Stressed plants emit ultrasound noise

Amazing stuff! It appears to be passive noise as opposed to active noise.

"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. ...
Plants do not have vocal cords or lungs. ... the current theory for how plants make noises centers on their xylem, the tubes that transport water and nutrients from their roots to their stems and leaves. Water in the the xylem is held together by surface tension, just like water sucked through a drinking straw. When an air bubble forms or breaks in the xylem, it might make a little popping noise; bubble formation is more likely during drought stress. But the exact mechanism requires further study ..."

From the highlights and abstract:

"Highlights

• Plants emit ultrasonic airborne sounds when stressed

• The emitted sounds reveal plant type and condition

• Plant sounds can be detected and interpreted in a greenhouse setting

Summary

Stressed plants show altered phenotypes, including changes in color, smell, and shape. Yet, airborne sounds emitted by stressed plants have not been investigated before. Here we show that stressed plants emit airborne sounds that can be recorded from a distance and classified. We recorded ultrasonic sounds emitted by tomato and tobacco plants inside an acoustic chamber, and in a greenhouse, while monitoring the plant’s physiological parameters. We developed machine learning models that succeeded in identifying the condition of the plants, including dehydration level and injury, based solely on the emitted sounds. These informative sounds may also be detectable by other organisms. This work opens avenues for understanding plants and their interactions with the environment and may have significant impact on agriculture."

Stressed plants ‘cry’ — and some animals can probably hear them Microphones capture ultrasonic crackles from plants that are water-deprived or injured.

Sounds emitted by plants under stress are airborne and informative (open access)

Can you hear me now! 😊

Graphical abstract