This is the sound that plants make when they cry.

Human beings have glorious ways of vocalizing discontent: we wail, complain, grunt, moan, and squeal. One might think that airing complaints requires, at the very least, a mouth. But recent research shows that this is not the case.

Stressed plants make audible sounds that can be heard meters away, and the type of sound corresponds to the type of bad day they’re having. The results were published March 30 in the journal Cell.

Researchers suspect that the nervous snap is a byproduct of cavitation, when tiny bubbles burst and produce mini shock waves within the plant’s vascular system, much like what happens in joints when you snap your fingers.

“Cavitation is the most likely explanation, at least for most of the sounds,” said Lilach Hadany, a biologist at Tel Aviv University in Israel.

Plants interact with organisms that make sounds at all times—such as bees and their buzzing—and they also communicate with other forms of life, including other plants, by emitting chemicals called volatiles. But there has been little research on plants detecting—or making—audible sounds.

After Hadany met Yossi Yovel, who was studying bat sounds in Tel Aviv, they decided to team up to address the issue of plant sounds. They focused on tomato and tobacco plants because they are easy to grow and have well-known genetics.

The plants were placed in soundproof boxes with two microphones pointed at their stems, ready to record anything. The researchers found that the plants not only made sounds, but also made a lot more racket when dehydrated or when their stems were cut (simulating herbivore attack).

The researchers were also able to pick up the same sounds from plants in a greenhouse. Since then, they have detected sounds made by other plants, such as vines and wheat.

The annoying vegetation made specific complaints that matched the type of stress they were experiencing. A machine learning program could tell with 70 percent accuracy whether the plant was thirsty or at risk of being decapitated.

Plant sounds are too high pitched to be heard by humans. But the sounds fall within the hearing range of other animals, such as mice and moths. There’s also the question of whether other plants might be listening in on their neighbors’ drama.

Hadany’s group previously showed in a 2019 study that some flowers respond to the sound of approaching pollinators by producing more nectar. Finding out if other organisms respond to the noises made by stressed plants is an important next step.

By: DARREN INCORVAIA