The Experts below are selected from a list of 43713 Experts worldwide ranked by ideXlab platform
HervÉ Cochard - One of the best experts on this subject based on the ideXlab platform.
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tree differences in primary and secondary growth drive convergent scaling in leaf area to sapwood area across europe
2018Co-Authors: Giai Petit, HervÉ Cochard, Natasa Kiorapostolou, Silvia Lechthaler, Angela Luisa Prendin, Tommaso Anfodillo, Maria C Caldeira, P Copini, Alan CrivellaroAbstract:Trees scale leaf (A(L)) and Xylem (A(X)) areas to couple leaf transpiration and carbon gain with Xylem water transport. Some species are known to acclimate in A(L) : A(X) balance in response to climate conditions, but whether trees of different species acclimate in A(L) : A(X) in similar ways over their entire (continental) distributions is unknown. We analyzed the species and climate effects on the scaling of A(L) vs A(X) in branches of conifers (Pinus sylvestris, Picea abies) and broadleaved (Betula pendula, Populus tremula) sampled across a continental wide transect in Europe. Along the branch axis, A(L) and A(X) change in equal proportion (isometric scaling: b similar to 1) as for trees. Branches of similar length converged in the scaling of A(L) vs A(X) with an exponent of b = 0.58 across European climates irrespective of species. Branches of slow- growing trees from Northern and Southern regions preferentially allocated into new leaf rather than Xylem area, with older Xylem rings contributing to maintaining total Xylem conductivity. In conclusion, trees in contrasting climates adjust their functional balance between water transport and leaf transpiration by maintaining biomass allocation to leaves, and adjusting their growth rate and Xylem production to maintain Xylem conductance.
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Improvement to the air-injection technique to estimate Xylem vulnerability to cavitation
2011Co-Authors: Mustapha Ennajeh, Mourad Nouiri, Habib Khemira, HervÉ CochardAbstract:Several techniques have been developed to quantify the degree of embolism of the Xylem using hydraulic conductance. Although there have been several improvements to these techniques, their reliability is still questionable and many technical pitfalls persist. We are proposing here a manometric approach to improve the accuracy of Xylem cavitation measurement by the original air-injection technique which uses twigs exposed to pressurized air to cause cavitation. The measured parameter is air bubble production (P (b)) caused by Xylem cavitation in birch (Betula pendula Roth) twigs from which the percent increase in bubble production is calculated to quantify Xylem cavitation. Data produced by three different methods (bench-drying, air-injection, and manometric approach) are compared. Xylem vulnerability curves (VCs) constructed by the reference and reliable bench-drying technique and the manometric approach show similar sigmoid "S" shape, but a small anomaly appeared in the VC constructed by the original air-injection technique. The Xylem pressure inducing 50% of embolism (P (50)) was the same with the three techniques. Furthermore, there was a strong positive correlation between the estimators of Xylem cavitation measured by the three different methods. For its reliability, precision and ease we recommend the manometric technique as an improved version of the original hydraulic air-injection method.
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evaluation of a new centrifuge technique for rapid generation of Xylem vulnerability curves
2005Co-Authors: HervÉ Cochard, Ibrahim Tharwat, Magalie Poirier, Christian Bodet, Gaelle Damour, Thierry AmeglioAbstract:A new technique for generating Xylem cavitation and vulnerability curves was evaluated. The centrifugal force was used to lower the negative pressure in a Xylem segment and to induce a positive pressure difference between sample's ends. This enabled the determination of sample hydraulic conductance during centrifugation and, hence, its variation with decreasing Xylem pressures. The centrifuge technique was compared with standard methods on a large number of species including conifers, diffuse-porous and ring-porous woody angiosperms. A very good agreement was found for coniferous and diffuse-porous species. However, the technique was not appropriate for ring-porous species, probably because many vessels were cut open in the centrifuged Xylem segments. The main advantage of this technique is its rapidity, the vulnerability curve of a Xylem segment being constructed typically in less than half an hour. This will greatly facilitate the study of Xylem cavitation in ecological or genetic researches.
