3 ms·
>Giant trees have no trouble pumping water to top branches Hm, may be because they are not really "pumping" the water?
by nullorempty 3mo ago
>Giant trees have no trouble pumping water to top branches
Hm, may be because they are not really "pumping" the water?
- leni536 3mo agoWhat would you call it?
- cj 3mo agoNot that it really matters, but the article also refers to it as “drawing water to the top”. That seems more representative of reality than “pumping water from the bottom”.
- margalabargala 3mo agoYeah it's the difference between creating low vs high pressure.
- card_zero 3mo agoThe low pressure is up there already, for free. Or the high pressure is down here, whichever way you want to look at it.
- chowells 3mo agoIf you think of it that way, you have a real problem. It only takes about 10 meters for the weight of a column of water to create enough downward force that it starts vaporizing, at which point no pumping action works. This is why any deep well has a submerged pump. You simply can't pull water upward further than that with negative pressure in the Earth's atmosphere. It must be pushed with positive pressure instead. 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.
- pulvinar 3mo agoThe trick for trees is capillaries, which change the equation. The 10 meter limit only applies to larger columns. With capillaries there's a high negative tension that allows evaporation from leaves to pull the xylem sap up 100 meters or more. 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.
- tenuousemphasis 3mo ago>if the tree were in a closed system with no solar input ... that would be the least of the tree's problems.
- deleted 3mo ago[deleted]
- theendisney 3mo agoThis line of reasoning has always cracked me up. The internal dialog acidentally out loud at the least flattering moment. I believe the correct response to be: 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?
- lazide 3mo agoWell, if you chop it down and burn it to boil water, then Use it to spin up a turbine…
- taneq 3mo agoIt’s like the pop sci fact that if you took all your blood vessels and laid them end to end… you would die.
- hinkley 3mo ago
- gitaarik 3mo ago“Trees contain lots of thin, hollow vessels and they suck water upwards by creating low pressure at the top,” So sucking / pulling?
- IsTom 3mo agoSo a suction pump?
- card_zero 3mo agoSame principle as chimneys. But I also noticed this line: > 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.
- DANmode 3mo agoOr, it’s simply a rate to variably adjust to, so the tree is neither flooding nor parching the leaf.
- gitaarik 3mo agoMaybe it's not more trouble pumping, eh, sucking water up. But that the top branches are the last ones to get water in periods of draught, and have therefore more resilience?
- hinkley 3mo agoMy recollection is that capillary action is a little from column a and a little from column b.
- rolph 3mo agomore like capillary action. https://en.wikipedia.org/wiki/Xylem#Cohesion-tension_theory https://en.wikipedia.org/wiki/Xylem#Cohesion-tension_theory
- card_zero 3mo agoOh, so we don't really know how it works. Fun.
- rolph 3mo agothe research is relevant to the issue of transpiration column hieght as a postulated limitation to overall hieght of any tree. 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.
- fc417fc802 3mo ago> a transpiration stream, that ultimately ejects water vapour from the leaves 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).
- RetroTechie 3mo ago> 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 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.
- cwmoore 3mo agoThey do wave in the wind, and evolution is likely capturing some of that motion for work.
- hetspookjee 3mo agoNot sure if you’ve ever visited the groves in California where these huge trees grow but they seem to find the place where the wind doesn’t really seem to bother them, among other reasons (fog staying and little creeks terminating are others). And when the wind comes along it’s surprising how little they actually wave. Such tiny radii change I reckon cannot move much water like you’d need for a pumping notion. So I’d say it has barely if any an influence
- cwmoore 3mo agoI have seen trees before too, anecdotally, my random naysayer.
- cwmoore 3mo agoWatching trees not move much is a low standard for proof—maybe you misunderstood the intent of my comment. If it isn’t upthread, the seminal research on the mechanism (Cohesion Tension Theory) is from 1894: https://www.jstor.org/stable/91804 https://www.jstor.org/stable/91804
- HarHarVeryFunny 3mo agoThere seems to be a lot of things that come together to make it work, but it's basically sucking not pumping. The term to google is Transpiration. 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.