Thirsty or damaged plants produce up to 50 intermittent ultrasonic sounds in an hour, which nearby creatures can respond to, according to the researchers.
There comes a time in a plant’s life when its apex collapses, the leaves turn pale, and the body emits a burst of sounds that are the ultrasonic equivalent of stepping on bubble wrap.
While any gardener is familiar with the wilting and discoloration that accompany drought, a lack of water or a sudden injury can also cause plants to produce stuttering pops, which nearby critters can respond to, scientists say.
The discovery, described as “exciting and stimulating” by an independent expert, suggests that the plant kingdom is not as silent as it seems and that the ultrasonic sounds emitted by plants may even help shape their ecosystems.
Ultrasonic sounds according to your state
“When these plants are in good shape they make less than one sound per hour, but when stressed they make many more, sometimes 30-50 per hour.said Professor Lilach Hadany, a biologist and evolutionary theorist at Tel Aviv University.
“They are potentially important because other organisms may have evolved to hear these sounds and interpret them.“, he added. “We are now testing animals and plants to see if they respond.”.
Hadany and her colleagues recorded sounds produced by tomato and tobacco plants grown in greenhouses. Healthy plants made clicking and popping noises, but the sounds came in much faster bursts when the plants were deprived of water or had their stems cut. Noise can be picked up from 3 to 5 meters away.
Humans cannot hear these ultrasonic sounds, but other living things can.
From 40 to 80 kHz, sounds are too high-pitched for the human ear, which has an upper range of about 20 kHz. But insects like moths and small mammals, including mice, can detect such frequencies, raising the possibility that the noises could influence their behavior.
Writing in Cell, the scientists describe how plant sounds are as loud as human speech and are made more frequently after two days without water. The bursts peak on the fifth or sixth day and then decrease as the plant dries out.
By recording the sounds, the researchers trained an artificial intelligence algorithm to identify the plant and the cause of its stress from the explosion alone. It wasn’t 100% accurate, but it does show that the sounds contain information that might be useful to organisms in the environment, they say.
There is no evidence that the sounds are an attempt at communication, any more than a log declares distress by crackling in a fire. But Hadany said the sounds could be helpful to nearby creatures, perhaps affecting the plants the animals feed on or where insects lay their eggs. It’s not clear what creates the sounds, but the authors suspect a process called cavitation, where water columns in dehydrated plant stems break down, generating air bubbles.
Whether something is listening for the sounds or not, Hadany says the discovery could make irrigation more efficient by using microphones along with other sensors to detect when plants are short of water.
Exciting and stimulating, but is it intentional communication?
“This is exciting and thought-provoking – plants expressing their stress level, who knows,” said Marc Holderie, Professor of Sensory Biology at the University of Bristol. “While this appears to be a by-product of physiological stress rather than intentional communication, nothing can stop nearby organisms from trying to exploit this information.“
“No one has yet discovered an ear on a plant, but plants respond to many mechanical stimuli, so scientists might want to look for ultrasound detectors in these plants.’ he added.
In 2017, Carlos Vicient, a researcher at the Center for Research in Agricultural Genomics in Barcelona, reported that playing loud sounds for hours on plants made them more resistant to drought. But he is skeptical that they will respond to softer sounds in a noisy natural environment. “It seems much more likely that, if such communication exists, it is through the emission of volatile substances.“, he said.
“The fact that a plant emits sounds does not mean that it is communicating with its congeners”, he added. “Any pipe system carrying a fluid generates sounds and this does not mean that a water pipe is trying to communicate with someone.”.
By Ian Sample. Article in English