Posted by hhs 19 hours ago
This sentence undersells the phenomenon quite a bit: the “extreme low pressure” is in fact several bars of negative pressure and the challenge of maintaining water in liquid form is avoiding cavitation.
I was exposed to the physics of trees though the entrance exam to École Polytechnique (France's best University) and it's been carved in my mind since then: http://alainrobichon.free.fr/Concours/X_PC_PH1_01.pdf
AFAIK students are still being given this masterpiece for practice even though it's now 25 years old.
See also Veritasium on that topic:
Plants will do what they need to do in the end. I've done stuff like co2 bombing, and increasing nutrients to the point to where I get a whole new ecosystem of insects and an entirely new situation.
It is such fascinating stuff that it's actually the life I want to live. I'm a computer scientist but now I yearn for the botanical sciences.
I highly recommend checking out defoliation strategies and low-stress training methods for anyone interested. Plants are not dumb creatures. The results you can get from them are astonishing and the science of what plants actually are becomes more profound by the day.
Another area that might be easier to break in to as far as work goes is labouring for an irrigation business, kinda agricultural plumbing.
You’ve probably seen pivots[1] and side-roll irrigation systems.
This would put you in more direct contact with the farm operators, expose you to a wide range of agricultural crops, and also tie neatly in to your existing CS skill set with regard to agricultural SCADA (Supervisory Control and Data Acquisition), or Industrial Arduino as I like to call it.
Working for seed processes / distributors and fertiliser and pest & weed control industries could also be another foot-in-the-door move.
Horticulture is about growing plants and multiplying it, often with flower power overtones and moon myths that vastly underestimate its importance.
Veganism is often mistaken as a synonym of "botany loving people", but is just a religious movement started by a priest, and centered around the random ideas that:
1) Plants occupy a lower rank of importance among life beings because they lack a single particular type of sensor that only the cool animals have, and...
2) Plants are safe to eat, because they were designed by god for us
None of those ideas are validated by real facts. As people grows in the cozy comfort of their religious group they lose the capability to see the whole picture and turn into food zombies that move and hate just by inertia. You can show science here for weeks and weeks without finding a sign of intelligent life.
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Many people stop here and will never heard about:
Geobotany. Be afraid, very afraid. This is what a cabal of Da Vincy code linguists would do in the dark to bring pain to the world.
Most people will be put off by it in seconds, by the strange words and tedious lists, but there is an unexpected reward at the end when all pieces fall in place. You will never see the wildlife in the same way.
And plant physiology, that is like a really good sci-fi book.
Very complicated, defiant, dealing with really futuristic problems, and with more "hit the coin" moments that Mario. Who would imagine that the future of the humanity is linked with the capability to huge organisms to do physical work that makes the stronger animal look like crap
Botany is great because the results are basically what I'd call magic. It's such beauty (and horror on occasion).
The marriage of CS and botany seems like a match made in heaven and just from writing these comments I've convinced myself that it's probably the most practical way to go forward in life.
— Carl Sagan
My hunch is that torsion, flex and their effect on the capillary structures are at play, but I haven't been able to step away from CS myself.
[1] https://www.sfgate.com/science/article/REDWOODS-How-tall-can...
I know it is quite distant, but from my experience in large-scale data engineering, 90% of the time goes in addressing subtle issues that can only be observed hours into a job, the rest of the issues are quickly resolved earlier. I am assuming that such complexities will be so much harder in physical systems, and even more so in biological systems.
Or do you mean to suggest that the failure of any accepted tree height records to surpass the maximum capillary distance can be explained by some other factor? (Based on your other comment it seems safe to assume that isn't what you meant but anyhow.) That seems far too convenient given that the observed cutoff is within the expected range.
500ft is taller than the max ever, not 1640 ft
A bucket brigade works just as well up ten flights of stairs as up one hundred. So does a system of opening and closing valves.
We can pump water from a bucket on one floor of building to a bucket on the next floor easily. Then we can repeat the same thing at the next floor; the pressure from the numerous floors above doesn't factor in because there isn't a connected water column.
Too bad we cut it down, along with almost every other giant Douglas-fir.
