Much like babies or hardworking science journalists, plants “cry” when stressed, a study published in the journal Cell avows.
Scientists pointing microphones at tobacco and tomato plants found that specimens stressed by lack of water or recent cutting emitted high-pitched sounds inaudible to the human ear (about 20-100 kilohertz). The sounds arrived at about 35 instances per hour, in contrast with the non-stressed plants that emitted about one noise per hour.
Scientists recorded plants under stress, then used machine learning to classify the sounds. Illustration: Khait et al
Scientist Itzhak Khait and her team at Tel Aviv University recorded the sounds with high-powered microphones, then modified the recordings by pitching down and speeding up. And while a certain fictional talking tree might take umbrage at such a hasty treatment of plant sounds, the modification allowed the noises to become audible to humans.
The result is, “a bit like popcorn — very short clicks,” Lilach Hadany, another researcher on the project, told Nature. “It is not singing.”
While science has long known that plants changed color, shape, and smell in response to stress, this study marks the first time “airborne sounds” have been studied and — even more interestingly — classified. The scientists behind the study hope the findings might help farmers care more precisely and effectively for plants in the future.
“We developed machine learning models that succeeded in identifying the condition of the plants, including dehydration level and injury, based solely on the emitted sounds,” the paper’s authors wrote. “This work opens avenues for understanding plants and their interactions with the environment and may have a significant impact on agriculture.”
Okay, plants make noises. But…how?
Hadany told Nature that the exact method by which the plants produced the noises needs further study. But one theory, the scientist said, has to do with xylem.
Xylem are the tubes that plants use to transport water and nutrients through their structures. The theory goes that bubbles form and then pop in the xylem when a plant is under stress, which could create the “cries.”
A leaf from a tobacco plant, one of the species scientists used in the study. Further research indicates corn, wheat, and wine grapes also make noises when stressed. Photo: Shutterstock
And even though humans can’t hear the strange sounds, other animals might be able to. Nature reports that mice, moths, and bats can all detect noises in the 20-100 kilohertz range. But before you imagine the auditory landscape of a mouse as filled with the screams of vegetables, heed the words of retired biologist Graham Pyke:
“It is unlikely that these animals are really able to hear the sound at such distances,” the former researcher at Macquarie University shared with Nature.
But it’s a different story in the other direction.
The team responsible for the Cell study published a paper in 2019 that showed some flowers respond to the sound of a flying bee by producing sweeter nectar within three minutes. That’s moving pretty fast (for a plant).
