Sustained and significant negative water pressure in xylem

  title={Sustained and significant negative water pressure in xylem},
  author={William T. Pockman and John S. Sperry and James W. O'leary},
DESPITE two centuries of research, the mechanism of water transport in plants is still debated1–8.The prevailing cohesion–tension theory2,3, which states that water is pulled upwards by capillarity in cell-wall pores, remains vulnerable to challenge because its corollary is difficult to prove: that large negative pressures exist in xylem conduits4–7. Recent xylem pressure-probe and z-tube experiments suggest that cavitation limits xylem pressures to above −0.5 MPa, despite the much more… 
New evidence for large negative xylem pressures and their measurement by the pressure chamber method
Pressure probe measurements have been interpreted as showing that xylem pressures below c. -0.4 MPa do not exist and that pressure chamber measurements of lower negative pressures are invalid. We
Xylem Surfactants Introduce a New Element to the Cohesion-Tension Theory1[OPEN]
It is hypothesized that xylem surfactants support water transport under negative pressure as explained by the cohesion-tension theory by coating hydrophobic surfaces and nanobubbles, thereby keeping the latter below the critical size at which bubbles would expand to form embolisms.
Sap Ascent in Vascular Plants: Challengers to the Cohesion Theory Ignore the Significance of Immature Xylem and the Recycling of Münch Water
The release of water from the phloem can explain not only some discrepancies claimed by the cohesion challengers, but also explain the refilling of cavitated xylem conduits: a hitherto unsuspected role for thephloem transport system.
Water ascent in plants: do ongoing controversies have a sound basis?
Analysis of Freeze-Thaw Embolism in Conifers. The Interaction between Cavitation Pressure and Tracheid Size1
The centrifuge method was used to evaluate the relationship between freeze-thaw embolism and conduit diameter across a range of xylem pressures (Px) in the conifers Pinus contorta and Juniperus scopulorum and suggested that the bubbles causing cavitation are smaller in proportion to tracheid diameter in narrow tracheids than in wider ones.
Capillary-driven desalination in a synthetic mangrove
These findings support the applicability of the cohesion-tension theory to desalination in mangroves, provide a new platform to study plant hydraulics, and create possibilities for engineered membrane separations using large, passively generated capillary pressures.
Xylem Wall Collapse in Water-Stressed Pine Needles
Investigating the changes in xylem geometry during water stress in needles of four pine species found a progressive collapse of tracheids below a specific threshold pressure that correlates with the onset of cavitation in the stems, suggesting a tradeoff betweenxylem efficiency, xyleM vulnerability to collapse, and the cost of wall stiffening.
Applications of the compensating pressure theory of water transport.
  • M. Canny
  • Environmental Science
    American journal of botany
  • 1998
Far from being a metastable system on the edge of disaster, the water transport system of the xylem is ultrastable: robust and self-sustaining in response to many kinds of stress.
The relationship between xylem conduit diameter and cavitation caused by freezing.
The centrifuge method, modified to include freeze-thaw cycles, may be useful in separating the interactive effects of xylem pressure and freezing on cavitation, and vulnerability to cavitation by freezing was correlated with the hydraulic conductivity per stem transverse area.


Xylem Transport and the Negative Pressures Sustainable by Water
Experimental measurements of water's ability to sustain negative pressures are reviewed with special emphasis on the relevance of the results to xylem transport, and one can predict the most likely range of negative pressures that can be sustained in thexylem.
Xylem water transport: is the available evidence consistent with the cohesion theory?
Since its introduction in the late 19th century, the so-called cohesion theory has become widely accepted as explaining the mechanism of the ascent of sap. According to the cohesion theory, the
Mechanism of water stress-induced xylem embolism.
The hypothesis that water stress-induced xylem embolism is caused by air aspirated into functional vessels from neighboring embolized ones via pores in intervessel pit membranes is investigated and experiments with sugar maple support the hypothesis.
A New Theory for the Ascent of Sap—Cohesion Supported by Tissue Pressure
A new theory is proposed that the driving force and the transmission of the force are the same as in the Cohesion Theory, but the operating pressure of the xylem is raised into a stable range by compensating tissue pressures pressing upon the tracheary elements.
Mechanisms of long-distance water transport in plants: a re-examination of some paradigms in the light of new evidence
According to the widely accepted Cohesion Theory, water is pulled by transpiration from the roots through the xylem to the leaves. It is believed that this process results in the development of large
A method for measuring hydraulic conductivity and embolism in xylem
Abstract Hydraulic conductivity of the xylem is computed as the quotient of mass flow rate and pressure gradient. Measurements on excised plant stems can be difficult to interpret because of
Intra‐ and inter‐plant variation in xylem cavitation in Betula occidentalis
A modified version of a method that uses positive air pressures to determine the complete cavitation response of a single axis is presented. Application of the method to Betula occidentalis Hook,
Sap Pressure in Vascular Plants
A method is described which permits measurement of sap pressure in the xylem of vascular plants, and finds that in tall conifers there is a hydrostatic pressure gradient that closely corresponds to the height and seems surprisingly little influenced by the intensity of transpiration.
Water‐stress‐induced xylem embolism in three species of conifers
Abstract. The mechanism of water-stress-induced xylem embolism was studied in three species of conifers: Abies balsamea (L.) Mill., Picca rubens Sarg, and Juniperus virginiana L. Each species showed
A theoretical model of hydraulic conductivity recovery from embolism with comparison to experimental data on Acer saccharum
A theoretical model of bubble dissolution in xylem conduits of stems was designed using the finite differential method and iterative calculations via computer. The model was based on Fick's, Henry's