The sounds emitted by plants are ultrasonic, beyond the range of human hearing.
For the first time in the world, researchers at Tel Aviv University have recorded and analyzed sounds clearly emitted by plants. The clicks, similar to the popping of popcorn, are emitted at a volume similar to that of human speech, but at high frequencies, beyond the hearing range of the human ear. Plant sounds are informative: they are made mainly when the plant is under stress and contain information about its state.
The researchers mainly recorded tomato and tobacco plants, but also wheat, corn and cacti. This means that an idyllic field of flowers can be quite a noisy place, even if we cannot hear the sounds.
The sounds that plants make when they are under stress vary, and each plant and each type of stress is associated with a specific, identifiable sound. Although imperceptible to the human ear, the sounds emitted by plants can probably be heard by several animals, such as bats, mice and insects.
The study was conducted and led by researchers at Tel Aviv University. The teawork was published in the prestigious scientific journal Cell. From previous studies it was known that the vibrations were recorded when the vibrometers were attached to the plants, but until now it had not been verified whether these vibrations were converted into sound waves carried by the air, that is, into sounds that can be recorded at a distance. This is a question that researchers have debated for many years.
In the first phase of the study, the researchers placed the plants in a speaker box in a quiet, isolated basement with no background noise. Ultrasonic microphones were placed at a distance of about 10 cm from each plant, recording sounds at frequencies from 20 to 250 kilohertz (the maximum frequency detected by an adult human being is about 16 kilohertz).
Before placing the plants in the acoustic box, they were subjected to various treatments to stress them: some plants were not watered for five days, in some the stems were cut, while others were intact. The intention was to test whether plants made sounds and whether these were somehow affected by the state of the plant. The recordings indicated that the plants made sounds at frequencies from 40 to 80 kilohertz. Unstressed plants made less than one sound per hour, on average, while stressed, dehydrated or injured plants made dozens of sounds every hour.
The recordings thus collected were analyzed using machine learning (AI) algorithms specially developed for the experiment. The algorithms learned to distinguish between different plants and different types of sounds, and eventually were able to identify the plant and determine the type and stress level of the recordings. Furthermore, the algorithms identified and classified plant sounds even when the plants were in a greenhouse with a lot of background noise. In the greenhouse, the researchers followed the dehydrated plants over time and found that the amount of noise they made increased up to a certain peak and then decreased.
The researchers believe that humans can use this information if they have the right tools, such as sensors that tell growers when to water their plants.
REFERENCE
The sounds emitted by plants under stress are airborne and informative.