The cactus absorbs water and stores it at its roots -

© Tomi Siivonen / Pixabay

  • Mimicking the retention system of cacti could lead to the development of new techniques for collecting water in arid regions, according to our partner The Conversation.

  • To achieve this, a Belgian team models cactus thorns in 3D to observe the circulation of water on its architecture.

  • The analysis of this phenomenon was carried out by Joséphine Van Hulle, assistant specializing in microfluidics at the University of Liège.

Here is a cactus thorn imitation made with a 3D printer:

Photo © Joséphine Van Hulle

On the tip of the cone, a droplet is deposited, imitating the water which condenses naturally on the tip of cactus thorns, thanks to rain, fog, and dew, but also thanks to the water naturally present in air (humidity).

This photograph is a superposition of several images: a drop is deposited at the level of the tip, then it moves towards the base of the cone, from left to right, passively, i.e. the drop moves on its own, without any external addition of energy.

During this advance, the drop is photographed at different times: the first image of the drop, at the tip of the cone, was taken 45 seconds before the last image of the drop, then close to the base of the cone.

Why study water transport on very small structures?

Throughout biological evolution, flora and fauna have been able to take advantage of their environments, even in the most hostile regions.

Deserts are areas where rainfall is scarce and drought is usual.

And yet, life is present there, there are both animals and plants, including many cacti.

For some of these species, notably the cactus

Opuntia microdasys

, the thorns act like small watering cans, collecting water naturally present in the air and redistributing it to the plant.

Opuntia microdasys from the greenhouses of the Hanging Gardens of Le Havre © F. Bisson / Flickr CC BY-SA 2.0

The collection of water by cactus thorns can be broken down into three physical phenomena.

First of all, the water present in the air condenses at the tip of the spine thanks to the phenomenon of "heterogeneous nucleation".

Then, the water collects until it forms a drop, this is the growth phase.

This drop is transported towards the plant thanks to the particular geometry of the spine by "capillary transport".

From this, we learn that it is necessary to meet two conditions to collect water, we need a structure allowing the condensation of water, but also a structure allowing to transport the drop of water formed in a determined direction.

Our “Plants” file

In the laboratory of the

Group of Research and Applications in Statistical Physics

at the University of Liège, we are physically characterizing this liquid transport as observed on cactus spines.

This research, based on a biomimetic approach, could lead to the development of new techniques for collecting water in arid regions and thus supplying water to the populations who live there.

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This analysis was written by Joséphine Van Hulle, assistant specializing in microfluidics at the University of Liège.


The original article was published on The Conversation website.

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  • Water

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