Efficience d'utilisation de l'eau chez le peuplier noir (Populus nigra L.) : variabilité et plasticité en réponse aux variations de l'environnement.

This work aimed (i) to quantify variability of water-use efficiency (WUE) on black poplar (Populus nigra L.), (ii) to quantify the phenotypic plasticity in response to water deficit and increase of temperature and (iii) to precise the relationships between WUE, growth and leaf survival. Studies on seedlings in growth chambers and in natural conditions, and on populations established in common garden studies were realized. Significant variations and significant plasticity of water-use efficiency were observed on seedlings and adults whatever growth conditions and genetic background. A significant decrease of WUE was observed in response to increase of temperature while an increase of WUE was observed in response to moderate water deficit. Under elevated temperature a significant relationship was observed between WUE and leaf survival suggesting that low WUE confers an advantage for individuals under these conditions. Moreover in situ, a negative relationship between WUE and seedlings density was detected suggesting that low WUE are observed under high seedlings densities. The complex trait ‘water-use efficiency’ should be a limiting character of species establishment under increase of temperatures; this temperature elevation should have consequences on genetic structuration of populations in the future. Our results suggest a geographical structuration of WUE variability but results must be confirmed on several others populations. This present work opens prospects for identification of physiological bases of WUE variations, its plasticity and its geographical structuration.Cette thèse visait (i) à quantifier la variabilité de l’efficience d’utilisation de l’eau (WUE) chez le peuplier noir (Populus nigra L.), (ii) à juger de sa plasticité phénotypique en réponse à des contraintes hydrique et thermique et (iii) à juger des liens entre WUE, croissance et survie. A cette fin, des études à partir de semis, en chambre de croissance et en milieu naturel, ainsi qu’à partir de populations installées en dispositifs de pépinière ont été réalisées. Nos travaux ont permis de montrer une importante variabilité et une importante plasticité du caractère ‘efficience d’utilisation de l’eau’ quels que soient l’échelle d’étude, le fond génétique et les conditions de croissance. Une diminution de WUE a été observée en réponse à la contrainte thermique alors qu’une augmentation de WUE a été observée en réponse à un déficit hydrique modéré. Nos travaux démontrent également un lien entre WUE et la survie sous de fortes températures suggérant que sous ces conditions, une faible efficience d’utilisation de l’eau conférerait un avantage pour les individus. De plus in situ, un lien négatif entre WUE et la densité de régénération a été observé démontrant que les plus faibles valeurs de WUE sont observées pour les plus fortes densités. Le caractère ‘efficience d’utilisation de l’eau’ pourrait donc s’avérer un caractère limitant de la régénération de l’espèce dans des conditions d’augmentation de température ; une telle augmentation pourrait alors avoir une conséquence directe sur la structuration génétique des populations futures. Ces travaux suggèrent enfin une structuration géographique de la variabilité de WUE qui reste à confirmer à partir d’un plus grand nombre de populations. Ce travail ouvre des perspectives intéressantes pour l’identification des bases physiologiques à l’origine des variations de WUE, de sa plasticité et de sa structuration géographique

Water-use efficiency in black poplar (Populus nigra L.) : variability and plasticity in response to environmental variations

Cette thèse visait (i) à quantifier la variabilité de l’efficience d’utilisation de l’eau (WUE) chez le peuplier noir (Populus nigra L.), (ii) à juger de sa plasticité phénotypique en réponse à des contraintes hydrique et thermique et (iii) à juger des liens entre WUE, croissance et survie. A cette fin, des études à partir de semis, en chambre de croissance et en milieu naturel, ainsi qu’à partir de populations installées en dispositifs de pépinière ont été réalisées. Nos travaux ont permis de montrer une importante variabilité et une importante plasticité du caractère ‘efficience d’utilisation de l’eau’ quels que soient l’échelle d’étude, le fond génétique et les conditions de croissance. Une diminution de WUE a été observée en réponse à la contrainte thermique alors qu’une augmentation de WUE a été observée en réponse à un déficit hydrique modéré. Nos travaux démontrent également un lien entre WUE et la survie sous de fortes températures suggérant que sous ces conditions, une faible efficience d’utilisation de l’eau conférerait un avantage pour les individus. De plus in situ, un lien négatif entre WUE et la densité de régénération a été observé démontrant que les plus faibles valeurs de WUE sont observées pour les plus fortes densités. Le caractère ‘efficience d’utilisation de l’eau’ pourrait donc s’avérer un caractère limitant de la régénération de l’espèce dans des conditions d’augmentation de température ; une telle augmentation pourrait alors avoir une conséquence directe sur la structuration génétique des populations futures. Ces travaux suggèrent enfin une structuration géographique de la variabilité de WUE qui reste à confirmer à partir d’un plus grand nombre de populations. Ce travail ouvre des perspectives intéressantes pour l’identification des bases physiologiques à l’origine des variations de WUE, de sa plasticité et de sa structuration géographique.This work aimed (i) to quantify variability of water-use efficiency (WUE) on black poplar (Populus nigra L.), (ii) to quantify the phenotypic plasticity in response to water deficit and increase of temperature and (iii) to precise the relationships between WUE, growth and leaf survival. Studies on seedlings in growth chambers and in natural conditions, and on populations established in common garden studies were realized. Significant variations and significant plasticity of water-use efficiency were observed on seedlings and adults whatever growth conditions and genetic background. A significant decrease of WUE was observed in response to increase of temperature while an increase of WUE was observed in response to moderate water deficit. Under elevated temperature a significant relationship was observed between WUE and leaf survival suggesting that low WUE confers an advantage for individuals under these conditions. Moreover in situ, a negative relationship between WUE and seedlings density was detected suggesting that low WUE are observed under high seedlings densities. The complex trait ‘water-use efficiency’ should be a limiting character of species establishment under increase of temperatures; this temperature elevation should have consequences on genetic structuration of populations in the future. Our results suggest a geographical structuration of WUE variability but results must be confirmed on several others populations. This present work opens prospects for identification of physiological bases of WUE variations, its plasticity and its geographical structuration