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seasonal variation in Xylem pressure of walnut trees root and stem pressures
2001Co-Authors: Frank W Ewers, Christian Bodet, HervÉ Cochard, Thierry Ameglio, Francois Beaujard, Michel Martignac, Marc Vandame, Pierre CruiziatAbstract:Measurements of air and soil temperatures and Xylem pressure were made on 17-year-old orchard trees and on 5-year-old potted trees of walnut (Juglans regia L.). Cooling chambers were used to determine the relationships between temperature and sugar concentration ([glucose] + [fructose] + [sucrose], GFS) and seasonal changes in Xylem pressure development. Pressure transducers were attached to twigs of intact plants, root stumps and excised shoots while the potted trees were subjected to various temperature regimes in autumn, winter and spring. Osmolarity and GFS of the Xylem sap (apoplast) were measured before and after cooling or warming treatments. In autumn and spring, Xylem pressures of up to 160 kPa were closely correlated with soil temperature but were not correlated with GFS in Xylem sap. High root pressures were associated with uptake of mineral nutrients from soil, especially nitrate. In autumn and spring, Xylem pressures were detected in root stumps as well as in intact plants, but not in excised stems. In contrast, in winter, 83% of the Xylem sap osmolarity in both excised stems and intact plants could be accounted for by GFS, and both GFS and osmolarity were inversely proportional to temperature. Plants kept at 1.5 degrees C developed positive Xylem pressures up to 35 kPa, Xylem sap osmolarities up to 260 mosmol l(-1) and GFS concentrations up to 70 g l(-1). Autumn and spring Xylem pressures, which appeared to be of root origin, were about 55% of the theoretical pressures predicted by osmolarity of the Xylem sap. In contrast, winter pressures appeared to be of stem origin and were only 7% of the theoretical pressures, perhaps because of a lower stem water content during winter.
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developmental control of Xylem hydraulic resistances and vulnerability to embolism in fraxinus excelsior l impacts on water relations
1997Co-Authors: HervÉ Cochard, Marianne Peiffer, Karine Le Gall, Granier AndreAbstract:The hydraulic properties and leaf gas exchanges of Fraxinus excelsior L. branches differing by their age and their vertical crown position, but in comparable ambient air conditions (vapour pressure deficit and global radiation) were compared. The variations in leaflet water potential ψleaflet, leaflet stomatal conductance and transpiration rate, E, were small between different branches of the same crown. Whole branch hydraulic resistances (r branch ), and partitioning between leaf (r leaf ) and Xylem resistance (r Xylem ) were assessed with a high pressure flowmeter. r leaf represented 90% and 10% of r branch for upper and lower crown branches, respectively. The changes resulted from increases in r Xylem caused by the formation of short shoot internodes mostly located in secondary axes. However, leaf area-specific branch resistances (r branch =r branch x LA) were nearly constant throughout the crown. This was consistent with the vertical variations in ψ leaflet because r branch x E represents the water potential drop from the trunk to the leaves. Because r Xylem was higher, lower ψXylem values were predicted in lower crown rachises. However, rachises from lower crown branches were less vulnerable to embolism than in upper branches ( ψXylem at onset of embolism, ψ cav, were -3 and -2MPa, respectively). It was concluded that r Xylem increased with branch age, but r* branch remained constant because LA decreased. As a consequence, E was maximized and ψXylem remained above ψcav, This suggested that, in Fraxinus, leaf gas exchanges and leaf areas were coupled with Xylem hydraulic capacities probably through a control of bud activity.
Kenji Fukuda - One of the best experts on this subject based on the ideXlab platform.
