Observations of Hydrogen and Oxygen Isotopes in Leaf Water Confirm the Craig-Gordon Model under Wide-Ranging Environmental Conditions1

Roden, John S.; Ehleringer, James R.

doi:10.1104/pp.120.4.1165

Cited by 234 publications

(246 citation statements)

References 36 publications

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“…There have been conflicting reports on the existence of such a relationship. Wang et al (1998) and Roden and Ehleringer (1999) observed no clear dependency of ⌬ C Ϫ ⌬ lw, bulk on E, with the former study based on a collection of 90 plant species grown under the same climatic conditions. The positive relationship between ⌬ C Ϫ ⌬ lw, bulk and E, illustrated by Wang and Yakir (2000) and Gillon and Yakir (2000), appears to be in agreement with the Péclet model but may well collapse after normalization against ⌬ C .…”

Section: Lower Enrichment Of Bulk Leaf Water Arising From Péclet Effectmentioning

confidence: 99%

“…Direct and indirect leaf water measurements supporting the different leaf water models have been reported: Craig-Gordon model (Roden and Ehleringer, 1999), Péclet model (Walker et al, 1989;Flanagan et al, 1991b;Barbour et al, 2000), and string-of-lakes model (Yakir, 1992;Wang and Yakir, 1995;Ehleringer, 2000, 2002). Given the importance of leaf water modeling to studies of plant-environment interactions, there is a pressing need to reconcile these apparently disparate results.…”

mentioning

confidence: 99%

“…After the removal of the mid-vein from leaves of Betula occidentalis and Populus angustifolia, the estimated unenriched water fraction in the remaining leaves was reduced to 10% (Roden and Ehleringer, 1999). modified the physical model of a single-leaf water pool to one having a continuum of isotopic composition (Fig.…”

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18O Spatial Patterns of Vein Xylem Water, Leaf Water, and Dry Matter in Cotton Leaves

et al. 2002

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Three leaf water models (two-pool model, Péclet effect, and string-of-lakes) were assessed for their robustness in predicting leaf water enrichment and its spatial heterogeneity. This was achieved by studying the 18 O spatial patterns of vein xylem water, leaf water, and dry matter in cotton (Gossypium hirsutum) leaves grown at different humidities using new experimental approaches. Vein xylem water was collected from intact transpiring cotton leaves by pressurizing the roots in a pressure chamber, whereas the isotopic content of leaf water was determined without extracting it from fresh leaves with the aid of a purpose-designed leaf punch. Our results indicate that veins have a significant degree of lateral exchange with highly enriched leaf water. Vein xylem water is thus slightly, but progressively enriched in the direction of water flow. Leaf water enrichment is dependent on the relative distances from major veins, with water from the marginal and intercostal regions more enriched and that next to veins and near the leaf base more depleted than the Craig-Gordon modeled enrichment of water at the sites of evaporation. The spatial pattern of leaf water enrichment varies with humidity, as expected from the string-of-lakes model. This pattern is also reflected in leaf dry matter. All three models are realistic, but none could fully account for all of the facets of leaf water enrichment. Our findings acknowledge the presence of capacitance in the ground tissues of vein ribs and highlight the essential need to incorporate Péclet effects into the string-of-lakes model when applying it to leaves.The isotopic composition of leaf water reflects local humidity, and its imprints on plant cellulose and other fossil materials have been widely explored for palaeoclimatic reconstruction. To date, isotopic values of wood cellulose (Epstein et al., 1977;Yapp and Epstein, 1982;Edwards et al., 1985;Edwards and Fritz, 1986;Roden et al., 2000), grassland phytoliths (Webb and Longstaffe, 2000), and deer bone (Cormie et al., 1994) have been shown to be related to leaf water isotopic composition. Leaf water isotopic signature is not only imprinted on plant organic matter but is also recorded in atmospheric CO 2 and O 2 . The CO 2 interacts and undergoes isotopic exchange with leaf water, and O 2 is released by the plant during photosynthesis. Changes in the oxygen isotope ratios of CO 2 and O 2 can thus be used to study variations in the net exchange of CO 2 in terrestrial ecosystems and in the balance of terrestrial and marine productivity (Bender et al., 1985;Bender et al., 1994). Because all of these applications critically depend on estimation of the leaf water oxygen isotopic ratio, a good understanding of the nature of leaf water enrichment is needed.The isotopic composition of leaf water is most commonly estimated from the model of a freely evaporating water surface (Craig and Gordon, 1965) where isotopic fractionation is driven by the lower vapor pressure and diffusivity of the heavier molecules. Although the Craig-Gordon m...

