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Arthur Gessler - One of the best experts on this subject based on the ideXlab platform.
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effect of water availability on leaf water Isotopic Enrichment in beech seedlings shows limitations of current fractionation models
Plant Cell and Environment, 2009Co-Authors: Juan Pedro Ferrio, Matthias Cuntz, Christine Offermann, Rolf T W Siegwolf, Matthias Saurer, Arthur GesslerAbstract:Current models of leaf water Enrichment predict that the differences between Isotopic Enrichment of water at the site of evaporation (De) and mean lamina leaf water Enrichment (DL) depend on transpiration rates (E), modulated by the scaled effective length (L) of water isotope movement in the leaf. However, variations in leaf parameters in response to changing environmental conditions might cause changes in the water path and thus L. We measured the diel course of DL for 18 O and 2 H in beech seedlings under well-watered and water-limited conditions. We applied evaporative Enrichment models of increasing complexity to predict De and DL, and estimated L from model fits. Water-limited plants showed moderate drought stress,with lower stomatal conductance, E and stem water potential than the control. Despite having double E, the divergence between De and DL was lower in well-watered than in water-limited plants, and thus, L should have changed to counteract differences in E. Indeed, L was about threefold higher in water-limited plants, regardless of the models used. We conclude that L changes with plant water status far beyond the variations explained by water content and other measured variables, thus limiting the use of current evaporative models under changing environmental conditions.
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carbon Isotopic composition and oxygen Isotopic Enrichment in phloem and total leaf organic matter of european beech fagus sylvatica l along a climate gradient
Plant Cell and Environment, 2006Co-Authors: Claudia Keitel, Andreas Matzarakis, Heinz Rennenberg, Arthur GesslerAbstract:This study investigated the influence of climate on the car- bon Isotopic composition ( d 13 C) and oxygen Isotopic Enrichment ( D 18 O) above the source water of different 13 C and D 18 O were determined in phloem carbohydrates and in bulk foliage of adult beech trees along a transect from central Germany to southern France, where beech reaches its southernmost distributional limit. The data were related to meteorological and physiological parameters. The climate along the transect stretches from temperate (subcontinental (SC)) to submediterranean (SM). Both d 13 C leaf and D 18 O leaf were representative of site- specific long-term environmental conditions. d 13 C of leaves
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carbon Isotopic composition and oxygen Isotopic Enrichment in phloem and total leaf organic matter of european beech fagus sylvatica l along a climate gradient
Plant Cell and Environment, 2006Co-Authors: Claudia Keitel, Andreas Matzarakis, Heinz Rennenberg, Arthur GesslerAbstract:This study investigated the influence of climate on the carbon Isotopic composition (sigma13C) and oxygen Isotopic Enrichment (delta18O) above the source water of different organic matter pools in European beech. In July and September 2002, sigma13C and delta18O were determined in phloem carbohydrates and in bulk foliage of adult beech trees along a transect from central Germany to southern France, where beech reaches its southernmost distributional limit. The data were related to meteorological and physiological parameters. The climate along the transect stretches from temperate [subcontinental (SC)] to submediterranean (SM). Both sigma13Cleaf and delta18Oleaf were representative of site-specific long-term environmental conditions. sigma13C of leaves collected in September was indicative of stomatal conductance, vapour pressure deficit (VPD) and radiation availability of the current growing season. delta18O was mainly correlated to mean growing season relative humidity (RH) and VPD. In contrast to the leaves, sigma13Cphloem varied considerably between July and September and was well correlated with canopy stomatal conductance (Gs) in a 2 d integral prior to phloem sampling. The relationship between sigma13C and delta18O in both leaves and phloem sap points, however, to a combined influence of stomatal conductance and photosynthetic capacity on the variation of sigma13C along the transect. delta18Ophloem could be described by applying a model that included 18O fractionation associated with water exchange between the leaf and the atmosphere and with the production of organic matter. Hence, isotope signatures can be used as effective tools to assess the water balance of beech, and thus, help predict the effects of climatic change on one of the ecologically and economically most important tree species in Central Europe.
Sharon E Ashbrook - One of the best experts on this subject based on the ideXlab platform.
