title: Weak tradeoff between xylem safety and xylem-specific hydraulic efficiency across the world's woody plant species.
abstract: The evolution of lignified xylem allowed for the efficient transport of water under tension, but also exposed the vascular network to the risk of gas emboli and the spread of gas between xylem conduits, thus impeding sap transport to the leaves. A well-known hypothesis proposes that the safety of xylem (its ability to resist embolism formation and spread) should trade off against xylem efficiency (its capacity to transport water). We tested this safety-efficiency hypothesis in branch xylem across 335 angiosperm and 89 gymnosperm species. Safety was considered at three levels: the xylem water potentials where 12%, 50% and 88% of maximal conductivity are lost. Although correlations between safety and efficiency were weak (r(2)  < 0.086), no species had high efficiency and high safety, supporting the idea for a safety-efficiency tradeoff. However, many species had low efficiency and low safety. Species with low efficiency and low safety were weakly associated (r(2)  < 0.02 in most cases) with higher wood density, lower leaf- to sapwood-area and shorter stature. There appears to be no persuasive explanation for the considerable number of species with both low efficiency and low safety. These species represent a real challenge for understanding the evolution of xylem.
authors.affiliation: Department of Biological Sciences, Macquarie University, Sydney, NSW, 2109, Australia.|USDA-ARS, Water Management Research, 2150 Center Ave, Build D, Suite 320, Fort Collins, CO, 80526, USA.
authors.forename: Sean M
authors.initials: SM
authors.lastname: Gleason
authors.affiliation: Department of Biological Sciences, Macquarie University, Sydney, NSW, 2109, Australia.
authors.forename: Mark
authors.initials: M
authors.lastname: Westoby
authors.affiliation: Institute of Systematic Botany and Ecology, Ulm University, Albert-Einstein-Allee 11, 89081, Ulm, Germany.
authors.forename: Steven
authors.initials: S
authors.lastname: Jansen
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Richmond, NSW, 2753, Australia.
authors.forename: Brendan
authors.initials: B
authors.lastname: Choat
authors.affiliation: Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2E3, Canada.
authors.forename: Uwe G
authors.initials: UG
authors.lastname: Hacke
authors.affiliation: Department of Biology, California State University, Bakersfield, CA, 93311, USA.
authors.forename: Robert B
authors.initials: RB
authors.lastname: Pratt
authors.affiliation: Department of Biology, Haverford College, 370 Lancaster Avenue, Haverford, PA, 19041, USA.
authors.forename: Radika
authors.initials: R
authors.lastname: Bhaskar
authors.affiliation: School of Biological Sciences, University of Tasmania, Hobart, Tasmania, 7001, Australia.
authors.forename: Tim J
authors.initials: TJ
authors.lastname: Brodribb
authors.affiliation: Grupo de Estudios Biofísicos y Eco-fisiológicos (GEBEF), Universidad Nacional de la Patagonia San Juan Bosco, 9000, Comodoro Rivadavia, Argentina.
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Bucci
authors.affiliation: Plant Ecophysiology and Evolution Group, State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, and College of Forestry, Guangxi University, Daxuedonglu 100, Nanning, Guangxi, 530004, China.
authors.forename: Kun-Fang
authors.initials: KF
authors.lastname: Cao
authors.affiliation: INRA, UMR547 PIAF, F-63100, Clermont-Ferrand, France.|Clermont Université, Université Blaise Pascal, UMR547 PIAF, F-63000, Clermont-Ferrand, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Cochard
authors.affiliation: INRA, University of Bordeaux, UMR BIOGECO, F-33450, Talence, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Delzon
authors.affiliation: Bordeaux Sciences AGRO, UMR1391 ISPA INRA, 1 Cours du général de Gaulle, 33175, Gradignan Cedex, France.|Nicholas School of the Environment, Duke University, Durham, NC, 27708, USA.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Domec
authors.affiliation: Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan, 666303, China.
