13 research outputs found
Traits fonctionnels, tolérances et distributions des espÚces herbacées sur un gradient de disponibilité en eau : une approche prédictive par modÚle d'équation structurale
Lâassemblage des espĂšces (leurs prĂ©sences/absence) dans une communautĂ© naturelle est la consĂ©quence de plusieurs mĂ©canismes de filtrage rĂ©alisĂ©s par l'environnement. Parmi ces filtres, le filtre abiotique sĂ©lectionne les espĂšces capables de tolĂ©rer les conditions environnementales locales. La variation de la disponibilitĂ© de l'eau dans le sol est l'un des principaux gradients environnementaux selon lesquels les espĂšces vĂ©gĂ©tales sont diffĂ©remment rĂ©parties. ConsidĂ©rant lâhypothĂšse que les traits fonctionnels et leurs relations sont hiĂ©rarchisĂ©es, les prĂ©fĂ©rences dâhabitat des espĂšces le long de gradients environnementaux devraient ĂȘtre dĂ©terminĂ©es par une combinaison de traits physiologiques et morpho-anatomiques hiĂ©rarchisĂ©s.
Au cours de ce doctorat, mon objectif gĂ©nĂ©ral est d'identifier les traits fonctionnels morphologiques, anatomiques et physiologiques de tolĂ©rance Ă la sĂ©cheresse qui peuvent prĂ©dire la prĂ©sence des espĂšces le long d'un gradient dâhydrologie des sols. Plus spĂ©cifiquement, nous cherchons Ă savoir : (i) Quels sont les traits physiologiques qui reflĂštent le mieux la tolĂ©rance Ă la sĂ©cheresse ? (ii) Quelles sont les relations entre les traits morpho-anatomiques et les traits physiologiques de tolĂ©rance ? (iii) Quels sont les traits morpho-anatomiques en conditions optimales permettant de prĂ©dire la tolĂ©rance des espĂšces herbacĂ©es Ă la sĂ©cheresse ? (iv) Quelles formes ont les relations qui existe entre les traits morpho-anatomiques de tolĂ©rance en condition optimale et la prĂ©sence des espĂšces en cas de sĂ©cheresse ? (v) Peut-on prĂ©dire les prĂ©sences des espĂšces en cas de sĂ©cheresse Ă partir de leurs traits morpho-anatomiques?
Nos rĂ©sultats montrent (1) quâil est possible de prĂ©dire la distribution des espĂšces sur un gradient dâhydrologie des sols Ă partir de cinq traits physiologiques de tolĂ©rance Ă la sĂ©cheresse. Ces cinq traits sont la photosynthĂšse nette maximale, la conductance stomatique maximale, le potentiel hydrique du sol au point de flĂ©trissement, la conductance stomatique au point de flĂ©trissement et lâefficacitĂ© dâutilisation de lâeau au point de flĂ©trissement. Nous avons montrĂ© que (ii) les traits physiologiques de tolĂ©rance Ă la sĂ©cheresse sont prĂ©dits par les traits morpho-anatomiques en conditions optimales (surface spĂ©cifique foliaire, teneur en matiĂšre sĂšche des feuilles, teneur en azote foliaire, longueur spĂ©cifique racinaire et surface stomatique). (iii) Les traits morpho-anatomiques seuls ne sont pas de bons prĂ©dicteurs de lâhydrologie des espĂšces et (iv) que la sĂ©quence « traits morpho-anatomiques â traits physiologiques â hydrologie des espĂšces » donne les meilleures prĂ©dictions. Cependant, (v) le modĂšle ne donne pas de prĂ©dictions fiables si lâon utilise des traits morpho-anatomiques mesurĂ©s en conditions naturelles. Ces rĂ©sultats confirment, au moins partiellement, lâhypothĂšse que la distribution des espĂšces sur un gradient hydrologiques peut ĂȘtre prĂ©dite Ă partir de leurs traits de tolĂ©rance Ă la sĂ©cheresse eux-mĂȘmes prĂ©dits par leurs traits morpho-anatomiques.
