4 ms·

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

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 3mo 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.
- 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 ago
    This 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 ago
      Well, if you chop it down and burn it to boil water, then Use it to spin up a turbine…
  - taneq 3mo ago
    It’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
      This is still one of my all time favorites, although alveoli work the same way and are more fun to say. The other day my friend said they wanted a new nervous system and my brain went down this route of pulling out the old one and putting in the new one.
      - theendisney 3mo ago
        I once coin the philosophical construct: the wireless p**s. The idea is to send the body to work while you stay at home and have fun. Is the new nervous system really you?
- hinkley 3mo ago
  One of the things Susan Simard proved was that deep rooted trees that had found subterranean water continue pulling that water at full speed at night when transpiration is low, and that water finds its way into the fungal networks in the soil and into nearby plants. 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.
  - fc417fc802 3mo ago
    I don't understand how osmosis enters into this? Capillary action is sufficient to explain water traveling up the roots to a point where it was removed. Evaporation from leaves is sufficient to explain removal during the day. You'd need some other explanation for extraction by fungi or etc at night. 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.
    - hinkley 3mo ago
      In retrospect what I wrote became a bit more of a non sequitur than I meant. Trees aren't even accessing water at ground level most times but pulling it up from 5-30 feet down. Fungal distribution is also a capillary action network (with asterisks) and ends up making some of that pumping more horizontal, but at the expense that if a tree's root sap is high in sugar due to dehydration, then the fungal network both introduces water to those roots but also exports sugar at the same time. Simard tries to anthropomorphize this process. It's my only real complaint with her work. The asterisks are that fungal networks can react to information faster than the documented transport mechanisms work so we don't really know how the heck they do their thing yet. So it's possible that they're also maintaining nutrient gradients to feed themselves beyond the straight arbitrage that osmosis represents.
- left-struck 3mo ago
  The 10 metre thing assumes you have a suction side which is 10 metres lower than the pump, or at least a suction that is long/low enough that it can’t meet the pump’s NPSHr (Net Positive Suction Head required). 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.
deleted 3mo ago
[deleted]
kijin 3mo ago
Yeah, that "extreme low pressure" part of the article had me scratching my head. Even a complete vacuum at the top will not suck water up more than 10 meters! The author was probably oversimplifying for a lay audience.
fc417fc802 3mo ago
That analysis only applies to a single discreet pump. A line of pumps in series does not suffer from that problem and that is roughly what a biological system would be expected to consist of.
- Sharlin 3mo ago
  There are no pumps in a tree, in series or not. There’s nothing between the roots and leaves that actively drives water upward in any way. The xylem is literally dead tissue.
  - fc417fc802 3mo ago
    Please notice that the comment I was responding to there made claims of physical infeasibility that I was responding to. I was not expressing any claims regarding actual concrete trees that you could go and visit. More generally you seem to be dismissing out of hand the primary topic of discussion which is neither constructive nor enlightening.

pulvinar 3mo 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.

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 ago
  This 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 ago
    Well, if you chop it down and burn it to boil water, then Use it to spin up a turbine…
- taneq 3mo ago
  It’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
    This is still one of my all time favorites, although alveoli work the same way and are more fun to say. The other day my friend said they wanted a new nervous system and my brain went down this route of pulling out the old one and putting in the new one.
    - theendisney 3mo ago
      I once coin the philosophical construct: the wireless p**s. The idea is to send the body to work while you stay at home and have fun. Is the new nervous system really you?
hinkley 3mo ago
One of the things Susan Simard proved was that deep rooted trees that had found subterranean water continue pulling that water at full speed at night when transpiration is low, and that water finds its way into the fungal networks in the soil and into nearby plants. 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.
- fc417fc802 3mo ago
  I don't understand how osmosis enters into this? Capillary action is sufficient to explain water traveling up the roots to a point where it was removed. Evaporation from leaves is sufficient to explain removal during the day. You'd need some other explanation for extraction by fungi or etc at night. 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.
  - hinkley 3mo ago
    In retrospect what I wrote became a bit more of a non sequitur than I meant. Trees aren't even accessing water at ground level most times but pulling it up from 5-30 feet down. Fungal distribution is also a capillary action network (with asterisks) and ends up making some of that pumping more horizontal, but at the expense that if a tree's root sap is high in sugar due to dehydration, then the fungal network both introduces water to those roots but also exports sugar at the same time. Simard tries to anthropomorphize this process. It's my only real complaint with her work. The asterisks are that fungal networks can react to information faster than the documented transport mechanisms work so we don't really know how the heck they do their thing yet. So it's possible that they're also maintaining nutrient gradients to feed themselves beyond the straight arbitrage that osmosis represents.
left-struck 3mo ago
The 10 metre thing assumes you have a suction side which is 10 metres lower than the pump, or at least a suction that is long/low enough that it can’t meet the pump’s NPSHr (Net Positive Suction Head required). 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.

deleted 3mo ago

[deleted]

kijin 3mo ago

Yeah, that "extreme low pressure" part of the article had me scratching my head. Even a complete vacuum at the top will not suck water up more than 10 meters! The author was probably oversimplifying for a lay audience.

fc417fc802 3mo ago

That analysis only applies to a single discreet pump. A line of pumps in series does not suffer from that problem and that is roughly what a biological system would be expected to consist of.

Sharlin 3mo ago
There are no pumps in a tree, in series or not. There’s nothing between the roots and leaves that actively drives water upward in any way. The xylem is literally dead tissue.
- fc417fc802 3mo ago
  Please notice that the comment I was responding to there made claims of physical infeasibility that I was responding to. I was not expressing any claims regarding actual concrete trees that you could go and visit. More generally you seem to be dismissing out of hand the primary topic of discussion which is neither constructive nor enlightening.