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The Hidden Life of Trees: Chapters 7 - 12

#187: May - July 2023 (Non-Fiction)
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LanDroid

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Re: The Hidden Life of Trees: Chapters 7 - 12

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Yes, the author is saying we do not know how water moves from roots to the tops of trees. As noted before, he dismisses capillary action, transpiration, and osmosis. He mentions one study saying there are tiny CO2 bubbles "in the narrow water filled tubes." He speculates that might be part of the answer. He occasionally makes statements like "this seems equally unlikely to me" as if he is personally not convinced by certain information.

The book was written in 2015, so perhaps we have figured it out since then... Like you I find it hard to believe we truly do not understand that process, but if this book is correct, we have is an astonishing level of ignorance.
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Re: The Hidden Life of Trees: Chapters 7 - 12

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ChatGPT wrote:The movement of water from the soil to the tops of trees is facilitated by a process known as transpiration, which is a crucial part of the plant's water cycle. Here's a simplified explanation of how water moves through a tree:

Absorption: Tree roots absorb water from the soil through tiny, hair-like structures called root hairs. These root hairs increase the surface area for water absorption and allow the tree to take in water and dissolved nutrients.

Xylem transport: Once inside the root, water travels upward through specialized tissues called xylem. The xylem vessels act as a network of tubes that extend from the roots to the leaves, providing a pathway for water movement. Xylem tissue is composed of long, hollow cells that are dead at maturity, forming continuous conduits.

Cohesion and tension: Water molecules in the xylem are attracted to each other through a force called cohesion. As water evaporates from the leaves during transpiration, it creates a negative pressure or tension in the xylem, pulling water upward.

Transpiration: Transpiration is the process by which water vapor exits the stomata, small openings on the underside of leaves. Stomata open to allow the entry of carbon dioxide for photosynthesis and the exit of oxygen, but this opening also leads to water loss. As water molecules evaporate from the leaf surface, they create a "pull" that draws more water up from the roots to replace it.

Capillary action: Capillary action, also known as capillarity, helps in the movement of water through the xylem. It is the result of the attraction between water molecules and the walls of the narrow xylem vessels. Capillary action allows water to rise against gravity.

By combining the processes of cohesion, tension, and capillary action, water is effectively transported from the roots to the tops of trees. This continuous flow of water is known as the transpiration stream. It not only supplies the tree with the necessary water for various physiological functions but also helps in the transportation of nutrients and minerals absorbed from the soil.
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Re: The Hidden Life of Trees: Chapters 7 - 12

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Interesting, but at this point ChatGPT can't provide definitive answers. Not sure what to tell you other than to read the whole chapter. Here are more excerpts. He starts on capillary action as an explanation.
Narrow vessels, however, are not enough to explain how water reaches the crown of trees that are more then 300 feet tall. In even the narrowest of vessels, there is only enough force to account for a rise of 3 feet at most. (References a study in German)

Ah, but we have another candidate: transpiration. In the warmer part of the year, leaves and needles transpire by steadily breathing out water vapor. In the case of a mature beech, the tree exhales hundreds of gallons of water a day. This exhalation causes suction, which pulls a constant supply of water up through the transportation pathways in the tree. Suction works as long as the columns of water are continuous. Bonding forces cause the water molecules to adhere to each other, and because they are strung together like links in a chain, as soon as space becomes available in the leaf thanks to transpiration, the bonded molecules pull each other a little higher up the trunk.

And because even this is not enough, osmosis also comes into play. When the concentration of sugar in one cell is higher than in a neighboring cell, water flows through the cell walls into the more sugary solution until both cells contain the same percentage of water. And when that happens from cell to cell up into the crown, water makes its way up to the top of the tree.

...Hmm. When you measure water pressure in trees, you find it is highest shortly before the leaves open up in the spring.
That last statement indicates transpiration is not involved. Capillary action accounts for only 3 feet of rise, and “osmosis works only in the roots and leaves, not in the trunk…”
So where does that leave us? We don’t know.
The author seems to base skepticism on the high water pressure just prior to leaves opening in the spring. As stated before he mentions tiny CO2 bubbles.
Bubbles in the pipes? That means the supposedly continuous column of water is interrupted thousands of times. And if that is the case, transpiration, cohesion, and capillary action contribute very little to water transport.
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