Functional analysis of embolism induced by air injection in Acer rubrum and Salix nigra

Abstract

The goal of this study was to assess the effect of induced embolism with air injection treatments on the function of xylem in Acer rubrum L. and Salix nigra Marsh. Measurements made on mature trees of A. rubrum showed that pneumatic pressurization treatments that created a pressure gradient of 5.5 MPa across pit membranes (ΔPpit) had no effect on stomatal conductance or on branch-level sap flow. The same air injection treatments made on 3-year-old potted A. rubrum plants also had no effect on whole plant transpiration. A separate study made on mature A. rubrum trees showed that 3.0 and 5.5 MPa of ΔPpit values resulted in an immediate 100% loss in hydraulic conductance (PLC) in petioles. However, the observed change in PLC was short lived, and significant hydraulic recovery occurred within 5–10 min post air-pressurization treatments. Similar experiments conducted on S. nigra plants exposed to ΔPpit of 3 MPa resulted in a rapid decline in whole plant transpiration followed by leaf wilting and eventual plant death, showing that this species lacks the ability to recover from induced embolism. A survey that measured the effect of air-pressurization treatments on seven other species showed that some species are very sensitive to induction of embolism resulting in leaf wilting and branch death while others show minimal to no effect despite that in each case, the applied ΔPpit of 5.5 MPa significantly exceeded any native stress that these plants would experience naturally.

Relax and refill: xylem rehydration prior to hydraulic measurements favours embolism repair in stems and generates artificially low PLC values

“…The above observations and findings would be in overall agreement with considerations by Melcher & Zwieniecki (), suggesting that refilling mechanisms might be continuously activated by the plant, concurrently with increasing levels of embolism formation as water potential decreases from morning to midday. Sealing mechanisms of refilling conduits have been proposed to be an important component of the embolism reversal mechanism (Zwieniecki & Holbrook ).…”

“…As a consequence, it is unlikely that the gas supersaturation artefact had affected other reports of xylem refilling observed after pressure‐driven embolism induction (Secchi & Zwieniecki ; Secchi et al . ; Melcher & Zwieniecki ).…”

“…This artificial facilitation of the final phase of conduits' refilling might lead to erroneous measurements of native PLC (Wheeler et al . ) and misleading estimates of high resistance to embolism (Melcher & Zwieniecki ).…”

“…It is likely that the above reported artefacts arising from xylem rehydration prior to hydraulic measurements are rather species‐specific because refilling mechanisms are apparently not active in all plant species (Brodersen & McElrone ; Melcher & Zwieniecki ; Ogasa et al . ).…”

Signal coordination before, during and after stomatal closure in response to drought stress

“…Any AE events originating from the same vessels, caused by continual cavitation refilling cycles, could have limited our ability to measure a loss in hydraulically functional xylem vessels (Canny, ; Trifilò et al ., ). However, the wide range of reported refilling response times: from 10 to 30 min in Acer rubrum (Melcher & Zwieniecki, ; Zwieniecki et al ., , respectively), 2–3 h in Vinus vinifera (Holbrook, ), and up to 17–47 h in Crocus sativus (Scheenen et al ., ) make it difficult to determine what level of refilling could have occurred or if any refilling occurred during the one hour of intense AE events that was measured during the present experiment. It also is unlikely that embolism events in nonconducting tissues were the source of AE events because this type of embolism event has only been observed under severe drought conditions where xylem vessels are fully embolized (Hacke & Sauter, ; Kowalski & Smoczkiewicz, ; Wolkerstorfer et al ., ; Rosner, ).…”