Leaf vein fraction influences the Péclet effect and 18O enrichment in leaf water. (21st September 2016)

• Record Type: Journal Article
• Authors: Holloway‐Phillips, Meisha; Cernusak, Lucas A.; Barbour, Margaret; Song, Xin; Cheesman, Alexander; Munksgaard, Niels; Stuart‐Williams, Hilary; Farquhar, Graham D.
• Is Part Of: Plant, cell and environment. Volume 39:Number 11(2016)
• Page Start: 2414
• Page End: 2427
• Publication Date: 2016-09-21
• Subjects: δ18O -- evaporative enrichment -- leaf water isotopes -- Péclet -- tree‐rings -- vein volume fraction; Plant physiology -- Periodicals; Plant cells and tissues -- Periodicals; Plant communities -- Periodicals; 581.105
• DOI: 10.1111/pce.12792
• Languages: English
• ISSNs: 0140-7791

Abstract

Abstract: The process of evaporation results in the fractionation of water isotopes such that the lighter 16 O isotope preferentially escapes the gas phase leaving the heavier 18 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 18 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 18 O of organic matter. Abstract : The 18 O enrichment of leaf water during transpiration is often less than that predicted for the sites of evaporation. The Péclet effect remains the most compelling explanation; however, evidence has been varied. We provide strong evidence for a Péclet effect within the xylem which, if unaccounted for, can lead to confounding of the estimated enrichment within the mesophyll water.