Natures wonders: complex water control in trees (Introduction)

by David Turell , Wednesday, October 16, 2019, 01:44 (1864 days ago) @ David Turell

Ponderosa pines demonstrate a very complex system:

https://blogs.scientificamerican.com/artful-amoeba/how-a-tiny-pit-decides-a-pine-trees-...

"In trees, water is essential for producing food from sunlight and carbon dioxide, a process called photosynthesis, but also for maintaining pressure in plant cells, a concept called turgor. For both these reasons, the more water a tree transports, the faster it grows.

"Trees accomplish this by exploiting two physical properties of water: evaporation and the capillary effect. Openings in needles or leaves called stomata permit gas exchange by the plant, an important ability in its own right (plants must breathe just as we do). But stomata also permit evaporation. This might seem like a bad thing, but under normal circumstances it is all part of the plant’s plan.

"...the capillary effect is why water magically ascends capillary tubes or a paper towel that even briefly grazes a spill below it. In a tree, water is hoisted through the water-conducting tissues in the trunk with zero effort on the plant’s part.

"The water pipes in pine trees are not like the plumbing in your house, though. Instead of long, uninterrupted tubes, they are constructed of many short tubes called tracheids with angled ends. These shorter tubes connect to each other along their sides via structures called bordered pits, which look a lot like speakers.

***

"In cross section the bordered pit takes on more of a donut shape. The pit is made of three parts: the aperture, the torus, and the margo. The aperture is the little hole through which water enters the pit. The torus is the donut hole, which is suspended in the middle of the pit by the margo, a porous barrier made of the tracheid’s primary cell wall (the much thicker secondary cell wall makes up the torus and surrounds the pit).

***

"The oldest trees the scientists studied had slower average growth rates throughout their lives than the young trees they sampled. Even when they were young these old trees had grown slower. And, crucially, these older trees had larger torus overlap -- the width of the pit border covered by the torus -- than younger trees. The difference was largely the result of having smaller apertures.

"Trees with smaller apertures resist drought better because when the torus is drawn up against them, they seal better. But smaller apertures also means water travels more slowly through the tree when the doors are open, slowing growth.

"So there’s the rub: grow fast — get big, compete for light better, reproduce faster, and increase your chances of early survival — but make it easier for drought to kill you. Or make your drought-tight doors smaller and stronger, slow growth and prolong success, but increase the chance you’ll live to see your grandkids make cones of their own."

Comment: these are complex designs to help the trees handle changing wet and drier climates where they exist. The complexity can be appreciated by looking at the article's illustrations. Only design explains this system.