Jake Massey
What do people and plants have in common? They're both alive and make sounds.
That's not a joke, but it is true, apparently.
Much like how you might scream your favourite swear word when you stub your toe, a study from Tel Aviv University in Israel - published in 2019 - discovered plants emit a high-frequency, ultrasonic scream when in distress.
Previous studies attached recording devices directly to plants, allowing researchers to listen for secret sounds inside their stems, but this study looked to ascertain whether their noises can travel through the air.
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Using 'stressed' tobacco and tomato plants, researchers placed microphones next to them at a distance of around four inches (10cm). One set of crops were subjected to drought conditions, while the other endured physical damage, aka snipping their stems.
In both cases, they found the plants began to emit ultrasonic sounds between 20 and 100 kilohertz – not a frequency us humans can pick up on without assistance, but a volume that could feasibly 'be detected by some organisms from up to several meters away', according to the study published on the bioRxiv database.
Tomato plants that had their stems cut let out around 25 ultrasonic screams every hour, while tobacco plants undergoing the same damage let out 15 distress squeals.
Interestingly, the plants exhibited different levels of stress depending on the conditions they were subjected to, with starvation appearing to be the catalyst for much more intense cries in tomatoes.
Drought-stressed tomato plants emitted about 35 ultrasonic squeals every hour, while tobacco plants only let out 11.
And it's not a coincidence either: plants that were left untouched - without any adverse environmental conditions - let out less than one squeal every hour, according to Live Science.
Summarising their findings, the group wrote: "These findings can alter the way we think about the plant kingdom, which has been considered to be almost silent until now."
With the assistance of machine learning, the researchers were even able to pick out distinct features of the sounds and identify the condition of the plants: dry, cut or intact.
The authors of the study even suggested a future in which farmers are able to identify different plants based solely on their screams alone.
As for how exactly these mouthless crops can squeal, the researchers said that it may be the result of an internal process known as cavitation, whereby air bubbles form and explode in the xylem, which is the tissue that transports water and minerals from the roots up the plant stem and into the leaves.
The study concluded: "We demonstrated for the first time that stressed plants emit remotely detectable sounds, similarly to many animals, using ultrasound clicks not audible to human ears.
"We also found that the sounds contain information, and can reveal plant state. The results suggest a new modality of signaling for plants and imply that other organisms could have evolved to hear, classify and respond to these sounds."