En rĂ©sumĂ©, nous avons utilisĂ© une approche fonctionnelle en construisant un modĂšle causal prĂ©dictif qui nous a permis de nous intĂ©resser aux mĂ©canismes de filtrage environnementaux et plus prĂ©cisĂ©ment au rĂŽle de la niche hydrologique des espĂšces dans lâassemblage des communautĂ©s vĂ©gĂ©tales.Abstract : Species assembly (their presence/absence) in a natural community is the consequence of several filtering mechanisms made by the environment. Among these filters, the abiotic filter selects
species able to tolerate local environmental conditions. Variation in water availability in the soil is one of the main environmental gradients according to which plant species are differently distributed. Considering the hypothesis that functional traits and their relationships are hierarchical, habitat preferences of species along environmental gradients should be determined by a combination of hierarchical physiological and morpho-anatomical traits. During this PhD, my overall goal is to identify morphological, anatomical and physiological drought tolerance functional traits that can predict the presence of species along a soil hydrology gradient. More specifically : (i) What are the physiological traits that best reflect drought
tolerance? (ii) What are the relationships between morpho-anatomical traits and physiological traits of tolerance? (iii) What are the optimal morpho-anatomical traits for predicting tolerance of herbaceous species to drought? (iv) What forms of relationships exist between optimal morpho-anatomical traits of tolerance and the presence of species in drought condition? (v) Can the presence of species in drought condition be predicted from their morpho-anatomical features? Our results show (1) that it is possible to predict the distribution of species on a soil hydrology gradient from five physiological traits of drought tolerance. These five traits are maximum net photosynthesis, maximum stomatal conductance, water potential of the soil at the wilting point, stomatal conductance at the wilting point, and efficiency of water use at the wilting point. We have shown that (ii) the physiological traits of drought tolerance are predicted by optimal morpho-anatomical traits (leaf area, leaf dry matter content, leaf nitrogen content, root length
and stomatal surface). (iii) Morpho-anatomical features alone are not good predictors of species hydrology and (iv) the sequence âmorpho-anatomical traits physiological traits species hydrologyâ gives the best predictions. However (v) the model does not provide reliable predictions using morpho-anatomical traits measured under natural conditions. These results confirm, at least partially, the hypothesis that the distribution of species on a hydrological gradient can be predicted from their drought tolerance traits themselves predicted by their morpho-anatomical features. In summary, we used a functional approach by constructing a predictive causal model that allowed us to focus on environmental filtering mechanisms and more specifically on the role of the species hydrological niche in assembling plant communities
Traits fonctionnels, tolérances et distributions des espÚces herbacées sur un gradient de disponibilité en eau : une approche prédictive par modÚle d'équation structurale
Lâassemblage des espĂšces (leurs prĂ©sences/absence) dans une communautĂ© naturelle est la consĂ©quence de plusieurs mĂ©canismes de filtrage rĂ©alisĂ©s par l'environnement. Parmi ces filtres, le filtre abiotique sĂ©lectionne les espĂšces capables de tolĂ©rer les conditions environnementales locales. La variation de la disponibilitĂ© de l'eau dans le sol est l'un des principaux gradients environnementaux selon lesquels les espĂšces vĂ©gĂ©tales sont diffĂ©remment rĂ©parties. ConsidĂ©rant lâhypothĂšse que les traits fonctionnels et leurs relations sont hiĂ©rarchisĂ©es, les prĂ©fĂ©rences dâhabitat des espĂšces le long de gradients environnementaux devraient ĂȘtre dĂ©terminĂ©es par une combinaison de traits physiologiques et morpho-anatomiques hiĂ©rarchisĂ©s.
Au cours de ce doctorat, mon objectif gĂ©nĂ©ral est d'identifier les traits fonctionnels morphologiques, anatomiques et physiologiques de tolĂ©rance Ă la sĂ©cheresse qui peuvent prĂ©dire la prĂ©sence des espĂšces le long d'un gradient dâhydrologie des sols. Plus spĂ©cifiquement, nous cherchons Ă savoir : (i) Quels sont les traits physiologiques qui reflĂštent le mieux la tolĂ©rance Ă la sĂ©cheresse ? (ii) Quelles sont les relations entre les traits morpho-anatomiques et les traits physiologiques de tolĂ©rance ? (iii) Quels sont les traits morpho-anatomiques en conditions optimales permettant de prĂ©dire la tolĂ©rance des espĂšces herbacĂ©es Ă la sĂ©cheresse ? (iv) Quelles formes ont les relations qui existe entre les traits morpho-anatomiques de tolĂ©rance en condition optimale et la prĂ©sence des espĂšces en cas de sĂ©cheresse ? (v) Peut-on prĂ©dire les prĂ©sences des espĂšces en cas de sĂ©cheresse Ă partir de leurs traits morpho-anatomiques?
