For the first time in the world, researchers at Tel Aviv University recorded and analyzed sounds distinctly emitted by plants. The click-like sounds, similar to the popping of popcorn, are emitted at a volume similar to human speech, but at high frequencies, beyond the hearing range of the human ear. The researchers say they 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 research paper was published in the scientific journal Cell.
At the first stage of the study the researchers placed plants in an acoustic box in a quiet, isolated basement with no background noise. The maximum frequency detected by a human adult is about 16 kilohertz. Ultrasonic microphones recording sounds at frequencies of 20-250 kilohertz were set up at a distance of about 10cm from each plant. The study focused mainly on tomato and tobacco plants, but wheat, corn, cactus and henbit were also recorded.
Before placing the plants in the acoustic box the researchers subjected them to various treatments: some plants had not been watered for five days, in some the stem had been cut, and some were untouched.The researcher says that their intention was to test whether the plants emit sounds, and whether these sounds are affected in any way by the plant’s condition. Their recordings indicated that the plants in the experiment emitted sounds at frequencies of 40-80 kilohertz. 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 recordings collected in this way were analyzed by specially developed machine learning (AI) algorithms. The algorithms learned how to distinguish between different plants and different types of sounds, and were ultimately able to identify the plant and determine the type and level of stress from the recordings. Moreover, the algorithms identified and classified plant sounds even when the plants were placed in a greenhouse with a great deal of background noise. In the greenhouse the researchers monitored plants subjected to a process of dehydration over time and found that the quantity of sounds they emitted increased up to a certain peak, and then diminished.
The researcher says that their 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. The researchers 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. The researchers believe that humans can also utilize this information, given the right tools – such as sensors that tell growers when plants need watering.
News source: Eurekalert
