When deprived of water or snipped with scissors, plants emit a flurry of staccato "screams" that are too high-frequency for humans to hear, a study suggests. When lowered into a range that human ears can detect, these stress-induced pops sound like someone furiously tap dancing across a field of bubble wrap.
Although humans cannot hear these ultrasonic pops without technological assistance, various mammals, insects, and even other plants may be able to detect these noises in the wild and respond to them, researchers reported Thursday (March 30) in the journal Cell. (The same researchers first shared their popping-plant discovery in 2019 on the preprint database bioRxiv, but the work has now been peer-reviewed.)
"First, we recorded plants within an acoustic box and developed machine learning algorithms to classify the recorded sounds. Then we tested the system in a greenhouse while monitoring the physiological parameters of the recorded plants", the researchers shared. "We recorded tomato and tobacco plants under different treatments—drought stress, cutting (of the stem, before recording), and controls, within an acoustically isolated box.
The researchers focused on the ultrasonic sound range (20–150 kHz) and found that plants emit sounds and that stressed plants—both drought-stressed and cut plants emit significantly more sounds than plants of any of the control groups.
In the future, humans could harness recording devices and artificial intelligence (AI) to monitor crops for these signs of dehydration or disease, the scientists suggest.
Past research revealed that drought-stressed plants undergo a process called cavitation — where air bubbles form and collapse within the plant's vasculature tissue — which makes a popping sound that can be detected by recording devices attached to the plant(opens in new tab). But it wasn't clear if such popping sounds could be heard at a distance, the authors wrote in Cell.
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