Status: 03/30/2023 5:42 p.m
Plants aren’t as quiet as many might think: if they don’t have enough water or are experiencing other stresses, they make noises, according to a study. Humans cannot hear them, but insects can.
According to a study, stressed plants can make a lot of noise – but people don’t hear it. The noises are about as loud as a normal conversation, but the frequency of the tones in the ultrasonic range is too high for humans, write scientists from Tel Aviv University in the journal Cell.
Pop like bubble wrap
“The sounds in the ultrasonic range could be heard from a distance of three to five meters by many mammals and insects,” say the researchers. For the study, they placed microphones about ten centimeters away from the plants, according to the preprint version, which was published in 2019. The recordings were made in a soundproof room and also in a greenhouse.
The sounds of the plants were therefore in the range between 20 and 100 kilohertz – too high for the human ear. However, the researchers have modified the audio signals to make them perceptible to humans as well. You can hear a pop that is a bit reminiscent of bursting bubble wrap.
How do plants sound under stress?
Khait et al. – Cell Press 3/30/2023 5:42 p.m
Algorithm can distinguish sounds by stress type
For the study, the researchers examined tomato and tobacco plants under different conditions. In one of the experiments, the plants had too little water, in another their stems were cut. Whether the plants produce such sounds to communicate with other organisms is unclear.
For comparison, the team also looked at undisturbed specimens. The result: According to the study, stressed plants emitted significantly more noise than healthy ones. Under stress, they made around 30 to 50 tones per hour. “When tomatoes aren’t stressed at all, they’re very quiet,” says Hadany. Using an algorithm, the team was also able to see how the sounds differed depending on the type of stress.
Concrete application conceivable
And other plants, such as maize or wheat, also make noises under stress, the scientists explain. “Therefore, it’s likely that noise is also emitted when the crop is cut,” says Lilach Hadany, an evolutionary biologist at Tel Aviv University. The team was also able to show that cacti, vines and deadnettles also make noises.
According to the researchers, the findings could also have a concrete use in agriculture: With the help of sound recordings, for example, the irrigation of plants in the field or in the greenhouse can be monitored and made more effective.
Air bubbles in the vascular system
The researchers assume that the cause of this phenomenon takes place inside a plant. Studies have shown that so-called cavitation occurs in plants that suffer from drought stress – the phenomenon has been known for some time. Roughly speaking, air bubbles form in the vascular system, which expand and collapse again. This leads to vibrations.
“The design of the study is good,” says Sibaji Kumar Sanyal, a molecular biologist at Heinrich Heine University in Düsseldorf, who was not involved in the study. You can quickly understand from the sounds if the plants were not watered properly. “Above all, the algorithms and the recording technology are very good.” For future studies, however, it is important to examine other plant species in addition to tomatoes and tobacco.