The team, led by Itzhak Khait, examined the sounds emitted by tomato and tobacco plants when stressed by insufficient water or when their stems are cut. Microphones recorded ultrasonic sounds between 20 and 100 kilohertz emitted by the plants in both cases, the study found.
The sounds emitted by the stressed plants are at frequencies unable to be heard by humans, however the team of scientists believes “some organisms” can hear the sounds from up to several meters away.
A tomato plant emitted 25 ultrasonic distress sounds in the space of an hour when its stem was cut, according to the study. In contrast, tobacco plants emitted 15 distress sounds when their stems were cut.
When deprived of water, the tomato plants sent out 35 ultrasonic sounds in the course of an hour, while 11 were emitted by the tobacco plants. The team observed that the sounds released when the plants were deprived of water were louder compared to the ones when having their stems cut.
In comparison, plants not placed under any environmental stress emitted less than one distress sound per hour.
The authors noted that other plants and animals—and humans with the correct tools—could hear and listen to the plants’ silent screams. A moth, for example, may choose to lay its eggs elsewhere if it is able to detect that a plant is water-stressed, according to the study, which has not yet been published in a journal.
In other cases, plants could react accordingly to others which lack water, the authors suggest.
“These findings can alter the way we think about the plant kingdom, which has been considered to be almost silent until now,” the researchers write in their study.
The Tel Aviv University team then took the data and used it to train a machine-learning model to predict the possible frequencies plants could emit while undergoing different forms of environmental stress, such as during intense rain or wind.
The team also believes other plants may release distress sounds when placed under stress.
“More investigation on plant bioacoustics in general and on sound emission in plants in particular may open new avenues for understanding plants and their interactions with the environment, and it may also have a significant impact on agriculture,” the authors suggested.
The notion that “sounds that drought-stressed plants make could be used in precision agriculture seems feasible if it is not too costly to set up the recording in a field situation,” Anne Visscher, a fellow in the Department of Comparative Plant and Fungal Biology at the Royal Botanic Gardens in the UK told New Scientist.