Have you ever heard plants… cry for help? It may sound like a science fiction story, but in reality, scientists have discovered that plants actually emit sounds when they are under stress. From tomato plants to tobacco, these sounds are not just whispers but carry specific meanings about the plant’s health status. Let’s uncover this secret!
So, What Are Plants “Saying” to Us?
The story begins with a biological phenomenon called cavitation – when a plant lacks water, air bubbles form and burst in the water-conducting vessels, causing vibrations. But this is not just “internal noise”! New research shows that these vibrations produce ultrasonic sounds (20–150 kHz), which are inaudible to the human ear but can be detected with special microphones.
In experiments, both tomato and tobacco plants, when dehydrated or cut, emitted sounds at much higher frequencies compared to healthy plants. Specifically:
- Dehydrated tomato plants: Emitted 35 sounds/hour.
- Dehydrated tobacco plants: Emitted sounds at a lower frequency, about 11 sounds/hour.
- Healthy plants: Almost completely silent.
What Did the Scientists Do?
To answer this question, the researchers designed two main experiments:
- Soundproof Room Experiment:
- Sounds from tomato and tobacco plants were recorded using directional microphones in drought and cut conditions.
- Frequency range detected: 20–150 kHz, beyond the capability of the human ear.
- Greenhouse Experiment:
- Plants were monitored in a more natural environment, with background noise like wind and air conditioning.
- A convolutional neural network (CNN) was used to classify the sounds and filter out noise.
- The AI system was able to distinguish the drought and cut conditions of the plants with an accuracy of up to 84%.
Additionally, the research team measured soil moisture and transpiration rates to compare with the frequency of sounds emitted by the plants. When soil moisture dropped below 5%, the number of sounds increased significantly. The sounds peaked on the 4th-5th day after the plant started to dry out, and then gradually declined as the plant nearly dried out.
Potential Applications
Precision Agriculture:
- The technology of detecting plant sounds could provide early warnings when plants are lacking water, helping save up to 50% of irrigation water.
- It can also enable automatic monitoring of plant health in greenhouses or fields.
Ecology:
- Understanding plant behavior to interact with other organisms: Sounds from plants might be a form of communication between plants or with animals. Scientists suspect that animals or insects have evolved to “hear” the sounds of plants, forming survival strategies based on this information.
- Potential applications in studying ecosystem adaptation and responses to climate change.
Conclusion
This discovery is not only fascinating but also has significant practical implications in resource conservation and enhancing agricultural efficiency. The sounds emitted by plants are no longer a mystery but a useful tool that helps us connect more deeply with the natural world.
What Assumptions Were Used in This Study?
- The sounds emitted by plants are primarily caused by the cavitation process. This assumption needs to be further validated with more plant species and varying conditions.
- Ultrasonic sounds are not significantly affected by background noise in natural environments. This requires more field testing.
- Machine learning algorithms could be applied more broadly to different plant species. This needs data from more plant species.
Original Research Paper:
“Sounds emitted by plants under stress are airborne and informative”
Khait, Itzhak et al.
Cell, Volume 186, Issue 7, 1328 – 1336.e10