Leaf vein fraction influences the Péclet effect and ¹⁸O enrichment in leaf water

Abstract

The process of evaporation results in the fractionation of water isotopes such that the lighter O isotope preferentially escapes the gas phase leaving the heavier O isotope to accumulate at the sites of evaporation. This applies to transpiration from a leaf with the degree of fractionation dependent on a number of environmental and physiological factors that are well understood. Nevertheless, the O enrichment of bulk leaf water is often less than that predicted for the sites of evaporation. The advection of less enriched water in the transpiration stream has been suggested to limit the back diffusion of enriched evaporative site water (Péclet effect); however, evidence for this effect has been varied. In sampling across a range of species with different vein densities and saturated water contents, we demonstrate the importance of accounting for the relative 'pool' sizes of the vascular and mesophyll water for the interpretation of a Péclet effect. Further, we provide strong evidence for a Péclet signal within the xylem that if unaccounted for can lead to confounding of the estimated enrichment within the mesophyll water. This has important implications for understanding variation in the effective path length of the mesophyll and hence potentially the δ O of organic matter.

Oxygen isotope fractionations across individual leaf carbohydrates in grass and tree species

“…Species‐specific difference in ε bio might be also explained by differences in carbohydrate turnover times and by mixing with ‘older’ carbohydrates in storage (Gessler et al ). It remains to be determined if compound synthesis water is influenced by vein water via a Péclet effect or if it is a distinct pool (Song et al ; Holloway‐Phillips et al ) and to be investigated how compound synthesis rates change across leaves.…”

Investigating old‐growth ponderosa pine physiology using tree‐rings, δ13C, δ18O, and a process‐based model

“…, Holloway‐Phillips et al. ). The δ 18 O es and thus δ 18 O cell without the Peclet effect were not sensitive to any of the tested parameters because both are calculated solely with δ 18 O s and climate inputs (Eq.…”

“…, , Holloway‐Phillips et al. ), the importance of the Peclet effect for estimating δ 18 O has been debated (Ripullone et al. , Xiao et al.…”

Isotopic Equilibrium Between Precipitation and Water Vapor in Northern Patagonia and Its Consequences on δ18Ocellulose Estimate

“…The isotopic composition at the evaporative site (calculated δ 18 O site ) is 4.5‰ higher than the measured leaves water (measured δ 18 O leaf of 5.9‰). Bulk leaf water is a mixing between unfractionated source water and enriched water at the evaporative sites (Cernusak et al, 2016; Holloway‐Phillips et al, 2016, and references herein). Therefore, its oxygen isotopic composition is expected to be lower than δ 18 O site .…”