Israeli scientists have discovered that plants can emit noises that can travel through the air and be detected up to a metre away, particularly when they are experiencing stress.
Researchers from Tel Aviv University said it is possible that insects, animals and even other plants can detect the sounds, meaning a whole cacophony of plant-based noise could be going on above the range of human ears.
Using a soundproofed chamber and some sensitive microphones, the scientists studied tomato and tobacco plants. They subjected the plants to withholding water, causing the plants to become dehydrated, and made cuts in the plants’ stems.
The scientists used microphones to record both healthy and stressed plants in a soundproofed acoustic chamber and then in a normal greenhouse. An AI programme analysed the difference between the sounds created by healthy, thirsty and cut plants.
“When tomatoes are not stressed at all, they are very quiet,” said Lilach Hadany, an evolutionary biologist at Tel Aviv University. After being denied water, the plants started to emit more pops and clicks — between 30 and 50 sounds per hour at intervals that seemed random. The plants started emitting the sounds before there were visible signs of dehydration, peaking after five days before dying out as the plant dried up completely.
“We found that many plants — corn, wheat, grape, and cactus plants, for example — emit sounds when they are stressed,” Hadany said.
Whilst it is not certain how the plants create the sounds, researchers believe it may come from the formation and popping of air bubbles within the plant’s vascular system.
Hadany said it was unclear whether the sounds could be classed as a form of communication and whether plants may be able to detect distress in nearby vegetation. She said that plants have been shown to increase the sugar levels in their nectar in response to vibrations created by pollinators, akin to a rudimentary form of “hearing”.
“Now that we know that plants do emit sounds, the next question is: ‘Who might be listening?’” she said. “We are currently investigating the responses of other organisms, both animals and plants, to these sounds.”
The authors of the study, published in the journal Cell, said that sound recordings could help farmers to monitor how well-hydrated their crops are.
“The fact that plants are making these sounds opens a whole new avenue of opportunities for communication, eavesdropping, and exploitation of these sounds,” said Yossi Yovel, a neuroecologist at Tel Aviv University and co-author of the study.
