This is why the question is interesting. You can't just suck water to the top of a 60 meter tree. There must be some kind of positive-pressure pumping involved.
There's no free lunch here. The Sun drives the evaporation, and if the tree were in a closed system with no solar input, the humidity would eventually get high enough to stop it.
Simard attributes intention to this, but osmosis is “fair”. It seeks to move water to where sugars are and sugars to where water is. So a plant giving up sugars will receive water, and one low on water will give up sugars in the process of equalization.
Do fungi contain pumps to maintain disequilibrium in this work? I could not say. But even when they first learned the trick of tapping roots the basic premise would have worked in a rudimentary fashion woth no further optimization.
As a largely unrelated aside, there will still be a chemical potential across a membrane that doesn't permit a solute to cross. So water can diffuse into a concentrated solution without the solute flowing backwards into the reservoir. Alternatively, small solutes can leave while larger solutes are retained. This is the basis of dialysis.
In a tree the inlet to the “pump” is at the base of the tree. It’s not like there’s a pump sitting in the tree at 80 metres trying to suck water up from the ground, that would obviously fail. It’s more like a very long pump.
... that would be the least of the tree's problems.
The tree is a perpetual motion machine hooked up directly to the wheelworks of nature! It PUMPS 500 liters per day usibg Wind, solar, capilar action and evaporation! How do i charge my car with this?
More generally you seem to be dismissing out of hand the primary topic of discussion which is neither constructive nor enlightening.
Or the high pressure is down here, whichever way you want to look at it.
It's a bit like a siphon effect with water evaporating from the leaves creating low pressure internally which draws more water up, and the reason it's able to pull a whole column of water up is because water molecules stick together to some extent via hydrogen bonds.
Given that evaporation is what is driving it, I wonder how that works with evergreens with low evaporation - I guess it's basically a replacement system, so you only need to pull what you evaporate.
If you put a straight thin capillary tube upright in water so it sucks up water from the bottom, no matter how thin, it can't draw water up above ~10m of water level.
xylem is not a straw, is no where near the diameter of a straw, and its[transpiration] is not about increased pressure its about decrease.
psi values at the apical mesenchyme are around -100 to -150 megapascals dependent on species and relative humidity at the stoma.
physics and biology although intertrined are not the same catechisms, heres a link toward most of m.j. canny's work.
https://www.researchgate.net/scientific-contributions/M-J-Ca...
here is is a basic scheme of things
Water Movement in Xylem:
https://oercommons.org/courseware/lesson/87595/student-old/?...
Xylem:
https://en.wikipedia.org/wiki/Xylem
Hydrogen bond:
a column of water is pulled by hydrogen bonding between molecules in a tug of war fashion, the top of the column is where water is dissociated from the column at such a rate as to maintain low pressure with respect to the column[xylem]
in summary water moves from bottom to top in a transpiration stream, that ultimately ejects water vapour from the leaves, resulting in a low efficiency mechanism, that loses a lot of the water but occurs at such a rate that the low efficiency is "good enough" for whats needed.
I don't believe this is correct, or rather is not a required component of the system but rather incidental. The chemical system within the leaf removes water via chemical reaction. There is a respiration process to dispose of waste gasses. Water vapor happens to be lost to this process not of necessity but rather because keeping it separate is quite difficult (ie requires significant complexity and additional energy expenditure). I expect that many desert adapted species approach perfection (but have not bothered to verify).
No they have different strategies to minimize water loss that comes with exhanging CO2 & O2 to the atmosphere. For example:
https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism
Portulacaria Afra (elephant bush) is a nice example. It can switch between C3 and CAM photosynthesis pathways as needed.
So sucking / pulling?
> leaves which have adapted to withstand greater water stress before wilting.
That must be one of the "adjustments to water transport" mentioned. So I suggest that they do, in fact, have trouble pumping water to top branches.