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Beyond Silence: Plants Let Out Clicking Sounds When Thirsty or Hurt, Study Shows

Illustration of a plant letting out clicking sounds when thirsty or hurt
Illustrated by Cristina Mezuk

In a world of secrets, plants are speaking up. And science is all ears! As a recent study from the Cell journal shows, our leafy friends make popping or clicking sounds when under duress – such as when they are thirsty or injured.

But how exactly do plants make sounds? A team of scientists from Tel Aviv University led by Prof. Lilach Hadany decided to find out by placing tomato and tobacco plants in a soundproof box, as well as grapevine and wheat in a greenhouse. They used a device that can pick up very high-pitched sounds that are beyond the range of human hearing but seem to be just fine to field critters and other plants. To them, it may encode and transmit information about the plant’s condition and needs.

To be sure, a certain amount of vocalizing is normal in plants, as the scientists discovered. A happy plant that isn’t deprived of sustenance and isn’t experiencing any physical harm will make one such sound per hour on average. Cut it, and it will let out in between 15 and 25 sounds per hour. Dry it out, and the distress signals will bump up to 35 sounds per hour! Even more interestingly, not all of these sounds were created equal. Their quality varies depending on not only type but also the amount of stress. To sort them out and classify, the researchers resorted to machine learning models which, after being trained, managed to correctly “translate” the signals with up to 81% accuracy.

plants clicking sounds
Cactus plant with Microphones. Credit: Tel Aviv University

But what could be the purpose of this clickety fuss? Moths or mice, for example, can detect the hubbub within the 3-5-meter radius. In communicating with them, the plants are exhibiting a behavior that we humans can’t help but call altruistic. To a moth looking for a perfect green host to lay its larvae on, this signal may convey, for example, that a particular plant is in bad shape and not very likely to survive. But it’s not just rodents or insects that this botanical racket could be aiming at. Other plants may also be able to “hear” and interpret it as a distress call, a Morse code of sorts – and do what they can to adapt and survive dry spells in response.

However, that doesn’t mean that sound is the only communication channel in the plant kingdom. Earlier studies have shown that plants emit volatile organic compounds (that is, scent molecules) when they are thirsty or being munched on by an animal. Not to mention quirky responses to tactile stimuli as shown by the likes of Venus Flytrap or Mimosa Pudica that we at Backyard Brains have been researching. (And you can too!)

Social dynamics of plants and animals aside, what lesson is in it for us? And how can we put these findings to good use? This breakthrough, the researchers theorize, has a potential to revolutionize plant monitoring techniques, enabling farmers and gardeners to assess the well-being of their crops and intervene promptly if their plants are thirsty or besieged by pests. “We believe that humans can also utilize this information, given the right tools – such as sensors that tell growers when plants need watering. Apparently, an idyllic field of flowers can be a rather noisy place. It’s just that we can’t hear the sounds,” says prof. Hadany. But it’s not just about the plants’ trials and tribulations. Watering plants exactly where and when they need it can cut water waste by half while also increasing the yield.

In other words, when plants say they are thirsty or unwell in an era of precipitous climate change, the least we should do is – listen.

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