Spatial Variation of Deuterium Enrichment in Bulk Water of Snowgum Leaves

Abstract

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.

A direct and rapid leaf water extraction method for isotopic analysis

“…Leaves from live plants were harvested from seven different species, four aquatic and three terrestrial. Aquatic plants provided uniform samples not sensitive to the large isotopic heterogeneity observed across transpiring leaves 17–21. The aquatic species sampled included: Elodea densa and crispa , one species of the genus Barcopa and stem from the water lily, Nymphaea sp.…”

Kinetic analyses of plant water relocation using deuterium as tracer – reduced water flux of Arabidopsis pip2 aquaporin knockout mutants

“…In particular, a higher ambient humidity will decrease R leaf , since it enhances the contribution of the usually lower value of R a . Thus, stable isotope ratios also contain information to track ambient changes such as diurnal variation, but also changes on a long-term or ecological scale when extending the analysis for incorporation of 18 O into organic matter (Roden et al 2000;Gan et al 2003;Pendall et al 2005;Sheshshayee et al 2005;West et al 2006;Šantrů ček et al 2007;Ripullone et al 2008;Kahmen et al 2009). Besides the analysis of natural isotope ratios, the intentional injection of deuterium oxide or long-term growth in hydroponic culture with an elevated 2 H content has also been used as a tracer to characterise the timing of whole-tree water transport, as well as transformation into and storage as organic matter (Roden & Ehleringer 1999;Meinzer et al 2006).…”

Validation of a coupled δ<sup>2</sup>H<sub><i>n</i>-alkane</sub>-δ<sup>18</sup>O<sub>sugar</sub> paleohygrometer approach based on a climate chamber experiment

“…Allison et al, 1985;Barbour et al, 2004;Cernusak et al, 2016;section 2.3). Especially under low relative humidity conditions, the discrepancy between Craig-Gordon model results and the measured values is shown to be more pronounced, associated with higher transpiration fluxes and higher isotope heterogeneity within the leaf water due to a nonuniform closure of the stomata (Flanagan et al, 1991;Santrucek et al, 2007). An overestimation of the Craig-Gordon models can hardly be observed here ( Fig.…”