These sounds somewhat resemble the popping of bubble wrap, although humans can’t hear them. Imagine this: you’re about to eat a salad, you bring a knife down over a tomato, and the vegetable responds with a frantic scream. That’s a gross exaggeration. But biologists at Tel Aviv University found that stressed plants emit characteristic sounds. Their frequency is too high for the human ear to detect them. Yet insects, mammals, and even other plants might be able to hear them.
Professor Lilach Hadani, the study’s lead author, says that plant sounds can carry across a quiet field — but we can’t hear them. And these sounds carry information. The team thinks there’s a lot of acoustic interaction in nature — involving not just animals but plants too.
What the Researchers Discovered
The team recorded sounds from stressed tomato and tobacco plants — first in a soundproof acoustic chamber, then in a noisy greenhouse (scientists favor these plants because they’re easy to grow). In both cases, the biologists stressed the plants by withholding water for several days and by cutting their stems. They used machine-learning algorithms to analyze the plants’ responses in the recordings.
The scientists found that stressed plants produced 30 to 50 high-pitched clicks or pops per hour (with varying intervals), while unstressed plants made significantly fewer sounds. Moreover, the machine-learning algorithm could distinguish different types of sounds. These differences depended on the cause of the stress as well as the species of the plant. The researchers also tested their findings on other plants, including corn, wheat, grapes, and cacti. All of them emitted sounds during stress, as reported by BBC Science Focus.
Exactly where the sounds come from remains unclear. However, researchers speculate that the popping may be caused by the formation and bursting of air bubbles within the plants. Why plants make the sounds is still a mystery. But other plants and animals might “listen in” to gain an advantage. Hadani says other organisms may have evolved to detect and respond to these sounds. For example, a butterfly deciding where to lay eggs or an animal deciding what to eat could use the sounds to make quick choices. If nearby plants pick up on stress signals before the stress reaches them, they might be able to prepare.
