Comparison of measured and modeled variations in piñon pine leaf water isotopic enrichment across a summer moisture gradient

Deuterium enrichment of bulk water was measured and modeled in snowgum (Eucalyptus pauciflora Sieber ex Sprengel) leaves grown under contrasting air and soil humidity in arid and wet conditions in a glasshouse. A map of the enrichment was constructed with a resolution of 4 mm by using a newly designed cryodistillation method. There was progressively increasing enrichment in both longitudinal (along the leaf midrib) and transversal (perpendicular to the midrib) directions, most pronounced in the arid-grown leaf. The whole-leaf average of the enrichment was well below the value estimated by the Craig-Gordon model. The discrepancy between model and measurements persisted when the estimates were carried out separately for the leaf base and tip, which differed in temperature and stomatal conductance. The discrepancy was proportional to the transpiration rate, indicating the significance of diffusion-advection interplay (Péclet effect) of deuterium-containing water molecules in small veins close to the evaporating sites in the leaf. Combined Craig-Gordon and desert-river models, with or without the Péclet number, P, were used for predicting the leaf longitudinal enrichment. The predictions without P overestimated the measured values of ddeuterium. Fixed P value partially improved the coincidence. We suggest that P should vary along the leaf length l to reconcile the modeled data with observations of longitudinal enrichment. Local values of P, P(l), integrating the upstream fraction of water used or the leaf area, substantially improved the model predictions.

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“…It has also been observed several times in leaves (e.g. Gan et al, 2002;Pendall et al, 2005) and many times as…”

Section: Discussionmentioning

confidence: 84%

Spatial Variation of Deuterium Enrichment in Bulk Water of Snowgum Leaves

et al. 2006

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“…Water was extracted from the leaf and soil samples using a cryogenic vacuum distillation apparatus and collected in traps cooled continuously with liquid N 2 [Farris and Strain, 1978]. The distillation temperature was 95°C, and the process took up to 4 h [Pendall et al, 2005]. Extracted water was stored in cryogenic vials.…”

Section: Sampling and Measurementmentioning

confidence: 99%

Influences of relative humidity and Indian monsoon precipitation on leaf water stable isotopes from the southeastern Tibetan Plateau

Lai

et al. 2014

Geophysical Research Letters

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This project report results of the first leaf water δ 18O and δD time series of the woody plant Quercus aquifolioides undertaken on the southeastern Tibetan Plateau (STP). The data show that δD of leaf water underwent less enrichment than δ 18O relative to precipitation and soil water, and could "inherit" the δD value characteristics of precipitation far better than δ 18O. The leaf water δD values were strongly modified by evaporative enrichment in response to lower and more drastically changing relative humidity observed outside of the rainy season. In comparison, leaf water δD values more closely tracked those observed in the monsoon precipitation (acted as source water) in the rainy season. Our findings suggest that leaf water δD values from the STP were sensitive to the Indian monsoon activities, and the effects of relative humidity and the Indian monsoon precipitation should be considered for stable isotopes in tree ring cellulose or other biomarkers studies on the STP.

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“…However, it should be noted that the basic background value of leaf d 18 O is primarily determined by the isotopic composition of the source water used by the plant (Yakir, 1992;Jäggi et al, 2003;Pendall et al, 2005;Marshall and Monserud, 2006). Water stored in deeper layers of the soil/bedrock profile is less exposed to evaporative isotopic enrichment than water stored in the upper soil, and therefore has more negative d 18 O, particularly in dry environments (Allison et al, 1983).…”

Section: Discussionmentioning

confidence: 98%

“…On the other hand, the oxygen isotopic composition of plants depends primarily on the isotopic signature of source water and on plant transpiration rates (Yakir, 1992). It is therefore also affected by stomatal conductance, but is not influenced by photosynthetic rate (Barbour et al, 2002;Jäggi et al, 2003;Keitel et al, 2003;Pendall et al, 2005). The simultaneous analysis of carbon and oxygen isotopic composition of leaf material can thus provide useful information on photosynthetic activity, stomatal conductance and water use efficiency throughout the period of leaf development (Scheidegger et al, 2000;Xu et al, 2000;Dawson et al, 2002).…”

Section: Introductionmentioning

confidence: 98%