Microphones are set up to listen to this cactus plant. Photo courtesy of Tel Aviv University
March 30 (UPI) -- Plants are talking, but people didn't know because the frequency is too high for he human ear, according to researchers at Israel's Tel Aviv University, who managed to record and analyze the sounds for the first time.
The study about the sounds that plants make was published Thursday in the scientific journal Cell.
The research, led by Lilach Hadany from the School of Plant Sciences and Food Security at the Wise Faculty of Life Sciences, found that plants often give of ultrasonic sounds, often when they are stressed.
The authors were able to record sound, similar to popcorn popping, of mostly tomatoes and tobacco plants. They also identified sounds made by cacti, corn, henbit and wheat, as well.
Even though the sounds are emitted at roughly the same volume as human speech, they are at such high frequencies that they are never picked up by the human ear, the researchers said.
"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," the researchers said.
"While imperceptible to the human ear, the sounds emitted by plants can probably be heard by various animals, such as bats, mice, and insects."
In the study's first stage, researchers placed plants in an acoustic box in a quiet, isolated basement with no background noise. Ultrasonic microphones recording sounds at frequencies of 20 to 250 kilohertz were set up to listen. The maximum frequency detected by a human adult is about 16 kilohertz.
"From previous studies, we know that vibrometers attached to plants record vibrations, Hadany said. "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 been debating for many years."
Hadany performed the study with Yossi Yovel, head of the Sagol School of Neuroscience and faculty member at the School of Zoology and the Steinhardt Museum of Natural History, and research students Itzhak Khait and Ohad Lewin-Epstein.
They were joined by researchers from the Raymond and Beverly Sackler School of Mathematical Sciences, the Institute for Cereal Crops Research and the Sagol School of Neuroscience at Tel Aviv University
The recordings were analyzed by specially developed machine learning algorithms that learned how to distinguish between different plants and different types of sounds. It was ultimately possible to identify the plant and determine the type and level of stress from the recordings.
"In this study, we resolved a very old scientific controversy: we proved that plants do emit sounds," Hadany said. "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.
"We assume that in nature the sounds emitted by plants are detected by creatures nearby, such as bats, rodents, various insects, and possibly also other plants -- that can hear the high frequencies and derive relevant information," she said.
"We believe that humans can also utilize this information, given the right tools -- such as sensors that tell growers when plants need watering. Apparently, an idyllic field of flowers can be a rather noisy place. It's just that we can't hear the sounds."