The idea of a plant making noise might evoke a vision of the mandrake from Harry Potter.
But a new study suggests that plants do indeed issue distress calls when they don’t get enough water.
They also seem to make alarm sounds after being cut, as these sounds have been found to come from tomato and tobacco plants, as well as corn and grape vines used to make Cabernet Sauvignon.
Ultrasonic vibrations from plants have been previously recorded, using direct contact sensors.
The new study now provides the first evidence that plants make airborne sounds, which the researchers estimate can be heard by acute-hearing animals like mice and moths from up to 16 feet (five meters) away.
Now, a study has found that plants do indeed make sounds when they’re stressed — albeit more of a popping sound than a shriek
For humans, who can’t hear in the high-frequency “ultrasound” range, the researchers have helpfully lowered the frequency so that we can experience plant noises—which are delivered fairly loudly at the same volume as normal human conversation.
Plants typically make a popcorn-like noise—thought to be caused by air bubbles bursting in their stem—less than once an hour.
But tomato plants that had not been watered for up to five days produced this frantically sparse sound—more than once every two minutes on average.
When they were cut down, the tomato plants beeped an alarm every two and a half minutes.
Professor Lilac Hadani, an evolutionary biologist at Tel Aviv University and lead author of the study looking at hundreds of plants, said: ‘Our results indicate that the world around us is full of plant sounds, and that these sounds contain information – for example about water scarcity or injury.
We hypothesize that in nature the sounds made by plants are detected by nearby organisms, such as bats, rodents, various insects, and perhaps also other plants – which can hear higher frequencies and elicit relevant information.
Plants typically make a popcorn-like noise — thought to be caused by air bubbles bursting in their stem — less than once an hour
The idea of a plant making noise might evoke a vision of the mandrake from Harry Potter
Do plants feel “pain”?
Researchers at the University of Wisconsin said last year that when an insect bites on a plant leaf, the wound triggers a release of calcium.
This sets off a chain reaction in the cells along the plant’s leaves and stem.
The response takes about one to two minutes to reach each part of the plant.
Calcium triggers a hormonal response from the plant to protect its leaves.
Some plants release harmful chemicals that make them taste bad to other invading insects.
Others, such as grass, secrete hormones that attract nearby parasitoid wasps, which then eat the attacking insects.
We think humans could benefit from this information too, if given the right tools, such as sensors that tell farmers when plants need watering.
Apparently, an ideal field of flowers can be a rather noisy place. It’s just that we can’t hear voices! “
Ultrasound recordings taken by two microphones placed next to each plant in the study support the theory that they can use sound to warn each other of the danger of drought or starvation.
If plants know that water is scarce ahead of time, they can close the pores in their leaves to conserve water.
If a plant hears a noise from another plant whose stem was cut off by an animal that ate it, that plant can emit volatile compounds to deter the hungry animal.
The researchers used artificial intelligence algorithms to compare the noises made by tomato and tobacco plants to those that were cut off or deprived of water for up to two weeks in a soundproofed room.
The team found that plants that were not watered began making distress calls before they were visibly dry, with the noise peaking after five days without water, before decreasing before the plants were completely dry.
In the future, the noise could help people use a sensor to tell if their houseplants are unhappy and need a watering, or help farmers save water by watering crops only when they get dry.
In the future the noise could help people use a sensor to tell if their houseplants are unhappy and need watering, or help farmers save water by watering crops only when they get dry.
The researchers also found that plants including grapevines, wheatgrass, corn and cacti made noises when cut or dried.
The noise lasted longer when the plant was drought than when it was cut, and different plants seemed to make different sounds, based on factors such as the frequency of the noise.
Experts believe that this noise may be beneficial to creatures such as moths, which lay their larvae on plants, so those suffering from drought will find it unsuitable.