The nanofluidics can explain ascent of water in tallest trees

TL;DR

This paper proposes a nanofluidic model to explain how water can ascend to the heights of the tallest trees, overcoming limitations of classical theories by considering nanoscale effects like disjoining pressure.

Contribution

It introduces a novel nanofluidic approach incorporating disjoining pressure to explain water ascent in tall trees, extending beyond traditional cohesion-tension theory.

Findings

Nanolayers of water can sustain negative pressure at high altitudes.

Disjoining pressure enables stable water layers in xylem microtubes.

Model explains maximum tree height limits based on nanolayer stability.

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.