New research finds plants make noise when stressed

Stressed tomato (Solanum lycopersicum) plants emit remotely-detectable and informative airborne sounds
Stressed tomato (Solanum lycopersicum) plants emit remotely-detectable and informative airborne sounds. Image credit: V. Wald.

Researchers have realized a video of the sound that plants make when they are under stress. Every plant and stress is associated with a specific sound. These high-frequency sounds are inaudible to humans but can be heard by animals like bats, mice, and insects, researchers added. The sound volume is similar to human speech and resembles like he popping popcorn.

Plants emit informative airborne sounds under stress

The team recorded tomato (Solanum lycopersicum) and tobacco (Nicotiana tabacum) plants under different treatments: drought stress, cutting of the stem, and controls.

The number of sounds emitted by drought-stressed plants was about 35 and 11 per hour for tomato and tobacco, respectively, and cut tomato and tobacco plants emitted about 25 and 15 sounds per hour, respectively.

Spectrograms of sounds emitted by stressed plants.
Spectrograms of sounds emitted by stressed plants. Image credit: Khait et al, doi: 10.1101/507590.

In contrast, the number of sounds emitted by plants from all the control groups was lower than one per hour.

“We show, to our knowledge for the first time, that stressed plants emit airborne sounds that can be recorded remotely, both in acoustic chambers and in greenhouses,” the scientists said.

“We recorded 65 dB SPL (dB of sound pressure level) ultrasonic sounds 4 inches (10 cm) from tomato and tobacco plants, implying that these sounds could be detected by some organisms from up to several feet (meters) away.”

Professor Hadany and co-authors also developed machine learning models that were capable of distinguishing between plant sounds and general noises and identifying the condition of the plants — dry, cut, or intact — based solely on the emitted sounds.

“Our results suggest that animals, humans, and possibly even other plants, could use sounds emitted by a plant to gain information about the plant’s condition,” they said.

“More investigation on plant bioacoustics in general and on sound emission in plants, in particular, may open new avenues for understanding plants and their interactions with the environment, and it may also have a significant impact on agriculture.”

Do plants make a noise when they’re in pain?

Researchers at Tel Aviv University in Israel have found evidence that plants do make noises when they are under stress. Their findings were published this week in the peer-reviewed journal Cell Press. Scientists say the frequency of the sound is too high for human ears but could be heard by insects or mammals.

How did researchers record the sound of plants?

The researchers used microphones to record healthy and stressed plants.

“We recorded the sounds emitted by plants, we used mostly tomato and tobacco, but we also recorded wheat corn, grapevine, cacti,” says lead author Lilach Hadany. Hadany explains that the team used different methods to distress the plants along with colleagues.
“We used mostly two stresses, drying the plant and cutting it with scissors, and in both cases they emit sounds. During dehydration, if we stop watering the plant, it started emitting a sound, and about day two it peaks.”

The recordings were made in a soundproofed acoustic chamber with a greenhouse environment.
After recording the plants, the researchers trained a machine-learning algorithm to differentiate between unstressed plants, thirsty plants, and cut plants. They took several examples of ultrasonic sounds, compiled them in a small time frame, and changed the frequency to be audible to human hearing. According to Hadany, an evolutionary biologist, ultrasonic vibrations have been recorded from plants before, but not when transmitted through the air.

Do plants communicate through sound?

The scientists believe further research could reveal more about how plants interact with their environment. Hadany says just because we can’t hear plants, it doesn’t mean that they are silent to other forms of life. Insects like moths, or mammals such as mice and bats, can hear plants. But the reason why plants make noise is “an exciting question that is not yet clear.”

“There are two options, the exciting direction is that it is used for communication, but there is also the option that the sounds are a byproduct of physiological processes,” explains Hadany. What’s also not yet clear is whether the sound-emitting plants are hoping to distract predators or attract pollinators.

“So we can think of a female moth intending to lay eggs. It can lay eggs on a tomato, and now there are several tomato bushes, some emitting sound, and others are not,” Hadany says. “Would it prefer the ones that emit sounds or those that do not? This is something we’re looking at, at the moment.”

What are the sounds plants make when happy?

The “happier” plants are the fewer sounds they make.

Source: Biorxiv

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