Science Writing (EFE).- When plants are stressed, they emit sounds at a frequency that humans cannot hear, but which resemble the bursting of bubble wrap, which can be detected at more than a meter and its volume is similar to that of a normal conversation.
Research from Tel Aviv University published by Cell has studied these sounds in stressed tomato and tobacco plants, either due to lack of watering or because a stem has been cut.
The frequency of those sounds is too high for our ears to pick up, but there are animals and plants that “can hear these sounds, so there’s a chance there’s a lot of acoustic interaction going on,” said study coordinator Lilach Hadany. from Tel Aviv University.
Although ultrasonic vibrations have already been recorded in plants, this is the first evidence that they are transmitted through the air, a fact that makes them more relevant to other organisms in the environment, the publication explains.
Plants interact with insects and other animals, many of which use sound to communicate, “so it would be highly suboptimal for plants not to use sound at all,” Hadany said.
The sounds of plants: “Pops” or “clicks”
The researchers used microphones to record healthy and stressed tomato and tobacco plants, first in a soundproof acoustic chamber and then in a noisier greenhouse.
After recording the plants, they trained a machine learning algorithm to differentiate between stressed and unstressed plants, as well as between thirsty and cut plants.
The team discovered that stressed plants make more sounds than non-stressed ones, and that these sound like “pops” or clicks.
A single stressed plant emits between 30 and 50 of these clicks per hour at what seem like random intervals, while healthy ones make fewer sounds. “When the tomato plants are not stressed they are very, very quiet,” Hadany noted.
The types of sounds emitted differed depending on the cause of the stress, and the algorithm was able to differentiate between dehydration and cutting stress, as well as discern whether the sounds were coming from a tomato or tobacco plant.
Plants stressed by lack of water emit sounds before they are visibly dehydrated and the frequency reaches its maximum after five days without watering, after which it decreases and ends up completely drying up.
Although the study focused on tomato and tobacco plants, because they are easy to grow in a standard laboratory, the team also recorded a variety of other plant species.
“We discovered that many plants – corn, wheat, grapes and cacti, for example – make sounds when they are stressed,” Hadany said.
The exact mechanism of the noises is not clear.
The exact mechanism of these noises is not clear, but the researchers suggest that it could be due to the formation and bursting of air bubbles in the vascular system of the plant, a process called cavitation.
It is also not known whether they make these sounds to communicate with other organisms, but the fact that they exist has major ecological and evolutionary implications.
“It is possible that other organisms have evolved to hear and respond to these sounds”, for example -explained the researcher- “a moth that intends to lay eggs on a plant or an animal that intends to eat a plant could use the sounds to guide their decision ”.
Other plants could also be listening and benefiting from the sounds. Previous studies have shown that plants increase the concentration of sugar in their nectar when they “hear” the sounds made by pollinators, and that they change their gene expression in response to the sounds.
“If other plants have information about stress before it actually occurs, they could prepare for it,” Hadany said.
According to the authors, the sound recordings of the plants could be used in agricultural irrigation systems to monitor the hydration status of crops and help distribute water more efficiently.
The fact that plants produce these sounds “opens up a whole new avenue of opportunities for communication, listening and exploiting these sounds,” said another of the authors of the research, Yossi Yovel of Tel Aviv University.
The team is now studying the responses of other organisms, both animal and plant, to these sounds, and the researchers’ ability to identify and interpret sounds in completely natural settings.