How does a tree work?

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Main Question or Discussion Point

Hello all you folks!

This question might not be the most advanced in universe yet I wonder.

How does a tree for instance suck up water and nutricians from the ground?

And why does it get rid of all the leaves in the winter (if it is not a pine tree that is)?

Does it get rid of all the leaves due to not "wanting" to loose heat, or what?

And the sucking of water, where comes the negative pressure from?

And if you don't mind, please explain the photo synthesis too.

Thanks!

Best regards, Edison
 

Answers and Replies

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And why does it get rid of all the leaves in the winter (if it is not a pine tree that is)?
Dropping the leaves saves resources that would be required to protect them against low temperatures and low humidity and it reduces wind force and snow load.
 
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Trees don't need to suck water. The tiny capillaries increase suface tension as compared to weight of water.
 
Ygggdrasil
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jim hardy
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Trees don't need to suck water. The tiny capillaries increase surface tension as compared to weight of water.
My junior high school science book said the same thing.

I watched trees sway in the breeze and decided something akin to peristalsis must be going on in those capillaries too, else Royal Palms would blow apart at their base from the hydrostatic pressure.
Decades later when Hurricane Andrew killed all the Carribean Pines around Homestead i speculated their capillaries got overstressed by the extreme compression / tension and ruptured. The trees more than a couple feet tall that didn't snap or uproot just died.

http://pelagiaresearchlibrary.com/advances-in-applied-science/vol3-iss4/AASR-2012-3-4-2355-2368.pdf
It is also speculated that peristalsis may be involved in the translocation of water in tall trees. The translocation of water involves its motion through the porous matrix of the trees.
So, i'm not alone in my speculation about peristalsis .
Is there anyplace on earth where the wind never blows? Do trees grow there?

old jim
 
256bits
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else Royal Palms would blow apart at their base from the hydrostatic pressure.
Why would that be?

At the base of a capillary tube, in which the water level has risen higher than the free surface, the hydrostatic pressure is just pgh, where h is the depth of the base of the capillary tube from the free surface. I do not see an increase in hydrostatic pressure from the H, the height of water in the capillary tube.
 
jim hardy
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Quite so.

How high though can capillary action raise water in a capillary ? Surely not to the top of a tall tree.

http://web.mst.edu/~numbere/cp/chapter 3.htm#_Toc506795445]
upload_2016-3-5_4-27-54.png


.....
The air/water interfacial tension is 70 dynes/cm with a wetting angle of 0.0
If σaw is 70 dynes/cm
and cos(anything) ≤ 1
then Pc ≤ 2 X 70 /r dynes/cm2
if 100 microns is a typical xylem diamter
50 microns is r and is 5X10-3 cm
Pc is ≤ 2 X 70 / 5X10-3 = 28000 dynes/cm2

1 dyne/cm2 = 0.0000334553 ftH2O 4°C (39.2°F)
http://www.sensorsone.com/dyncm2-dyne-per-square-centimetre-pressure-unit/#dyncm-pressure-conversion-factors

so Pc is 28000 X 0.0000334553 = 0.94 feet

so capillary action seemed inadequate even for a small tree
but this is first time i ever put a number on it.

"Cohesion" seems counterintuitive but from what i can find is accepted.

http://www.appstate.edu/~neufeldhs/bio1102/lectures/lecture9.htm

Since water can evaporate faster than it can be taken up, tension begins
to build up in the xylem. Eventually, the plant is under quite severe tension.
Studies show that these tensions "pull" water from the soil into the root, up
the stem, and then to the leaf, where it evaporates. Henry Dixon and J. Joly
first offered up this theory at the turn of the century, and it is still the most
widely accepted theory for the ascent of sap in plants.
What is needed for this theory to be viable?
1. negative pressures in the xylem - this has indeed been found. Trees
shrink during the day when transpiring due to the tensions in the xylem.
Further, if you cut into a tree, no water comes squirting out. In fact,
if you put a drop of water over a cut, it gets sucked in!
2. water must be able to tolerate great tensions in the xylem - verified as
noted above, and also recently by spinning not glass tubes in a centrifuge,
but stems themselves, and finding no evidence that the water columns
broke.
3. Tensions that develop must be of sufficient magnitude to move water
fast enough to account for the transpiration rates that are measured.
This has indeed been found.
So, in conclusion - the cohesion-tension theory of sap ascent is the most widely
accepted theory.
Cellulose and water are both remarkable substances.

