The Naked Scientists

The Naked Scientists Forum

Author Topic: How do Trees Really lift Water to their Leaves?  (Read 244874 times)

Offline YourUncleBob

  • Jr. Member
  • **
  • Posts: 23
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #150 on: 29/04/2008 09:11:53 »
Andrew, Rosy and Dave, interesting dicussion, thought you guys might like to check out these papers on the subject of trees and osmosis.


http://arxiv.org/ftp/physics/papers/0305/0305011.pdf [nofollow]

http://www.fasebj.org/cgi/content/full/13/2/213#F4 [nofollow]
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #151 on: 29/04/2008 16:14:21 »
The paper Evolving ideas about osmosis and capillary fluid exchange  Ted Hammel is known to me, the other however is not. Thank you for the comment and glad you enjoyed the read.
Have you anything to add regarding points you have picked up on within this thread?

Kind regards

Andrew
 

Offline YourUncleBob

  • Jr. Member
  • **
  • Posts: 23
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #152 on: 06/05/2008 02:13:58 »
Andrew,
Apologies for my tardiness, been a bit busy as of late, I've been thinking about trees and their ability to lift water for a long time now.

I've been working with my material science students on creating an artificial tree encased in a glass-like sphere to lift water over 300 meters.

Our goal is to take energy from the sun in the form of heat to create electricity. Our basic design involves several of these 'trees' releasing the water they collect at the bottom of their glasslike domes into a central reservoir.Once the reservoir reaches a predetermined level, the water is released, passes through a turbine before being deposited in another reservoir under their 'roots'. This is a complete closed system.

Obviously there has been a lot of interesting problems to overcome!

But one of our biggest problems right now is getting the balance right between evaporation and solute concentration. The evaporation rate from our artificial leaves has to be such that the concentration levels of salt&sugar in our respiratory system don't get too dense and clog up the works!

I posted a question on this in the plant section but with no replies.


With regards to your experiments and whether or not there's a syphon effect I'm of the opinion that you've not created a syphon, as there doesn't seem to be any vacuum involved.

We've yet to test the fluid dynamics of a solute heavy liquid travelling down a 50 meter pipe (nevermind 300meter) into a pure water reservoir (where the pipe's 'skin' is semipermeable) then back up 50 meters.

Would the flow offset the 'osmotic push'?

Would we have fresh water pushing against the downward flow of the solutes?

Or would the two forces combine to provide some additional upward lift?

Your thoughts would be much appreciated.

Blaine
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #153 on: 07/05/2008 22:17:09 »
My thoughts on this is rather than using a single large conduit is to use multi-conduits so that cavitations can be isolated.

I think you are shortly going to realise that osmosis might not be all that it is cracked up to be and that the flow and return system should provide the force. I cannot see osmosis push adding much if anything to the model. Reverse osmosis on the other hand where the pressure is obvious when applied on the other side of the model becomes logical and works efficiently in desalination of seawater. Maybe rather than raising the apparatus up we should be thinking about harnessing the density differences in seawater giving us a desalinated by product which could prove very useful. This is where I have been considering an application to lift sea water, remove some water by evaporation and collect it for drinking or irrigation and return the denser saline water back down the return flow giving us the capacity to turn an impeller and provide the force to return more salt water up the less dense side of the model. Alternatively just harnessing the depth of the ocean to generate electricity is something worthy of consideration.

Your tree model ironically represents much of what has been discussed on this thread and others over the years and I am glad that someone is investigating this simple paradigm further.

Thanks for letting me know about your experiments.

Kind regards

Andrew 
 

Offline YourUncleBob

  • Jr. Member
  • **
  • Posts: 23
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #154 on: 08/05/2008 04:21:36 »
Andrew your name keeps popping up whenever we use the internet to do research on this subject, so I feel honored to be sharing our thoughts with you.

Quote
My thoughts on this is rather than using a single large conduit is to use multi-conduits so that cavitations can be isolated.


Yes, that's exactly our plan with heavy solute pipes (Down) 10 times narrower than their corresponding low solute pipes (Up). Though we've included several bridges from the 'down' pipes to their corresponding up pipes, each bridge getting progressively narrower as we get closer to the bottom of the 'tree'. This was to help with any osmotic push, something I know you don't believe has much effect. We're counting on your 'gravity flow' to be aided by these 'little' osmotic pushes.

