Plants emit acoustic signals when they are in stressful situations, according to a study led by Tel Aviv University (Israel), revealing a possible communication mechanism between plants and animals.
Although the signals are imperceptible to the human ear because their frequency is in the ultrasonic range, they can be instructive for other species and play a role in ecosystems, the research authors claim in the journal Cell, where they present their findings Today.
The ultrasound emitted by plants has a volume similar to that of a human conversation, the study authors report. They sound, to those who can hear them, similar to the popping of the small plastic bubbles used in packaging when they rupture.
Plants produce acoustic information in the ultrasonic range that cannot be heard by the human ear.
In stressful situations, such as drought or infection, plants change color or shed molecules that signal other species whether or not they are interested in the plant, such as laying its eggs or eating its leaves, the researchers recall. However, whether they also produce acoustic signals in addition to the sound of the wind in the plant has not yet been investigated.
“Plants constantly interact with insects and other animals, and many of these organisms use sound to communicate; It would be very suboptimal for plants not to use sounds at all,” says Lilach Hadany, the research leader, in a statement.
To illustrate, Hadany and his team subjected tomato and tobacco plants to two different stresses, in one case by depriving them of water and in another case by cutting off their stems. The experiments were carried out using ultrasound pick-up microphones placed at a distance of 3 to 5 meters from the plants.
The volume is similar to that of a human conversation and the sound is similar to that of the plastic bubbles in packaging when they break
The results show that both tomato plants and tobacco plants make more noise when they are stressed than when they are well cared for, and that the noises they make change depending on the type of stress they are experiencing.
Tomato plants emit an average of 35 clicks per hour when they are short of water, 25 when a stem is cut off, and less than 1 when they are doing well. The tobacco plants that suffer the most yield 11 when lacking water, 3 when a stem is cut, and also less than 1 when doing well.
An artificial intelligence program has learned to correctly recognize which of the two plants it came from and what kind of stress is acting on a given click, suggesting that “sounds carry information,” the researchers write in Cell.
The sound comes from the stems of the plants; No audio was recorded from logs
Experiments with wheat, corn, grapevines, stinging nettles and a species of cacti have shown that these species also make more noise in stressful situations. Given these results, ‘we expect many plants to emit sounds, but the diversity and properties of these sounds remain to be explored,’ the researchers point out.
The sound comes from the stems of the plants and appears to be produced by a phenomenon of cavitation – that is, the formation of cavities in the stem. On the contrary, no sounds were recorded from the wooden parts of the vine or from the trunk of the almond trees.
“It’s an emerging and controversial issue,” says Maria Lois, director of the Center for Agricultural Genomics Research (CRAG), who did not participate in the research. “The fact that plants emit sounds in response to stress appears to be related to a mechanical problem.”
The authors of the research never claim that plants have the will to produce sound – something that would be inexplicable since will is a function of the nervous system that plants lack.
Farmers could record plant sounds to optimize water use
But “it’s possible that other organisms evolved to hear and respond to these sounds,” says Lilach Hadany. “For example, a moth that is going to lay eggs on a plant, or an animal that is going to eat a plant, might use sound to guide its decision.”
“Even in a silent field, there are sounds that we don’t hear,” says Hadany, according to the researcher. “There are animals that can hear these sounds, so there’s a chance that a lot of acoustic interactions are happening.”
Other plants could also react to sounds of plant origin. Several recent studies have found that some plants regulate the activity of their genes in response to insect-made sounds, for example increasing nectar production in flowers when pollinators approach.
Even in a quiet field there are sounds we don’t hear.”
Lilach Hadany Director of Research
According to the hypothesis of the researchers at Tel Aviv University, the function of the sounds that plants make in stressful situations is to warn their fellow species so that they prepare for a drought situation, for example.
In the future, farmers may also be interested in listening to the sounds of plants to identify those experiencing stress and to optimize water use, the researchers say.
“The most direct potential application of this research would be a sensor, which could be very important for precision agriculture,” says Maria Lois. “It’s definitely a topic to look at.”