That paper continues:
4. Some caveats - it is a passive process - that is, the plant need not expend
any energy to bring water up the stem (makes sense since the xylem cells
are dead at maturity).
5. There are trade-offs. Let's discuss these now.
C. Cavitation and Embolisms - what happens when tensions run too high!
1. Remember, cavitation is when the water column breaks due to too high tension.
2. The air bubble left in the xylem after cavitation is called an embolism.
a. when a xylem conduit cavitates, the tension is relieved, and water no longer
moves up the plant in that tube. Thus cavitation is bad because it takes
active xylem out of commission.
3. What causes cavitation?
a. freezing
i. when you freeze water, bubbles form (see your ice cubes). If this happens
in a xylem cell, it can result in an embolism.
1. larger diameter cells are more prone to freezing-induced embolisms
2. easier for bubbles to form in large conduit xylem cells. This is one
reason vines are a tropical phenomenon - they have large conduits and
are very prone to freezing-induced embolisms.
b. drought
i. drought increases tension in the xylem.
ii. when tension increases to a certain point, air can be sucked into the xylem
from adjoining spaces, causing an embolism.
iii. air sucked through pits. Pits with large pore diameters allow air to enter
easier, so embolisms form more readily. Not related so much to cell
diameter, like freezing-induced embolisms are.
:

He didn't mention physical damage to the xylems from mechanical stress. So that's my personal idea and doesn't meet PF criteria, so take it as just idle chat.

But i sure learned a good bit figuring out your post. I never thought of it quite that way, my only experience with meniscus was in manometers with comparatively large diameter.
so thank you for challenging me. Scientific method at work. I learn by asking.
Another introductory article here, if anybody else is curious.
https://www.warnell.uga.edu/outreach/pubs/pdf/forestry/Water%20&%20Trees%20Manual%20pub%2012-11.pdf [Broken]


old jim
 
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So that is to say instead of the strong ionic forces that hold water together, it would not have been possible, for example, for another fluid like oils to rise.
 
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Hi old jim!

I loved to read your posts, they were very interesting and educational. I also liked the way you verified that capillary "suction" does not work higher than roughtly a feet :) The information regarding cohesion-tension theory was also very interesting not to mention the last part of the paper regarding cavitation and embolism. Finally, I find it very nice when people like you don't just deliver links when someone is asking a question. If you know the answer why not just tell it otherwise you may as well ignore the post.

Best regards, Edison
PS
I also love your signature :)
 
jim hardy
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So that is to say instead of the strong ionic forces that hold water together, it would not have been possible, for example, for another fluid like oils to rise.
I think that might be so.
The Missouri University page i linked is really speaking to extracting oil out of sand, and the graphs (if i understand them) show more height from capillary action with lesser concentrations of water.
 
jim hardy
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Best regards, Edison
Why, Thanks Edison for your kind words. Helps an old guy feel less useless.

As you can tell that's something i've wondered about for years.
It always feels good when a previously dark corner of my abysmal ignorance gets partly illuminated.

Serendipitously, that school in Missouri is my old Alma Mater(bsee 1969) so it was nostalgic to see that old paper with its cgs units. Fresman year I took drafting in the creaky old mining building with its "quaint" 1920's drafting tables and stools.
Looking to understand Mr 256Bits' inquiry, stumbling across that link took me right back to 1964..

Thanks to all .

.....I still wonder why all the Caribbean Pines died.....

old jim
 
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Let's make room for ingnorant me. After rereading the above papers so thankfully supplied by jim hardy a third time, I have come to a tiny understanding of it all when it comes to the sucking part. Water can evaporate (from the leaves?) faster than it can be taken up (by the xylem=cells?) so this creates a tension (suction in my ignorant book). This tension pulls water from the soil up the roots, the stem and to the leaves where it evaporates (again).

How close to the truth am I?

