Stressed plants 'scream'
A study of tomato and tobacco plants suggests they emit ultrasonic popping sounds when dehydrated or physically damaged.
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.
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 droughtstressed 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. But it wasn't clear if such popping sounds could be heard at a distance, the authors wrote in Cell.
The team set up microphones near healthy and stressed tomato (Solanum lycopersicum) and tobacco (Nicotiana tabacum) plants. The stressed plants were either dehydrated or had their stems snipped.
On average, healthy plants let out less than one pop per hour, but stressed plants emitted about 11-35, depending on the plant species and stressor. Drought-stressed tomato plants were noisiest, with some plants emitting more than 40 pops per hour. The team fed these recordings into a machine-learning algorithm — an AI system used to identify patterns in data — and found that the trained algorithm had about a 70% success rate in distinguishing the sounds made by different plants exposed to different stressors.
The team successfully captured the cries of a slew of other stressed plants, such as wheat (Triticum aestivum), corn (Zea mays) and pincushion cactuses (Mammillaria spinosissima).
Although the researchers gathered recordings by setting microphones about 10 cm away from the plants, they suggest that these ultrasonic sounds could potentially be heard by mammals and insects with great hearing from 3-5m away.
"These findings alter the way we think about the plant kingdom, which has been considered to be almost silent until now," the study authors wrote.