When you walk through a quiet field, you wouldn't suspect that the plants around you are emitting ultrasonic clicks. Yet recent research shows that stressed plants produce sounds at frequencies inaudible to us. These noises, comparable to popping bubbles, could be a means of communication.
A team of biologists from Tel Aviv University recorded tomato and tobacco plants under different conditions. The sounds, described in the journal
Cell, reach about 60 decibels, the volume of a normal conversation.
Illustration image Unsplash
To capture these ultrasounds, the researchers placed microphones in a soundproof chamber and then in a greenhouse with ambient noise. The plants were subjected to two types of stress: water deprivation and stem cutting. A machine learning algorithm then analyzed the recordings.
Surprisingly, it could distinguish healthy plants from stressed ones, and even identify the cause of stress. The results show that dehydrated plants emit about 30 to 50 sounds per hour, compared to near silence in healthy plants.
The researchers attribute these clicks to cavitation, a process where air bubbles form and burst in the plant's conducting vessels. This phenomenon occurs when the plant lacks water or suffers an injury. The sounds begin even before visible signs of stress, such as wilting, appear. Moreover, each type of stress produces a distinct sound pattern. The researchers even managed to differentiate the sounds emitted by tomatoes from those of tobacco.
Could other organisms hear them and react? Moths, for example, use ultrasound for communication. It is possible that they pick up distress signals from plants to choose where to lay their eggs. Similarly, neighboring plants might perceive these vibrations and adjust their defenses.
Credit: Ohad Lewin-Epstein
In agriculture, this discovery opens promising prospects. Microphones installed in fields could detect water stress in crops early. Farmers could then irrigate more precisely, saving water and improving yields.
This non-invasive and inexpensive method could complement soil sensors. Additionally, by identifying diseases before they become visible, it would allow faster and more effective interventions.
The researchers now plan to study who listens to these ultrasounds in nature. They are testing the reactions of animals and other plants in multiple environments. Understanding this acoustic network could reveal unknown ecological interactions.