Abstract
In recent years, the validity of embolism quantification methods has been questioned, especially for long-vesseled plants. Some studies have suggested that cutting xylem while under tension, even under water, might generate artificial cavitation. Accordingly, a rehydration procedure prior to hydraulic measurements has been recommended to avoid this artefact. On the other hand, concerns have been raised that xylem refilling might occur when samples are rehydrated. Here, we explore the potential biases affecting embolism quantification for grapevine (Vitis vinifera L.) petioles harvested under tension or after xylem relaxation. We employ direct visualization of embolism through X-ray micro-computed tomography (microCT) to test for the occurrence of fast refilling (artifactually low per cent loss of conductivity (PLC) due to rehydration prior to sample harvest) as well as excision-induced embolism (artifactually high embolism due to air introduction during harvest). Additionally, we compared the response functions of both stomatal regulation and xylem embolism to xylem pressure (Ψx). Short-time (20 min) xylem tension relaxation prior to the hydraulic measurement resulted in a lower degree of embolism than found in samples harvested under native tensions, and yielded xylem vulnerability curves similar to the ones obtained using direct microCT visualization. Much longer periods of hydration (overnight) were required before xylem refilling was observed to occur. In field-grown vines, over 85% of stomatal closure occurred at less negative Ψx than that required to induce 12% PLC. Our results demonstrate that relaxation of xylem tension prior to hydraulic measurement allows for the reliable quantification of native embolism in grapevine petioles. Furthermore, we find that stomatal regulation is sufficiently conservative to avoid transpiration-induced cavitation. These results suggest that grapevines have evolved a strategy of cavitation resistance, rather than one of cavitation tolerance (diurnal cycles of embolism and repair).
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Claims 7
Claim · model-written summary
Twenty minute tension relaxation produced less embolism than native tension harvest.
- Treatment
- Short-time (20 min) xylem tension relaxatione0
- Outcome
- degree of embolisme0
- Direction
- lowere0
- Comparator
- samples harvested under native tensionse0
VitisOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Short-time (20 min) xylem tension relaxation prior to the hydraulic measurement resulted in a lower degree of embolism than found in samples harvested under native tensions”
t0“grapevine”
Claim · model-written summary
Relaxed petioles gave vulnerability curves like direct microCT curves.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“yielded xylem vulnerability curves similar to the ones obtained using direct microCT visualization.”
t0“grapevine”
Claim · model-written summary
Xylem refilling occurred only after overnight hydration.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Much longer periods of hydration (overnight) were required before xylem refilling was observed to occur.”
t0“grapevine”
Claim · model-written summary
In field vines, more than 85% stomatal closure preceded the xylem pressure for 12% conductivity loss.
Verbatim
e0“In field-grown vines, over 85% of stomatal closure occurred at less negative Ψx than that required to induce 12% PLC.”
Claim · model-written summary
The authors conclude that short relaxation reliably quantifies native embolism.
- Outcome
- reliable quantification of native embolisme0
Not reportedComparatorValue
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“relaxation of xylem tension prior to hydraulic measurement allows for the reliable quantification of native embolism in grapevine petioles.”
Claim · model-written summary
The authors infer that stomatal regulation avoids transpiration induced cavitation.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“stomatal regulation is sufficiently conservative to avoid transpiration-induced cavitation.”
t0“grapevine”
Claim · model-written summary
The authors infer a cavitation resistance strategy for grapevines.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“grapevines have evolved a strategy of cavitation resistance, rather than one of cavitation tolerance”