Your ideas of lifting sea water have been proofed to be possible. Checkout this.
http://www.seawatergreenhouse.com/the_process.htm [nofollow]

Here's a couple of diagrams of our basic design, for ease of viewing we've only included one 'circular tube' and kept their diameters the same.

Kind regards Blaine


 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #155 on: 08/05/2008 07:50:31 »
As you are generating a small amount of electricity it could be used to open and close valves to regulate pressure, prevent the column of water from collapsing while cavitations are refilled and to divert flow into cavitations.

If we stretched a closed loop of tubing capable of withstanding the pressures without collapse or ballooning to the top of the tallest tree, filled it with water and injected 1 mil of coloured salt solution at the top of the closed loop, we would see a complete rotation of the water inside the tube, now if we had one open ended tube the same height and joined at the bottom to the circuit and injected say 10 mils of coloured salt solution at the top of the loop that has been opened to the atmosphere via the added tube we would not only see rotation of water but we should see that water exudes from the top of the opened end allowing water to pass to the evaporation chamber. Making use of the return flow in the upward rotating flow on the juxtapose side of the complete loop to draw water back in could be achieved by using an outer tube to represent the bark of the tree and filling this tube with water. Having a sleeve of water around the tubes will provide a means to repair and prevent cavitations.

I have already shown that you can use a much smaller pipe as a down flow, even two pipes returning flow and one pipe flowing down.

Thank you for recognising my work :)

Where are you based?
« Last Edit: 08/05/2008 07:53:28 by Andrew K Fletcher »
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #156 on: 08/05/2008 10:44:37 »
Your diagram could also represent a human cerebro spinal fluid circuit. Which is where my research got really exciting for me.

Theere is going to be a bulging effect at the bottom membrane when the salts are released to flow down inducing a positive pressure, and i'm not sure that having a clean water bath at the bottom will not cause a dialysis effect from the membrane polluting the clean water?
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #157 on: 08/05/2008 20:02:20 »

MessageID: 172310
Today at 18:52:46 »       

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.

There is also evidence of concentrations of heavy metals around the roots of plants growing in salt marsh. Could this be evidence for leeching from the roots in addition to leeching from the soils to the roots? Could the regular influx of  brackish water in estuaries stimulate dialysis effect at the semi-permeable membrane in the roots?

Hope it's ok to copy your question to this thread as the answers are pertinent to my theory? If you object let me know and I will remove them.

Quote from: YourUncleBob on Today at 03:59:45
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


Lmnol. Ocmno~r 43(2), 1998. 245-252
0 1998. by the American Society of Limnology and Oceanography. Inc.
Metal-rich concretions on the roots of salt marsh plants:
Mechanism and rate of formation
Bjorn Sundby
INRS-Octanologie, University du Qubec, Rimouski, QC G5L 3Al
Carlos Vale
IPIMAR, Avenida Brasilia, 1400 Lisboa, Portugal
Zsabel CaCador and Fernando Catarino
Departemento de Biologia Vegetal, Universidade de Lisboa, Campo Grande C2, Lisboa, Portugal
Maria-JoLio Madureira and Miguel Caetano
IPIMAR
Abstract
The roots of the vascular plant Spartina maritima, growing in the saltmarshes of the Tagus Estuary, Portugal,
are surrounded by tubular concretions whose diameter can reach >0.2 cm. Concretions are also found scattered
within the sediment matrix in and below the root zone. The concretions comprise 4% (DW) of the sediment and
contain 11.7 2 1.6% iron compared to 4.9 -C 0.3% iron in the sediment in which they are found. They are formed
by the precipitation of iron oxides in the pores between the sediment grains; this has filled about one-sixth of the
originally available pore space. To produce the concretions, the plants have extracted 0.25% Fe from the anoxic
bulk sediment and concentrated it into the oxidized microenvironment surrounding each root. A mass-balance model
using cylindrical geometry shows that the observed concretion density can be produced by a network of roots with
l-cm spacing. The space between the roots limits the amount of Fe that is available to a given root and thus
determines the size of the individual concretion. Field observations and mathematical modeling show that plants
can produce concretions on their roots in the space of a few weeks. The rhizoconcretions are 5-10 times enriched
in Cd, Cu, Pb, and Zn with respect to the sediment surrounding them, and the smaller diameter concretions are
more enriched than the larger ones. The preferential enrichment of the smaller diameter concretions, which was not
observed for Fe and Mn, is independent of depth in the sediment for Cd and Cu; however, for Zn and Pb, the
preferential enrichment is most pronounced within the upper trace metal-contaminated sediment layer. The rhizoconcretions
have acquired their load of metals via diffusion from the surrounding sediment. In the case of Fe and
Mn, the concentration gradient that drives the diffusion is maintained by the precipitation of insoluble oxides. In
the case of Cd, Cu, Zn, and Pb, the mechanism that maintains a concentration gradient toward the surface of the
root is not know, but our data show that S. maritima is capable of mobilizing trace metals dispersed in reducing
anoxic estuarine sediment and concentrating them into the distinct oxidized microenvironments that surround the
roots.
 