Best regards, Edison
 
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Dropping the leaves saves resources that would be required to protect them against low temperatures and low humidity and it reduces wind force and snow load.
Hi DrStupid!

Would you mind explaining exactly all you say here because it does not make any sense at all to ignorant me?

To make it easy for you:

1) Saves resources-in what way?
2) Protection against low temperatures-why and how?
3) Low humidity-why is that a problem (water and nutricians comes from the ground)?
4) Wind force and snow load-how can that at all be a problem (and if so, how can the tree know that)?

Best regards, Edison
 
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1) Saves resources-in what way?
All processes in living cells need resources and even more resources under stress. These cost for keeping the leaves alive needs to be out- or even overbalanced by a corresponding benefit. It seems this is not the case for broad-leafed trees in winter.

2) Protection against low temperatures-why and how?
Living cells must not freeze. That can be prevented by antifreezing compounds.

3) Low humidity-why is that a problem (water and nutricians comes from the ground)?
In most cases ground water is recharged by precipitation. In winter the average precipitation is significant lower compared to other seasons. That means there is less water available but transpiration is increased due to low humidity of the air.

4) Wind force and snow load-how can that at all be a problem (and if so, how can the tree know that)?
The risk to brake off by spring or autumn storms is increased for trees with leaves compared to similar trees without leaves. That's an advantage in evolution.
 
jim hardy
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How close to the truth am I?
I think you're pretty close to the generally accepted 'cohesion' hypothesis ,
which is what my junior high school science book offered ca 1959 .

Water can evaporate (from the leaves?) faster than it can be taken up (by the xylem=cells?) so this creates a tension (suction in my ignorant book). This tension pulls water from the soil up the roots, the stem and to the leaves where it evaporates (again).
Sounds counterintuitive, doesn't it? Well, it does to anybody who's siphoned gas .

That's why i latched onto a "pumping action" from the tree's swaying in the breeze which places its opposing sides alternately in tension and compression. Not unlike human veins, where the check valves let our leg muscles aid in pumping blood back toward our heart.

But there's only scant mention of "check valves" in tree articles.

I did some searching, check valve xylem
found a plumbing supply company named Xylem that makes check valves

and this article which says botanists are developing new techniques to study wood cells
http://www.amjbot.org/content/early/2013/09/09/ajb.1300004.abstract?sid=50af6d0d-07d2-4d31-a423-fac9fd533de1

and this spinoff from it
http://www.vtnews.vt.edu/articles/2013/09/092013-cnre-treesinjured.html

BLACKSBURG, Va., Sept. 20, 2013 – Researchers from Virginia Tech; George-August University in Gottingen, Germany; and the Jackson Laboratory in Bar Harbor, Maine, have discovered how “check valves” in wood cells control sap flow and protect trees when they are injured.

A powerful new type of microscope, the 4Pi, has allowed scientists to see nanostructures inside of microscopic structures known as bordered pits within wood fiber cells.
upload_2016-3-6_12-44-12.png
Some mechanical pumping aid would sure be easier for me to accept.

So many interesting questions, so little time..


old jim
 
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Some mechanical pumping aid would sure be easier for me to accept.

old jim
I agree with you, check valves in trees just sounds stupid :D

Best regards, Edison
 
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All processes in living cells need resources and even more resources under stress. These cost for keeping the leaves alive needs to be out- or even overbalanced by a corresponding benefit. It seems this is not the case for broad-leafed trees in winter.
I like this reply. You can almost relate to it by being a human being. The last sentence is however not understood but interesting.
Living cells must not freeze. That can be prevented by antifreezing compounds.
Understood but in what way does a tree with or without its leaves not freeze? I don't understand the difference if it's not the fact that the actual area of leaves makes heat escape (transpire?) the tree if it would keep them in winter.
In most cases ground water is recharged by precipitation. In winter the average precipitation is significant lower compared to other seasons. That means there is less water available but transpiration is increased due to low humidity of the air.
So if there is a low amount of water vapor in the air (low humidity) vapor exchange (transpiration) with the air is higher? How can that be? How can a low humidity give rise to higher tranpiration? Would I sweat more if the air was dry? I would almost believe the contrary!
The risk to brake off by spring or autumn storms is increased for trees with leaves compared to similar trees without leaves. That's an advantage in evolution.
Please don't just referre to evolution like that, I would almost call that ignorant.