Nos rĂ©sultats montrent (1) quâil est possible de prĂ©dire la distribution des espĂšces sur un gradient dâhydrologie des sols Ă partir de cinq traits physiologiques de tolĂ©rance Ă la sĂ©cheresse. Ces cinq traits sont la photosynthĂšse nette maximale, la conductance stomatique maximale, le potentiel hydrique du sol au point de flĂ©trissement, la conductance stomatique au point de flĂ©trissement et lâefficacitĂ© dâutilisation de lâeau au point de flĂ©trissement. Nous avons montrĂ© que (ii) les traits physiologiques de tolĂ©rance Ă la sĂ©cheresse sont prĂ©dits par les traits morpho-anatomiques en conditions optimales (surface spĂ©cifique foliaire, teneur en matiĂšre sĂšche des feuilles, teneur en azote foliaire, longueur spĂ©cifique racinaire et surface stomatique). (iii) Les traits morpho-anatomiques seuls ne sont pas de bons prĂ©dicteurs de lâhydrologie des espĂšces et (iv) que la sĂ©quence « traits morpho-anatomiques â traits physiologiques â hydrologie des espĂšces » donne les meilleures prĂ©dictions. Cependant, (v) le modĂšle ne donne pas de prĂ©dictions fiables si lâon utilise des traits morpho-anatomiques mesurĂ©s en conditions naturelles. Ces rĂ©sultats confirment, au moins partiellement, lâhypothĂšse que la distribution des espĂšces sur un gradient hydrologiques peut ĂȘtre prĂ©dite Ă partir de leurs traits de tolĂ©rance Ă la sĂ©cheresse eux-mĂȘmes prĂ©dits par leurs traits morpho-anatomiques.
En rĂ©sumĂ©, nous avons utilisĂ© une approche fonctionnelle en construisant un modĂšle causal prĂ©dictif qui nous a permis de nous intĂ©resser aux mĂ©canismes de filtrage environnementaux et plus prĂ©cisĂ©ment au rĂŽle de la niche hydrologique des espĂšces dans lâassemblage des communautĂ©s vĂ©gĂ©tales.Abstract : Species assembly (their presence/absence) in a natural community is the consequence of several filtering mechanisms made by the environment. Among these filters, the abiotic filter selects
species able to tolerate local environmental conditions. Variation in water availability in the soil is one of the main environmental gradients according to which plant species are differently distributed. Considering the hypothesis that functional traits and their relationships are hierarchical, habitat preferences of species along environmental gradients should be determined by a combination of hierarchical physiological and morpho-anatomical traits. During this PhD, my overall goal is to identify morphological, anatomical and physiological drought tolerance functional traits that can predict the presence of species along a soil hydrology gradient. More specifically : (i) What are the physiological traits that best reflect drought
tolerance? (ii) What are the relationships between morpho-anatomical traits and physiological traits of tolerance? (iii) What are the optimal morpho-anatomical traits for predicting tolerance of herbaceous species to drought? (iv) What forms of relationships exist between optimal morpho-anatomical traits of tolerance and the presence of species in drought condition? (v) Can the presence of species in drought condition be predicted from their morpho-anatomical features? Our results show (1) that it is possible to predict the distribution of species on a soil hydrology gradient from five physiological traits of drought tolerance. These five traits are maximum net photosynthesis, maximum stomatal conductance, water potential of the soil at the wilting point, stomatal conductance at the wilting point, and efficiency of water use at the wilting point. We have shown that (ii) the physiological traits of drought tolerance are predicted by optimal morpho-anatomical traits (leaf area, leaf dry matter content, leaf nitrogen content, root length
and stomatal surface). (iii) Morpho-anatomical features alone are not good predictors of species hydrology and (iv) the sequence âmorpho-anatomical traits ï physiological traits ï species hydrologyâ gives the best predictions. However (v) the model does not provide reliable predictions using morpho-anatomical traits measured under natural conditions. These results confirm, at least partially, the hypothesis that the distribution of species on a hydrological gradient can be predicted from their drought tolerance traits themselves predicted by their morpho-anatomical features. In summary, we used a functional approach by constructing a predictive causal model that allowed us to focus on environmental filtering mechanisms and more specifically on the role of the species hydrological niche in assembling plant communities
Linking hard and soft traits: Physiology, morphology and anatomy interact to determine habitat affinities to soil water availability in herbaceous dicots
<div><p>Background and aims</p><p>Speciesâ habitat affinities along environmental gradients should be determined by a combination of physiological (hard) and morpho-anatomical (soft) traits. Using a gradient of soil water availability, we address three questions: How well can we predict habitat affinities from hard traits, from soft traits, and from a combination of the two? How well can we predict species' physiological responses to drought (hard traits) from their soft traits? Can we model a causal sequence as soft traits â hard traits â species distributions?</p><p>Methods</p><p>We chose 25 species of herbaceous dicots whose affinities for soil moisture have already been linked to 5 physiological traits (stomatal conductance and net photosynthesis measured at soil field capacity, water use efficiency, stomatal conductance and soil water potential measured when leaves begin to wilt). Under controlled conditions in soils at field capacity, we measured five soft traits (leaf dry matter content, specific leaf area, leaf nitrogen content, stomatal area, specific root length).</p><p>Key results</p><p>Soft traits alone were poor predictors (R<sup>2</sup> = 0.129) while hard traits explained 48% of species habitat affinities. Moreover, hard traits were significantly related to combinations of soft traits. From <i>a priori</i> biological knowledge and hypothesized ecological links we built a path model showing a sequential pattern soft traits â hard traits â species distributions and accounting for 59.6% (<i>p</i> = 0.782) of habitat wetness.</p><p>Conclusions</p><p>Both direct and indirect causal relationships existed between soft traits, hard traits and speciesâ habitat preferences. The poor predictive abilities of soft traits alone were due to the existence of antagonistic and synergistic direct and indirect effects of soft traits on habitat preferences mediated by the hard traits. To obtain a more realistic model applicable to a population level, it has to be tested in an experiment including species competition for water supply.</p></div
Stepwise backward linear regression, based on AIC values, of each of five hard traits (A<sub>wilt</sub>, gswilt, Κ<sub>wilt</sub>, gsmax, A<sub>max</sub>) on a linear combination of five soft traits (leaf dry matter content (LDMC, g g<sup>-1</sup>), specific leaf area (SLA, m<sup>2</sup> kg<sup>-1</sup>), leaf nitrogen content (LNC, mg g<sup>-1</sup>), stomatal area (stom<sub>area</sub>, (Όm) and specific root length (SRL, m g<sup>-1</sup>)).
