A stressful study
Itzhak Khait and his team at Tel Aviv University have been studying the ability of plants to communicate. Admittedly, plants do not have organs as such. However, on December 2nd 2019, the researchers published the results of their research on BioRxiv. The graduate student is formal: plants use ultrasound! Just like the TEE probes we repair.
While humans can hear ultrasound between 20 and 20,000 Hz, it is impossible to hear ultrasound from a plant. This is because plants emit ultrasound between 20 and 100 kHz when they are under stress.
For plants, stress can take many different forms. A lack of water, for instance, or the cutting of a root or stem. As Itzhak Khait explains: “Plants under stress produce observable phenomena such as changes in colour, smell and shape. However, the possibility that they make sounds in the air when stressed, like many animals, has never been studied”. This is the purpose of this study.
How was the experiment conducted ?
The team placed tomato and tobacco plants in three groups under stress. The first group was put in a drought situation by being deprived of water for 10 days. Meanwhile, the researchers cut the stems of the second group. Finally, the third group was a ‘control’ group and was not subjected to anything.
The test was carried out in an acoustic chamber and then in a greenhouse to simulate natural conditions… With special microphones placed 10 cm from the plants for one hour at a time.
Ultrasound in the acoustic chamber…
In the first group, under dry conditions, tobacco plants emitted 11 sounds per hour and tomato plants 35. In the second group, when cut, the tobacco plants produced 15 sounds per hour and the tomato plants 25. The control group made only one sound per hour.
… and in the greenhouse
The greenhouse findings were identical. However, the researchers point out that “the volume of the ultrasonic sound” can be detected by certain devices up to several meters away”.
Ultrasound for an agricultural application
For Itzhak Khait, this study has potential agricultural applications: “Our results suggest that animals, other plants and perhaps even humans could listen to the ‘silent cries’ emitted by plants and use them to gain information about their condition. The scope of the study is rather limited as we did not investigate the effects of disease, excessive salinity or unfavorable temperatures on the plants. However further research into plant bioacoustics in general, and plant sound emission in particular, could open up new avenues for understanding plants and their interactions with the environment, and also have significant implications for precision agriculture, especially if the sounds emitted by drought-stressed plants signal that they need more water.”