What if trees had hearts?

A classical theme in vegetal physiology and vegetal biology is how do plants absorb water from the ground and distribute it up to every branch, leaf and flower?

Although it can seem a quite easy process, it hides a pretty complicated process. Water doesn’t go all the way up thanks to the mere diffusion motion, neither it does thanks to the mere coesion forces and capillary actions. They surely help the process but one thing is fundamental to take all the way up all that water: Pressure. A lot of pressure.

When one thinks about pressure, he/she may think about something like a piston. It pushes air or water in a more constrained space raising the pressure inside the piston. Looking from this way one can think a sort of piston from the roots of a tree that pushes all the way up the water needed. You mustn’t be a genius to see the erroneous point of view.

So if there isn’t a positive pressure from below what pushes the water up? A negative pressure from the top! What? Yes!

This mechanism has something fenomenal. Plants loose water through their stomes (little openable cavities needed to exchange gasses with the air and then loose water) – in a process known as Transpiration – and that process causes a negative pressure inside the sealed tubes along the trunk provoking the water going up all the way. For this reason it’s really important that the tracheids and tracheas are reinforced and strong. To resist the pressure and avoid to collapse this dead cells that forms the conducts are stronged with many woody substances we won’t enter in details. This is another amazing mechanism: plants use the power of the sun to loose water to gain more water! Although it can sound strange, there are a lot of mathematical calculations with the concept of Idric Potential that proves the difference in pressure from the top to the bottom of a tree and so the tendency of the water to go up.

This mechanism works with almost every plant, but there are some exception, like desert plants, that have other solutions. This doesn’t change that nature has pretty much every solutions. Can you imagine the possibility of using the same mechanism of trees to take water from the ground up to the roof of skycrapers? There’s no consume in energy, that’s amazing! there would be a lot of electricity power saved.

Plants use this flow of water from the bottom to the top even to transport the mineral and nutrients absorbed by the roots to the main body of the plant. On the other hand there’s another flow from the top to the bottom which transports the lymphatic water rich in sugars from the photosynthesis to every living cell of the tree (this flow doesn’t use the same negative pressure mechanism obvisously). These flows are the famous Xilem and Phloem which I talked about in another post.

A simple drawing illustrating Xilem and Phloem flows in both directions.
A simple drawing illustrating Xilem and Phloem flows in both directions.

Let’s put this concept forward. Many animals on Earth has a vascular circulation to do the same things plants do through the Xilem and Phloem. And the core of this circulation is a Heart. The Heart in opposition, causes a positive pressure pretty high, so the vessels has to be reinforced too. But in this case by some muscular tissues. The Heart is an autonomous muscle that keeps pumping using energy. Can you think a tree with a Heart? I would love to see one!

I mean, the conducts of a tree are already reinforced so probably they would be capable of standing the pressure. A lot of energy is produced by the photosynthesis process. The only thing needed is a Heart and something similar to a close circulation instead of flows parallel to the trunk. Having a moving organ like a Heart inside a plant could be mind disturbing, because we are not used to think in this optic. But there are moving parts in plants right? There are carnivorous plant that can move and move back to their original position. There are plants that, when touched, moves. That’s the only thing you need to have a Heart: continuos, cyclic movements. Maybe it will not relies on muscles but on some other pressure or lever mechanims. Anyway I would love having live heart-beating trees. Maybe many people will start considering them more like a living organism.

A permanent flow of water, enriched by the mineral nutrient from the ground and sugars from the leaves. I don’t see why that wouldn’t be possible. Perhaps too anthropocentric but still mind-stimulating.

Next time you see a tall tree try to lay you ear to the bark, maybe you’ll hear a beating heart that pumps water in the trunk. Or maybe you’ll hear another of my stories.

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