Old Hans Halbig always sang to the tomato plants in his greenhouse. The 85-year-old Calgarian green thumb (my neighbor) had an inkling that singing helped them grow. What Hans might not have known was that his plants were probably making sounds back to him.
Hans wasn’t too far off the mark.
Recently, for the first time, scientists at Tel Aviv University have recorded and analyzed distinctive noises made by different plant species—including tomato plants—and revealed that those noises correspond to the subjects’ level of stress.
Plants were recorded making high-pitched “clicks,” which sound something like popcorn popping, and though those sounds are about the same volume as human speech, their frequency is too high for the human ear to hear.
“From previous studies we know that vibrometers attached to plants record vibrations, but do these vibrations also become airborne soundwaves—sounds that can be recorded from a distance?” asked professor Lilach Hadany from the School of Plant Sciences and Food Security. “Our study addressed this question, which researchers have been debating for many years.”
The research team, led by Hadany, published their paper in the journal Cell. The authors wrote: “We found that plants usually emit sounds when they are under stress, and that each plant and each type of stress is associated with a specific identifiable sound. While imperceptible to the human ear, the sounds emitted by plants can probably be heard by various animals, such as bats, mice, and insects.”
The first stage of the study involved the plants’ being placed in acoustic boxes in a quiet basement with no background noise. Focusing mainly on tomato and tobacco plants, they set up ultrasound microphones about 4 inches (10 centimeters) from each and recorded sounds at frequencies ranging from 20-250 kilohertz—the highest frequency the human ear can detect is 16 kilohertz. Wheat, corn cactus, and henbit were also tested.
The plants were subjected to different treatments: some had not been watered in five days; others’ stems had been cut; while a third group remained untouched. The experiments would test whether they made sounds and if those sounds were affected by their treatment.
“Our recordings indicated that the plants in our experiment emitted sounds at frequencies of 40-80 kilohertz,” the authors wrote. “Unstressed plants emitted less than one sound per hour, on average, while the stressed plants—both dehydrated and injured—emitted dozens of sounds every hour.”
The collected recordings were analyzed by specially developed machine learning AI algorithms, which successfully distinguished between the different plants and types and levels of stress they were subjected to.
The plants were then moved into a greenhouse that had a lot of background noise, yet the algorithms were able to distinguish the sounds with an accuracy of 81 percent. The plants were subjected to a process of dehydration while their sounds were monitored. The experiment determined that the quantity of sounds increased as the plants’ stress levels increased but diminished after reaching a peak.
The discovery could be harnessed to monitor crops for moisture and disease, the researchers wrote. This could potentially save “up to 50 percent of the water expenditure and increase the yield.” Further studies could inquire as to: what mechanism is behind the sounds and whether other plants can hear them as well.
https://youtu.be/hOWaXi0I2YE
“Our findings suggest that the world around us is full of plant sounds, and that these sounds contain information—for example about water scarcity or injury,” Hadany said. “We assume that in nature the sounds emitted by plants are detected by creatures nearby, such as bats, rodents, various insects, and possibly also other plants—that can hear the high frequencies and derive relevant information. 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.”
Old gardener Hans would have probably loved to hear that.
