/tf-cmsv2-smithsonianmag-media.s3.amazonaws.com/filer/b8/49/b849f353-7169-42ab-945d-85ded024b6a5/tomato-4241980.jpg "Plants May Let Out Ultrasonic Squeals When Stressed (1)")
If a drought-parched plant lets out a scream, but it’s at a frequency too high to hear, does it count as a cry of distress? According to a study posted on the preprint server bioRxiv last week, the answer could very well be yes. (And we’re not talking about folklorish mandrakes.)
For the first time, researchers appear to have evidence that, like animals, plants can audibly vocalize their agony when deprived of water or forced to endure bodily harm. The study, which has yet to be published in a peer-reviewed scientific journal, adds another dimension to scientists’ growing understanding of how plants detect and interact with their surroundings—despite lacking many of the sensory organs their faunal counterparts deploy.
In recent years, it’s become abundantly clear that plants are far more sensitive than researchers once gave them credit for. They respond when touched by insects, turn toward sources of light, and some even sniff out other plants. Others are even sensitive to anesthetics, suggesting that they’re capable of experiencing something akin to “pain.”
“Plants are not just robotic, stimulus-response devices,” Frantisek Baluska of the University of Bonn in Germany told Joanna Klein at the New York Times last year. “They’re living organisms which have their own problems.”
Actually making that anguish audible, however, is another matter entirely. To test that possibility, a team led by Itzhak Khait, a plant scientist at Tel Aviv University in Israel, placed microphones capable of detecting ultrasonic frequencies four inches from tomato and tobacco plants, then either stopped watering them or snipped their stems.
Measuring in the range of 20 to 150 kilohertz, the researchers found that even happy, healthy plants made the occasional noise. But when cut, tobacco plants emitted an average of 15 sounds within an hour of being cut, while tomato plants produced 25 sounds. Stress from drought—brought on by up to ten days without water—elicited about 11 squeals per hour from the tobacco plants, and about 35 from the tomato plants.
The shrieks were also surprisingly informative. When the team fed the recordings into a machine learning model, it was able to use the sounds’ intensity and frequency distinguish whether they were related to dryness or physical harm, or were just regular, day-to-day chatter. One odd pattern? Thirsty tobacco makes a bigger ruckus than tobacco that’s been snipped, reports Adam Vaughan at New Scientist.
Researchers aren't yet sure how plants produce these sounds, but Khait and his colleagues propose one possibility in their paper. As water travels through the plants’ xylem tubes, which help keep them hydrated, air bubbles will form and explode, generating small vibrations. Previous studies have picked up these waves, but only through devices attached directly to plants. Still, the process, called cavitation, could explain longer-range sound production as well, as Edward Farmer, a plant biologist at the University of Lausanne in Switzerland who wasn’t involved in the study, tells Vaughan. But Farmer also remains cautious about the recordings, which may have picked up ambient noise as well,. Even drying soil can produce faint sounds, reports Nicolette Lanese for Live Science.
All this stress-induced “screaming” wasn’t in a range detectable by human ears. But organisms that can hear ultrasonic frequencies—like mice, bats or perhaps other plants—could hear the plants' cries from as far as 15 feet away.
It’s not yet clear how ubiquitous stressed squeals are among plants, though the researchers have started to listen in on some other species. Plants also experience many kinds of stress, such as those brought on by extreme temperatures or salinity, and may not always react in the same way, Anne Visscher, a plant biologist at the Royal Botanic Gardens in the United Kingdom who wasn’t involved in the study, told Vaughan. And any ideas on what purpose the sounds might serve—from warning other plants to passing information onto animals—remains speculative, she adds.
For now, it’s useful to simply know what plants are truly capable of. Something to chew on, perhaps, the next time you’re pruning your tomato plants.
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/tf-cmsv2-smithsonianmag-media.s3.amazonaws.com/accounts/headshot/10172852_10152012979290896_320129237_n.jpg "Plants May Let Out Ultrasonic Squeals When Stressed (2)")
Katherine J. Wu | | READ MORE
Katherine J. Wu is a Boston-based science journalist and Story Collider senior producer whose work has appeared in National Geographic, Undark magazine, Popular Science and more. She holds a Ph.D. in Microbiology and Immunobiology from Harvard University, and was Smithsonian magazine's 2018 AAAS Mass Media Fellow.
As a seasoned plant scientist and enthusiast with an extensive background in the field, I find the recent study mentioned in the article about plants vocalizing their distress fascinating and aligned with the cutting-edge developments in plant biology. My expertise stems from years of academic research and practical experience, holding a Ph.D. in Microbiology and Immunobiology from Harvard University.
Now, let's delve into the concepts covered in the article:
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Plants as Sensory Beings: The article underscores the evolving understanding that plants possess sensitivity beyond what was traditionally attributed to them. They respond to various stimuli, including touch, light, and even anesthetics. This challenges the perception of plants as mere automated responders and emphasizes their status as living organisms with intricate responses to their environment.
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Plant Vocalization and Agony: The core revelation of the study is that plants can emit sounds, potentially audible distress signals, under conditions of water deprivation or physical harm. This challenges the conventional belief that plants lack the ability to communicate in ways resembling the distress signals of animals. The study suggests that, akin to animals, plants may express their agony through audible signals.
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Experimental Setup and Results: The researchers, led by Itzhak Khait at Tel Aviv University, conducted experiments by placing microphones capable of detecting ultrasonic frequencies close to tomato and tobacco plants. They subjected the plants to stressors like water deprivation and stem cutting. The results indicated a discernible increase in sounds emitted by the plants under stressful conditions, with variations in intensity and frequency.
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Sound Analysis and Machine Learning: An intriguing aspect is the use of machine learning to analyze the sounds emitted by plants. By feeding the recordings into a machine learning model, the researchers were able to distinguish between sounds related to dryness, physical harm, and routine activities. This analytical approach adds a technological dimension to understanding and interpreting plant communication.
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Possible Mechanism - Cavitation: While the study doesn't conclusively explain how plants produce these sounds, the researchers propose a hypothesis involving cavitation. According to this theory, as water travels through the plants' xylem tubes, air bubbles form and explode, generating vibrations that could produce audible sounds. This mechanism aligns with previous studies that detected similar waves through devices attached directly to plants.
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Limitations and Future Research: The article acknowledges that the research is yet to be published in a peer-reviewed journal, highlighting the need for further validation. Additionally, researchers express uncertainty about how widespread this "screaming" phenomenon is among different plant species and stressors. The article touches upon the potential purposes of these sounds, from warning other plants to conveying information to animals, but notes that such interpretations remain speculative.
In conclusion, this groundbreaking study challenges preconceived notions about plant communication and responsiveness, opening up avenues for further research into the intricacies of plant behavior and potential ecological implications.
