Surprising Study: Plants Make Sounds When Stressed

Tomatoes that urgently need water or are stressed for other reasons show this with noises. Hard to believe, but that's the result of a study by scientists from Israel's Tel Aviv University.

Plants communicate in different ways. This is well known, at least since the now famous forester Peter Wohlleben (pictured) published 'The Secret Life of Trees' as a film and book. But it was previously unclear whether plants really make targeted noises.

The researchers from Tel Aviv University in Israel explain that they were able to show for the first time how tomatoes and tobacco plants sound and why they emit sounds.

Stressed plants show altered appearance, including changes in color, smell, and shape. However, airborne noise emanating from stressed plants has not yet been studied.

The scientists explain their study in the journal Cell as follows: "Here we show that stressed plants emit airborne noise that can be remotely recorded and classified. We recorded ultrasonic sounds from tomato and tobacco plants in an acoustic chamber and in a greenhouse and while monitoring the physiological parameters of the plants."

The sounds were recorded with microphones placed 10 centimeters from the plants, with each plant being picked up by two microphones simultaneously. The scientists recorded ultrasonic noises in the range of 20 to 100 kilohertz.

"We have developed machine learning models that can be used to identify the condition of plants, including the degree of desiccation and injury, just from the sounds emitted. These informative sounds can also be perceived by other organisms," said the scientists according to the journal Cell.

"The sounds in the ultrasonic range could be heard from a distance of three to five meters by many mammals and insects," the researchers explain. "This could lead to a moth, for example, deciding after hearing the noise not to lay its eggs in a water-stressed plant."

The researchers were even able to determine the type of plant stress from the sounds. They developed a model that could distinguish whether the stress was caused by wind, rain, drought or a cut.

The tones varied in intensity and frequency. Dry tobacco, for example, makes "louder noises" than tobacco that is being cut.

We humans cannot hear the sounds because the frequencies are too high for our hearing. However, the researchers have modified the audio signals to make them perceptible to humans as well. You can hear a pop that is a bit reminiscent of bursting bubble wrap.

For comparison, the team also looked at undisturbed specimens. The result: According to the study, stressed plants emitted significantly more noise than healthy ones.

Under stress, they made around 30 to 50 tones per hour. "If tomatoes are not stressed at all, they are very quiet," Lilach Hadany, an evolutionary biologist at Tel Aviv University, told dpa.

The researchers assume that the cause of this phenomenon takes place inside a plant. Studies have shown that so-called cavitation occurs in plants that suffer from drought stress.

Roughly speaking, air bubbles form in the vascular system, which expand and collapse again. This leads to vibrations.

This work opens new avenues for understanding plants and their interactions with the environment, and could have implications for agriculture.

The researchers also successfully recorded sounds from several other crops, including wheat and corn, both extremely important to the global diet, according to the Cell report.

"It is therefore likely that noises will also be emitted during harvesting (in the form of cutting)," said Lilach Hadany, an evolutionary biologist at Tel Aviv University, to DPA.

According to the research team, this evidence could open up a whole new field in precision farming, where farmers could hear the sounds of plants that are too dry, for example.

In the study, the scientists explain that plant noise emissions could offer a way to monitor water and possibly also disease status of plants. Questions that are of crucial importance in agriculture.

More precise irrigation can save up to 50% in water expenses and increase yield, which would have economic implications. This is the conclusion of the scientists.

"The design of the study is good," Sibaji Kumar Sanyal, a molecular biologist at Heinrich Heine University in Düsseldorf, who was not involved in the study, told the Tagesschau far from certain, and in any case there is still a long way to go.