Excising stem samples underwater at native tension does not induce xylem cavitation

Abstract

Xylem resistance to water stress-induced cavitation is an important trait that is associated with drought tolerance of plants. The level of xylem cavitation experienced by a plant is often assessed as the percentage loss in conductivity (PLC) at different water potentials. Such measurements are constructed with samples that are excised underwater at native tensions. However, a recent study concluded that cutting conduits under significant tension induced cavitation, even when samples were held underwater during cutting. This resulted in artificially increased PLC because of what we have termed a 'tension-cutting artefact'. We tested the hypothesized tension-cutting artefact on five species by measuring PLC at native tension compared with after xylem tensions had been relaxed. Our results did not support the tension-cutting artefact hypothesis, as no differences were observed between native and relaxed samples in four of five species. In a fifth species (Laurus nobilis), differences between native and relaxed samples appear to be due to vessel refilling rather than a tension-cutting effect. We avoided the tension-cutting artefact by cutting samples to slightly longer than their measurement length and subsequent trimming of at least 0.5 cm of sample ends prior to measurement.

In Situ Visualization of the Dynamics in Xylem Embolism Formation and Removal in the Absence of Root Pressure: A Study on Excised Grapevine Stems

“…This method, however, is performed with the implicit assumption that no novel refilling (to our knowledge) is occurring. Nevertheless, more recent data indicate that the rehydration procedure may facilitate vessel refilling (Trifilò et al, 2014;Venturas et al, 2015). Venturas et al (2015) concluded that differences in hydraulic conductivity were mainly caused by a refilling artifact as opposed to a cutting-artifact.…”

“…Nevertheless, more recent data indicate that the rehydration procedure may facilitate vessel refilling (Trifilò et al, 2014;Venturas et al, 2015). Venturas et al (2015) concluded that differences in hydraulic conductivity were mainly caused by a refilling artifact as opposed to a cutting-artifact. Here, the experimental design effectively simulated the methods many labs currently use for the preparation/maintenance of samples in xylem hydraulic conductivity measurements.…”

“…To minimize potential artifacts when using invasive hydraulic methods, Wheeler et al (2013) suggested that stem segments be rehydrated after excision to allow tissue equilibration before analysis. However, as speculated by Trifilò et al (2014) and Venturas et al (2015), this may facilitate vessel refilling, which would lead to an overestimation in xylem hydraulic transport capacity. To date, directly visualization of embolism formation and removal in excised plant segments has been limited to a single study (Rolland et al, 2015), and the corresponding biological mechanism that may induce these phenomena is still unknown.…”

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

“…However, we note that the long-vessel artefact has been rebutted by other studies Hacke et al 2014), and this issue remains unresolved. (2) To avoid artefactual embolism induction caused by the cutting of a branch, while the xylem is under tension, rehydration/relaxation of samples has been suggested, followed by re-cutting under degassed water (Wheeler et al 2013), although this artefact has not been found by others (Venturas et al 2015). Alternatively, the relaxation procedure has been shown to introduce other potential errors related to rehydration-induced embolism refilling (Trifilo`et al 2014b).…”

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

“…Whereas Scoffoni and Sack (2014) showed that the artifact described by Wheeler et al (2013) has no impact on leaf xylem hydraulic conductance, there is some uncertainty about its importance in stems or shoots (Trifilò et al, 2014;Venturas et al, 2014). The results of Wheeler et al (2013) indicate that more embolism could be induced by cutting samples that are under midrange xylem tension (e.g.…”