Finally, thank you for all the detailed answers, I am much obliged!

Best regards, Edison
 
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Understood but in what way does a tree with or without its leaves not freeze?
I'm talking about the leaves and not about the rest of the tree.

Would I sweat more if the air was dry?
Yes. Edit: But this is a bad analogy because the purpose of transpiration of plants is not temperature-control.

Please don't just referre to evolution like that, I would almost call that ignorant.
If you don't want the answer than don't ask the question.
 
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I have learned something :) I actually wondered about how water can rise to the clouds at a temperature far below the boiling point (where it turns to steam and the process is obvious). It turns out that evaporation is a mechanism that involves extreme kinetic energy differences in a compound with average kinetic energy (or temperature). Some molecules thus seam to have an energy equal to or above that for the boiling point so that they can escape and, and this is even more interesting, when this happens temperature for the compound actually decreases because average kinetich energy is lowered. This is the procedure animals use to cool down while sweating(?)

Let me try to apply this to trees. In summertime when the tree holds leaves there will be evaporation from their leaves. Temperature will rise to a certain point where water will evaporate. This procedure almost sounds like it has some kind of hysteresis. Because all the time, temperature will neither climb over a certain point nor shrink below a certain point. All of it due to being supplied with water from the soil all the time. Now, in wintertime evaporation is harmful to the tree because it lowers its temperature while there is no water to suck up due to ice in the ground. But while no evaporation is taking place due to no leaves, the tree will not cool down any further than ambient temperature(?).

How far from the truth am I now?

Best regards, Edison
 
jim hardy
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You're getting beyond my realm .

I actually wondered about how water can rise to the clouds at a temperature far below the boiling point
Water has molecular weight pf 18 (two hydrogens and one oxygen.)
Air that's dry is a mix of gases that approximate a molecular weight of 29. (4/5 nitrogen, 1/5 oxygen)
A mole of air contains Avogadro's Number of molecules and the more water vapor molecules in it the lighter that mole is.
Therefore adding water vapor to air lightens it . It'd be not much of an exaggeration to say "Steam floats".

Look at summer clouds, you can watch them roil and grow as the moist air moves upwards.
300px-Cumulus_congestus_cloud.jpg

https://en.wikipedia.org/wiki/Cumulus_congestus_cloud
The moisture gives up its heat of vaporization warming the rising air and further boosting its bouyancy.
Ask anybody who's sky-dived down through a cloud to describe it.

Have fun watching physics at work in your everyday experiences.
 
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There is also an idea out there that leaves are the "excreted" waste place. So any toxins that build up can be mobilized into leaves and dropped. Maple leaves have a peculiar feature in that they contain toxins that keep other competing plants from growing. So a maple uses leaf drop to take over a plot of ground.

There is also an error of asking why a certain biological design is the way it is, by assuming it is the optimal design. Therefore leaves dropping must be OPTIMAL and GOOD. Nature and evolution are efficient, but not perfect. Frequently, trade-offs matter. One plant may grow rather ineffective leaves quickly, to optimize first access, and another might grow more efficient leaves, to optimize length of access.

The most likely explanation for a tree species to drop leaves is because that tree is exposed to freezing temperatures, and the process of preserving the leaf is more difficult than the process of dropping the leaf and growing a new one in the spring. Go freeze a lettuce leaf and watch the cellular damage happen. It is not easy to freeze and come back.

I'm crossing my fingers at the moment. We've had early spring temperatures. Last year my peach tree bloomed early, and then the frost killed every flower but one ... a harvest of a single peach.
 
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May I inject a related question please? I've searched books about trees without finding this answer.

How do the nutrients formed by photosynthesis is the leaves get transported down to the trunk and the roots? Actually, I'm thinking of molecules more than complex nutrients. The trunk and roots have lots of carbon that I think was captured from the atmosphere. I'm trying to imagine how it got down there from the leaves.
 

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