Patterns of drought-induced embolism formation and spread in living walnut saplings visualized using X-ray microtomography

Tree Physiol. 2015 Jul;35(7):744-55. doi: 10.1093/treephys/tpv040. Epub 2015 Jun 9.


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.

Keywords: Juglans microcarpa; air-seeding; cavitation; microCT; network connectivity; nucleation; water stress; xylem.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Droughts
  • Juglans / physiology*
  • Plant Stems
  • Water
  • X-Ray Microtomography
  • Xylem / physiology*


  • Water