Vulnerability to cavitation in Olea europaea current-year shoots: further evidence of an open-vessel artefact associated with centrifuge and airinjection techniques

Abstract

Different methods have been devised to analyze vulnerability to cavitation of plants. Although a good agreement between them is usually found, some discrepancies have been reported when measuring samples from long-vesseled species. The aim of this study was to evaluate possible artefacts derived from different methods and sample sizes. Current-year shoot segments of mature olive trees (Olea europaea), a long-vesseled species, were used to generate VCs by bench dehydration, pressure collar and both static- and flow-centrifuge methods. For the latter, two different rotors were used to test possible effects of the rotor design on the curves. Measurements of native embolism and High- Resolution Computed Tomography images were used in order to validate the VC methods. The pressure collar and the two centrifugal methods showed greater vulnerability to cavitation than the dehydration method. The shift in vulnerability thresholds in centrifuge methods was more pronounced in shorter samples, supporting the open vessels artefact hypothesis since a higher proportion of vessels was open in short samples. The two different rotor designs used for the flow-centrifuge method revealed similar vulnerability to cavitation. Only the bench dehydration method or x-ray methods produced VCs that agreed with native levels of embolism measured in the field and measured water potentials.