title: A broad survey of hydraulic and mechanical safety in the xylem of conifers.
abstract: Drought-induced forest dieback has been widely reported over the last decades, and the evidence for a direct causal link between survival and hydraulic failure (xylem cavitation) is now well known. Because vulnerability to cavitation is intimately linked to the anatomy of the xylem, the main objective of this study was to better understand the xylem anatomical properties associated with cavitation resistance. An extensive data set of cavitation resistance traits and xylem anatomical properties was developed for 115 conifer species, with special attention given to the micro-morphology of bordered pits. The ratio of torus to pit aperture diameter, so-called torus overlap, increased with increasing cavitation resistance, while the flexibility of the margo does not seem to play a role, suggesting that air-seeding is located at the seal between the aspirated torus and pit aperture. Moreover, punctured tori were reported in various Pinaceae species. Species resistant to cavitation had thicker tracheid walls, while their lumen diameter (conduit size) was only slightly reduced, minimizing the impact on hydraulic conductance. The results also demonstrated (i) the existence of an indirect trade-off between hydraulic safety and mechanical strength; and (ii) a consistency between species distribution and xylem anatomy: species with a wide torus overlap and high valve effects are found in arid environments such as the Mediterranean region.
authors.affiliation: Institute for Systematic Botany and Ecology, Ulm University, Ulm, Germany INRA, UMR BIOGECO, F-33610 Cestas, France University of Bordeaux, UMR BIOGECO, 33405 Talence, France.
authors.forename: Pauline S
authors.initials: PS
authors.lastname: Bouche
authors.affiliation: INRA, UMR BIOGECO, F-33610 Cestas, France University of Bordeaux, UMR BIOGECO, 33405 Talence, France.
authors.forename: Maximilien
authors.initials: M
authors.lastname: Larter
authors.affiliation: Bordeaux Sciences Agro, University of Bordeaux, 33175 Gradignan, France INRA, UMR TCEM, F-33140 Villenave d'Ornon, France.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Domec
authors.affiliation: University of Bordeaux, UMR BIOGECO, 33405 Talence, France.
authors.forename: Régis
authors.initials: R
authors.lastname: Burlett
authors.affiliation: Jodrell Laboratory, Royal Botanic Garden, Kew, Richmond, Surrey, TW9 3DS, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Gasson
authors.affiliation: Institute for Systematic Botany and Ecology, Ulm University, Ulm, Germany.
authors.forename: Steven
authors.initials: S
authors.lastname: Jansen
authors.affiliation: INRA, UMR BIOGECO, F-33610 Cestas, France University of Bordeaux, UMR BIOGECO, 33405 Talence, France sylvain.delzon@u-bordeaux1.fr.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Delzon
mesh_terms: D005075:Biological Evolution; D055595:Mechanical Phenomena; D064028:Tracheophyta / Q000033:anatomy & histology / Q000502:physiology*; D014867:Water / Q000502:physiology*; D052584:Xylem / Q000033:anatomy & histology / Q000502:physiology*
chemical_list: D014867:Water
keywords: Cavitation resistance; hydraulic efficiency; mechanical strength; seal capillary–seeding; torus–margo pit; wall implosion.; xylem anatomy