The Secret Life of Plants: Research Shows They Make Audible Noises When Under Stress

For a long time, it was commonly believed that plants suffered in silence, enduring the hardships of being neglected, dehydrated, or diseased with an unwavering sense of resilience. However, recent findings suggest otherwise.

Scientists have revealed that plants emit distress signals when they require watering, even though these high-pitched emergency calls are inaudible to humans. By recording the sounds of various plants such as tomato, tobacco, wheat, corn, and cactus, researchers have discovered that plants produce occasional ultrasonic popping noises, resembling the sound of bubble wrap, which become more frequent and intense when they are under stress.

Although the sounds emitted by distressed or thirsty plants are as loud as regular human conversation, they are too high-pitched for the human ear to perceive. Nevertheless, it is probable that insects, other mammals, and even other plants are capable of detecting these sounds.

“An idyllic field of flowers can be a rather noisy place,” points out Professor Lilach Hadany, “it’s just that we can’t hear the sounds.”

The findings of the study, published in the journal Cell, “suggest that the world around us is full of plant sounds, and that these sounds contain information – for example about water scarcity or injury.

“We assume that in nature the sounds emitted by plants are detected by creatures nearby, such as bats, rodents, various insects, and possibly also other plants – that can hear the high frequencies and derive relevant information.”

There has been controversy regarding the idea that plants emit sounds, with some studies suggesting that they emit “screams” when cut or uprooted. While vibration detectors have picked up pulses from plants, it was unclear whether these pulses translate into audible sound waves.

To investigate this further, the research team placed plants in a soundproof acoustic box in an isolated basement, devoid of any background noise. Ultrasonic microphones were positioned about four inches away from each plant, recording sounds at frequencies ranging from 20-250 kilohertz, which are beyond the range of human hearing (with the maximum frequency detected by an adult human being around 16 kilohertz).

The plants were subjected to various treatments, including being deprived of water for five days or having their stems cut. A control group was left untouched to compare the results.

The recorded sounds indicated that plants produced noises ranging from 40-80 kilohertz. The study revealed that plants which were not subjected to any stress produced fewer than one clicking sound per hour, on average. In contrast, the plants which were stressed due to either dehydration or injury emitted several dozen sounds every hour.

Interestingly, water-stressed plants began producing sounds even before displaying visible signs of dehydration. It was possible to identify both the type of plant and the specific stress it was experiencing based on the pattern of clicks it emitted. For instance, a dehydrated tomato plant produced a different sequence of clicks compared to a dehydrated cactus. Plants that were well-hydrated and healthy were notably quiet in comparison.

The researchers are optimistic that in the future, it may be feasible to monitor plants and detect any signs of distress or struggle by analyzing their sound patterns. According to the study’s authors, this technology could have a multitude of practical applications, including the use of sound recordings in agricultural irrigation systems to track crop hydration levels and enable more efficient water distribution.

“The fact that plants are making these sounds opens a whole new avenue of opportunities for communication, eavesdropping, and exploitation of these sounds,” adds co-senior author Yossi Yovel.

The precise mechanism by which plants produce these sounds remains unclear, but the research team posits that the popping noises could result from the formation and bursting of air bubbles in the plant’s vascular system, a phenomenon referred to as cavitation.

The researchers speculate that other plants may be capable of hearing and benefiting from these sounds. Previous studies have demonstrated that plants respond to the sounds produced by pollinators by increasing the sugar concentration in their nectar.

According to Prof Hadany, “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.”

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