Astonishing Findings: Stressed Plants Emit Sounds That Animals Hear
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Chapter 1: Understanding Plant Communication
What occurs when plants experience drought or injury? Surprisingly, they begin to emit ultrasound waves, which can be recorded. This discovery raises the possibility that in the future, we could determine when crops need watering based on these sounds.
Plants are often viewed as silent beings, associated with peace and quiet. However, this perception may only apply to humans. Creatures like bats, rats, and hamsters, which can detect ultrasound, might have a different perspective.
A recent article in the scientific journal Cell presents evidence that plants do indeed generate sounds, specifically ultrasounds. These sounds are produced continuously, but their frequency increases significantly under stress from drought or physical damage. Healthy plants emit sounds roughly once an hour, while those suffering from lack of water or injury can "cry out" up to 35 times more frequently.
Section 1.1: Why Can't We Hear Plants?
Unfortunately, humans cannot hear the sounds made by our houseplants asking for water. The noises produced by plants range from 20 to 100 kilohertz (kHz), which falls within the ultrasound range—too high for human ears. While the upper limit of human hearing is around 20 kHz, even those sounds are only audible to some individuals.
In contrast, many animals are equipped to hear and produce ultrasound. For instance, bats utilize these sounds for echolocation, aiding in their nocturnal hunts. Moths can detect these frequencies, giving them a chance to evade their predators. Other species, such as dolphins, whales, hamsters, and dogs, also possess this ability.
Subsection 1.1.1: The Sounds of Plants
Prof. Lilach Hadany, who led the research, recorded the sounds emitted by plants and manipulated the playback speed. The resulting audio resembled the quiet popping of popcorn, which can be listened to here.
The research team examined various plant species, including tobacco (Nicotiana tabacum) and tomatoes (Solanum lycopersicum). Seedlings were placed in small enclosures equipped with microphones to capture the sounds of both well-watered and stressed plants.
Interestingly, plants lack vocal cords or lungs, so how do they produce sounds? Scientists propose that the sounds originate in the xylem, the tissue responsible for transporting water and nutrients. The process is akin to drinking through a straw, where air bubbles can form and burst, leading to the sounds produced by the plant. As drought conditions worsen, the frequency of these sounds increases.
Section 1.2: Can We Detect Plant Thirst?
This research could have significant implications for agriculture. The scientists explored whether it’s possible to determine a plant's need for water based on its sounds. By developing and training a machine learning model, they achieved a 70 percent accuracy rate in identifying stressed plants.
In the future, such technology could facilitate an automated system for monitoring crop needs based on emitted sounds. The research team successfully recorded plant sounds in greenhouse environments.
Chapter 2: The Intriguing Discoveries of Plant Behavior
Additionally, Prof. Hadany's team made another remarkable finding: the evening primrose (Oenothera drummondii) starts secreting nectar in response to the sound of an approaching bee. This suggests that plants not only emit sounds but are also capable of "listening."
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