In fact, most people probably give little thought to how plants feel when they dry out or are pruned. But in fact, tomatoes, for example, feel stress in such a situation – and also communicate it. In a study, Israeli researchers found that plants make a noise when they are stressed, which sounds similar to a base foil bursting. Humans can’t hear this sound because of the high frequency, but that doesn’t mean the environment doesn’t hear it.
Plant trees, but do it right: what matters in reforestation projects
Plants stressed when drying out or cutting
A research team from Tel Aviv University conducted the study and published the results in the journal Cell. In addition to tomatoes, the researchers also examined tobacco plants. According to them, dehydration or cut stems cause these plants to emit sounds that are comparable in volume to normal human conversation. The frequency of these sounds is too high for our ears to pick up, but likely they can hear insects, other mammals, and possibly other plants.
“Even in a quiet field, there are sounds that we don’t hear, and those sounds carry information,” says lead author Lilach Hadany, an evolutionary biologist and theorist at Tel Aviv University. “There are animals that can hear these sounds, so there’s a possibility that there’s a lot of acoustic interaction going on.” Researchers used microphones to record healthy and stressed tomato and tobacco plants, first in a soundproofed acoustic chamber and then in a noisier greenhouse environment.
Climate neutral by planting trees? Environmental protection NGOs see it “critically”
Machine learning AI can distinguish sounds
After recording the sounds, the researchers trained a machine learning algorithm to distinguish between unstressed, thirsty, and cut-off plants. The team found that stressed plants made more noise than unstressed ones. The plant sounds resemble pops or clicks, and a single stressed plant will emit around 30-50 of these clicks per hour at seemingly random intervals, while unstressed plants make far fewer sounds. “If tomatoes aren’t stressed at all, they’re very quiet,” says Hadany.
The frequency of murmurs peaked after five days without water before decreasing again as the plants dried out completely. The type of sounds emitted differed depending on the cause of the stress. The algorithm was able to accurately distinguish between dehydration and cutting stress, and was also able to determine whether the sounds came from a tomato or tobacco plant.
Photosynthesis without sunlight – US researchers grow plants in the dark
Sounds can bring important information
Although the study focused on tomato and tobacco plants because they are easy to grow and standardize in the laboratory, the research team also included a variety of other plant species. “We found that many plants – for example corn, wheat, grapes and cacti – emit noises when they are stressed,” says Hadany.
The researchers suspect that these sounds could be due to the formation and bursting of air bubbles in the plant’s vascular system, a process known as cavitation. It’s unclear if the plants make these sounds to communicate with other organisms. In any case, the researchers believe that these sounds can probably bring a lot of valuable information. Hobby gardeners who do not want to stress their plants should definitely always be careful not to leave them dry.