Stressed plants emit sounds that can be heard by animals

Stressed plants emit sounds and these noises can be heard by animals, a new study finds.

The frequency of these noises ware too high for humans to detect, but researchers believe they can be heard by insects, other mammals, and possibly other plants.

According to the research, “stressed” plants that have not been watered for several days or had their stems cut emit sounds.

The research was carried out by a team in Isreal and published in the journal Cell on 30 March.

The sounds occurred when the tomato and tobacco plants were dehydrated or had their stems severed.

Senior author Lilach Hadany, an evolutionary biologist and theoretician at Tel Aviv University, said: “Even in a quiet field, there are actually sounds that we don’t hear, and those sounds carry information.”

“There are animals that can hear these sounds, so there is the possibility that a lot of acoustic interaction is occurring,” Professor Hadany added.

The experiments were carried out in a soundproofed acoustic chamber and then in a noisier greenhouse environment.

Researchers trained a machine-learning algorithm to differentiate between plants that were not stressed, thirsty plants, and cut plants.

What do stressed plants sound like?

When these plants were put in a stressful situation, they emitted sounds which resembled popping or clicks.

A single stressed plant gave off around 30-50 of these clicks per hour at seemingly random intervals, but unstressed plants made far fewer sounds.

“When tomatoes are not stressed at all, they are very quiet,” Professor Hadany said.

The plants not getting enough water began emitting noises before they were visibly dehydrated.

After five days of no water, the sounds began to peak and eventually, the sounds slowly faded as the plants dried up completely. The types of sounds also differed depending on the cause of stress.

The team also recorded various other plant species.

“We found that many plants – corn, wheat, grape, and cactus plants, for example – emit sounds when they are stressed,” Professor Hadany said.

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‘Other organisms could’ve evolved to hear these sounds’

The reason for these noises remains unclear, but the study suggests that it might be due to the formation and bursting of air bubbles in the plant’s vascular system – a process known as cavitation.

Speaking on plants and their communication with their environment, Professor Hadany said “it’s possible that other organisms could have evolved to hear and respond to these sounds”.

“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,” she added.

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The authors also found that these sounds could benefit other plants, as previous research has found plants can respond to sounds and vibrations.

“We know that there’s a lot of ultrasound out there every time you use a microphone, you find that a lot of stuff produces sounds that we humans cannot hear – but the fact that plants are making these sounds opens a whole new avenue of opportunities for communication, eavesdropping, and exploitation of these sounds,” said co-senior author Yossi Yovel, a neuro-ecologist at Tel Aviv University.

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