Plants that experience stress, from dehydration or cutting their stems, emit sounds, they tracked down investigators in Israel and recorded them.

According to the published research in the journal Cellthe frequency of these noises is too high for our ears to detect, but they can probably be heard by insects, other mammals, and possibly other plants.

The researchers used microphones to record healthy and stressed tobacco and tomato plants, first in a soundproof acoustic chamber and then in a noisier greenhouse environment. They stressed the plants in two ways: by not watering them for several days and cutting their shoots. After recording the plants, the researchers trained a machine learning algorithm to differentiate the unstressed plants from the thirsty and cut plants.

The team found that stressed plants emitted more sounds than non-stressed plants. Plant sounds resemble clicks, and an individual stressed plant emits about 30-50 such sounds per hour at seemingly random intervals, while non-stressed plants emit far fewer sounds.

The water-stressed plants started making noises before becoming visibly dehydrated, and the frequency of the sounds peaked after five days without water before decreasing again as the plants dried out. The types of sound emitted varied according to the cause of the stress. The machine learning algorithm was able to accurately differentiate dehydration and stress from cutting, and could also distinguish whether the sounds were coming from a tomato or tobacco plant.

Although the research focused on these two plants, due to their ease of growing and standardization in the laboratory, the research team also recorded a variety of other species. “We found that many plants, for example corn, wheat, grapes, and cacti, emit sounds when they are stressed,” says Lilah Hadani, lead author of the study, an evolutionary biologist and theorist at the University of Tel Aviv.

Although ultrasonic vibrations from plants have been recorded in the past, this is the first time they have been shown to be airborne, making them more relevant to other organisms in the environment. The exact mechanism behind these noises is not clear, but researchers speculate that it may be due to the formation and bursting of air bubbles in the plant’s vascular system, a process called cavitation.

It is also unclear whether plants produce these sounds to communicate with other organisms or not, but the fact that these sounds exist has major ecological and evolutionary implications. “It is possible that other organisms could evolve to hear and respond to these sounds,” says Lilah Hadani, adding: “For example, a moth intending to lay eggs on a plant or an animal intending to eat a plant could use the sounds to help their decision.”

Other plants could also hear and benefit from the sounds. It is known from previous research that plants can respond to sounds and vibrations, and studies have shown that they change their gene expression in response to sounds. Lilah Hadani and other members of the research team had previously found that plants increase the concentration of sugars in their nectar when they “hear” the sounds pollinators make.

The study’s authors say plant recordings could be used in agricultural irrigation systems to monitor crop hydration status and help distribute water more efficiently.

Link to the scientific publication: