Plants create 'pop' records in the studio when dehydrated or stems torn

This is the first evidence that stressed plants emit airborne sounds that can be detected over a meter away.
Sade Agard
This is a photo of three tomato plants whose sounds are being recorded in a greenhouse.
This is a photo of three tomato plants whose sounds are being recorded in a greenhouse.

Ohad Lewin-Epstein 

What does a plant stressed from dehydration or severed stems sound like? A bit like bubble wrap being popped, according to new research published in Cell on March 30.

Although ultrasonic vibrations from plants have previously been observed, this is the first evidence that they are airborne. While the frequency is too high for humans to detect, being airborne makes them that much more relevant for nearby species (that might be listening!).

Are plants making beats?

"Plants interact with insects and other animals all the time, and many of these organisms use sound for communication, so it would be very suboptimal for plants to not use sound at all," said senior author Lilach Hadany in a press release, an evolutionary biologist and theoretician at Tel Aviv University.

The researchers recorded healthy and stressed tomato and tobacco plants using microphones, first in a soundproofed acoustic laboratory and later in a noisier greenhouse setting.

They used two techniques to stress the plants: chopping their stems and depriving them of water. After being recorded, the researchers taught a machine-learning algorithm to distinguish between healthy, thirsty, and cut plants.

The team discovered that stressed plants produce more noise than non-stressed plants. The noises resembled pops or clicks, with a single stressed plant producing between 30 and 50 of these clicks each hour at what seemed to be random intervals. Unstressed plants made much fewer sounds. 

"When tomatoes are not stressed at all, they are very quiet," said Hadany.

The machine-learning algorithm could distinguish between dehydration and cutting-related stress accurately, as well as between sounds coming from tobacco or tomato plants.

Plants create 'pop' records in the studio when dehydrated or stems torn
A cactus in a recording session

"We found that many plants—corn, wheat, grape, and cactus plants, for example—emit sounds when they are stressed," she added.

Why are plants making noises?

The precise cause of these noises is unknown. Still, the researchers hypothesize that cavitation—the production and bursting of air bubbles in the plant's vascular system—might be to blame.

Although it is uncertain if the plants are making these noises to communicate with other living things, the researchers argue that their existence has significant ecological and evolutionary ramifications. "It's possible that other organisms could have evolved to hear and respond to these sounds," explained Hadany.

"For example, a moth that intends to lay eggs on a plant or an animal that intends to eat a plant could use the sounds to help guide their decision."

What if other plants are listening too? "If other plants have information about stress before it actually occurs, they could prepare," said Hadany.

The team explained how plant sounds in agricultural irrigation systems may be utilized to monitor crop hydration levels and facilitate more effective water distribution.

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