Ground Breaking Study: Plants Emit Sounds When Stressed
Plants are not as silent as previously thought, according to a groundbreaking study by researchers at Tel Aviv University. Although we cannot hear them with our ears, plants emit clicking sounds, similar in volume to human speech, but at frequencies too high for us to pick up. Researchers found that plants produce more sounds when stressed and that the sound varies according to plant species and the type of stress experienced. The sounds contain information that other animals and plants may be able to understand, meaning that the acoustic environment around us is full of plant sounds.
To record these sounds, researchers isolated plants in an acoustic box in an environment free of background noise. The study involved different plant species, including wheat, corn, cactus, henbit, tomato, and tobacco plants. Researchers subjected plants to various treatments before placing them in the acoustic box to test whether they emitted sounds and whether these sounds were affected by the plant’s condition. They used recording equipment capable of picking up frequencies between 20 and 250 kilohertz, exceeding the maximum frequency that the average adult can hear by 15 times.
Plants emitted ultrasonic sounds within the 40-80 kilohertz range, with dehydrated or injured plants producing dozens of sounds every hour, loud enough to be heard by any creature within three to five meters that can hear within the proper frequency. Sounds emitted by tomato plants were heavier and thicker than those emitted by grapevines, and researchers could distinguish between the type of plant and stress it was experiencing by listening to the sounds. After recording isolated sounds, researchers rerecorded them in a greenhouse setting surrounded by other plants and sounds and found that they could still recognize the distinct sounds from the plants.
The study resolved the controversy over whether plants emit sounds and suggests that the world around us is full of plant sounds containing information about water scarcity or injury. Many animals, such as bats and rodents, can hear higher frequencies than humans, meaning they have probably known about plant sounds for longer. Researchers believe animals have learned how to interpret the information communicated by plant sounds, and other plants may also be gleaning information from these sounds.
The researchers theorized that changing pressures within the stem of the plants could be creating the sounds, with different stem sizes corresponding to the different frequencies observed between plant types, but further research is needed.
The findings of the study could have practical implications, such as developing sensors that tell growers when plants need watering.
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