HQ Team
April 3, 2023: Israeli researchers found that plants emit a distinct high-frequency sound similar to human speech that is beyond the hearing range of the ear.
“We found that plants usually emit sounds when they are under stress and that each plant and each type of stress is associated with a specific identifiable sound,” according to researchers at Tel Aviv University.
For the first time, scientists recorded and analysed the sounds emitted by plants. “While imperceptible to the human ear, the sounds emitted by plants can probably be heard by various animals, such as bats, mice, and insects.”
The click-like sounds, like popcorn popping, are emitted at a volume similar to human speech.
The study was led by Prof. Lilach Hadany from the School of Plant Sciences and Food Security at the Wise Faculty of Life Sciences and published in Cell.
Vibrometers
“From previous studies, we know that vibrometers attached to plants record vibrations. But do these vibrations also become airborne soundwaves – namely, sounds that can be recorded from a distance? Our study addressed this question, which researchers have debated for many years,” Prof Hadany said.
In the first stage of the study, the researchers placed plants in an acoustic box in a quiet, isolated basement with no background noise.
Ultrasonic microphones recording sounds at 20-250 kilohertz frequencies — the maximum frequency detected by a human adult are about 16 kilohertz — were set up at about 10cm from each plant.
The study mainly recorded sounds emitted by tomato and tobacco plants, wheat, corn, cactus, and henbit.
“Before placing the plants in the acoustic box, we subjected them to various treatments: some plants had not been watered for five days, in some the stem had been cut, and some were untouched,” Prof Hadany said.
Stressed plants
The aim was to test whether the plants emit sounds and whether these sounds are affected in any way by the plant’s condition.
The recordings indicated that the plants emitted sounds at 40-80 kilohertz frequencies.
Unstressed plants, on average, emit less than one sound per hour, while the stressed plants – dehydrated and injured – emit dozens of sounds every hour.
Specially developed machine learning algorithms analyzed the recordings. The algorithms learned to distinguish between different plants and different sounds.
The researchers identified the plant and determined the type and level of stress from the recordings. The algorithms identified and classified plant sounded even when the plants were placed in a greenhouse with a great deal of background noise.
In the greenhouse, the researchers monitored plants subjected to dehydration over time and found that the number of sounds they emitted increased to a certain peak and then diminished.
“In this study, we resolved a very old scientific controversy: we proved that plants emit sounds!
Water scarcity, injury
“Our findings suggest that the world around us is full of plant sounds and that these sounds contain information – for example, about water scarcity or injury,” Prof Hadany said.
Scientists assume that in nature, the sounds emitted by plants are detected by creatures, such as bats, rodents, insects, and possibly other plants that can hear the high frequencies and derive relevant information.
“We believe that humans can also utilize this information, given the right tools, such as sensors that tell growers when plants need watering.
“An idyllic field of flowers can be a rather noisy place. It’s just that we can’t hear the sounds!” Hadany said.
Researchers plan to explore a range of questions, such as the mechanism behind plant sounds. How do moths detect and react to sounds emitted by plants? Do other plants also hear these sounds?