<p>Stepwise backward linear regression, based on AIC values, of each of five hard traits (A<sub>wilt</sub>, gswilt, Κ<sub>wilt</sub>, gsmax, A<sub>max</sub>) on a linear combination of five soft traits (leaf dry matter content (LDMC, g g<sup>-1</sup>), specific leaf area (SLA, m<sup>2</sup> kg<sup>-1</sup>), leaf nitrogen content (LNC, mg g<sup>-1</sup>), stomatal area (stom<sub>area</sub>, (Όm) and specific root length (SRL, m g<sup>-1</sup>)).</p
Cumulative link model analysis of the hard and soft traits as predictors of the habitat wetness preferences.
<p>Cumulative link model analysis of the hard and soft traits as predictors of the habitat wetness preferences.</p
Path analysis of the physiological and morphological traits.
<p>There is no significant misfit between the empirical data and the causal structure specified by the model (Satorra-Bentler robust Chi-square = 40.795; 42 df; <i>p</i> = 0.782; Comparative Fit Index (CFI) = 1.00; Root Mean Square Error of Approximation (RMSEA) = 0.00), Akaike information criterion (AIC) = 804.037. All path coefficients are significantly different from zero, otherwise the pathsâ significativity are specified in the diagram. The R<sup>2</sup> are the percentage of variance explained by the causal variables. Values on the lines are the path coefficients between the causal variable and the caused variable. Solid lines are positive causal relationships and dashed lines are the negative ones. Thickness of the lines is proportional to the strength of path coefficients. For all traits, we used the average value of five individuals per species. For all leaf traits, we excluded the petioles because petioles donât belong to the same function as the leaf blade (i.e. support for petioles and acquisition for leaf blade). Leaves were chosen to be representative of the average mature leaf into one individual and we avoided newly formed leaves or ones showing any sign of senescence.</p
List and description of the soft and hard traits used in the analysis.
<p>List and description of the soft and hard traits used in the analysis.</p
Box plots showing the differences between species means of the soft trait values.
<p>Traits are measured at field capacity and grouped by species according to affinity for habitat wetness. "D" (species typical of "dry" soils), "I" (species typical of "intermediate" soils), "W" (species typical of "wet" soils). Non-parametric (Kruskal-Wallis) 1-way ANOVAs did not detect any significant differences between the three species groups for any of these five traits.</p
<i>Arabidopsis</i> growth under prolonged high temperature and water deficit: independent or interactive effects?
International audienceHigh temperature (HT) and water deficit (WD) are frequent environmental constraints restricting plant growth and productivity. These stresses often occur simultaneously in the field, but little is known about their combined impacts on plant growth, development and physiology. We evaluated the responses of 10 Arabidopsis thaliana natural accessions to prolonged elevated air temperature (30 °C) and soil WD applied separately or in combination. Plant growth was significantly reduced under both stresses and their combination was even more detrimental to plant performance. The effects of the two stresses were globally additive, but some traits responded specifically to one but not the other stress. Root allocation increased in response to WD, while reproductive allocation, hyponasty and specific leaf area increased under HT. All the traits that varied in response to combined stresses also responded to at least one of them. Tolerance to WD was higher in small-sized accessions under control temperature and HT and in accessions with high biomass allocation to root under control conditions. Accessions that originate from sites with higher temperature have less stomatal density and allocate less biomass to the roots when cultivated under HT. Independence and interaction between stresses as well as the relationships between traits and stress responses are discussed