Plants make clicking sounds that animals may hear,
travel 16 feet, and have now been tuned down for human
ears to hear for the first time.
Becky Ferreira
By Becky Ferreira
March 30, 2023, 10:00am
Plants Make Sounds When Hurt, Scientists Confirm, And
Now You Can Hear It
Your tomato plant may be crying out for you to water
it, but although other animals and plants might hear
it, your human ears are deaf to the sound of its
laments. That’s the finding of new research that
captured the pops and clicks of stressed plants, which
have been tuned down to the human hearing range.
The novel experiment revealed that plants exposed to
harmful pressures, such as injuries and dehydration,
produce ultrasonic noises that may be audible to
animals and plants as far as 16 feet away. In this way,
plants may use sound to communicate with their wider
ecosystems, a finding that sheds light on their
mysterious inner worlds and could help mitigate
agricultural challenges presented by climate change.
Plants have devised many ways to interact with their
fellow creatures that humans can appreciate, such as
complex fragrances, visual splendor, spiky surfaces,
and tasty treats like fruits and nuts. However, they
are not especially famous for being noisy. Though
scientists have previously recorded botanical sounds by
placing devices directly on plants, it has remained
unclear whether these acoustic signals carried over a
significant distance, thereby allowing other species in
an environment to listen in to the plant world.
Now, researchers led by Itzhak Khait, a plant scientist
at Tel Aviv University, have recorded tobacco and
tomato plants making high-frequency noises that could
be detectable at distances of five meters, or 16 feet.
The sound of the stressed plants was so specific that a
machine learning tool was able to tell whether a plant
was thirsty, suffering from cuts, or part of a control
group based only on the pattern of its acoustic
vibrations.
The results “can alter the way we think about the plant
kingdom, which has been considered to be almost silent
until now,” according to a study published on Thursday
in the journal Cell.
“We started this project from the evolutionary
question: why are plants mute?” said Lilach Hadany, an
evolutionary biologist at Tel Aviv University and the
senior author of the study, in an email to Motherboard.
“It appears that plants could have a lot to benefit
from acoustic communication.”
Hadany added that her team had predicted that plants
would make airborne sounds, and yet they were still
surprised by the clear results. “We were particularly
happy that the sounds turned out to be informative—
containing information on the type of the plant and the
type of the stress,” she noted.
Previous research has suggested that plants can emit
acoustic vibrations by forming and collapsing air
bubbles in their vascular system as part of a process
called cavitation. To test out the range of these
sounds, Hadany and her colleagues deliberately stressed
out a bunch of tomato and tobacco plants by cutting
their stems and depriving them of water.
The results show that a stressed plant can produce up
to 50 sounds a minute—far more than their unstressed
counterparts—and that the patterns of their clicks are
linked to specific complaints. For instance, a machine
learning tool that listened to the plants in a silent
acoustic chamber was then able to identify the ailments
of plants in a later version of the test conducted in a
noisier greenhouse environment, with a high degree of
accuracy.
“Here we show that plants indeed emit airborne sounds,
which can be detected from several meters away, both in
acoustic chambers and in greenhouses,” the team said in
the study. "Moreover, we show that the emitted sounds
carry information about the physiological state of the
plant. By training machine learning models, we were
able to distinguish between drought-stressed, cut, and
control plants, based only on the sounds they emit.”
The study focused on tobacco and tomato plants because
these species are so well-studied, but the researchers
were also able to record sounds from a variety of other
plants, such as wheat, corn, cactus, and the grapevine
that makes Cabernet Sauvignon. Hadany said that it’s
not yet known whether the noises are a specific mode of
botanical communication, or they are just an incidental
acoustic byproduct of cavitation, but it does seem to
be a common response across a diversity of species.
“What we do know is that there are sounds in the air,
and they contain information,” she explained. “Thus,
natural selection may be acting on other organisms
(animals and plants) to whom the sounds are relevant,
to be able to hear the sounds and interpret them. That
includes animals that can hear the sounds and can use
the information to choose a food source or a laying
site, or potentially plants that can prepare for the
stress.”
“That may or may not lead to natural selection acting
on the plants emitting the sounds (to emit more or
less) but this is a complete speculation at the
moment,” Hadany continued. “I think future studies
would reveal who is listening to the sounds, and that
may give us a hint on their evolution as a mode of
communication.”
To that end, future studies might unravel the
ultrasonic language of plants, allowing us to listen in
on their conversations (though it seems they get most
chatty when they’re upset). In addition to helping
scientists understand how plants interact with wild
environments, these efforts might give farmers a new
tool for evaluating the health of their crops.
“Plant sound emissions could offer a way for monitoring
crops water and possibly disease states—questions of
crucial importance in agriculture,” the team said. “In
times when more and more areas are exposed to drought
due to climate change, efficient water use becomes even
more critical, for both food security and ecology.”
“Plants were already shown to react to sounds, and
specifically to increase their drought tolerance in
response to sounds,” the team concluded. “Could plants
potentially respond adaptively to the sounds of their
drought-stressed or injured neighbors? We suggest that
more investigation in the plant bioacoustics field, and
particularly in the ability of plants to emit and react
to sounds under different conditions and environments,
may reveal a pathway of signaling between plants and
their environment.”
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