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Comment by malfist | Hacker News Reader

Maybe, but evaporation is critical for plants. They don't have a heart to pump blood and supply nutrients, they have to rely on evaporation to move nutrients from the roots up

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Plants rely on on capillary action to bring water up: https://www.usgs.gov/special-topics/water-science-school/sci....

There's probably some aspect of evaporation, but the density of water is much, much higher when it's kept in liquid form.

That's part of the process, but not all of it. The overall process of water movement through vascular tissue is called transpiration [0]. Yes, capillary action plays a part, but the underlying process is due to differences in water potential. To avoid saturation (which would halt the flow of nutrients), water is released through pores in the leaves called stomata [1], where it evaporates, creating a differential that results in additional water being pulled in from the soil.

[0] transpiration: https://en.wikipedia.org/wiki/Transpiration

[1] stoma: https://en.wikipedia.org/wiki/Stoma

Disclaimer: I'm not a biologist. I'm a third-generation home gardener; my grandfather was the youngest of his family and the to leave the family farm in Kansas to go to college. He always maintained a large garden and loved sharing his knowledge along with his vegetables.

Edit: added links and a disclaimer

Watch Veritasium’s awesome video on this

https://www.youtube.com/watch?v=BickMFHAZR0

It's an old video, more than ten years ago, but it aged well IMHO. I re-watched it and re-learned things I have forgotten.

I imagine the leaves being green would encourage this evaporation. The upper layers of cells are probably effectively translucent and might be awash in green light, perhaps increasing the rate of evaporation and improving overall transpiration.

That’s my guess as well. The green chlorophyll is inside of the cell. It absorbs sunlight for food but reflects the green light back through the water-air boundary. Perhaps the effect on evaporation or water movement provides a better benefit for the plant than absorbing the energy of that spectra. For instance, by increasing the efficiency of respiration.

At its simplest, reflecting green light would send the light through the water twice instead of once. Neat trick, plants.

Well, the chloroplast was evolved when all life forms were submerged in the sea

The sea is on the other side of a very carefully policed barrier.

Still, it's less of a challenge to pump water from your roots if you're in the sea. Did the earliest green plants even have roots?

> Did the earliest green plants even have roots?

No. Not even all land plants have roots.

That’s a good point actually. I never thought about the fact that a tree is evaporating 100L a day without any heat. They must have figured this out.

It still uses heat. Evaporation actually helps plants keep cool by using up the heat from sun that would otherwise heat the plant too much.

No doubt. I’m just toying with the idea of how this might impact our understanding of how plants work.

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