Though it has been assumed that plants are generally silent, new research now challenges this assumption. Scientists have discovered that stressed plants, specifically, make several noises.
The Sound of Stressed Plants
Lilach Hadany, the study's senior author and an evolutionary biologist and theoretician from Tel Aviv University, says that even in a quiet field, there are inaudible sounds that hold vital information. Their study was published in the Cell journal.
According to Nature, dehydrated plants or those whose stems were recently chopped off may produce around 35 sounds per hour. On the other hand, plants that are uncut and hydrated are significantly quieter. They only produce one sound per hour.
Both tobacco and tomato plants were the focus of the study due to their easy control and growth in a lab setting. However, the team also looked into the sounds of other plants, such as cacti, wheat, and corn. Both tobacco and tomatoes mainly produce clicking sounds when being chopped off or dehydrated, as reported by the Verge. The other plants also issue distress sounds.
The research suggests that if these plant species release sounds, others may also do so. It also indicates the possibility of audio-monitoring plants in horticulture or farming. There is a need, however, for further research.
The sounds of distress were prolonged for the water-deprived plants. They made more noise in their first few days of dehydration. In fact, before drying out, the plants reached a high crescendo.
Due to this, it was possible to differentiate between minimally dehydrated and extremely dehydrated plants. The researchers were also able to program an algorithm for machine learning that can tell the difference between healthy, cut, and dry plants. The model had 70% accuracy.
Because of the sounds' extremely high frequency, humans have been unable to detect them. These sounds are ultrasonic, with a frequency of around 20 to 100 kilohertz. This means the noises are too high-pitched for humans to hear them barely.
Nevertheless, the researchers were able to record the clicking plant sounds, which can be accessed here. This marks the first time scientists have documented plant-sourced airborne sounds.
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How Do Plants Make Sounds?
How plants were able to make such sounds remains a mystery. However, one possible explanation for the phenomenon is that the sounds trace back to air bubbles created and pop inside a plant's vascular system. Such a phenomenon is referred to as cavitation. It is known to occur among plants that are drying.
Hadany notes that the exact mechanism needs to be studied further.
Can Animals Hear Them?
As per the Verge, there may be some animals and plants that can interpret these noises. This listening ability could even aid humans in crop production, especially considering how climate change continues to be a pressing stressor.
However, Graham Pyke, a retired biologist from Macquarie University, expresses skepticism regarding whether animals hear stressed plant moans. He notes that animals are unlikely to pick up such sounds at particular distances. Pyke thinks that the sounds are too faint. Further research on the matter is necessary.
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