How do Trees Really lift Water to their Leaves?

Cohesion tension theory states transpiration pulls on vertical columns of water dragging it up to the leaves from the soil! How? Why can't we see a model? Why should introducing a density change at the roots (adding salt to the soil) stop this imaginary process?

Why do the leaves bother to fall from the tree in the Autumn if they are so efficient at dragging water from the ground?

All answers welcome, here is a chance to do some "science"

Ben was speaking metaphorically about the constraints of the cohesion tension theory as it stands. Not literally but yes according to the tension theory if a brick evaporates water it should also apply the same tension to the water below so stacking one brick onto another should cause rising damp to travel to the tops of walls but it clearly does nothing of the kind.

If you are bored BenV, perhaps you should read something more interesting

B.C aka Bored Chemist:

Quote from: Andrew K Fletcher on 12/07/2009 09:32:32
All answers welcome, here is a chance to do some "science"
Not literally but yes according to the tension theory if a brick evaporates water it should aslo apply the same tension to the water below so stacking one brick onto another should cause rising damp to travel to the tops of walls but it clearly does nothing of the kind.

If you cover the walls with a layer of waterproof material (I can't say I have tried tree bark- but it would be interesting) then that's exactly what happens. The water soaks up to the top and evaporates there.
Of course, without that cover, it evaporates before it reaches the top.
Science is based on observation. My observation is that your assertion is false.
This tends to support (though it does not prove) the opposite viewpoint.
In effect you have just proved your own ideas to be faulty.

Show us how a few leaves can suck water up tubes stretching a hundred metres when we struggle to suck water up a tube a metre high.

Explain how the buds get water delivered to them when there is not a single leaf on a tree?

Explain Strasburger's observations with circulation taking place for several weeks in a tree that has every single living process killed by introducing picric acid into it at a severed trunk immersed in a bath full of the stuff.

I repeat the Cohesion tension hypothesis sucks and is nonsense and deserves it’s rightful place deep within a fictional blackhole.

Nice try on the rising damp but one that has been put forward several times over the years and in this thread capillary action was debunked as it could not address the diameters of the tubes involved and the flow rates observed, let alone the heights achieved by trees..




HOW ON EARTH CAN A TREE EVAPORATE WATER WITHOUT ALTERING THE DENSITY OF THE SAP?

Quote from: sophiecentaur on 16/07/2009 10:22:19
Of course there will be dense solutions at the top. The question is whether there is enough to provide the motive power mechanism you propose.

Well yes someone has said the density changes will not take place because more water will arrive to re-dilute it and take it’s place. This of course does not prevent the change in density but merely supports a circulation theory rather than a redundant one way ticket to the atmosphere hypothesis.

If 98% of all the water drawn through the roots evaporates . . . . .

So you are implying that the 2%, falling can lift the 98% for transpiration? Fantastic. We have a brilliant new way of making skyscraper lifts work, for free.
You are still locked onto this circulation theory with not a single numerical reason to justify it. If the numbers don't tally, there must be another reason. But of course, Maths is just there in order to discredit the unqualified, isn't it?

Well it appears to work for the Californian Redwoods and a few other magnificent specimens towering well over a hundred metres. Did anyone observe a mechanical lift used in their construction?

BenV
Andrew, the current explanation may be inaccurate.

Right now, yours is a long way from being complete enough to even faintly threaten it. Stop whinging and do the science. Start with the sums, as sophie has been asking you to do for ages.

Until you do that, you're pissing in the wind.

Modeling xylem and phloem water flows in trees according to cohesion theory and münch hypothesis

HÖLTTÄ T. (1) ; VESALA T. (1) ; SEVANTO S. (1) ; PERÄMÄKI M. (2) ; NIKINMAA E. (2) ;

(1) Department of Physical Sciences, University of Helsinki, P.O. Box 64, 00014, FINLANDE
(2) Department of Forest Ecology, University of Helsinki, P.O. Box 24, 00014, FINLANDE
Abstract
Water and solute flows in the coupled system of xylem and phloem were modeled together with predictions for xylem and whole stem diameter changes. With the model we could produce water circulation between xylem and phloem as presented by the Münch hypothesis. Viscosity was modeled as an explicit function of solute concentration and this was found to vary the resistance of the phloem sap flow by many orders of magnitude in the possible physiological range of sap concentrations. Also, the sensitivity of the predicted phloem translocation to changes in the boundary conditions and parameters such as sugar loading, transpiration, and hydraulic conductivity were studied. The system was found to be quite sensitive to the sugar-loading rate, as too high sugar concentration, (approximately 7 MPa) would cause phloem translocation to be irreversibly hindered and soon totally blocked due to accumulation of sugar at the top of the phloem and the consequent rise in the viscosity of the phloem sap. Too low sugar loading rate, on the other hand, would not induce a sufficient axial water pressure gradient. The model also revealed the existence of Münch counter flow, i.e., xylem water flow in the absence of transpiration resulting from water circulation between the xylem and phloem. Modeled diameter changes of the stem were found to be compatible with actual stem diameter measurements from earlier studies. The diurnal diameter variation of the whole stem was approximately 0.1 mm of which the xylem constituted approximately one-third.
Revue / Journal Title
Trees ISSN 0931-1890 CODEN TRESEY
Source / Source
2006, vol. 20, no1, pp. 67-78 [12 page(s) (article)] (43 ref.)

Lyner:
AKF
Very interesting but does it say anywhere that the whole thing is "driven by gravity", which is the claim you make and with which I (several of us) disagree? I don't think anyone has a problem with the idea that solutions flow around plants. I don't think you have posted anything to support the gravity idea, have you?

Lyner:

AFK

A tree grows slowly and is filled with fluids from the onset so does not require fluids to be lifted to the leaves as per Sophies rope and bucket analogy

I just re-read this comment. Do you not see what rubbish it is? If a tree is 30m high, it GREW there. All materials needed to be lifted up there during the growing process. How long it took is irrelevant to the energy needed.

How can you expect to be taken seriously when you misunderstand elementary things like that?

If you accept that Energy is conserved in chemical and physical processes then you need to apply that principle in all of your ideas. You can't pick and choose what Science to use and what not to use. It's a consistent package - not mumbo jumbo, like your ideas.

Your blinkered approach is limiting Sophie. Circulation of fluids is all that is required, not a one way Indian rope trick but a gentle rotation of fluids where the downward flow provides an increase head of flow in the return / xylem side providing the impetus for vertical growth.

The paper abstract mentions circulation when transpiration has stopped. read it.

Lyner:
Blinkered or careful? My question was whether the reference supports your gravity idea. If it does then you could, perhaps, cut and paste the paragraph for us.