Plants make noises when they are thirsty, scientists discovered.
Tomato and tobacco plants studied were found to emit high-frequency pops and clicks when stressed by thirst, or when their stems are cut.
The noises could be detected from more than a metre away by some animals and other plants. Though similar in volume to human conversation, they are out of our hearing range.
Plant sounds have been recorded before, as underground vibrations, but this study is the first to confirm they also travel through air.
Recordings were made of healthy and stressed plants, first in a soundproofed chamber and then in a noisier greenhouse. Researchers stressed some plants either by not watering them for several days or by cutting their stems.
They then trained a computer to differentiate between unstressed plants, thirsty plants and cut plants. Stressed plants emitted 30 to 50 clicks per hour at seemingly random intervals.
Unstressed plants made far fewer sounds. Senior author Prof Lilach Hadany of Tel Aviv University, Israel, said: “Even in a quiet field, there are actually sounds that we don’t hear, and those sounds carry information.
“There are animals that can hear these sounds, so there is the possibility a lot of acoustic interaction is occurring.”
Prof Haldany said it was not proven that the sounds were used for communication but added: “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.” The study was published in the journal Cell.
