If you’ve ever spent time around babies, you’ll know that the main way they communicate their needs and feelings is through crying. New research suggests plants take a similar approach – when they’re thirsty or stressed, they make “airborne sounds.”
How to detect a crying plant
While you’d be hard-pressed not to hear a tiny human screaming right next to you, the same can’t be said for plants. Researchers had to use microphones to pick up the sounds emitted by plants, as it turns out they’re ultrasonic, pitched between 20 to 100 kilohertz.
The team focused on tomato and tobacco plants, first placing them in a soundproof acoustic chamber. They recorded both healthy and stressed plants, the latter of which were stressed by either not watering them for several days or by cutting their stems – understandable that the plants would be a bit peeved by that.
The recordings revealed that plants did indeed produce sounds, high-pitched noises resembling pops or clicks. The stressed plants produced around 25 to 35 of these sounds per hour, whereas the healthy plants were comparably quiet, emitting only around one sound per hour.
To test if these results could be reflected in a busier setting, the team developed a machine-learning algorithm to tell the difference between stressed and unstressed plants and tested it in a noisy greenhouse. The program successfully filtered out background noise, and the plants could still be heard – it could even deduce whether a plant had been stressed out by dehydration or cutting with about 70 percent accuracy.
How do the plants make sounds?
Given that plants don’t have lungs, how do they produce their popcorn-esque sounds? In their paper, the researchers explain that it could be down to a mechanism called cavitation in the plants’ water-transporting tubes, aka the xylem. Occasionally, air bubbles can form in the xylem, more so when a plant is under stress. The authors hypothesize that when these air bubbles form or burst, it could produce the popping sounds they recorded in the study.
Is anyone listening?
“[N]ow that we know that plants do emit sounds, the next question is – ‘who might be listening?’” said senior author Lilach Hadany in a statement. Unless we have microphones, the answer is not humans – the sounds are too high-pitched for us to hear without them. However, it’s possible that other mammals, insects, and other plants could hear them, although further research would be required to confirm that theory.
“Plants interact with insects and other animals all the time, and many of these organisms use sound for communication, so it would be very suboptimal for plants to not use sound at all,” said Hadany. As for what purpose communication would have, Hadany had a potential explanation: “It’s possible that other organisms could have evolved to hear and respond to these sounds. For example, a moth that intends to lay eggs on a plant or an animal that intends to eat a plant could use the sounds to help guide their decision.”
So, screaming when stressed may well be helpful after all – for plants, at the very least.
The study is published in Cell.