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17o solid state nmr spectroscopy of a2b2o7 oxides quantitative Isotopic Enrichment and spectral acquisition
RSC Advances, 2018Co-Authors: Arantxa Fernandes, Daniel M Dawson, Robert F Moran, Scott Sneddon, David Mckay, Giulia P M Bignami, Frederic Blanc, Karl R Whittle, Sharon E AshbrookAbstract:The potential of 17O NMR spectroscopy for the investigation of A2B2O7 ceramic oxides important in the encapsulation of radioactive waste is demonstrated, with post-synthetic Enrichment by exchange with 17O2 gas. For Y2Sn2O7, Y2Ti2O7 and La2Sn2O7 pyrochlores, Enrichment of the two distinct O species is clearly non quantitative at lower temperatures (∼700 °C and below) and at shorter times, despite these being used in prior work, with preferential Enrichment of OA2B2 favoured over that of OA4. At higher temperatures, the 17O NMR spectra suggest that quantitative Enrichment has been achieved, but the integrated signal intensities do not reflect the crystallographic 1 : 6 (O1 : O2) ratio until corrected for differences in T1 relaxation rates and, more importantly, the contribution of the satellite transitions. 17O NMR spectra of Y2Zr2O7 and Y2Hf2O7 defect fluorites showed little difference with any variation in Enrichment temperature or time, although an increase in the absolute level of Enrichment (up to ∼7.5%) was observed at higher temperature. DFT calculations show that the six distinct resonances observed cannot be assigned unambiguously, as each has contributions from more than one of the five possible next nearest neighbour environments. For La2Ti2O7, which adopts a layered perovskite-like structure, little difference in the spectral intensities is observed with Enrichment time or temperature, although the highest absolute levels of Enrichment (∼13%) were obtained at higher temperature. This work demonstrates that 17O NMR has the potential to be a powerful probe of local structure and disorder in oxides, but that considerable care must be taken both in choosing the conditions for 17O Enrichment and the experimental acquisition parameters if the necessary quantitative measurements are to be obtained for more complex systems.
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determining the surface structure of silicated alumina catalysts via Isotopic Enrichment and dynamic nuclear polarization surface enhanced nmr spectroscopy
Journal of Physical Chemistry C, 2017Co-Authors: Andrew G M Rankin, Paul B Webb, Daniel M Dawson, Jasmine Vigergravel, Brennan J Walder, Lyndon Emsley, Sharon E AshbrookAbstract:Isotopic Enrichment of 29Si and DNP-enhanced NMR spectroscopy are combined to determine the detailed surface structure of a silicated alumina catalyst. The significant sensitivity enhancement provided by DNP is vital to the acquisition of multinuclear and multidimensional experiments that provide information on the atomic-level structure of the species present at the surface. Isotopic Enrichment not only facilitates spectral acquisition, particularly given the low (1.5 wt %) Si loading, but also enables spectra with higher resolution than those acquired using DNP to be obtained. The unexpected similarity of conventional, CP, and DNP NMR spectra is attributed to the presence of adventitious surface water that forms a sufficiently dense 1H network at the silica surface so as to mediate efficient polarization transfer to all Si species regardless of their chemical nature. Spectra reveal the presence of Si–O–Si linkages at the surface (identified as Q4(3Al)–Q4(3Al)) and confirm that the anchoring of the surfa...
Claudia Keitel - One of the best experts on this subject based on the ideXlab platform.
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carbon Isotopic composition and oxygen Isotopic Enrichment in phloem and total leaf organic matter of european beech fagus sylvatica l along a climate gradient
Plant Cell and Environment, 2006Co-Authors: Claudia Keitel, Andreas Matzarakis, Heinz Rennenberg, Arthur GesslerAbstract:This study investigated the influence of climate on the car- bon Isotopic composition ( d 13 C) and oxygen Isotopic Enrichment ( D 18 O) above the source water of different 13 C and D 18 O were determined in phloem carbohydrates and in bulk foliage of adult beech trees along a transect from central Germany to southern France, where beech reaches its southernmost distributional limit. The data were related to meteorological and physiological parameters. The climate along the transect stretches from temperate (subcontinental (SC)) to submediterranean (SM). Both d 13 C leaf and D 18 O leaf were representative of site- specific long-term environmental conditions. d 13 C of leaves
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carbon Isotopic composition and oxygen Isotopic Enrichment in phloem and total leaf organic matter of european beech fagus sylvatica l along a climate gradient
Plant Cell and Environment, 2006Co-Authors: Claudia Keitel, Andreas Matzarakis, Heinz Rennenberg, Arthur GesslerAbstract:This study investigated the influence of climate on the carbon Isotopic composition (sigma13C) and oxygen Isotopic Enrichment (delta18O) above the source water of different organic matter pools in European beech. In July and September 2002, sigma13C and delta18O were determined in phloem carbohydrates and in bulk foliage of adult beech trees along a transect from central Germany to southern France, where beech reaches its southernmost distributional limit. The data were related to meteorological and physiological parameters. The climate along the transect stretches from temperate [subcontinental (SC)] to submediterranean (SM). Both sigma13Cleaf and delta18Oleaf were representative of site-specific long-term environmental conditions. sigma13C of leaves collected in September was indicative of stomatal conductance, vapour pressure deficit (VPD) and radiation availability of the current growing season. delta18O was mainly correlated to mean growing season relative humidity (RH) and VPD. In contrast to the leaves, sigma13Cphloem varied considerably between July and September and was well correlated with canopy stomatal conductance (Gs) in a 2 d integral prior to phloem sampling. The relationship between sigma13C and delta18O in both leaves and phloem sap points, however, to a combined influence of stomatal conductance and photosynthetic capacity on the variation of sigma13C along the transect. delta18Ophloem could be described by applying a model that included 18O fractionation associated with water exchange between the leaf and the atmosphere and with the production of organic matter. Hence, isotope signatures can be used as effective tools to assess the water balance of beech, and thus, help predict the effects of climatic change on one of the ecologically and economically most important tree species in Central Europe.
