title: Are needles of Pinus pinaster more vulnerable to xylem embolism than branches? New insights from X-ray computed tomography.
abstract: Plants can be highly segmented organisms with an independently redundant design of organs. In the context of plant hydraulics, leaves may be less embolism resistant than stems, allowing hydraulic failure to be restricted to distal organs that can be readily replaced. We quantified drought-induced embolism in needles and stems of Pinus pinaster using high-resolution computed tomography (HRCT). HRCT observations of needles were compared with the rehydration kinetics method to estimate the contribution of extra-xylary pathways to declining hydraulic conductance. High-resolution computed tomography images indicated that the pressure inducing 50% of embolized tracheids was similar between needle and stem xylem (P50 needle xylem  = -3.62 MPa, P50 stem xylem  = -3.88 MPa). Tracheids in both organs showed no difference in torus overlap of bordered pits. However, estimations of the pressure inducing 50% loss of hydraulic conductance at the whole needle level by the rehydration kinetics method were significantly higher (P50 needle  = -1.71 MPa) than P50 needle xylem derived from HRCT. The vulnerability segmentation hypothesis appears to be valid only when considering hydraulic failure at the entire needle level, including extra-xylary pathways. Our findings suggest that native embolism in needles is limited and highlight the importance of imaging techniques for vulnerability curves.
authors.affiliation: Institute for Systematic Botany and Ecology, Ulm University, D-89081, Ulm, Germany.|UMR1202 BIOGECO, INRA, F-33610, Cestas, France.|BIOGECO, University of Bordeaux, UMR 1202, F-33600, Pessac, France.
authors.forename: Pauline S
authors.initials: PS
authors.lastname: Bouche
authors.affiliation: UMR1202 BIOGECO, INRA, F-33610, Cestas, France.|BIOGECO, University of Bordeaux, UMR 1202, F-33600, Pessac, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Delzon
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, New South Wales, 2753, Australia.
authors.forename: Brendan
authors.initials: B
authors.lastname: Choat
authors.affiliation: INRA, UMR 457 PIAF, Clermont University, F-63100, Clermont-Ferrand, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Badel
authors.affiliation: School of Plant Science, University of Tasmania, Hobart, Tasmania, 7001, Australia.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Brodribb
authors.affiliation: UMR1202 BIOGECO, INRA, F-33610, Cestas, France.|BIOGECO, University of Bordeaux, UMR 1202, F-33600, Pessac, France.
authors.forename: Regis
authors.initials: R
authors.lastname: Burlett
authors.affiliation: INRA, UMR 457 PIAF, Clermont University, F-63100, Clermont-Ferrand, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Cochard
authors.affiliation: INRA, UMR 457 PIAF, Clermont University, F-63100, Clermont-Ferrand, France.
authors.forename: Katline
authors.initials: K
authors.lastname: Charra-Vaskou
authors.affiliation: UMR1202 BIOGECO, INRA, F-33610, Cestas, France.|BIOGECO, University of Bordeaux, UMR 1202, F-33600, Pessac, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Lavigne
authors.affiliation: Institute for Systematic Botany and Ecology, Ulm University, D-89081, Ulm, Germany.
authors.forename: Shan
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Botany, University of Innsbruck, A-6020, Innsbruck, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mayr
authors.affiliation: Institute for Systematic Botany and Ecology, Ulm University, D-89081, Ulm, Germany.
authors.forename: Hugh
authors.initials: H
authors.lastname: Morris
authors.affiliation: UMR1202 BIOGECO, INRA, F-33610, Cestas, France.|BIOGECO, University of Bordeaux, UMR 1202, F-33600, Pessac, France.
authors.forename: José M
authors.initials: JM
authors.lastname: Torres-Ruiz
authors.affiliation: Institut des sciences en production végétale IPV, Agroscope, CH-1260, Nyon, Switzerland.
authors.forename: Vivian
authors.initials: V
authors.lastname: Zufferey
authors.affiliation: Institute for Systematic Botany and Ecology, Ulm University, D-89081, Ulm, Germany.
authors.forename: Steven
authors.initials: S
authors.lastname: Jansen
mesh_terms: D003681:Dehydration; D028223:Pinus / Q000502:physiology*; D018515:Plant Leaves / Q000502:physiology*; D018547:Plant Stems / Q000033:anatomy & histology / Q000502:physiology*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014197:Trees / Q000502:physiology; D052584:Xylem / Q000033:anatomy & histology / Q000502:physiology*
keywords: Conifer; direct visualization of water content; embolised tracheids; hydraulic failures; wall deformation