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.
