title: Patterns of drought-induced embolism formation and spread in living walnut saplings visualized using X-ray microtomography.
abstract: Embolism formation and spread are dependent on conduit structure and xylem network connectivity. Detailed spatial analysis has been limited due to a lack of non-destructive methods to visualize these processes in living plants. We used synchrotron X-ray computed tomography (microCT) to visualize these processes in vivo for Juglans microcarpa Berl. saplings subjected to drought, and also evaluated embolism repair capability after re-watering. Cavitation was not detected in vivo until stem water potentials (Ψ(stem)) reached -2.2 MPa, and loss of stem hydraulic conductivity as derived from microCT images predicted that 50% of conductivity was lost at Ψ(stem) of ∼ -3.5 MPa; xylem vulnerability as determined with the centrifuge method was comparable only in the range of Ψ(stem) from -2.5 to -3.5 MPa. MicroCT images showed that cavitation appeared initially in isolated vessels not connected to other air-filled conduits. Once embolized vessels were present, multiple vessels in close proximity cavitated, and 3-D analysis along the stem axis revealed some connections between cavitated vessels. A tomography-derived automated xylem network analysis found that only 36% of vessels had one or more connections to other vessels. Cavitation susceptibility was related to vessel diameter, with large diameter vessels (>40 μm, mean diameter 25-30 μm) cavitating mainly under moderate stress (Ψ(stem) > -3 MPa) and small diameter vessels (<30 μm) under severe stress. After re-watering there was no evidence for short or longer term vessel refilling over 2 weeks despite a rapid recovery of plant water status. The low embolism susceptibility in 1-year-old J. microcarpa may aid sapling survival during establishment.
authors.affiliation: Department of Viticulture and Enology, University of California, Davis, CA 95616, USA.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Knipfer
authors.affiliation: School of Forestry and Environmental Studies, Yale University, 195 Prospect Street, New Haven, CT 06511, USA.
authors.forename: Craig R
authors.initials: CR
authors.lastname: Brodersen
authors.affiliation: Department of Viticulture and Enology, University of California, Davis, CA 95616, USA.
authors.forename: Amr
authors.initials: A
authors.lastname: Zedan
authors.affiliation: US Department of Agriculture, Agricultural Research Service, Davis, CA 95616, USA.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Kluepfel
authors.affiliation: Department of Viticulture and Enology, University of California, Davis, CA 95616, USA US Department of Agriculture, Agricultural Research Service, Davis, CA 95616, USA ajmcelrone@ucdavis.edu.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: McElrone
mesh_terms: D055864:Droughts; D031324:Juglans / Q000502:physiology*; D018547:Plant Stems; D014867:Water; D055114:X-Ray Microtomography; D052584:Xylem / Q000502:physiology*
chemical_list: D014867:Water
keywords: Juglans microcarpa; air-seeding; cavitation; microCT; network connectivity; nucleation; water stress; xylem