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Section: Lower Enrichment Of Bulk Leaf Water Arising From Péclet Effectmentioning

confidence: 99%

mentioning

confidence: 99%

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18O Spatial Patterns of Vein Xylem Water, Leaf Water, and Dry Matter in Cotton Leaves

et al. 2002

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“…O are enriched at the sites of evaporation (Craig and Gordon, 1965;Yakir et al, 1989;Barbour et al, 2000), the location of those sites affects the mixing of isotopically enriched water with xylem water and, thus, bulk leaf enrichment (Yakir et al, 1990;Roden and Ehleringer, 1999;Farquhar and Gan, 2003). (6) The location of the evaporating sites determines the extent to which the diffusion pathways for CO 2 and water vapor overlap, which, in turn, affects the interpretation of correlations between K leaf and mesophyll conductance to CO 2 (g m ; Flexas et al, 2013;Tomás et al, 2013), as well as (7) the opportunity for diffusive interference between water vapor and CO 2 (reflected in the ternary corrections for gas-exchange calculations; Farquhar and Cernusak, 2012).…”

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confidence: 99%

The Sites of Evaporation within Leaves

et al. 2017

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The sites of evaporation within leaves are unknown, but they have drawn attention for decades due to their perceived implications for many factors, including patterns of leaf isotopic enrichment, the maintenance of mesophyll water status, stomatal regulation, and the interpretation of measured stomatal and leaf hydraulic conductances. We used a spatially explicit model of coupled water and heat transport outside the xylem, MOFLO 2.0, to map the distribution of net evaporation across leaf tissues in relation to anatomy and environmental parameters. Our results corroborate earlier predictions that most evaporation occurs from the epidermis at low light and moderate humidity but that the mesophyll contributes substantially when the leaf center is warmed by light absorption, and more so under high humidity. We also found that the bundle sheath provides a significant minority of evaporation (15% in darkness and 18% in high light), that the vertical center of amphistomatous leaves supports net condensation, and that vertical temperature gradients caused by light absorption vary over 10-fold across species, reaching 0.3°C. We show that several hypotheses that depend on the evaporating sites require revision in light of our findings, including that experimental measurements of stomatal and hydraulic conductances should be affected directly by changes in the location of the evaporating sites. We propose a new conceptual model that accounts for mixed-phase water transport outside the xylem. These conclusions have far-reaching implications for inferences in leaf hydraulics, gas exchange, water use, and isotope physiology.The pathways for water transport through a plant are often perceived to end at the sites of evaporation outside the xylem within leaves (Holmgren et al

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“…Through a series of known fractionation events, d 18 O (and d 2 H) variation derived from hydrologic inputs is incorporated into the organic matter that makes up tree rings (Yapp and Epstein 1982;White et al 1994;Roden and Ehleringer 1999b;Roden et al 2000;Treydte et al 2006;Gessler et al 2009). Tree-ring cellulose d 18 O values can be modified by variation in atmospheric humidity and the unique isotope values it possesses, by vapor pressure deficit and therefore the magnitude of leaf evaporative enrichment associated with transpiration (Edwards and Fritz 1986;Roden and Ehleringer 1999a;Wright and Leavitt 2006;Kahmen et al 2008), by variation in source water (Wright et al 1999;Roden andEhleringer 1999b, 2007) and by post-photosynthetic but pre-biosynthetic factors shown to dampen the original isotope values of sucrose made at the leaf-level before it becomes incorporated into tree-ring cellulose (Brandes et al 2006). Carbon isotope ratios (d 13 C) in tree-ring cellulose have been used to study historical variations in plant water status, temperature, solar radiation and vapor pressure deficit (Saurer et al 1995;Stewart et al 1995;Hemming et al 1998;Schleser et al 1999;Barbour et al 2002;Leavitt et al 2002;Young et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Regional And Watershed-Scale Coherence In the Stable-Oxygen and Carbon Isotope Ratio Time Series In Tree Rings Of Coast Redwood (Sequoia sempervirens)

Roden¹,

Johnstone²,

Dawson³

2011

Tree-Ring Research

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Coast redwood (Sequoia sempervirens) ecosystems are strongly influenced by the presence of summer marine fog, and variation in fog frequency is closely linked to climate variation in the NE Pacific region. Because oxygen isotope composition (d 18 O) of organic matter records distinct water sources (e.g. summertime fog vs. winter precipitation) and carbon isotopes (d 13 C) are typically sensitive to humidity and water status, it then follows that inter-annual variation in tree-ring isotope ratios, which are coherent across multiple sites, should preserve a potentially powerful proxy for climate reconstruction. Here we present an analysis of a 50-year time series for both d 18 O and d 13 C values from subdivided tree rings obtained from multiple redwood trees at multiple sites. Within-site and betweensite correlations were highly significant (p , 0.01) for the d 18 O time series indicating a regionally coherent common forcing of d 18 O fractionation. Within-site and between-site correlation coefficients were lower for the d 13 C than for the d 18 O time series although most were still significant (at least to p , 0.05). The hypothesized reason for the differences in the correlation is that carbon isotope discrimination is more sensitive to microenvironmental and tree-level physiological variation than is d 18 O fractionation. Stable-isotope variation in tree-ring cellulose was similar between slope, gully and riparian micro-habitats within a single watershed, implying that minor topographic variation when sampling should not be a major concern. These results indicate that stable-isotope time series from redwood tree rings are strongly influenced by regional climate drivers and potentially valuable proxies for Pacific coastal climate variability.

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Observations of Hydrogen and Oxygen Isotopes in Leaf Water Confirm the Craig-Gordon Model under Wide-Ranging Environmental Conditions1

Cited by 234 publications

References 36 publications

18O Spatial Patterns of Vein Xylem Water, Leaf Water, and Dry Matter in Cotton Leaves

18O Spatial Patterns of Vein Xylem Water, Leaf Water, and Dry Matter in Cotton Leaves

The Sites of Evaporation within Leaves

Regional And Watershed-Scale Coherence In the Stable-Oxygen and Carbon Isotope Ratio Time Series In Tree Rings Of Coast Redwood (Sequoia sempervirens)

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