Ulrik Ilstedt - One of the best experts on this subject based on the ideXlab platform.
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canopy cover effects on local soil water dynamics in a tropical agroforestry system evaporation drives soil water Isotopic Enrichment
Hydrological Processes, 2018Co-Authors: Niles J Hasselquist, Laura Benegas, Olivier Roupsard, Anders Malmer, Ulrik IlstedtAbstract:Despite the widely held assumption that trees negatively affect the local water budget in densely planted tree plantations, we still lack a clear understanding of the underlying processes by which canopy cover influences local soil water dynamics in more open, humid tropical ecosystems. In this study, we propose a new conceptual model that uses a combination of stable isotope and soil moisture measurements throughout the soil profile to assess potential mechanisms by which evaporation (of surface soil water and of canopy‐intercepted rainfall) affects the relationship between surface soil water Isotopic Enrichment (lc‐excess) and soil water content. Our conceptual model was derived from soil water data collected under deciduous and evergreen plants in a shade grown coffee agroforestry system in Costa Rica. Reduced soil moisture under shade trees during the “drier” season, coinciding when these trees were defoliated, was largely the result of increase soil water evaporation as indicated by the positive relationship between soil water content and lc‐excess of surface soil water. In contrast, the evergreen coffee shrubs had a higher leaf area index during the “drier” season, leading to enhanced rainfall interception and a negative relationship between lc‐excess and soil water content. During the wet season, there was no clear relationship between soil water content and between lc‐excess of surface soil water. Greater surface soil water under coffee during the dry season may, in part, explain greater preferential flow under coffee compared with under trees in conditions of low rainfall intensities. However, with increasing rainfall intensities during the wet season, there was no obvious difference in preferential flow between the two canopy covers. Results from this study indicate that our new conceptual model can be used to help disentangling the relative influence of canopy cover on local soil water Isotopic composition and dynamics, yet also stresses the need for additional measurements to better resolve the underlying processes by which canopy structure influences local water dynamics.
Graham D Farquhar - One of the best experts on this subject based on the ideXlab platform.
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can hydraulic design explain patterns of leaf water Isotopic Enrichment in c3 plants
Plant Cell and Environment, 2021Co-Authors: Margaret M Barbour, Karen E Loucos, Erin L Lockhart, Arjina Shrestha, Daniel Mccallum, Kevin A Simonin, Xin Song, D Griffani, Graham D FarquharAbstract:H2 18 O Enrichment develops when leaves transpire, but an accurate generalized mechanistic model has proven elusive. We hypothesized that leaf hydraulic architecture may affect the degree to which gradients in H2 18 O develop within leaves, influencing bulk leaf stable oxygen isotope Enrichment (ΔL ) and the degree to which the Peclet effect is relevant in leaves. Leaf hydraulic design predicted the relevance of a Peclet effect to ΔL in 19 of the 21 species tested. Leaves with well-developed hydraulic connections between the vascular tissue and the epidermal cells through bundle sheath extensions and clear distinctions between palisade and spongy mesophyll layers (while the mesophyll is hydraulically disconnected) may have velocities of the transpiration stream such that gradients in H2 18 O develop and are expressed in the mesophyll. In contrast, in leaves where the vascular tissue is hydraulically disconnected from the epidermal layers, or where all mesophyll cells are well connected to the transpiration stream, velocities within the liquid transport pathways may be low enough that gradients in H2 18 O are very small. Prior knowledge of leaf hydraulic design allows informed selection of the appropriate ΔL modelling framework.
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on the Isotopic composition of leaf water in the non steady state
Functional Plant Biology, 2005Co-Authors: Graham D Farquhar, Lucas A CernusakAbstract:An expression is derived for the Isotopic composition of water in leaves under conditions where the composition of water entering the leaf is not necessarily the same as that of water being transpired. The treatment is simplified and considers the average composition of the lamina and of the sites of evaporation. The concept of 'isostorage' is introduced as the product of leaf water content and the Isotopic Enrichment of leaf water above source water. It is shown that the rate of increase of isostorage is minus the 'isoflux' through the stomata, with the latter expressed as the product of the transpiration flux and the Enrichment of the transpired water beyond source water. The approach of the isostorage to the steady state depends on the deviation of the Isotopic Enrichment of water at the evaporating sites from the steady value, and on the gross (one way) diffusive flux out of the leaf. To achieve model closure, it is assumed that the relationship between leaf water Enrichment and that at the sites of evaporation depends on the radial Peclet number in the same manner as in the steady state. The equations have an analytical solution, and we also show how to calculate the results simply using a commonly available computer tool. The form of the equations emphasises that the one-way fluxes of water into and out of the stomata must sometimes be considered separately, rather than as a net outward flux. In this narrow sense we come to the interesting conclusion that more water usually enters the leaf from the air than from the roots.