Giant trees have no trouble pumping water to top branches

https://news.exeter.ac.uk/faculty-of-environment-science-and-economy/giant-trees-have-no-trouble-pumping-water-to-top-branches/

43•hhs•1h ago

Comments

nullorempty•51m ago

>Giant trees have no trouble pumping water to top branches

Hm, may be because they are not really "pumping" the water?

leni536•45m ago

What would you call it?

cj•39m ago

Not 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•36m ago

Yeah it's the difference between creating low vs high pressure.

card_zero•30m ago

The low pressure is up there already, for free.

Or the high pressure is down here, whichever way you want to look at it.

chowells•16m ago

If 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•6m ago

The 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.

dataflow•1m ago

[delayed]

gitaarik•37m ago

“Trees contain lots of thin, hollow vessels and they suck water upwards by creating low pressure at the top,”

So sucking / pulling?

IsTom•34m ago

So a suction pump?

card_zero•32m ago

Same 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•23m ago

Or, it’s simply a rate to variably adjust to, so the tree is neither flooding nor parching the leaf.

gitaarik•21m ago

Maybe 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?

rolph•28m ago

more like capillary action.

https://en.wikipedia.org/wiki/Xylem#Cohesion-tension_theory

card_zero•11m ago

Oh, so we don't really know how it works. Fun.

alldayhaterdude•29m ago

Happy for them.

lukeholder•11m ago

This made me laugh out loud. Thanks.

nomel•17m ago

This goes against all previous research/measurements for actually tall trees (looks like they only considered up to 80m) and the fact that there are exactly zeros trees in the world taller than 130 meters [1]. Wide capillaries at the base, like stated in the article, don't seem to be related.

[1] https://www.sfgate.com/science/article/REDWOODS-How-tall-can...

m463•13m ago

on the other hand, many giant trees get the water out of the air via fog:

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...

https://en.wikipedia.org/wiki/Sequoia_sempervirens

nomel•7m ago

Sequoia are still limited in height by gravity, probably due to capillary pressures. [1] If they evolved to be segmented, they could probably do it.

[1] https://www.sfgate.com/science/article/REDWOODS-How-tall-can...

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Giant trees have no trouble pumping water to top branches

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