[Physics] How is it possible for tall trees to pull water to heights more than 10m

capillary-actionfluid-staticsosmosispressurewater

Which force actually drives water so high up, since pure atmospheric pressure will only get you up to about 10 meters if you're using suction and a long straw and yet tallest trees are over 100 meters ( trees do basically have long continuous 'straws' all the way up.)

Best Answer

It's not only atmospheric pressure which is involved in water delivery to a tree, but mainly the capillary action and osmosis.

Osmosis and Hydrostatic Pressure

Roots take advantage of "pressures" when water and its solutions are unequal. The key to remember about osmosis is that water flows from the solution with the lower solute concentration (the soil) into the solution with higher solute concentration (the root).

Water tends to move to regions of negative hydrostatic pressure gradients. Water uptake by plant root osmosis creates a more negative hydrostatic pressure potential near the root surface. Tree roots sense water (less negative water potential) and growth is directed towards water (hydrotropism).

(From “Process of How Trees Absorb and Evaporate Water via Roots and Leaves”, ThoughCo.)

Only for the sake of your interest:

Current hypotheses of height limitation focus on increasing water transport constraints in taller trees and the resulting reductions in leaf photosynthesis. We studied redwoods (Sequoia sempervirens), including the tallest known tree on Earth (112.7 m), in wet temperate forests of northern California.

Our regression analyses of height gradients in leaf functional characteristics estimate a maximum tree height of 122–130 m barring mechanical damage, similar to the tallest recorded trees of the past. As trees grow taller, increasing leaf water stress due to gravity and path length resistance may ultimately limit leaf expansion and photosynthesis for further height growth, even with ample soil moisture.

(From Koch, George W.; Sillett, Stephen C.; Jennings, Gregory M.; Davis, Stephen D.: “The limits to tree height”. Nature. 428 (6985): 851–854.)

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