"The placard recorded that the Nooksack tree produced 96,345 board feet (227.348 cubic meters) of the "finest quality" lumber.
The New York Times regarded the tree in a March 7, 1897 issue as the "most magnificent fir tree ever beheld by human eyes" and called its destruction a "truly pitiable tale" and a "crime".
The Morning Times of February 28, 1897 claimed that the wood, sawed into one-inch strips, would reach from "Whatcom [the tree's location] to China"."
to be fair, without humans there would be nobody to declare "barbarism". At one time, all humans were barbarians, it took a certain level of cultural development before the word "barbarism" was necessary, so at that point it was "new". It remains be be shown whether cultures that call other cultures "barbaric" are actually "better".
For a while there were people poaching the moss that facilitated this, which is a problem because it grows only inches per year.
We're lucky to have a handful of big Doug Firs, Sitka Spruce, and Western Red Cedars left on Vancouver Island.
Hm, may be because they are not really "pumping" the water?
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.
Coalescence of coastal fog accounts for a considerable part of the trees' water needs.[23]
https://en.wikipedia.org/wiki/Sequoia_sempervirens#Fog_and_f...
Weirder still is the realization that all the air is just trapped light.
[1] https://www.sfgate.com/science/article/REDWOODS-How-tall-can...
While admittedly contested and only reproduced by a few labs outside Gerald Pollack's at University of Washington, there is a solid case that it could play a role in transporting water and sap to the tops of trees. At least, it's involved in the motion induced in hydrophilic tubes when there is sufficient ambient radiant energy (uv/infrared).
Relevant papers:
"Exclusion-zone water inside and outside of plant xylem vessels." 2024 Scientific Reports. https://www.nature.com/articles/s41598-024-62983-3
"Surface-induced flow: a natural microscopic engine using infrared energy as fuel." 202 Science Advances. https://www.science.org/doi/10.1126/sciadv.aba0941
"Long-range forces extending from polymer-gel surfaces." 2003 Phys. Rev. E. https://link.aps.org/doi/10.1103/PhysRevE.68.031408
Pollack's site: https://www.pollacklab.org/
Some critiques of Pollack's theory:
Schurr, J.M. (2013). Phenomena associated with gel–water interfaces: analyses and alternatives to the long-range ordered water hypothesis. J. Phys. Chem. B, 117(25), 7653–7674. https://doi.org/10.1021/jp302589y Elton, D.C., Spencer, P.D., Riches, J.D. & Williams, E.D. (2020). Exclusion zone phenomena in water — a critical review of experimental findings and theories. Int. J. Mol. Sci., 21(14), 5041. https://doi.org/10.3390/ijms21145041 (open access; the most thorough critical review) Elton, D.C. & Spencer, P.D. (2021). Pathological water science — four examples and what they have in common. In Water in Biomechanical and Related Systems (Biologically-Inspired Systems, vol. 17), pp. 155–170. Springer. https://doi.org/10.1007/978-3-030-67227-0_8 (preprint: https://arxiv.org/abs/2010.07287)
Yours shall be filed under homeopathy :)
And then there's homeopathy which is a largely unrelated and entirely nonsensical thing.
It seems that trees just don't grow that tall anymore. Even common trees such as the spruce seem to be able to reach 100m, they just kind of don't.
One possibility is the depletion of nutrients. But what I think is to blame is the lack of elephants. They constantly ruined young trees and the lucky few that survived then grew huge. Perhaps the redwoods were actually created by the natives, who removed young trees, and kept the old trees standing.
That would work, but it's not how to works apparently. According to this veritasium video, it's because of "negative pressure" aka tension.
https://www.youtube.com/watch?v=BickMFHAZR0
I recommend watching, I think it's one of the best veritasium Dereck has ever produced.
I suppose that’s not particularly relevant for more recent old growth tall trees that seem to have got by fine in a colder Earth.
But it’s easy to imagine a warmer, wetter, Earth with higher atmospheric CO2 concentrations being more conducive to taller tree growth.
On the other hand, I probably don’t really know what I’m talking about, not my area of expertise.