Offline Bass

  • Neilep Level Member
  • ******
  • Posts: 1340
  • Thanked: 5 times
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #158 on: 09/05/2008 00:50:05 »
Andrew
We have been doing geochemistry surveys using needles from alpine fir with some good success.  After several orientation surveys, it was determined that new growth in the early summer best concentrates the minerals.  We collect around 500 ml (1/2 quart) of needles per site.  Analyze for Sb, Ag, Pb, Zn, Cu and As- searching for antimony-silver veins and gold-arsenic veins in an area of almost impenetrable undergrowth.  Seems to work very well for known veins and have found some anomalous areas that bear further investigation.
With your discussion, should we also be looking at roots during other times of year as potential mineral collectors- or do you think that collecting soils in the vicinity of the trunks might work as well (if your process enriches the area around the trunk in heavy metals)?  Any thoughts?
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #159 on: 09/05/2008 14:11:05 »
Bass, thats a great idea :) The roots would contain these minerals in higher concentrations during the fall in deciduous trees, colloids containing metals should also be found in higher concentrations in the soil close to the roots, as trees will inevitably find trace netals and minerals with their long reaching roots and should therefore give a reliable indication of what lies in the ground beneath them. Needles on the other hand would be less rich in metals as they move due to gravity down the tree once concentrated and become locked away in the trunks and branches rather than stagnating in the needles, so taking samples close to the roots might be more accurate than collecting needles and you may have missed some important deposits. Scraping the outer part of the root for analysis should provide some interesting data, and you don't have to go to the lowest roots in order to do this because we should be looking for concentrations that have gone around the trees circuit and been excreted into the soil. Deciduous might prove better than pine as the fall changes the location of solutes due to the circulation being arrested.

http://www.lbl.gov/Science-Articles/Research-Review/Magazine/1999/stories/story3a.shtml
"We located a region of the live fungus only 400 by 400 microns in area (a micron is a millionth of a meter) where fluorescence revealed the presence of zinc," says Lamble. Graphs of x-ray absorption at electron orbitals, such as an atom's innermost K orbital, show steep rises called edges; edge shapes and positions are specific to individual elements and molecular bonds. "When we scanned the beam over the zinc K edge, we could see that the zinc was concentrated in regions only a few microns across. The shape of the K edge in the fungus sample matches the very distinctive standard graph for zinc oxalate."

 
Geraldine Lamble, an x-ray spectroscopist at the ALS.

 
 
Because the fungus stabilizes zinc in oxalate, which is indissoluble, the ectomycorrhiza can form a hard shell that keeps zinc away from the roots. "The fungus story has a happy ending," Lamble says. "Without human interference, ectomycorrhizae bind metal and stop it from leaching lower in the forest soil."

At a hundred thousand root tips per square meter, ectomycorrhizae make an effective sponge for toxic compounds. But, says Lamble, "you wouldn't want to be digging that stuff up."

Let me know what you find Bass. 
« Last Edit: 09/05/2008 20:48:29 by Andrew K Fletcher »
 

Offline YourUncleBob

  • Jr. Member
  • **
  • Posts: 23
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #160 on: 10/05/2008 03:26:47 »
Andrew

I'm based in Taiwan, and I'm presently snowed under with Mid Term exam papers to mark!

