Plants Really Do 'Scream' Out Loud. We Just Never Heard It Until Now.

It appears that Roald Dahl was correct all along: if you harm a plant, it cries.

I guess, sort of. Not like you or I may yell. Instead, when a plant is disturbed, they start to make louder popping or clicking noises at ultrasonic frequencies that are not audible to humans. Scientists believe that this may be one means by which plants express their anguish to others around them.

"There are sounds that we don't hear, even in a peaceful field, and those sounds contain information. There may be a lot of acoustic contact going on since animals can hear these noises, according to evolutionary scientist Lilach Hadany of Tel Aviv University in Israel.

It would be highly undesirable for plants to not use sound at all as they frequently interact with insects and other creatures, many of which rely on sound for communication.

Stressed plants aren't as docile as you would imagine. They go through some pretty significant changes, with the production of some quite potent smells being one of the most perceptible (to us humans, at least). They may change their form and color as well.

These alterations may alert surrounding plants to danger, which prompts them to fortify their own defenses; or they may entice animals to attack pests that may be endangering the plant.

However, it hasn't been well investigated if plants produce other signals, such noises. Hadany and her coworkers discovered a few years ago that plants are capable of hearing. The obvious follow-up query was if they can also create it.

They observed tomato and tobacco plants under various situations to find out. To establish a baseline, scientists first recorded unstressed plants. Then they noted plants that had lost moisture and plants whose stems had been clipped. These recordings were made in two different settings: first, a soundproofed acoustic room, and subsequently, a typical greenhouse.

In order to distinguish between the sounds made by unstressed plants, cut plants, and dehydrated plants, scientists next trained a machine learning system.

Within a range of more than a meter (3.3 feet), plants produce sounds that resemble popping or clicking noises but are much too high-pitched for humans to hear. Plants that are not under stress don't produce any noise at all; they simply hang around and go about their daily activities.

Stressed plants, on the other hand, make a lot more noise, averaging up to 40 clicks per hour, depending on the species. Additionally, dry plants have a distinct acoustic character. They begin to click more before the plant begins to exhibit obvious signs of dehydration, increase as the plant becomes more dry, and then decrease as the plant dries up.

These noises and the type of plant that generated them could be distinguished by the algorithm. And it's not only plants for tobacco and tomatoes. The scientists conducted tests on a range of plants and discovered that sound creation seems to be a fairly typical plant function. We captured the sounds of wheat, corn, grapes, cacti, and henbit.

But there remain a few unanswered questions. For instance, it's unclear how the noises are made. In earlier studies, it was discovered that dehydrated plants undergo a process called cavitation, in which air bubbles develop, grow, and then burst inside the stem. Human knuckle-cracking causes an audible pop; it's possible that plants experience a similar sound.

We are unsure at this time if other distressing situations can also cause sound. The plants might potentially begin to disintegrate like bubble wrap as a result of pathogens, attacks, UV exposure, temperature fluctuations, and other unfavorable circumstances.

Additionally, it is unclear if sound generation in plants is a natural occurrence or an adaptive evolution. However, the scientists demonstrated that an algorithm can be taught to recognize and differentiate between different plant noises. Other species may have performed the same function, for sure.

Additionally, these creatures could have acquired the ability to react in different ways to the sounds made by worried plants. According to Hadany, "for instance, a moth planning to lay eggs on a plant or an animal planning to eat a plant could use the sounds to help guide their decision." The ramifications for us as humans are rather obvious; we might listen for parched plants' distress sounds and water them before a problem arises.

However, it is uncertain if other plants are perceiving and reacting. It is likely conceivable because prior studies have demonstrated that plants may adapt their drought tolerance in response to sound. And it is in this direction that the study team will direct its next phase.

Who may be listening now that we are aware that plants actually generate sounds? Hadany declares. We are now examining human capacity to recognize and comprehend the sounds in entirely natural situations, as well as how other creatures, including animals and plants, react to these noises.

The research has been published in Cell.