The recording and analysis of sounds produced by plants have been achieved for the first time. These sounds, akin to the popping of kernels of corn, are emitted at high frequencies beyond the range of human auditory perception but at a similar volume as that of human speech.
The researchers who conducted the study verified that plants, at least those belonging to the categories examined, tend to produce these sounds when they are subjected to physiological stress, and each plant and type of stress elicits a distinct and identifiable sound. Despite being imperceptible to humans, the sounds emitted by plants can be potentially audible to various animals such as bats, mice, and many insects.
The discovery was made by a team of scientists from Tel Aviv University in Israel, including Lilach Hadany, Yossi Yovel, Itzhak Khait, and Ohad Lewin-Epstein.
Previous studies have shown that vibrometers attached to plants can record their vibrations. However, the current study explored whether these vibrations can become airborne sound waves, i.e., sounds that can be recorded from a distance. In the first phase of the study, tomato and tobacco plants were primarily analyzed, but other plants such as cacti and wheat and corn plants were also tested.
The researchers placed the plants in a speaker box located in a quiet, isolated basement devoid of background noise. Ultrasonic microphones were placed at a distance of about 10 centimeters from each plant to record sounds at frequencies ranging from 20 to 250 kilohertz, which is beyond the human range of hearing (16 kilohertz is the maximum frequency detected by an adult human). The plants were then exposed to various conditions that could cause physiological stress, such as not watering them for five days, cutting the stem, or keeping them intact, to test whether they produced sounds and if these sounds were influenced by the plant’s state.
A cactus surrounded by microphones. (Photo: Tel Aviv University. CC BY)
The recordings have demonstrated that the flora engaged in the trial have emitted noises at frequencies that range from 40 to 80 kilohertz. Under non-stressful circumstances, the plants produced less than one sound per hour on average. In contrast, the plants under stress, including those that were dehydrated or injured, emitted numerous noises every hour.
A set of artificial intelligence algorithms specifically designed for this purpose was utilized to analyze the recordings. The algorithms were educated to differentiate between various plants and sounds. They were ultimately capable of determining the plant’s identity and the degree of stress indicated by the sounds. Furthermore, the algorithms could categorize the sounds produced by the plants even in an environment such as a greenhouse, with a high degree of background noise.
The conclusions drawn from this study suggest that the sounds created by plants are abundant and convey information about their condition. It is presumed that nearby animals, such as bats, rodents, and insects, which can detect ultrasound, might detect the sounds generated by plants and extract pertinent information. It is also possible that other plants can hear these sounds.
“An idyllic meadow of flowers can apparently be a very noisy place, despite the fact that we are unable to hear this noise,” Hadany stated ironically.
The study’s title is “Sounds emitted by plants under stress are airborne and informative.” It has been published in the academic journal Cell.
In future studies within this line of research, Hadany and his colleagues will continue to search for answers to several intriguing questions: What is the underlying mechanism of plant sound generation? How do insects with ultrasonic hearing react to sounds made by plants? Do plants pick up the sounds emitted by their neighbors? And many others. (Fountain: NCYT by Amazings)