We really should try to get the advocates of osmosis, 'being the primary force for the transport of water in trees', to explain away the accumulation of heavy solutes at the tops of trees.

You seem to be providing them with a way to discount the 'down' flow in the phloem pipes as the driving force by suggesting that it is the fruits, nuts and seeds that provide the 'sink' for the solutes.

How do the leaves prevent oxygen entering the tree's plumbing while letting the larger H2O molecules out?

kind regards
Blaine

PS You can do what you wish with my quotes, but I've decided not to hijack your thread with our artificial Tree (I did so because at the time it seemed to be very quiet here) and will keep my thoughts on that on the 'creating electricity from global warming thread' Which I now might have to make more mathematically formal to keep the curious fluid dynamic experts on board!

Keep up the good fight!


« Last Edit: 10/05/2008 03:35:14 by YourUncleBob »
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #161 on: 10/05/2008 09:16:50 »
Blaine
The ever expanding roots are obviously the main sink, but we cannot deny that there is an accumulation of sugars and minerals deposited in the fruits and seeds, which fall or are eaten from the tree providing an exit point. Furthermore an apple for example acts as a kidney and bladder as solutes are flowing through it. Picture a T junction representing the flow through the branch as the horizontal part of the T and the solutes being denser flow down into the fruit causing less dense fluid to flow out of the fruit back into the horizontal flow along the branch leaving behind the sugars and minerals to ripen and sweeten the fruit.

The leaves do not prevent oxygen from entering during gas exchange to the atmosphere. It is the positive pressure and increased head of water shown in the short video on Youtube that provides the leaf with the ability to exude water from the leaf.

Picture a U tube of water filled with sap. Alter the density on the xylem side at the top and the water level in the less dense side exudes out of the other side. In the active part of the tree, instead of a U tube we have a multiple conduit system with each tubes contents affecting other tubes contents. For example, cavitations form in a xylem affecting the tension and negative pressure temporarily shutting down the circulation within changing the pressure to predominantly positive causing a reversal of the flow which inevitably changes the tension in juxtapose xylem and phloem. The gas bubbles now  are compressed and more dilute sap is pulled into the cavitated  xylem to replace the sap that was pushed out as cavities formed bringing the tube back into service as an active predominantly upwards transport to the leaves. It’s a bit like playing an organ except instead of having fingers to operate the valves we have pressure changes and density changes to regulate the flow. So to inspect a leaf to find the mechanism for selective diffusion will never provide anyone with the answers, after all it is just a leaf.

Quote
Quote from: YourUncleBob on Today at 03:03:06
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. You cannot apply suction to the top of a tube and draw water up over the 24 metre limit, whether it is in an artificial tube or inside a living or dead tree. We cannot bend the rules to suit a paper. The paper must always bend to wither fit the existing rules or re-write the rules that fit with all of the other papers.

To give us some idea of the problems the literature faces we need to look at this brilliant simple experiment involving a vertical suspended vine. Note the boiling effect. I have also observed this inside my many experiments at Brixham.

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
« Last Edit: 10/05/2008 12:12:54 by Andrew K Fletcher »
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #162 on: 10/05/2008 11:44:00 »
Pressure Flow Hypothesis
From Wikipedia, the free encyclopedia
 
The Pressure Flow Hypothesis is the best-supported theory to explain the movement of food through the phloem.[1] It was proposed by Ernst Münch, a German plant physiologist in 1930.[2] A high concentration of organic substance inside cells of the phloem at a source, such as a leaf, creates a diffusion gradient that draws water into the cells. Movement occurs by bulk flow; phloem sap moves from sugar sources to sugar sinks by means of turgor pressure. A sugar source is any part of the plant that is producing or releasing sugar. During the plant's growth period, usually during the spring, storage organs such as the roots are sugar sources, and the plant's many growing areas are sugar sinks. The movement in phloem is bidirectional, whereas, in xylem cells, it is unidirectional (upward).

After the growth period, when the meristems are dormant, the leaves are sources, and storage organs are sinks. Developing seed-bearing organs (such as fruit) are always sinks. Because of this multi-directional flow, coupled with the fact that sap cannot move with ease between adjacent sieve-tubes, it is not unusual for sap in adjacent sieve-tubes to be flowing in opposite directions.

