Scientists Have Discovered That Plants May Emit Ultrasonic ‘Squeals’ When Stressed

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During the previous years, it has been revealed that plants can see, hear, and smell, and they are still regarded as silent objects of nature. According to the research posted on December 2, 2019, on the bioRxiv database, plants have too high of a frequency for us to hear them.

Itzhak Khait and his colleagues from Tel Aviv University, Israel, discovered that tomato and tobacco plants produce some frequencies that we, humans, cannot hear when they have a lack of water or when their stem is cut. The research was done with a microphone placed 10 cm away from the plants, and it picked some frequencies, which we cannot hear, but some insects and mammals can listen to them on a 5 meters distance.

Some animals that can hear the plants will refuse to lay their eggs on a stressed plant. Furthermore, plants can listen to themselves, and if one plant screams for the lack of water, the others can react adequately and give them water.

The study of these students hasn’t been published yet, but they say that maybe we thought the plants were silent, but they aren’t, and they have the proof, recorded.

In the past, people attached some devices to the plants, to record some frequencies. The method is made by measuring the air bubbles which are formed and imploded, and this process is called cavitation. No one has ever tried to measure frequencies from a distance.

In normal circumstances, stressed tomato plants produce 35 sounds per hour, and tobacco made 11. When the stems were cut, the tomato made 25 sounds per hour, and the tobacco plants made 15.

If the plants are unstressed, they produce less than one sound per hour.

These students have created and trained a machine to make a distinction between the wind sound and the sound of the plants, the rain, and different nature sounds.

Mostly, the stress was made by dryness or a cut. And this conclusion is made based on the intensity and the frequency of the sound.

Besides the fact than the students from Israel experimented with tomato and tobacco plants, they believe that all other plants produce particular sound when they need water, or when their stem is cut.

In a preliminary study, they also tested a spiny pincushion cactus, Mammillaria spinosissima, and the Henbit dead-nettle, also known as Lamium amplexicaule, and they produced sound too.

Mammillaria spinosissima
The spiny pincushion cactus has been found to emit ultrasonic sounds/Wikipedia

According to Khait, the cavitation is the explanation for how the plants create the sound.

They recommend to the agriculture science to open a whole new field for researchers, and it will be very beneficial. The benefits will make their job easier regarding climate changes and how they influence the plants.

Anne Visscher, employed in the Royal Botanic Gardens, Kew, UK, says:

The suggestion that the sound that drought-stressed plants make could be used in precision agriculture seems feasible if it is not too costly to set up the recording in a field situation. 

Also, no experiments were made to find out whether mammals or different animals hear their sounds, and if they can answer them. According to these claiming, the idea remains speculative.

If the hypothesis of the students is correct, then the cavitation is the best mechanism. But many farmers are skeptical of the findings, and many of them would like to know more about the way of controls. Moreover, the farmers continue that the idea is too speculative. There are already too many theories about why some insects avoid individual plants.

Full Research Paper: bioRxiv

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