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  • 1
    Electronic Resource
    Electronic Resource
    On the progressive enrichment of the oxygen isotopic composition of water along a leaf (2003)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 26 (2003), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A model has been derived for the enrichment of heavy isotopes of water in leaves, including progressive enrichment along the leaf. In the model, lighter water is preferentially transpired leaving heavier water to diffuse back into the xylem and be carried further along the leaf. For this pattern to be pronounced, the ratio of advection to diffusion (Péclet number) has to be large in the longitudinal direction, and small in the radial direction. The progressive enrichment along the xylem is less than that occurring at the sites of evaporation in the mesophyll, depending on the isolation afforded by the radial Péclet number. There is an upper bound on enrichment, and effects of ground tissue associated with major veins are included. When transpiration rate is spatially nonuniform, averaging of enrichment occurs more naturally with transpiration weighting than with area-based weighting. This gives zero average enrichment of transpired water, the modified Craig–Gordon equation for average enrichment at the sites of evaporation and the Farquhar and Lloyd (In Stable Isotopes and Plant Carbon-Water Relations, pp. 47–70. Academic Press, New York, USA, 1993) prediction for mesophyll water. Earlier results on the isotopic composition of evolved oxygen and of retro-diffused carbon dioxide are preserved if these processes vary in parallel with transpiration rate. Parallel variation should be indicated approximately by uniform carbon isotope discrimination across the leaf.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2003.01013.x
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  • 2
    Electronic Resource
    Electronic Resource
    Do pathways of water movement and leaf anatomical dimensions allow development of gradients in H218O between veins and the sites of evaporation within leaves? (2004)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The oxygen isotope enrichment of bulk leaf water (ΔL)  is often observed to be poorly predicted by the Craig–Gordon-type models developed for evaporative enrichment from a body of water (Δe). The discrepancy between ΔL and Δe may be explained by gradients in enrichment within the leaf as a result of convection of unenriched water to the sites of evaporation opposing the diffusion of enrichment away from the sites; a Péclet effect. However, this effect is difficult to quantify because the velocities of water movement within the leaf are unknown. This paper attempts to model the complex anatomy of a leaf, and hence such velocities, to assess if the gradients in H218O required for a significant Péclet effect between the vein and the evaporation sites are possible within a leaf. Published dimensions of cells in wheat leaves are used to calculate the cross-sectional areas perpendicular to the flow velocities of water through assumed pathways. By combining the ratio of actual to ‘slab’ velocities with anatomical lengths, equivalent lengths (L) emerge. In this way, it is concluded that if water moves only through the cell walls, or from cell to cell via either aquaporins or plasmodesmata, and evaporates from mesophyll cells, or the substomatal cells, or from the peristomatal region (a total of 15 combinations of assumptions), then the 15 central estimates of the values of L are between 9 and 200 mm. Each of these central estimates is subject to uncertainty, but overall their magnitude is important and estimates of L are comparable with those made from fitting to isotopic data (8 mm for wheat). It is concluded that significant gradients in enrichment between the vein and the evaporation sites are likely.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.0016-8025.2003.01132.x
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  • 3
    Electronic Resource
    Electronic Resource
    Relative humidity- and ABA-induced variation in carbon and oxygen isotope ratios of cotton leaves (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Cotton (Gossypium hirsutum L. cv. CS50) plants were grown at two levels of relative humidity (RH) and sprayed daily with abscisic acid (ABA) at four concentrations. Plants grown at lower humidity had higher transpiration rates, lower leaf temperatures and lower stomatal conductance. Plant biomass was also reduced at low humidity. Within each humidity environment, increasing ABA concentration generally reduced stomatal conductance, evaporation rates, superficial leaf density and plant biomass, and increased leaf temperature and specific leaf area. As expected, decreased stomatal conductance resulted in decreased carbon isotope discrimination in leaf material (Δ13Cl). Plants grown at low humidity were more enriched in 18O than those grown at high RH, as theory predicts. Within each humidity environment, increasing ABA concentration increased oxygen isotope enrichment of leaf cellulose (Δ18Oc) and whole-leaf tissue (Δ18Ol). Values of Δ13Cl and Δ18Ol predicted by theoretical models were close to those observed, accounting for 79% of the measured variation in Δ13Cl and 95% of the measured variation in Δ18Ol. Supporting theory, Δ13Cl and Δ18Ol in whole-leaf tissue were negatively related.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00575.x
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  • 4
    Electronic Resource
    Electronic Resource