Efficience d'utilisation de l'eau chez le peuplier noir (Populus nigra L.) (variabilité et plasticité en réponse aux variations de l'environnement.)

Cette thèse visait (i) à quantifier la variabilité de l efficience d utilisation de l eau (WUE) chez le peuplier noir (Populus nigra L.), (ii) à juger de sa plasticité phénotypique en réponse à des contraintes hydrique et thermique et (iii) à juger des liens entre WUE, croissance et survie. A cette fin, des études à partir de semis, en chambre de croissance et en milieu naturel, ainsi qu à partir de populations installées en dispositifs de pépinière ont été réalisées. Nos travaux ont permis de montrer une importante variabilité et une importante plasticité du caractère efficience d utilisation de l eau quels que soient l échelle d étude, le fond génétique et les conditions de croissance. Une diminution de WUE a été observée en réponse à la contrainte thermique alors qu une augmentation de WUE a été observée en réponse à un déficit hydrique modéré. Nos travaux démontrent également un lien entre WUE et la survie sous de fortes températures suggérant que sous ces conditions, une faible efficience d utilisation de l eau conférerait un avantage pour les individus. De plus in situ, un lien négatif entre WUE et la densité de régénération a été observé démontrant que les plus faibles valeurs de WUE sont observées pour les plus fortes densités. Le caractère efficience d utilisation de l eau pourrait donc s avérer un caractère limitant de la régénération de l espèce dans des conditions d augmentation de température ; une telle augmentation pourrait alors avoir une conséquence directe sur la structuration génétique des populations futures. Ces travaux suggèrent enfin une structuration géographique de la variabilité de WUE qui reste à confirmer à partir d un plus grand nombre de populations. Ce travail ouvre des perspectives intéressantes pour l identification des bases physiologiques à l origine des variations de WUE, de sa plasticité et de sa structuration géographique.This work aimed (i) to quantify variability of water-use efficiency (WUE) on black poplar (Populus nigra L.), (ii) to quantify the phenotypic plasticity in response to water deficit and increase of temperature and (iii) to precise the relationships between WUE, growth and leaf survival. Studies on seedlings in growth chambers and in natural conditions, and on populations established in common garden studies were realized. Significant variations and significant plasticity of water-use efficiency were observed on seedlings and adults whatever growth conditions and genetic background. A significant decrease of WUE was observed in response to increase of temperature while an increase of WUE was observed in response to moderate water deficit. Under elevated temperature a significant relationship was observed between WUE and leaf survival suggesting that low WUE confers an advantage for individuals under these conditions. Moreover in situ, a negative relationship between WUE and seedlings density was detected suggesting that low WUE are observed under high seedlings densities. The complex trait water-use efficiency should be a limiting character of species establishment under increase of temperatures; this temperature elevation should have consequences on genetic structuration of populations in the future. Our results suggest a geographical structuration of WUE variability but results must be confirmed on several others populations. This present work opens prospects for identification of physiological bases of WUE variations, its plasticity and its geographical structuration.ORLEANS-SCD-Bib. electronique (452349901) / SudocSudocFranceF

La dysbiose, une nouvelle entité en médecine ?

