The nanofluidics can explain ascent of water in tallest trees
Abstract
In Amazing numbers in biology, Flindt reports a giant, 128 meter-tall eucalyptus, and a 135 meter-tall sequoia. However, the explanation of the maximum altitude of the crude sap ascent and consequently the main reason of the maximum size that trees can reach is not well understood. According to tree species, the crude sap is driven in xylem microtubes with diameters ranging between 50 and 400 micrometers. The sap contains diluted salts but its physical properties are roughly those of water; consequently, hydrodynamic, capillarity and osmotic pressure yield a crude sap ascent of a few tens of meters only. Today, we can propound a new understanding of the ascent of sap to the top of very tall trees thanks to a new comparison between experiments associated with the cohesion-tension theory and the disjoining pressure concept. Here we show that the pressure in the water-storing tracheids of leaves can be strongly negative whereas the pressure in the xylem microtubes of stems may remain positive when, at high level, inhomogeneous liquid nanolayers wet the xylem walls of microtubes. The nanofluidic model of crude sap in tall trees discloses a stable sap layer up to an altitude where the pancake layer thickness coexists with the dry xylem wall and corresponds to the maximum size of tallest trees. In very thin layers, sap flows are widely more significant than those obtained with classical Navier-Stokes models and consequently are able to refill stomatic cells when phloem embolisms supervene. These results drop an inkling that the disjoining pressure is an efficient tool to study biological liquids in contact with substrates at a nanoscale range.
Keywords
Cite
@article{arxiv.1204.4094,
title = {The nanofluidics can explain ascent of water in tallest trees},
author = {Henri Gouin},
journal= {arXiv preprint arXiv:1204.4094},
year = {2012}
}
Comments
Methods. We compare two experiments: - The Scholander pressure bomb experiment (1955) based on the cohesion-tension theory (1894) in which liquids are considered to be incompressible. - The Sheludko experiment (1967) based on the concept of disjoining pressure in DLVO theory (1948) that highlights a strong difference between liquid bulk and thin layer pressures. The theoretical results allow us to obtain: - The computation of tallest trees' level that fits with real facts - The interpretation of the motion in xylem microtubes by using the shallow water approximation and the slippage on walls at the nanometric scale. arXiv admin note: text overlap with arXiv:1106.1275