title: Rare pits, large vessels and extreme vulnerability to cavitation in a ring-porous tree species.
abstract: • The rare pit hypothesis predicts that the extensive inter-vessel pitting in large early-wood vessels of ring-porous trees should render many of these vessels extremely vulnerable to cavitation by air-seeding. This prediction was tested in Quercus gambelii. • Cavitation was assessed from native hydraulic conductivity at field sap tension and in dehydrated branches. Single-vessel air injections gave air-seeding pressures through vessel files; these data were used to estimate air-seeding pressures for inter-vessel walls and pits. • Extensive cavitation occurred at xylem sap tensions below 1 MPa. Refilling occurred below 0.5 MPa and was inhibited by phloem girdling. Remaining vessels cavitated over a wide range to above 4 MPa. Similarly, 40% of injected vessel files air-seeded below 1.0 MPa, whereas the remainder seeded over a wide range exceeding 5 MPa. Inter-vessel walls averaged 1.02 MPa air-seeding pressure, similar and opposite to the mean cavitation tension of 1.22 MPa. Consistent with the rare pit hypothesis, only 7% of inter-vessel pits were estimated to air-seed by 1.22 MPa. • The results confirm the rare pit prediction that a significant fraction of large vessels in Q. gambelii experience high probability of failure by air-seeding.
authors.affiliation: Institute for Ecohydrology Research, 1111 Kennedy Place Ste 4, Davis, CA 95616, USA.
authors.forename: Mairgareth A
authors.initials: MA
authors.lastname: Christman
authors.affiliation: Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112, USA.
authors.forename: John S
authors.initials: JS
authors.lastname: Sperry
authors.affiliation: Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112, USA.
authors.forename: Duncan D
authors.initials: DD
authors.lastname: Smith
mesh_terms: D000388:Air; D002940:Circadian Rhythm; D003681:Dehydration; D052585:Phloem / Q000033:anatomy & histology / Q000502:physiology; D018547:Plant Stems / Q000033:anatomy & histology / Q000502:physiology; D016062:Porosity; D029963:Quercus / Q000033:anatomy & histology* / Q000502:physiology*; D014197:Trees / Q000033:anatomy & histology* / Q000502:physiology*; D014867:Water / Q000502:physiology*; D052584:Xylem / Q000033:anatomy & histology* / Q000502:physiology*
chemical_list: D014867:Water