While movement of water and minerals through the xylem is driven by negative pressures (tension) most of the time, movement through the phloem is driven by positive hydrostatic pressures. This process is termed translocation, and is accomplished by a process called phloem loading and unloading. Cells in a sugar source "load" a sieve-tube element by actively transporting solute molecules into it. This causes water to move into the sieve-tube element by osmosis, creating pressure that pushes the sap down the tube. In sugar sinks, cells actively transport solutes out of the sieve-tube elements, producing the exactly opposite effect.

Some plants however appear not to load phloem by active transport. In these cases a mechanism known as the polymer trap mechanism was proposed by Robert Turgeon[3]. In this case small sugars such as sucrose move into intermediary cells through narrow plasmodesmata, where they are polymerised to raffinose and other larger oligosaccharides. Now they are unable to move back, but can proceed through wider plasmodesmata into the sieve tube element.

The symplastic phloem loading is confined mostly to plants in tropical rain forests and is seen as more primitive. The actively-transported apoplastic phloem loading is viewed as more advanced, as it is found in the later-evolved plants, and particularly in those in temperate and arid conditions. This mechanism may therefore have allowed plants to colonise the cooler locations.

Organic molecules such as sugars, amino acids, certain hormones, and even messenger RNAs are transported in the phloem through sieve tube elements.





[edit] References
^ Translocation of Food
^ Münch, E (1930). "Die Stoffbewegunen in der Pflanze". Verlag von Gustav Fischer, Jena: 234. 
^ Turgeon, R (1991). "Symplastic phloem loading and the sink-source transition in leaves: a model". VL Bonnemain, S Delrot, J Dainty, WJ Lucas, (eds) Recent Advances Phloem Transport and Assimilate Compartmentation. 
 

Offline YourUncleBob

  • Jr. Member
  • **
  • Posts: 23
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #163 on: 12/05/2008 14:22:01 »
Andrew big thanks for your useful links,

However looking carefully at the inner structure of the leaf it seems the gases are exchanged in the fleshy middle and are kept away from the incoming water/solute loaded veins.

Still busy here will get back at this next week.

in the meantime Something to consider when worrying about preventing cavitations

http://www.lsbu.ac.uk/water/explan5.html#foam [nofollow]


Some salts prevent the coalescence of small bubbles.
Higher concentrations (often about 0.1M) of many, but not all, salts prevent the coalescence of small gas bubbles (recently reviewed [672]) in contrast to the expectation from the raised surface tension and reduced surface charge double layer effects (DLVO theory). Higher critical concentrations are required for smaller bubble size [599]. This is the reason behind the foam that is found on the seas (salt water) but not on lakes (fresh water). The salts do not directly follow the Hofmeister effects with both the anion and cation being important with one preferentially closer to the interface than the other; for example, excess hydrogen ions [1205] tend to negate the effect of halides [622]. The explanation for this unexpected phenomenon is that bubble coalescence entails a reduction in the net gas-liquid surface, which acts as a sufficiently more favorable environment for the one out of a pair of ions rather than the bulk when their concentration is higher than a critical value. It has been proposed that anions and cations may be divided into two groups α and β with α cations (Na+, K+, Mg2+) and β anions (ClO4-, CH3CO2-, SCN-) ) avoiding the surface and α anions (OH-, Cl-, SO42-) and β cations (H+, (CH3)4N+) attracted to the interface; αα and ββ anion-cation pairs then cause inhibition of bubble coalescence whereas αβ and βα pairs do not [1305]. These groupings do not behave as bulk-phase ionic kosmotropes and chaotropes, which indicates the different properties of bulk water to that at the gas-liquid surface. It is likely that the ions reside in the interfacial region, between the exterior surface layer and interior bulk water molecules, where the hydrogen bonding is naturally most disrupted [605]. A similar phenomenon is the bubble (cavity) attachment to microscopic salt particles used in microflotation, where chaotropic anions encourage bubble formation [758].
 

Interestingly, the concentration of salt in our bodies corresponds to the minimum required for optimal prevention of bubble coalescence [622]. As small bubbles are much less harmful than large bubbles, this fact is very useful.

the references can be found at the above web site.

