Les arbres peuvent-ils communiquer entre eux ?

Can trees communicate with each other?

Bastien Castagneyrol , Inrae

Trees can communicate . Not like in the movie Avatar of course, but in their own way, they exchange information with each other, and with the microbes, insects or birds that live in their branches and around their roots. Most of the time, they communicate to defend themselves against attacks by herbivorous insects or parasitic fungi.

Let's first agree on the meaning of words, it's always useful in science. For there to be communication between two organisms (between two trees, or between a tree and a bird), a signal must be emitted by the transmitter (the tree), it must be conveyed by a channel of communication to a receiver (another tree, or a bird), and that the receiver modifies its behavior to its advantage and to the advantage of the sender.

In trees, the signal used for communication is a chemical signal carried by small molecules. This signal passes either through the air or through the roots and the microscopic filaments of fungi which extend them and which can connect the trees to each other (the fungi associated with the roots of trees are called mycorrhizae). To put it simply, let's say that trees use both wifi to communicate with each other and with certain animals, and fiber to communicate with other trees.

Trees communicate with each other...

The communication of trees plays an essential role in their response to attack by herbivorous insects. When a caterpillar eats a leaf, it tears it and leaves a little bit of saliva in the wound. The leaf is able to recognize this wound and can know that it was caused by a herbivore. In this case, a cascade of chemical reactions takes place in the attacked leaf. This cascade results in the production of so-called volatile organic compounds (VOCs).

VOCs are chemical messengers that diffuse into the air. They are the ones carrying the signal “ALERT! We are under attack!" When a leaf that has not been attacked perceives this message, it prepares a defense arsenal before the attacker arrives, just in case: it begins to accumulate the products that will allow it to produce toxic molecules for herbivores. And it works ! By carrying out experiments on the willow , researchers have shown that if caterpillars are fed two types of leaves, some which have received a warning message and others which have not, the leaves prepared to attack took 20-40% less damage.

…and with their allies

But that's not all: COVs also allow trees to recruit bodyguards. The scientist Elina Mäntylä and her colleagues have for example shown this with tits . They prepared two batches of pine branches and placed sawfly larvae (herbivorous insects that eat pine needles) on one of them. They then removed the larvae by enclosing the branches in opaque plastic tubes, the ends of which were closed with fabric. They then observed the behavior of tits that they had carefully captured for the experiment.

Why tits? Because they are insectivorous birds that love sawfly larvae! You guessed it, the tits were mainly attracted to the tubes that held the branches that had been attacked by the insects. Yet they couldn't see what was inside. It is therefore that they have perceived a signal emitted by the only branches attacked: the COV.

Results of Elina Mäntylä's experiment. Elina Mäntyla , Author provided

In this case, the benefit for the sender is clear: the aggressor can be eliminated. The benefit for the receiver is also clear: the transmitter signals the presence of food. It's communication, between a tree and a bird.

Questionable consequences at the ecosystem level

Scientists can create experimental conditions that demonstrate the reality of tree communication. But if the attack of a leaf by a caterpillar triggers the emission of a chemical signal by the attacked tree, when we imagine the quantity of leaves and caterpillars present in a forest, we can easily apprehend the olfactory cacophony in which bathes the trees and their allies. Under these conditions, what is the importance of this communication in forest ecosystems?

In a study conducted on beech , researchers showed that chemical communication is only effective within a radius of 5 meters around the source of the VOCs. If we add to that the fact that VOCs are mostly very small molecules that degrade rapidly in the air, we suspect that if the trees communicate with each other through this "chemical wifi", it's just with their nearest neighbor.

There are some clues to say that we could exploit this "chatter" of trees to protect forests against attacks by herbivorous insects, but as often in ecology, we must be careful not to extrapolate too much the discoveries which are done in the lab, you have to take the time to check that "it works" also outside the lab, in a much, much more complex real world. Great discoveries in perspective!

This article is republished from The Conversation under a Creative Commons license. Read the original article .

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