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dynamics of Xylem and phloem sap flow in an outdoor zelkova tree visualized by magnetic resonance imaging
2020Co-Authors: Yasuhiko Terada, Yusuke Horikawa, Akiyoshi Nagata, Katsumi Kose, Kenji FukudaAbstract:: Xylem and phloem sap flows in an intact, young Japanese zelkova tree (Zelkova serrata [Thunb.] Makino) growing outdoors were measured using magnetic resonance imaging (MRI). Two propagator-based sequences were developed for q-space imaging: pulse field gradient (PFG) with spin echo (PFG-SE) and stimulated echo (PFG-STE), which were used for Xylem and phloem flow measurements, respectively. The data evaluation methods were improved to image fast Xylem flow and slow phloem flow. Measurements were taken every 2-3 h for several consecutive days in August 2016, and diurnal changes in Xylem and phloem sap flows in a cross-section of the trunk were quantified at a resolution of 1 mm2. During the day, apparent Xylem flow volume exhibited a typical diurnal pattern following a vapor pressure deficit. The velocity mapping of Xylem sap flow across the trunk cross-section revealed that the greatest flow volume was found in current-year earlywood that had differentiated in April-May. The combined Xylem flow in the 1- and 2-year-old annual rings also contributed to one-third of total sap flow. In the phloem, downward sap flow did not exhibit diurnal changes. This novel application of MRI in visualization of Xylem and phloem sap flow by MRI is a promising tool for in vivo study of water transport in mature trees.
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short time Xylem tension relaxation prevents vessel refilling and alleviates cryo fixation artifacts in diffuse porous carpinus tschonoskii and cercidiphyllum japonicum
2019Co-Authors: Mayumi Y Ogasa, Naoko Miki, Kenichi Yazaki, Yasuhiro Utsumi, Kenji FukudaAbstract:Xylem tension relaxation is an important procedure that closely resembles the in vivo Xylem water distribution when measuring conductivity or observing water distribution of plant tissue samples by cryo-scanning electron microscopy (cryo-SEM). Recent studies have shown that partial Xylem embolism occurs when samples under tension are cut under water and that gas-filled vessels are refilled during tension relaxation. Furthermore, the frequency of gas-filled vessels has been reported to increase in samples without tension relaxation before cryo-fixation by liquid nitrogen, particularly in samples with significant tension. Here, we examined the effect of tension relaxation on these artifacts in Carpinus tschonoskii and Cercidiphyllum japonicum using magnetic resonance imaging. We observed that Xylem embolism rarely occurs in bench-dried samples cut under water. In both species, a small portion of the Xylem was refilled within ~1 h after tension relaxation. Cryo-SEM observations revealed that short-time (<1 h) Xylem tension relaxation decreases the frequency of gas-filled vessels in samples frozen after Xylem tension relaxation regardless of the water potential compared with that in samples frozen without rehydration in both species. Therefore, short-time tension relaxation is necessary to retain Xylem water distribution during sample preparation against artifacts.
Mayumi Y Ogasa - One of the best experts on this subject based on the ideXlab platform.
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short time Xylem tension relaxation prevents vessel refilling and alleviates cryo fixation artifacts in diffuse porous carpinus tschonoskii and cercidiphyllum japonicum
2019Co-Authors: Mayumi Y Ogasa, Naoko Miki, Kenichi Yazaki, Yasuhiro Utsumi, Kenji FukudaAbstract:Xylem tension relaxation is an important procedure that closely resembles the in vivo Xylem water distribution when measuring conductivity or observing water distribution of plant tissue samples by cryo-scanning electron microscopy (cryo-SEM). Recent studies have shown that partial Xylem embolism occurs when samples under tension are cut under water and that gas-filled vessels are refilled during tension relaxation. Furthermore, the frequency of gas-filled vessels has been reported to increase in samples without tension relaxation before cryo-fixation by liquid nitrogen, particularly in samples with significant tension. Here, we examined the effect of tension relaxation on these artifacts in Carpinus tschonoskii and Cercidiphyllum japonicum using magnetic resonance imaging. We observed that Xylem embolism rarely occurs in bench-dried samples cut under water. In both species, a small portion of the Xylem was refilled within ~1 h after tension relaxation. Cryo-SEM observations revealed that short-time (<1 h) Xylem tension relaxation decreases the frequency of gas-filled vessels in samples frozen after Xylem tension relaxation regardless of the water potential compared with that in samples frozen without rehydration in both species. Therefore, short-time tension relaxation is necessary to retain Xylem water distribution during sample preparation against artifacts.
