title: Cavitation and water fluxes driven by ice water potential in Juglans regia during freeze-thaw cycles.
abstract: Freeze-thaw cycles induce major hydraulic changes due to liquid-to-ice transition within tree stems. The very low water potential at the ice-liquid interface is crucial as it may cause lysis of living cells as well as water fluxes and embolism in sap conduits, which impacts whole tree-water relations. We investigated water fluxes induced by ice formation during freeze-thaw cycles in Juglans regia L. stems using four non-invasive and complementary approaches: a microdendrometer, magnetic resonance imaging, X-ray microtomography, and ultrasonic acoustic emissions analysis. When the temperature dropped, ice nucleation occurred, probably in the cambium or pith areas, inducing high water potential gradients within the stem. The water was therefore redistributed within the stem toward the ice front. We could thus observe dehydration of the bark's living cells leading to drastic shrinkage of this tissue, as well as high tension within wood conduits reaching the cavitation threshold in sap vessels. Ultrasonic emissions, which were strictly emitted only during freezing, indicated cavitation events (i.e. bubble formation) following ice formation in the xylem sap. However, embolism formation (i.e. bubble expansion) in stems was observed only on thawing via X-ray microtomography for the first time on the same sample. Ultrasonic emissions were detected during freezing and were not directly related to embolism formation. These results provide new insights into the complex process and dynamics of water movements and ice formation during freeze-thaw cycles in tree stems.
authors.affiliation: INRA, UMR PIAF, F-63100 Clermont-Ferrand, France Clermont Université, Blaise Pascal University, UMR PIAF, F-63100 Clermont-Ferrand, France katline.charravaskou@gmail.com.
authors.forename: Katline
authors.initials: K
authors.lastname: Charra-Vaskou
authors.affiliation: INRA, UMR PIAF, F-63100 Clermont-Ferrand, France Clermont Université, Blaise Pascal University, UMR PIAF, F-63100 Clermont-Ferrand, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Badel
authors.affiliation: Department of Botany, University of Innsbruck, A-6020 Innsbruck, Austria.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Charrier
authors.affiliation: INRA, UMR PIAF, F-63100 Clermont-Ferrand, France Clermont Université, Blaise Pascal University, UMR PIAF, F-63100 Clermont-Ferrand, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Ponomarenko
authors.affiliation: INRA, UMR PIAF, F-63100 Clermont-Ferrand, France Clermont Université, Blaise Pascal University, UMR PIAF, F-63100 Clermont-Ferrand, France.
authors.forename: Marc
authors.initials: M
authors.lastname: Bonhomme
authors.affiliation: INRA UR BIA, F-44316 Nantes, France.
authors.forename: Loïc
authors.initials: L
authors.lastname: Foucat
authors.affiliation: Department of Botany, University of Innsbruck, A-6020 Innsbruck, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mayr
authors.affiliation: INRA, UMR PIAF, F-63100 Clermont-Ferrand, France Clermont Université, Blaise Pascal University, UMR PIAF, F-63100 Clermont-Ferrand, France.
authors.forename: Thierry
authors.initials: T
authors.lastname: Améglio
mesh_terms: D005615:Freezing; D007053:Ice; D031324:Juglans / Q000502:physiology*; D009682:Magnetic Resonance Spectroscopy; D018547:Plant Stems / Q000033:anatomy & histology / Q000502:physiology; D014465:Ultrasonics; D055114:X-Ray Microtomography
chemical_list: D007053:Ice
keywords: Acoustic emissions; Juglans regia L.; X-ray microtomography.; bark shrinkage; embolism; microdendrometer; walnut tree; winter biology