title: How do trees die? A test of the hydraulic failure and carbon starvation hypotheses.
abstract: Despite decades of research on plant drought tolerance, the physiological mechanisms by which trees succumb to drought are still under debate. We report results from an experiment designed to separate and test the current leading hypotheses of tree mortality. We show that piñon pine (Pinus edulis) trees can die of both hydraulic failure and carbon starvation, and that during drought, the loss of conductivity and carbohydrate reserves can also co-occur. Hydraulic constraints on plant carbohydrate use determined survival time: turgor loss in the phloem limited access to carbohydrate reserves, but hydraulic control of respiration prolonged survival. Our data also demonstrate that hydraulic failure may be associated with loss of adequate tissue carbohydrate content required for osmoregulation, which then promotes failure to maintain hydraulic integrity.
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: Sanna
authors.initials: S
authors.lastname: Sevanto
authors.forename: Nate G
authors.initials: NG
authors.lastname: McDowell
authors.forename: L Turin
authors.initials: LT
authors.lastname: Dickman
authors.forename: Robert
authors.initials: R
authors.lastname: Pangle
authors.forename: William T
authors.initials: WT
authors.lastname: Pockman
mesh_terms: D002241:Carbohydrates / Q000032:analysis / Q000502:physiology; D002244:Carbon / Q000172:deficiency*; D019069:Cell Respiration / Q000502:physiology; D055864:Droughts; D009995:Osmosis; D052585:Phloem / Q000502:physiology; D010788:Photosynthesis / Q000502:physiology; D028223:Pinus / Q000502:physiology*; D018526:Plant Transpiration / Q000502:physiology*; D013997:Time Factors; D014197:Trees; D014867:Water / Q000502:physiology; D052584:Xylem / Q000502:physiology
chemical_list: D002241:Carbohydrates; D014867:Water; D002244:Carbon
keywords: cavitation; forest mortality; hydraulic conductance; non-structural carbohydrates; phloem; xylem