Stressed plants ‘cry’ — and some animals can probably hear them

Plants do not suffer in silence. Instead, when thirsty or stressed, plants make “airborne sounds,” according to a study published today in Cell1.

Plants that need water or have recently had their stems cut produce up to roughly 35 sounds per hour, the authors found. But well-hydrated and uncut plants are much quieter, making only about one sound per hour.

The reason you have probably never heard a thirsty plant make noise is that the sounds are ultrasonic — about 20–100 kilohertz. That means they are so high-pitched that very few humans could hear them. Some animals, however, probably can. Bats, mice and moths could potentially live in a world filled with the sounds of plants, and previous work by the same team has found that plants respond to sounds made by animals, too.

Crying crops
To eavesdrop on plants, Lilach Hadany at Tel-Aviv University in Israel and her colleagues placed tobacco (Nicotiana tabacum) and tomato (Solanum lycopersicum) plants in small boxes kitted out with microphones. The microphones picked up any noises made by the plants, even if the researchers couldn't hear them. The noises were particularly obvious for plants that were stressed by a lack of water or recent cutting. If the sounds are pitched down and sped up, “it is a bit like popcorn — very short clicks”, Hadany says. “It is not singing.”



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