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recovery performance in Xylem hydraulic conductivity is correlated with cavitation resistance for temperate deciduous tree species
2013Co-Authors: Mayumi Y Ogasa, Naoko Miki, Yuki Murakami, Ken YoshikawaAbstract:Woody species hydraulically vulnerable to Xylem cavitation may experience daily Xylem embolism. How such species cope with the possibility of accumulated embolism is unclear. In this study, we examined seven temperate woody species to assess the hypothesis that low cavitation resistance (high vulnerability to cavitation) is compensated by high recovery performance via vessel refilling. We also evaluated leaf functional and Xylem structural traits. The Xylem recovery index (XRI), defined as the ratio of Xylem hydraulic conductivity in plants rewatered after soil drought to that in plants under moist conditions, varied among species. The Xylem water potential causing 50% loss of hydraulic conductivity (Ψ50) varied among the species studied, whereas only a slight difference was detected with respect to midday Xylem water potential (Ψmin), indicating smaller hydraulic safety margins (Ψmin − Ψ50) for species more vulnerable to cavitation. Cavitation resistance (|Ψ50|) was negatively correlated with XRI across species, with cavitation-vulnerable species showing a higher performance in Xylem recovery. Wood density was positively correlated with cavitation resistance and was negatively correlated with XRI. These novel results reveal that coordination exists between cavitation resistance and Xylem recovery performance, in association with wood functional traits such as denser wood for cavitation-resistant Xylem and less-dense but water-storable wood for refillable Xylem. These findings provide insights into long-term maintenance of water transport in tree species growing under variable environmen tal conditions.
Thierry Ameglio - One of the best experts on this subject based on the ideXlab platform.
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Carbohydrate uptake from Xylem vessels and its distribution among stem tissues and buds in walnut (Juglans regia L.).
2010Co-Authors: Marc Bonhomme, Thierry Ameglio, Médéric Peuch, Rémy Rageau, Agnès Guillot, Mélanie Decourteix, Georges Alves, Soulaiman Sakr, André LacointeAbstract:Bud break pattern is a key determinant of tree architecture. The mechanisms leading to the precedence of certain buds over the others are not yet fully explained, but the availability of soluble sugars may play a significant role, especially those in the Xylem sap at the onset of the growing period. Here, we measured carbon availability in the different tissues (bud, Xylem and bark). To assess the capacity of buds to use the Xylem sap carbohydrates, the fluxes between Xylem vessels and parenchyma cells, bark and buds of walnut (Juglans regia cv 'Franquette') were measured during the rest period until bud break. This uptake capacity varies according to the temperature, the sugar and the position on the branch of the fragment studied. Between December and March, in Xylem tissues, the active component of sucrose uptake was predominant compared with diffusion (90% of the total uptake), whereas the active component accounted for more moderate amounts in buds (50% of the uptake). The active uptake of hexoses took place belatedly (April) in Xylem. The flow rates between Xylem vessels and buds increased 1 month before bud break and reached 2000 microg sucrose h(-)(1) g DW(-)(1). Fluxes seemed to depend on bud position on the branch. However, this study strongly suggests that they were mainly dependent on the sink strength of the buds and on the sink competition between bud, Xylem parenchyma and bark.
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evaluation of a new centrifuge technique for rapid generation of Xylem vulnerability curves
2005Co-Authors: HervÉ Cochard, Ibrahim Tharwat, Magalie Poirier, Christian Bodet, Gaelle Damour, Thierry AmeglioAbstract:A new technique for generating Xylem cavitation and vulnerability curves was evaluated. The centrifugal force was used to lower the negative pressure in a Xylem segment and to induce a positive pressure difference between sample's ends. This enabled the determination of sample hydraulic conductance during centrifugation and, hence, its variation with decreasing Xylem pressures. The centrifuge technique was compared with standard methods on a large number of species including conifers, diffuse-porous and ring-porous woody angiosperms. A very good agreement was found for coniferous and diffuse-porous species. However, the technique was not appropriate for ring-porous species, probably because many vessels were cut open in the centrifuged Xylem segments. The main advantage of this technique is its rapidity, the vulnerability curve of a Xylem segment being constructed typically in less than half an hour. This will greatly facilitate the study of Xylem cavitation in ecological or genetic researches.
