How do Trees Really lift Water to their Leaves?

@Stefan
That's the point. For the salts and sugars to percolate down to the roots it will take a long time, because any movement down will result in a return flow and the return flow will lift significant amounts of solute back up providing the return flow is more dilute than the downward flow.

This will counter act the imagined sudden influx into the root system when the trees leaves fall.

But supposing most of the solutes have arrived at the roots several months before the spring. We would still observe sap rather than pure water in the tree and sap always contains some dissolved salts and sugars.

Having thought about this problem it may also be that the more dilute sap will dissolve stored sugars and minerals from the bulk of the tree, just as the trees leaves lose their sugars and solutes, so providing we don't have a winter that overstays it's welcome the tre should be able to continue to circulate the sap for the duration of the colder weather. Furthermore the freezing temperatures would cause the sap to thicken and this too could delay the shift in solutes towards the roots for a longer period.

Bored Chemist:
"Mathematical calculations designed to show it can't happen or can happen appears a little pointless when we can show it taking place experimentally and reliably so."

Bollocks.

If I said that the movement of the water in the tubes was due to the gravitational influence of the planet Mars then some simple calculations would show that my suggestion is rubbish.

About a zillion years ago on a related thread where you were claiming that the differences in density were responsible for the actions of the kidneys (or some such thing) I did the maths to show that you were seeking to rely on an effect that was far too small. You can use maths to rule out an idea and you can also use it to show that an idea might be valid.

We know that water gets to the tops of trees.
What we are debating is whether or not your suggested idea might be responsible or whether it might be the conventional explanation.

To support your idea we need you to provide the maths which either shows that the conventional view is wrong or that your ideas about density are plausible.
Without them you are hardly in the realms of science.

Well go ahead and provide the maths then

Looking forward to your mathematical explanation as to how trees can evaporate 98% of all the water drawn through the roots at the leaf without affecting the density of the sap and how gravity cannot affect the migration of density changes in the canopy and how that migration cannot affect the movement of more dilute sap back to the leaf as it takes place.

Good luck!

BenV
You seem to have ignored this bit again Andrew:

Quote from: Bored chemist on 10/11/2009 19:06:21

To support your idea we need you to provide the maths which either shows that the conventional view is wrong or that your ideas about density are plausible.
Without them you are hardly in the realms of science.


Fair enough, you are convinced by your ideas - but you cant expect anyone else to be if you don't do the work.

You mentioned a while ago that you are working with a retired pyhsicist friend to refine this. He would, I hope, agree that the maths is essential.

Think of it this way - if a flea can jump 50 times it's body height, we don't take this as undoubtable evidence that a man sized flea can still jump 50 times it's body height. We could, however, calculate the energies required and available, and work out whether or not it could. The maths will tell us if our model is appropriate.

Common sense appears to be sadly lacking.


1. Of course the loss of moisture at the leaf will change the density of the sap.
2. More water arriving at the leaf will replace the denser sap, which has inevitably been moved from the leaf due to the effect of gravity on said solutes.
3. If the cohesion tension theory was correct as it stands, which incidentally it falls far short of being correct as a result of all of that evaporation from a one way trip to the leaf and ultimately the atmosphere, would you expect the salts and sugars to remain inside the leaf? If so why are the leaves able to avoid crystallization from the huge amount of sugars and salts accumulating?

Look into irrigation on arid soils to see that salt build up due to high evaporation rates becomes a problem

Rosy:
1. Yes, no-one said different.
2. Well, sort-of. "Sap" doesn't just move in and out of leaves like fluids round your plastic-tube experiments, it has to undergo transport across cell membranes. Apart from that, yes, denser liquids (on average) move down, and are replaced by less dense liquids.
3. No. I wouldn't expect the salts and sugars to remain in the leaf. This is a total straw man and you are avoiding doing the maths.

Our problem with your theory, as I have explained at length elsewhere, is that you have not accounted for sufficient energy being available to the system to lift the amount of water you're claiming it must lift. Since you've been expounding this theory, on this thread, for four-and-a-half years now, this is an extraordinary omission and, frankly, seems to me to justify BC's inclination to characterise you as a troll. My own assessment runs more to "faith nutter" but the two are not mutually exclusive (troll need not always, after all, imply malice).

And I have stated many times that the density change in the phloem sap gives the xylem an increased head or in simple terms raises it above the level of the phloem. Sophiecentaur related this to how locks between saline and fresh water show the different levels.

Therefore as the tree grows right from a seed, the dilute sap pushed higher and higher, as the phloem continues to support the less dense sap at a higher elevation than the falling sap, of course the tree does not directly afford the increased head of water but the pressure differences albeit minor affords the tree a direction to grow in with ease.

This is shown clearly in the video link provided using a water filled U tube. The density difference shows clearly the change in water levels.

How do you suggest we account for this in maths?

Rosy:
OK. This is what we mean:

You can calculate (easy physics) the energy required to raise a certain mass through a given distance (E=mgh, energy in joules = mass in kg x g x height in metres where g acceleration due to gravity and is 9.831 metres per second per second)

So to raise 1 kg by 1 metre using gravity, you must lower 1 kg by 1 metre to balance it (or 2 kg by 0.5 m or 0.5 kg by 2 m).

Your claim that gravity can drive the transport of fluids in plants therefore demands that to move 1 kg of water from the roots to the leaves, you must lower 1kg of something-or-other.
Some of that will be water, but if we assume that 90% of the water taken up by the roots is lost in transpiration*, that means that for every 1 kg of water that moves up the tree, 900 g of sugars (principally sugars, as most salts and nitrogen containing compounds have to come up from the roots in the first place) must be produced and moved down**.

Infact, crops transpire*** between 200 and 1000 kg of water for every 1 kg of dry mass (sugars plus all the other stuff) they produce.

If we could get that sort of biomass production out of trees there'd be much less call to be worrying about fossil fuels!!

OK, there's my first stab at the numbers. Can you point out how your system gets passed this apparently insurmountable energy barrier? Or not?


*(I got the figure off wikipedia, but it's a reasonable number and is something that's been measured lots of times)

**(even without accounting for the fact that water is used in sugar synthesis and making 900g of sugar would use of the order of 450 g of water)

***(again from wikipedia)