[YourUncleBob (OP)]

Figures as high as 98% are quoted for the evaporation rate of water from a tree's canopy, obviously this leaves concentrated 'heavy' water, full of minerals and salts at the top of the tree.

Are all these minerals absorbed and considered as nutritious for a tree?
 or
Does a tree have a kind of limbic/kidney/liver system that stores any unused solutes? or
Does a tree send the unused solutes back down to the roots?

And another question.

If a tree hates air getting into its plumbing, how do the leaves manage to let the relatively large H2O molecules out while keeping the smaller oxygen molecules from entering?


Any help with these questions would be most appreciated?

[YourUncleBob (OP)]

really could do with some answers to these questions guys!

[Carol-A]

The mechanism by which plants take up water means that they don't take up things like heavy metals, or only in a very limited way. They are very selective!

[YourUncleBob (OP)]

Unfortunately trees are not selective enough as they are killed quite quickly with an introduction of heavy metals to their water supply, or for that matter an abundance of salt!

The questions still remain.

After evaporation the trees are left with a heavy concentration of salts and minerals at their tops.

Are all these minerals absorbed and considered as nutritious for a tree?
 
or

Does a tree have a kind of limbic/kidney/liver system that stores any unused solutes?

or

Does a tree send the unused solutes back down to the roots?

And another question.

If a tree hates air getting into its plumbing, how do the leaves manage to let the relatively large H2O molecules out while keeping the smaller oxygen molecules from entering?

Any help on these questions would be most appreciated!

Blaine

[Carol-A]

The trees do not accumulate lots of heavy metals at the top. Yes, you can poison e tree, but it still doesn't mean you accumulate deposits at the top of the tree.
Leaves make oxygen, so why do you think they want to keep it out?

[YourUncleBob (OP)]

The standard picture for the transport of water within a tree requires there to be heavy solute at the top, heavy with minerals and salts (and any other 'unhealthy' metals), this enables osmosis to do it's thing. Trees hate oxygen getting into their xylem or their phloem because this causes cavitation's within these tubes and eventual embolism.

It is true that a by product of their 'consumption' of CO2 is oxygen, but that is what they spit out not what they eat!

[Andrew K Fletcher]

Not so, heavy metals are removed from the soil and locked up in timber, as is the case with salts. Put trees in amongst the plants your irrigating and you no longer have a problem with salt build up on the land in arid conditions.

The mechanism by which plants take up water means that they don't take up things like heavy metals, or only in a very limited way. They are very selective!

[Andrew K Fletcher]

If we take some tea leaves and boil them then squeeze the solutes out we can see that salts and sugars are stored in the leaves. However, gravity will always make sure that denser solutes are kept on the move so there is a constant flushing out of these salts and sugars as they are moved to sink areas, like fruits and seeds and stored as timber as tubes become redundant and more are manufactured.

Deciduous trees during the fall when the leaves are shed move solutes to the roots and higher than normal concentrations are located in the roots in autumn.

I am convinced that when the leaves fall the pressure changes in the sap to positive and forces the salts and sugars down to the roots. I have also postulated that leeching from the roots during the fall may serve as a detox ready for the spring. And this positive pressure would surely apply to the increased root growth during the fall. Let’s not forget that minerals are shed with the leaves also. During the fall the salts would remain very sluggish as transport is arrested. During the spring the warmer climate begins to change the density of the sap enabling it to circulate before the leaves are formed.

Fruits and seeds being shed also serve to remove concentrated sugars and minerals and could be considered as providing a renal function.

Unfortunately trees are not selective enough as they are killed quite quickly with an introduction of heavy metals to their water supply, or for that matter an abundance of salt!
The questions still remain.
After evaporation the trees are left with a heavy concentration of salts and minerals at their tops.
Are all these minerals absorbed and considered as nutritious for a tree?
 or
Does a tree have a kind of limbic/kidney/liver system that stores any unused solutes?
or
Does a tree send the unused solutes back down to the roots?
And another question.
If a tree hates air getting into its plumbing, how do the leaves manage to let the relatively large H2O molecules out while keeping the smaller oxygen molecules from entering?
Any help on these questions would be most appreciated!

Blaine

[YourUncleBob (OP)]

Thanks Andrew,

I'm siding with you with regards to what happens to all the heavy minerals at the tops of the trees. I know that you're not a fan of the theory that says it's osmosis that provides the main power for lifting water to the tops of the trees, but to give your ideas more solidity we need to let the advocates of osmosis explain away the accumulation of these solutes at the tops of trees!

Any ideas on how the leaves prevent oxygen entering the tree's plumbing while letting out the larger water molecules?

[Andrew K Fletcher]

Thanks Andrew,

I'm siding with you with regards to what happens to all the heavy minerals at the tops of the trees. I know that you're not a fan of the theory that says it's osmosis that provides the main power for lifting water to the tops of the trees, but to give your ideas more solidity we need to let the advocates of osmosis explain away the accumulation of these solutes at the tops of trees!

Any ideas on how the leaves prevent oxygen entering the tree's plumbing while letting out the larger water molecules?

I am not a fan of the current cohesion tension theory either, Trees are subject to the same problem that Galileo had with the 24 metre limit for drawing water up by suction. To say that water molecules evaporate and this causes the next water molecule to replace it is absurd. It’s a way of clouding the fact that we are still saying trees suck water from their roots and spit it out at the leaves. The flow rates observed in trees during active transpiration is impressive and always has needed an explanation that addresses observed bulk flow rates.

·   The rattan vine may climb as high as 150 ft on the trees of the tropical rain forest in northeastern Australia to get its foliage into the sun. When the base of a vine is severed while immersed in a basin of water, water continues to be taken up. A vine less than 1 inch in diameter will "drink" water indefinitely at a rate of up to 12 ml/minute.
If forced to take water from a sealed container, the vine does so without any decrease in rate, even though the resulting vacuum becomes so great that the remaining water begins to boil spontaneously. (The boiling temperature of water decreases as the air pressure over the water decreases, which is why it takes longer to boil an egg in Denver than in New Orleans.)
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html

[chris]

This is a really excellent question; any budding plant scientists (sorry!) who can help with the cellular detail of how this is achieved? Do the cells in the roots that supply the xylem have a mechanism for excluding the salts and then re-excreting them to the soil?

Chris

[Andrew K Fletcher]

I agree Chris, Blaines Question is a valid point in science and yet he has not had many people rolling up to address this. I have a PDF file containing some photographs that my friend took of a tree that had died along the River Dart Estuary. The photographs show concretions around the roots that could well have caused the death of the tree and I should imagine that a huge amount of the salt concretion was excreted from the roots as the minerals were flushed from the timber and percolated down the tubular structure of the trunk and upper branches. How do I arrive at this? Answer: There are many other trees along the bank that do not exhibit this impressive concretion of solutes. A while back I motioned this process as an explanation for fossilized tree trunks in deserts. I was delighted to find this specimen..

[YourUncleBob (OP)]

Chris, Andrew,

What is the standard plant theory for the disposal of any of these unused heavy solutes?

We can't have evaporation without a heavier solute being present at the tops of trees, and not all of these salts & minerals are healthy for the trees either.

Do trees have a mechanism that sends these unused solutes down and out at their roots?

Any help with these questions would be most appreciated.

Blaine

[Andrew K Fletcher]

Bump

Still waiting for a reply from plant physiologists.