Tomato plants could possible let out an ultrasonic scream whenever they’re under stress from water deprivation or from cutting a stem. (Image credit: pixabay)
You may think that humans and animals are the only living things that let out a sound, like a scream or a squeal, to express their distress, but what about plants? It seems they do. I heard about this story a bit ago, so I dug into the story for more info.
Researchers from Tel Aviv University in Israel have discovered that plants are capable of emitting sounds when they undergo stress, like drought or bodily harm. According to their research, which was posted on Dec 2nd on the bioRvix database, the sounds plants make are too high-frequency for humans to hear. The study has not been published in a peer-review scientific journal
The team led by Itzhak Khait placed condenser CM16 ultrasound microphones capable of detecting ultrasonic frequencies four inches away from tomato and tobacco plants that were undergoing stress. Afterward, they stopped watering the plants or cut off their stems. The noises could be detected within a range of 20 to 150 kilohertz, a volume that could be picked up by organisms from up to several meters away. Researchers found that sometimes healthy plants would also produce noise.
The team’s recordings were performed in a 50x100x150cm acoustically isolated box surrounded with acoustic foam to limit echoes. The two cable holes in two corners of the box were covered with PVC and acoustic foam. The plants were located inside the box with 6 microphones connected to an UltraSoundGata 1215H A/D converter, while the PC and electrical connections were located in the same room, just outside the acoustic box. Both USB cables connected the PC to the 1216H device inside the box. All recordings, which were filtered above 20 kHz, were digitized using the UltraSoundGate 1215H A/D converter with a sampling rate of 500 kHz per channel. Recordings started whenever it was triggered with a sound exceeding 2% of the maximum dynamic range of a microphone.
After being cut, tobacco plants emitted an average of 15 sounds within an hour. Meanwhile, tomato plants made 25 sounds. When the plants underwent water deprivation for ten days, the tobacco plants produced 11 squeals per hour, while the tomato plants had 35 squeals.
The noises produced by the plants were also pretty informative. When the team used their recordings with a machine learning model, they picked out the intensity and frequency of the plants’ sounds and sorted them into three categories, “dry, cut, or intact.” By using these three categories, the team discovered that a water-deprived tobacco plant emits more noise than one that has been cut. They also believe that farmers could use this technology in the future to listen to stressed crops in their fields.
It isn’t clear how the plants produce sounds, but Khait and his team have theorized on a possibility. When water travels through the plants’ xylem tubes, air bubbles begin to form and explode, creating tiny vibrations. Studies in the past were able to pick up these waves from devices that were directly attached to the plants.
The process, known as cavitation, could explain long-range sound production. However, the recordings also could have picked up faint sounds, like drying soil.
Some living organisms, like mice, bats or even other plants can pick up the plants’ sounds from as far as 15 feet away. The world must sound frightening to them.
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