Vulnerability to cavitation in Olea europaea current‐year shoots: further evidence of an open‐vessel artifact associated with centrifuge and air‐injection 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 artifacts 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 vulnerability curves (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. Indeed, high-resolution computed tomography (HRCT) images were used to evaluate the functional status of xylem at different water potentials. Measurements of native embolism were used to validate the methods used. 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-vessel artifact hypothesis as a higher proportion of vessels were open in short samples. The two different rotor designs used for the flow-centrifuge method revealed similar vulnerability to cavitation. Only the bench dehydration or HRCT methods produced VCs that agreed with native levels of embolism and water potential values measured in the field.

Comparative Drought Responses of Quercus ilex L. and Pinus sylvestris L. in a Montane Forest Undergoing a Vegetation Shift

“…Importantly, the iso-/anisohydric dichotomy does not account for differences in vulnerability to xylem embolism [12], nor for leaf traits involved in turgor regulation [65]. Given the current methodological controversy on the measurement of vulnerability to xylem embolism (e.g., [48,61]) we cannot be sure that the extremely high PLC values estimated here are real. However, several notes are in order: (i) extremely high (~80%) PLC is also predicted by more conservative vulnerability estimates under extreme drought ( Figures 8 and 9); (ii) extremely high PLC in the xylem is consistent with measured seasonal reductions in kS-L ( Figure 6); (iii) the relationship between ΨPD and ΨMD for this species (Figure 3) suggests a similar sensitivity of stomata and plant hydraulic conductance to declining water potential (cf.…”

“…Our PLC values were estimated from xylem vulnerability curves obtained using appropriate methods for each species-air injection for P. sylvestris and bench dehydration for Q. ilex [48,60]. However, none of these methods is free of potential artifacts [61], and estimated branch P50 values for Q. ilex in the study site (−2 MPa; [47]) are low compared to the range of values reported in other studies (between −3.8 and −6.6 MPa; [27,48,62,63]). If we use the vulnerability curves recently reported for a climatically similar Q. ilex population (−4.70 MPa; [48]) to estimate branch PLC, Q. ilex would keep PLC below ~20% except for the drought period in 2011, when PLC reached ~80% (Figure 8).…”

Xylem embolism refilling and resilience against drought‐induced mortality in woody plants: processes and trade‐offs

“…Alternatively, the relaxation procedure has been shown to introduce other potential errors related to rehydration-induced embolism refilling (Trifilo`et al 2014b). Recommendations for standardizing measurements of vulnerability curves have recently been described (Torres-Ruiz et al 2014). Future research should carefully evaluate the occurrence and magnitude of cutting or relaxation artefact in species investigated for their refilling capability.…”

Direct X-Ray Microtomography Observation Confirms the Induction of Embolism upon Xylem Cutting under Tension

“…However, recent publications have provided evidence that some measurement techniques used to evaluate the hydraulic function and vulnerability to cavitation of plant organs may be prone to artifacts (Sperry et al, 2012;Torres-Ruiz et al, 2014;Trifilò et al, 2014). The discovery of these artifacts has raised questions regarding the reliability of some previously published plant hydraulics data, in particular data relating to the refilling of embolized xylem conduits while the xylem is under tension.…”