Plants vent out ultrasonic squeaks when stressed; humans can’t hear them, but other plants and animals susceptible to ultrasonic sound certainly do.
The question is if a thirsty plant screams, why can’t we hear it?
We can’t hear a plant’s cry of distress because it is at a frequency too high, and humans can’t perceive high-frequency sounds. Many botanists have given evidence of plants producing ultrasound squeaks under stress. The state of a plant can be well judged by analyzing the emitted sounds. Plants are responsive when touched by insects, put in light, and in darkness. Researchers are suggesting they can experience pain too.
An experiment had been conducted using the tomato and tobacco plants. Both these plants had been subjected to two different levels of discomfort.
- Cutting of Stems
This experiment has been conducted by the School of Plant Sciences at Tel-Aviv University. They discovered that ultra-sound is emitted, ranging from 20-100 kHz. These sounds can be detected from approximately four meters. It is speculated that such sounds can be heard by neighboring plants or organisms in the range of four meters susceptible to sound levels of 20-100 kHz.
Many insects, such as moths and butterflies, which use plants as hosts for their larvae, can perceive and react to the sounds emitted by the plants. Such insects avoid laying eggs on a distressed or a discomforted plant. In the experiment conducted, proper computer intelligence has been used to differentiate between general sounds and plant sounds. Artificial Intelligence algorithms have been devised to diagnose different conditions of plants, whether cut or died out.
What is the science behind these sounds?
The process of cavitation is responsible for the ultrasound screams. Under this process, air bubbles form and explode in xylem, which creates vibrations. These vibrations are sounds recorded by the researchers experimenting. They even found that tomato plants subjected to thirst related discomfort emitted 35 sounds an hour, and the tobacco plant emitted 11 sounds an hour. The rate decreased to 25 sounds an hour for tomato plants when subjected to stress related to their stem being cut. However, the rate slightly increased to 15 sounds an hour for the tobacco plant when subjected to the discomfort associated with a cut stem.
The research was also conducted in a greenhouse too. A few adequately watered tomato plants had been set in the greenhouse for ten days. As the plants were watered, only a few sounds had been emitted for the first three days. From the fourth to seventh day, the plants were not watered, and the sounds per hour exceptionally increased. Conversely, the sounds diminished as the plants dried.
So far, the research has been conducted on tomato and tobacco plants. As quoted by the researchers, they will be extending the experiment to more species and conditions. The prospects for future research would be fascinating. Next time, you curse your bacia or let your cat ruin your lawn or forget to water your flowers, bear in mind that your leafy buddies have feelings too.