The last little bit I highlighted, maybe of particular interest to you as you seem to have thought a lot about homosapien flows!

kind Regards Blaine
« Last Edit: 12/05/2008 14:24:37 by YourUncleBob »
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #164 on: 12/05/2008 19:16:35 »
Reducing the pressure at the leaf would undoubtedly assist gas exchange. tension = reduced pressure = efficient gas exchange

Andrew big thanks for your useful links,

However looking carefully at the inner structure of the leaf it seems the gases are exchanged in the fleshy middle and are kept away from the incoming water/solute loaded veins.

kind Regards Blaine

« Last Edit: 12/05/2008 19:22:29 by Andrew K Fletcher »
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #165 on: 10/07/2008 21:03:53 »




Concretions found walking along the river dart Estuary at low tide. The dead tree trunk and roots were above the high tide water level and surrounded by living trees that did not exhibit these mineral deposits. I suspect the high level of salt and minerals deposited on the roots eventually killed the tree.

Very similar to lime scale deposits found on urinals probably having more in common with solutes excreted from urine. In an estuary the salinity of water varies from sea water to brackish water depending upon the flow of the river water mixing with either incoming salt water from the sea or outgoing less salty water as the tide turns. The trees ability to draw this water into it’s system presents the tree with a toxic overload. In the case of the kidneys, filtration from the blood increases the density of minerals in the urine, which builds up over time on urinals that are inadequately cleaned forming very similar concretions to those pictured on this tree.
A question that arises from this observation is why are the living trees not affected by the same concretions as the one that died. Clearly this cannot be a sedimentary deposit coating the tree from the outside but must be a concretion that is excreted from the root and trunk, otherwise other trees on the same bank around the same age would also exhibit the same characteristics as those pictured.

This is a reply to Blaine's post about http://www.thenakedscientists.com/forum/index.php?topic=14146.0

Andrew K Fletcher
« Last Edit: 10/07/2008 22:12:19 by Andrew K Fletcher »
 

lyner

  • Guest
Re: How do Trees Really lift Water to their Leaves?
« Reply #166 on: 14/07/2008 22:56:15 »
Quote
Reducing the pressure at the leaf would undoubtedly assist gas exchange. tension = reduced pressure = efficient gas exchange
What, still peddling this 'tension' idea? Where does it come from? Why doesn't it apply all the time?
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #167 on: 19/07/2008 22:20:42 »
Pay attention to the varicose vein study and learn how solutes change pressures and apply tension to liquids. Cohesion Tension Theory mean anything to you?
 

lyner

  • Guest
Re: How do Trees Really lift Water to their Leaves?
« Reply #168 on: 19/07/2008 23:34:46 »
That's surface tension - not internal tension. It's a feature of the asymmetry of forces at an interface - as you know, it is a very small force.
If it exists, it is amazing that it hasn't been used in some useful machine.
 

Online Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8664
  • Thanked: 42 times
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #169 on: 20/07/2008 14:39:48 »
Just a thought re the trees a few potst up. If only the dead trees roots are covered in mineral deposits could it be that the causation runs the other way. It's not the minerals that killed the rtree, but the deadness of the tree that caused the mineralisation. For example, could bacteria feeding on the dead tree's roots have excreted something that precipitated the minerals?
For example, CO2 might be a potential reason for the mineralisation.
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #170 on: 20/07/2008 18:00:05 »
Good point BC there is a possibility that the death of the tree caused the concretions. The remaining trunk and roots were coated in the same mineral deposits. I suspect not as a bacterial process, although this also could be worth investigating, but as a result of gravity and decay causing the migration of solutes back towards the roots. We discussed this possibility in another thread relating to fossilized tree trunks found in deserts and volcanic locations where the trunk has turned to stone. Polished these reveal the ring structure of the tree and are used for ornamental and scientific interests.

This is what drew my attention to this particular trunk while walking along the estuary in Dartmouth. It may also have been a combination of the trees equivalent blocked arteries and the resulting decay that caused the solutes to exude from the trunk and form the concretions.

