N m , and A maxm was observed with increasing light availability, while N a increased and A maxa remained unaffected. An ASD effect was also observed on A maxa and LMA but not on A maxm . These results demonstrated a weak ability of photosynthetic plasticity in response to light conditions, and that variations of leaf photosynthetic variables according to ASD can be explained by modifications in leaf nitrogen and LMA. Questions on the reliability of a height-based sampling strategy for evaluating the phenotypic plasticity of trees in relation to light conditions are raised.

Research paper thumbnail of Leaf photosynthetic traits of 14 tropical rain forest species in relation to leaf nitrogen concentration and shade tolerance

Tree Physiology, 2005

Variability of leaf traits related to photosynthesis was assessed in seedlings from 14 tree speci... more 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 CO 2 assimilation rate versus intercellular CO 2 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 massbased 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.