International audienc

NOD2 prevents emergence of disease-predisposing microbiota

International audienceThe gut flora is composed of a huge number of diverse, well-adapted symbionts that interact with epithelial lining throughout the host's entire life. Not all commensals have the same ability to maintain quiescent, protective inflammation. Importantly, instability in the composition of gut microbial communities (referred to as dysbiosis) has been linked to loss of gut barrier in the context of common human illnesses with increasing socio-economic impacts, such as Crohn disease and colorectal cancer. Our recent findings suggest that disease-predisposing dysbiosis can now be intentionally manipulated by targeting the major Crohn disease-predisposing NOD2 gene. That knowledge will not only add a new dimension to the often overlooked microbiology of Crohn disease and colorectal cancer, but will also have a broad impact on biomedical sciences worldwide

Hydraulic efficiency and coordination with xylem resistance to cavitation, leaf function, and growth performance among eight unrelated Populus deltoidesxPopulus nigra hybrids

Tests were carried out to determine whether variations in the hydraulic architecture of eight Populus deltoides3Populus nigra genotypes could be related to variations in leaf function and growth performance. Measurements were performed in a coppice plantation on 1-year-old shoots under optimal irrigation. Hydraulic architecture was characterized through estimates of hydraulic efficiency (the ratio of conducting sapwood area to leaf area, AX:AL; leaf- and xylem-specific hydraulic conductance of defoliated shoots, kSL and kSS, respectively; apparent whole-plant leaf-specific hydraulic conductance, kplant) and xylem safety (water potential inducing 50% loss in hydraulic conductance). The eight genotypes spanned a significant range of kSL from 2.63 kg s21 m22 MPa21 to 4.18 kg s21 m22 MPa21, variations being mostly driven by kSS rather than AX:AL. There was a strong trade-off between hydraulic efficiency and xylem safety. Values of kSL correlated positively with kplant, indicating that highpressure flowmeter (HPFM) measurements of stem hydraulic efficiency accurately reflected whole-plant water transport efficiency of field-grown plants at maximum transpiration rate. No clear relationship could be found between hydraulic efficiency and either net CO2 assimilation rates, water-use efficiency estimates (intrinsic wateruse efficiency and carbon isotope discrimination against 13C), or stomatal characteristics (stomatal density and stomatal pore area index). Estimates of hydraulic efficiency were negatively associated with relative growth rate. This unusual pattern, combined with the trade-off observed between hydraulic efficiency and xylem safety, provides the rationale for the positive link already reported between relative growth rate and xylem safety among the same eight P. deltoides3P. nigra genotypes

Architecture hydraulique du xylème, efficience d’utilisation de l’eau et croissance chez le peuplier. 1. Efficience hydraulique

National audienc

Common trade-offs between xylem resistance to cavitation and other physiological traits do not hold among unrelated Populus deltoidesx Populus nigra hybrids

We examined the relationships between xylem resistance to cavitation and 16 structural and functional traits across eight unrelated Populus deltoides x Populus nigra genotypes grown under two contrasting water regimes. The xylem water potential inducing 50% loss of hydraulic conductance (Psi(50)) varied from -1.60 to -2.40 MPa. Drought-acclimated trees displayed a safer xylem, although the extent of the response was largely genotype dependant, with Psi(50) being decreased by as far as 0.60 MPa. At the tissue level, there was no clear relationship between xylem safety and either xylem water transport efficiency or xylem biomechanics; the only structural trait to be strongly associated with Psi(50) was the double vessel wall thickness, genotypes exhibiting a thicker double wall being more resistant. At the leaf level, increased cavitation resistance was associated with decreased stomatal conductance, while no relationship could be identified with traits associated with carbon uptake or bulk leaf carbon isotope discrimination, a surrogate of intrinsic water-use efficiency. At the whole-plant level, increased safety was associated with higher shoot growth potential under well-irrigated regime only. We conclude that common trade-offs between xylem resistance to cavitation and other physiological traits that are observed across species may not necessarily hold true at narrower scales

Plasticité de la croissance de la résistance à la cavitation et des caractères anatomiques du xylème en réponse à la sécheresse chez Populus deltoides x Populus nigra

absen

Variations in bulk leaf carbon isotope discrimination, growth and related leaf traits among three Populus nigra L. populations

The ongoing global change could be an additional threat to the establishment and the long-term survival of Populus nigra L., an emblematic European riparian species. With the general aim of gaining insights into the adaptive potential of this species, we (i) quantified variations within and among three French P. nigra populations for key physiological attributes, i.e., water-use efficiency (assessed from bulk leaf carbon isotope discrimination, Δ13C), growth performance and related leaf traits, (ii) examined genotype and population by environment interactions, and (iii) explored the relationship between Δ13C and growth. Thirty genotypes were sampled in each of three naturally established populations and grown in two different sites, Orléans (ORL) and Guémené-Penfao (GMN). In ORL, two similar plots were established and different watering regimes were applied in order to test for the drought response. Significant variations were observed for all traits within and among populations irrespective of site and watering. Trait variation was larger within than among populations. The effect of drought was neither genotype- nor population-dependent, contrary to the effect of site. The population ranking was maintained in all sites and watering regimes for the two most complex traits: Δ13C and growth. Moreover, these two traits were unrelated, which indicates that (i) water-use efficiency and growth are largely uncoupled in this species, and (ii) the environmental factors driving genetic structuration for Δ13C and growth act independently. The large variations found within populations combined with the consistent differences among populations suggest a large adaptive potential for P. nigra