Either way, Gravity plays an important roll in both the trees survival and it’s inevitable death.
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #171 on: 20/07/2008 18:03:41 »
A 4 metre loop of soft walled latex or silicon tubing filled with clean water, add a little salt solution and close the loop using a union. Invert the tube and the salt flows down one side causing it to bulge visibly, while the opposite side of the vertically suspended loop is pulled in. As for a useful machine using it, it may interest you to know that our own organic machine we call the body uses it to great effect. So does another organic machine called a tree. And then there’s the massive machine called the Atlantic Conveyor system that drives the ocean currents, regulates the temperatures and powers the worlds weather, and is believed to have caused the last ice age and many others.
That's surface tension - not internal tension. It's a feature of the asymmetry of forces at an interface - as you know, it is a very small force.
If it exists, it is amazing that it hasn't been used in some useful machine.
« Last Edit: 20/07/2008 18:07:13 by Andrew K Fletcher »
 

lyner

  • Guest
Re: How do Trees Really lift Water to their Leaves?
« Reply #172 on: 21/07/2008 12:17:16 »
We've been here before but all of those examples work under positive pressure and their operation is totally explicable in terms of pressure differences.
I would love it if you could explain to us how a single molecule, which knows nothing about its surroundings apart from its nearest neighbours, would know whether it was in a loop of tube or just an inverted tube? Why should it behave differently?
« Last Edit: 21/07/2008 16:26:46 by sophiecentaur »
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #173 on: 21/07/2008 19:31:50 »
If they work under positive pressure then how the hell does a tube get pulled in? Stop thinking of water as water, start thinking of it as a solid. When the solutes flow down one side they apply tension to all of the molecules in the upward flowing side and a compressive force to the water molecules in front of the falling solutes. The tension generated causes the return flow tube to neck indicating that the molecules are pulling on the inside of the tubular wall while at the same time they in turn are being dragged upwards.

If the water was in the ocean rather than in a closed loop of tubing then the water molecules would still pull on all of the other molecules and initiate circulation and as there are no walls to pull on we do not see the same effects, yet the same affects apply and can be shown in tidal changes dragging water from one side of the planet to the other as the moon interacts with the earth's gravity. Same applies when pouring fuel into a car from a funnelled can. First the fluid flows slowly then it speeds up as the fuel flowing into the tank drags more fuel out of the can.
« Last Edit: 21/07/2008 19:42:00 by Andrew K Fletcher »
 

Offline Andrew K Fletcher

  • Neilep Level Member
  • ******
  • Posts: 2331
  • KIS Keep It Simple
    • View Profile
Re: How do Trees Really lift Water to their Leaves?
« Reply #174 on: 26/10/2008 09:44:40 »
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=59218

The current controversy about the “cohesion-tension” of water ascent in plants arises from the recent cryo-scanning electron microscopy (cryo-SEM) observations of xylem vessels content by Canny and coworkers (1995). On the basis of these observations it has been claimed that vessels were emptying and refilling during active transpiration in direct contradiction to the previous theory. In this study we compared the cryo-SEM data with the standard hydraulic approach on walnut (Juglans regia) petioles. The results of the two techniques were in clear conflict and could not both be right. Cryo-SEM observations of walnut petioles frozen intact on the tree in a bath of liquid nitrogen (LN2) suggested that vessel cavitation was occurring and reversing itself on a diurnal basis. Up to 30% of the vessels were embolized at midday. In contrast, the percentage of loss of hydraulic conductance (PLC) of excised petiole segments remained close to 0% throughout the day. To find out which technique was erroneous we first analyzed the possibility that PLC values were rapidly returned to zero when the xylem pressures were released. We used the centrifugal force to measure the xylem conductance of petiole segments exposed to very negative pressures and established the relevance of this technique. We then analyzed the possibility that vessels were becoming partially air-filled when exposed to LN2. Cryo-SEM observations of petiole segments frozen shortly after their xylem pressure was returned to atmospheric values agreed entirely with the PLC values. We confirmed, with water-filled capillary tubes exposed to a large centrifugal force, that it was not possible to freeze intact their content with LN2. We concluded that partially air-filled conduits were artifacts of the cryo-SEM technique in our study. We believe that the cryo-SEM observations published recently should probably be reconsidered in the light of our results before they may be used as arguments against the cohesion-tension theory.
 

The Naked Scientists Forum

Re: How do Trees Really lift Water to their Leaves?
« Reply #174 on: 26/10/2008 09:44:40 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums