Each spring enormous amounts of water rise up in trees and other vegetation. What causes this stream upwards?
Edit: I was under the impression that capillary action is a key factor: the original question therefore was: what are the fundamental forces involved in capillary action?
Can perhaps anybody make an estimation of the amount of gravity energy that is involved in this process earth-wide each season?
Answer
Water is transported through xylem tissue, which reassemble just a passive bundle of pipes. They are narrow enough to provide quite a huge capillary effect, but this is not a process of transport because it converges fast to equilibrium water levels and stops.
The flow is powered by two other processes; first and most important is evaporation of water from leafs (transpiration pull) and the second is a osmotic pressure in roots (root pressure). The first one is a passive process, powered by the difference of water potentials in air and soil; the second is active, plant consumes its own energy to produce ion gradient causing osmotic pressure.
I won't give you the accurate numbers in the second part; to give some imagination, about 90% of water absorbed from soil is transpired into atmosphere, so it is near transpiration rates. A single tree growing in humid continental climate zone (most of Europe and USA) transpires yearly something like 100 tons of water.
No comments:
Post a Comment