title: Transpiration rate relates to within- and across-species variations in effective path length in a leaf water model of oxygen isotope enrichment.
abstract: Stable oxygen isotope ratio of leaf water (δ(18)O(L)) yields valuable information on many aspects of plant-environment interactions. However, current understanding of the mechanistic controls on δ(18)O(L) does not provide complete characterization of effective path length (L) of the Péclet effect,--a key component of the leaf water model. In this study, we collected diurnal and seasonal series of leaf water enrichment and estimated L in six field-grown angiosperm and gymnosperm tree species. Our results suggest a pivotal role of leaf transpiration rate (E) in driving both within- and across-species variations in L. Our observation of the common presence of an inverse scaling of L with E in the different species therefore cautions against (1) the conventional treatment of L as a species-specific constant in leaf water or cellulose isotope (δ(18)O(p)) modelling; and (2) the use of δ(18)O(p) as a proxy for gs or E under low E conditions. Further, we show that incorporation of a multi-species L-E scaling into the leaf water model has the potential to both improve the prediction accuracy and simplify parameterization of the model when compared with the conventional approach. This has important implications for future modelling of oxygen isotope ratios.
authors.affiliation: Department of Biology, University of Pennsylvania, 433 S University Ave., Philadelphia, PA 19104, USA.  xinsong@sas.upenn.edu
authors.forename: Xin
authors.initials: X
authors.lastname: Song
authors.affiliation: Landcare Research, PO Box 40, Lincoln, 7640, New Zealand.|Faculty of Agriculture and Environment, University of Sydney, Private Bag 4110, Narellan, NSW, 2567, Australia.
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Barbour
authors.affiliation: Research School of Biology, The Australian National University, Canberra, ACT, 0200, Australia.
authors.forename: Graham D
authors.initials: GD
authors.lastname: Farquhar
authors.affiliation: Department of Biology, University of Pennsylvania, 433 S. University Ave., Philadelphia, PA, 19104, USA.
authors.forename: David R
authors.initials: DR
authors.lastname: Vann
authors.affiliation: Department of Biology, University of Pennsylvania, 433 S. University Ave., Philadelphia, PA, 19104, USA.
authors.forename: Brent R
authors.initials: BR
authors.lastname: Helliker
mesh_terms: D001692:Biological Transport; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism*; D010103:Oxygen Isotopes / Q000032:analysis; D018515:Plant Leaves / Q000378:metabolism; D018526:Plant Transpiration; D013045:Species Specificity; D014197:Trees / Q000378:metabolism*; D014867:Water / Q000378:metabolism*
chemical_list: D010103:Oxygen Isotopes; D014867:Water; D010100:Oxygen
keywords: L-E dynamics; Péclet effect; cellulose; evaporative enrichment