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seasonal variation in Xylem pressure of walnut trees root and stem pressures
2001Co-Authors: Frank W Ewers, Christian Bodet, HervÉ Cochard, Thierry Ameglio, Francois Beaujard, Michel Martignac, Marc Vandame, Pierre CruiziatAbstract:Measurements of air and soil temperatures and Xylem pressure were made on 17-year-old orchard trees and on 5-year-old potted trees of walnut (Juglans regia L.). Cooling chambers were used to determine the relationships between temperature and sugar concentration ([glucose] + [fructose] + [sucrose], GFS) and seasonal changes in Xylem pressure development. Pressure transducers were attached to twigs of intact plants, root stumps and excised shoots while the potted trees were subjected to various temperature regimes in autumn, winter and spring. Osmolarity and GFS of the Xylem sap (apoplast) were measured before and after cooling or warming treatments. In autumn and spring, Xylem pressures of up to 160 kPa were closely correlated with soil temperature but were not correlated with GFS in Xylem sap. High root pressures were associated with uptake of mineral nutrients from soil, especially nitrate. In autumn and spring, Xylem pressures were detected in root stumps as well as in intact plants, but not in excised stems. In contrast, in winter, 83% of the Xylem sap osmolarity in both excised stems and intact plants could be accounted for by GFS, and both GFS and osmolarity were inversely proportional to temperature. Plants kept at 1.5 degrees C developed positive Xylem pressures up to 35 kPa, Xylem sap osmolarities up to 260 mosmol l(-1) and GFS concentrations up to 70 g l(-1). Autumn and spring Xylem pressures, which appeared to be of root origin, were about 55% of the theoretical pressures predicted by osmolarity of the Xylem sap. In contrast, winter pressures appeared to be of stem origin and were only 7% of the theoretical pressures, perhaps because of a lower stem water content during winter.
Lawren Sack - One of the best experts on this subject based on the ideXlab platform.
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outside Xylem vulnerability not Xylem embolism controls leaf hydraulic decline during dehydration
2017Co-Authors: Christine Scoffoni, Andrew J Mcelrone, Caetano Pereira Pedroso De Albuquerque, Craig R Brodersen, Shatara V Townes, Grace P John, Megan K Bartlett, Thomas N Buckley, Lawren SackAbstract:Leaf hydraulic supply is crucial to maintaining open stomata for CO2 capture and plant growth. During drought-induced dehydration, the leaf hydraulic conductance (Kleaf) declines, which contributes to stomatal closure and, eventually, to leaf death. Previous studies have tended to attribute the decline of Kleaf to embolism in the leaf vein Xylem. We visualized at high resolution and quantified experimentally the hydraulic vulnerability of Xylem and outside-Xylem pathways and modeled their respective influences on plant water transport. Evidence from all approaches indicated that the decline of Kleaf during dehydration arose first and foremost due to the vulnerability of outside-Xylem tissues. In vivo x-ray microcomputed tomography of dehydrating leaves of four diverse angiosperm species showed that, at the turgor loss point, only small fractions of leaf vein Xylem conduits were embolized, and substantial Xylem embolism arose only under severe dehydration. Experiments on an expanded set of eight angiosperm species showed that outside-Xylem hydraulic vulnerability explained 75% to 100% of Kleaf decline across the range of dehydration from mild water stress to beyond turgor loss point. Spatially explicit modeling of leaf water transport pointed to a role for reduced membrane conductivity consistent with published data for cells and tissues. Plant-scale modeling suggested that outside-Xylem hydraulic vulnerability can protect the Xylem from tensions that would induce embolism and disruption of water transport under mild to moderate soil and atmospheric droughts. These findings pinpoint outside-Xylem tissues as a central locus for the control of leaf and plant water transport during progressive drought.
