title: Testing the 'microbubble effect' using the Cavitron technique to measure xylem water extraction curves.
abstract: Plant resistance to xylem cavitation is a major drought adaptation trait and is essential to characterizing vulnerability to climate change. Cavitation resistance can be determined with vulnerability curves. In the past decade, new techniques have increased the ease and speed at which vulnerability curves are produced. However, these new techniques are also subject to new artefacts, especially as related to long-vesselled species. We tested the reliability of the 'flow rotor' centrifuge technique, the so-called Cavitron, and investigated one potential mechanism behind the open vessel artefact in centrifuge-based vulnerability curves: the microbubble effect. The microbubble effect hypothesizes that microbubbles introduced to open vessels, either through sample flushing or injection of solution, travel by buoyancy or mass flow towards the axis of rotation where they artefactually nucleate cavitation. To test the microbubble effect, we constructed vulnerability curves using three different rotor sizes for five species with varying maximum vessel length, as well as water extraction curves that are constructed without injection of solution into the rotor. We found that the Cavitron technique is robust to measure resistance to cavitation in tracheid-bearing and short-vesselled species, but not for long-vesselled ones. Moreover, our results support the microbubble effect hypothesis as the major cause for the open vessel artefact in long-vesselled species.
authors.affiliation: La Kretz Center for California Conservation Science, University of California Los Angeles, Los Angeles, CA 90095, USA Université de Bordeaux, UMR BIOGECO, 33405 Talence, France Department of Botany and Plant Sciences, University of California Riverside, 2150 Batchelor Hall, Riverside, CA 92521, USA apivovaroff@ucla.edu.
authors.forename: Alexandria L
authors.initials: AL
authors.lastname: Pivovaroff
authors.affiliation: Université de Bordeaux, UMR BIOGECO, 33405 Talence, France.
authors.forename: Régis
authors.initials: R
authors.lastname: Burlett
authors.affiliation: Université de Bordeaux, UMR BIOGECO, 33405 Talence, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Lavigne
authors.affiliation: INRA, UMR 547 PIAF, Université Clermont Auvergne, 63100 Clermont-Ferrand, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Cochard
authors.affiliation: Department of Botany and Plant Sciences, University of California Riverside, 2150 Batchelor Hall, Riverside, CA 92521, USA.
authors.forename: Louis S
authors.initials: LS
authors.lastname: Santiago
authors.affiliation: Université de Bordeaux, UMR BIOGECO, 33405 Talence, France INRA, UMR 1202 BIOGECO, 33612 Cestas, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Delzon
keywords: Cavitation resistance; embolism; plant hydraulics; vessel length artefact; water relations