    A relationship between humidity response, growth form and photosynthetic operating point in C3 plants (1999)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 22 (1999), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Gas exchange experiments were performed with 13 plant species that differ from each other in growth-form and natural habitat. These comprised three herbaceous species, two ferns, two temperate deciduous trees, five rainforest trees and one liana from wet tropical forest. The aims were to investigate whether plants of similar growth-form and from similar habitats tended to respond similarly to a change in leaf-to-air vapour pressure difference (VPD), and to compare their ratio of intercellular to ambient partial pressures of CO2 for given conditions. Leaves were subjected to a step change in VPD and the initial and final steady rates of transpiration were used to calculate an index of sensitivity, φ, which enabled comparison of species. The results suggest that species of similar growth-form and habitat respond similarly to increasing VPD, with the temperate deciduous trees undergoing a greater reduction in stomatal conductance than the herbaceous plants in well-watered soil. Also, for these experimental conditions, the ratio of leaf internal to ambient CO2 partial pressure (pi/pa) was positively correlated with both CO2 assimilation rate and stomatal insensitivity to VPD, across the 13 species. The results are discussed in terms of growth strategies and possible advantages and limitations of hydraulic systems in different plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1999.00494.x
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  • 5
    Electronic Resource
    Electronic Resource
    Evaluation of models of leaf water 18O enrichment using measurements of spatial patterns of vein xylem water, leaf water and dry matter in maize leaves (2003)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 26 (2003), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effectiveness of several leaf water models (‘string-of-lakes’, ‘desert river’ and the Farquhar–Gan model) are evaluated in predicting the enrichment of leaf water along a maize leaf at different humidities. Progressive enrichment of both vein xylem water and leaf water was observed along the blade. At the tip, the maximum observed enrichment for the vein water was 17.6‰ at 50% relative humidity (RH) whereas that for the leaf water was 50‰ at 34% RH and 19‰ at 75% RH. The observed leaf water maximum was a fraction (0.5–0.6) of the theoretically possible maximum. The ‘string-of-lakes’ and ‘desert river’ models predict well the variation of leaf water enrichment pattern with humidity but overestimate the average enrichment of bulk leaf water. However, the Farquhar–Gan model gives good prediction for these two aspects of leaf water enrichment. Using the anatomical dimensions of vein xylem overestimates the effective longitudinal Péclet number (Pl). Possible explanations for this discrepancy between the effective and the xylem-based estimate of Pl are discussed. The need to characterize the heterogeneity of transpiration rate over the leaf surface in studies of leaf water enrichment is emphasized. The possibility that past atmospheric humidity can be predicted from the slope of the Δ18O spatial variation of leaf macrofossils found in middens is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2003.01070.x
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  • 6
    Electronic Resource
    Electronic Resource
    On the progressive enrichment of the oxygen isotopic composition of water along a leaf (2003)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 26 (2003), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A model has been derived for the enrichment of heavy isotopes of water in leaves, including progressive enrichment along the leaf. In the model, lighter water is preferentially transpired leaving heavier water to diffuse back into the xylem and be carried further along the leaf. For this pattern to be pronounced, the ratio of advection to diffusion (Péclet number) has to be large in the longitudinal direction, and small in the radial direction. The progressive enrichment along the xylem is less than that occurring at the sites of evaporation in the mesophyll, depending on the isolation afforded by the radial Péclet number. There is an upper bound on enrichment, and effects of ground tissue associated with major veins are included. When transpiration rate is spatially nonuniform, averaging of enrichment occurs more naturally with transpiration weighting than with area-based weighting. This gives zero average enrichment of transpired water, the modified Craig–Gordon equation for average enrichment at the sites of evaporation and the Farquhar and Lloyd (In Stable Isotopes and Plant Carbon-Water Relations, pp. 47–70. Academic Press, New York, USA, 1993) prediction for mesophyll water. Earlier results on the isotopic composition of evolved oxygen and of retro-diffused carbon dioxide are preserved if these processes vary in parallel with transpiration rate. Parallel variation should be indicated approximately by uniform carbon isotope discrimination across the leaf.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.0016-8025.2001.00829.x-i1
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  • 7
    Electronic Resource
    Electronic Resource
    A new analytical model for whole-leaf potential electron transport rate (2004)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A new analytical model for the response of whole-leaf potential electron transport rate (J) to light is presented. The model treats incident irradiance at the upper and lower leaf surfaces independently, describes transdermal profiles of light absorption and electron transport capacity explicitly, and calculates J by integrating the minimum of light- and capacity-limited rates among paradermal chlorophyll layers. The capacity profile is assumed to be a weighted average of two opposed exponential profiles, each of which corresponds to the profile of light-limited rate when only one surface is illuminated; the weights may take on any values, provided they sum to unity, so the model can describe leaves with a wide range of ‘preferred’ illumination regimes. By treating irradiance at either surface independently and assuming the capacity profile is fixed on short time scales, the model predicts observed effects of leaf inversion on light-response curves and their apparent convexity. By assuming the capacity profile can adapt on developmental time scales, the model can predict the observed dependence of inversion effects on the growth lighting regime. It is suggested that the new model, which is mathematically compact and formally similar to the standard non-rectangular hyperbola model for J, be used in place of the standard model in studies in which the effects of leaf angle or diffuse light fraction on gas exchange are of interest.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.2004.01232.x
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