Expressing leaf water and cellulose oxygen isotope ratios as enrichment above source water reveals evidence of a P�clet effect

Abstract

There is an increasing ecological interest in understanding the gradients in H(2)(18)O enrichment in leaf water (i.e. a Péclet effect), because an appreciation of the significance of the Péclet effect is important for improving our understanding of the mechanistic processes affecting the (18)O composition of leaf water and plant organic material. In data sets where both source water and leaf water (18)O data are available, we can evaluate the potential contribution of a Péclet effect. As an example, we recalculate data published earlier by Roden and Ehleringer (1999, Oecologia 121:467-477) as enrichments in leaf water (Delta(L)) and cellulose (Delta(cell)) above source water. Based on these recalculations, we present support for the relevance of a Péclet effect in leaves. Further, we demonstrate that the subtle variations in Delta(L) and Delta(cell) caused by a Péclet effect may be masked in experimental systems in which variation in the source water oxygen isotope ratio is considerable.

Needle cell elongation and maturation timing derived from pine needle cellulose δ18O

“…Equations from Barbour et al (2004) and Wang et al (1998), including a modified version of the Flanagan leaf water model (1991), were used to estimate the Péclet numbers pertinent to each sampling date, to calculate the effective mixing path lengths, and to assess the influence of a Péclet effect on this system. The version of the Flanagan leaf water model used in this study was acquired through an internet link provided in the text of the Barbour et al (2004) paper.…”

“…The version of the Flanagan leaf water model used in this study was acquired through an internet link provided in the text of the Barbour et al (2004) paper.…”

“…These estimates of stomatal conductance were used as input to the Flanagan et al (1991) model to estimate the transpiration rate. The mod-elled transpiration rate was then plotted against the fractional difference between measured leaf-water enrichment and the enrichment as predicted by the Craig and Gordon model (Barbour et al 2004).…”

“…(1991) was used in this study as an aid in interpreting the leaf-cellulose d 18 O. In addition, equations from recent research (Wang, Yakir & Avishai 1998;Barbour et al . 2004) were used to assess the importance of back diffusion from the point of evaporation, the Péclet effect, to leaf-water enrichment in this system.…”

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

“…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). The mechanistic foundations for variation in cellulose d 13 C and d 18 O are now fairly well established (Farquhar et al 1982(Farquhar et al , 1989Roden et al 2000;Barbour et al 2004). Thus, absolutely dated time series of d 18 O and d 13 C variation in redwood tree rings have the potential to provide valuable historical records of climate variation and fog water utilization.…”