authors.forename: Ze-Xin
authors.identifier: http://orcid.org/0000-0003-4623-6783
authors.initials: ZX
authors.lastname: Fan
authors.affiliation: School of Marine and Tropical Biology, James Cook University, Townsville, Qld, 4811, Australia.
authors.forename: Taylor S
authors.initials: TS
authors.lastname: Feild
authors.affiliation: Department of Biology, California State University, Bakersfield, CA, 93311, USA.
authors.forename: Anna L
authors.initials: AL
authors.lastname: Jacobsen
authors.affiliation: Department of Forest, Rangeland and Fire Sciences, University of Idaho, Moscow, ID, 83844, USA.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Johnson
authors.affiliation: Naturalis Biodiversity Center, Leiden University, PO Box 9517, 2300RA, Leiden, the Netherlands.
authors.forename: Frederic
authors.initials: F
authors.lastname: Lens
authors.affiliation: Department of Integrative Biology, University of Guelph, Guelph, Ontario, N1G2W1, Canada.
authors.forename: Hafiz
authors.initials: H
authors.lastname: Maherali
authors.affiliation: CREAF, Cerdanyola del Vallès, E-08193, Barcelona, Spain.|ICREA at CREAF, Cerdanyola del Vallès, E-08193, Barcelona, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Martínez-Vilalta
authors.affiliation: Department of Botany, University of Innsbruck, Sternwartestr. 15, 6020, Innsbruck, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mayr
authors.affiliation: Department of Botany, University of Wisconsin-Madison, Madison, WI, 53705, USA.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: McCulloh
authors.affiliation: ICREA at CREAF, Cerdanyola del Vallès, E-08193, Barcelona, Spain.|School of GeoSciences, University of Edinburgh, Crew Building, West Mains Road, Edinburgh, EH9 3FF, UK.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Mencuccini
authors.affiliation: CSIRO Land and Water Flagship, Sandy Bay, Tasmania, 7005, Australia.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Mitchell
authors.affiliation: Institute of Systematic Botany and Ecology, Ulm University, Albert-Einstein-Allee 11, 89081, Ulm, Germany.
authors.forename: Hugh
authors.initials: H
authors.lastname: Morris
authors.affiliation: Dipartimento Scienze della Vita, Università Trieste, Via L. Giorgieri 10, 34127, Trieste, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Nardini
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA, 95064, USA.
authors.forename: Jarmila
authors.initials: J
authors.lastname: Pittermann
authors.affiliation: Institute of Systematic Botany and Ecology, Ulm University, Albert-Einstein-Allee 11, 89081, Ulm, Germany.|Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2E3, Canada.
authors.forename: Lenka
authors.initials: L
authors.lastname: Plavcová
authors.affiliation: Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2E3, Canada.
authors.forename: Stefan G
authors.initials: SG
authors.lastname: Schreiber
authors.affiliation: Department of Biology, University of Utah, 257S 1400E, Salt Lake City, UT, 84112, USA.
authors.forename: John S
authors.initials: JS
authors.lastname: Sperry
authors.affiliation: Department of Biological Sciences, Macquarie University, Sydney, NSW, 2109, Australia.
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Wright
authors.affiliation: Department of Biological Sciences, George Washington University, Science and Engineering Hall, 800 22nd Street NW, Suite 6000, Washington, DC, 20052, USA.
authors.forename: Amy E
authors.initials: AE
authors.lastname: Zanne
mesh_terms: D032462:Cycadopsida / Q000502:physiology*; D019684:Magnoliopsida / Q000502:physiology*; D018515:Plant Leaves / Q000502:physiology; D018526:Plant Transpiration; D014867:Water / Q000502:physiology; D014934:Wood; D052584:Xylem / Q000502:physiology*
chemical_list: D014867:Water
keywords: cavitation; embolism; hydraulic conductivity; mean annual precipitation; mean annual temperature; xylem