Stressed plants make sounds that can be heard by animals, a new study finds.
The frequencies of these noises are too high for humans to detect, but the researchers believe that insects, other mammals, and possibly other plants can hear them.
According to the study, “stressed” plants that haven’t been watered for several days or whose stems have been cut off will make the sound.
The research, conducted by a team in Israel, was published March 30 in the journal Cell.
The sound is made when tomato and tobacco plants are dehydrated or stems are cut.
“Even in the quiet realm, there are actually sounds that we can’t hear, and those sounds carry information,” said senior author Lilach Hadany, an evolutionary biologist and theorist at Tel Aviv University.
Professor Hadany added: “Some animals can hear these sounds, so there could be a lot of acoustic interactions happening.”
Experiments were performed in a soundproof room and then in a noisy greenhouse environment.
The researchers trained a machine learning algorithm to distinguish between plants that were not stressed, those that were thirsty, and those that were felled.
What do stressed plants sound like?
When these plants are in a stressful environment, they make a sound that resembles a pop or click.
A stressed plant made about 30 to 50 of these clicks an hour, at seemingly random intervals, but an unstressed plant made far fewer.
“When the tomatoes are completely free of stress, they are very quiet,” Professor Hadani said.
Plants that don’t get enough water start to screech before they become visibly dehydrated.
After five days without watering, the sound started to peak and eventually died down as the plant dried out completely. The type of sound also varies depending on the cause of the stress.
The team also documented various other plant species.
“We found that many plants – such as corn, wheat, grape and cactus plants – produce sounds when they are stressed,” Professor Hadani said.
“Other organisms may have evolved to hear these sounds”
The reason for these noises is unknown, but research suggests it may be due to the formation and collapse of air bubbles in the plant’s vascular system – a process known as cavitation.
Speaking about plants and their communication with their environment, Professor Hadany said: “Other organisms may have evolved to be able to hear and respond to these sounds”.
“For example, moths intending to lay eggs on plants or animals intending to eat plants could use sound to help guide their decisions,” she added.
Read more on Sky News:
Deadly plant fungus infects humans in ‘world first’
The authors also found that these sounds may benefit other plants, since previous research has found that plants can respond to sound and vibrations.
“We know that every time you use a microphone there’s a lot of ultrasonic waves, and you’ll find a lot of things that create sounds that we humans can’t hear – but the fact that plants make these sounds opens up a whole new avenue of opportunity for us to communicate, eavesdrop and Harness those sounds,” says co-senior author Yossi Yovel, a neuroecologist at Tel Aviv University.