Courtesy Pravda.ru

It seems that Roald Dahl did guess something: when plants are harmed, they emit sound signals – not exactly as humans or animals do when they make screams, but in the form of beeping or clicking sounds at ultrasonic frequencies that go beyond human hearing.

Photo: Openverse

These sound signals are amplified as the plant is stressed. According to a recent study, this phenomenon may be the means by which plants communicate their plight to the outside world.

Lilah Hadani, an evolutionary biologist at Tel Aviv University in Israel, said: “Even in a calm field, there are sounds that we can’t hear, and these sounds convey information. Some animals are able to pick up these sounds, which suggests the possibility of a wide acoustic interaction.

Plants are constantly interacting with insects and other creatures, many of which use sound to communicate. Therefore, it would not be optimal if plants did not use sound as a means of communication.

Plants under stress are more dynamic than one might expect. They undergo significant changes, including emitting strong aromas, changing color and shape. These changes serve as a danger signal to neighboring plants, prompting them to strengthen their defenses or attract animals that are able to cope with pests that harm the affected plant.

However, the question of the extent to which plants emit different signals, such as sounds, has not yet been studied. A few years ago, Hadani and her colleagues demonstrated that plants are capable of perceiving sound. This led them to wonder if plants could also make sound.

To investigate this question, they recorded the sounds of tomato and tobacco plants in various conditions: unloaded, dehydrated, and with the stems cut off. Recordings were made both in a soundproof acoustic chamber and in standard greenhouse conditions. Then a neural network algorithm was trained, which makes it possible to distinguish between sounds made by plants in different states.

The sounds made by plants resemble pops or clicks at frequencies too high for human perception, detected within a radius of more than a meter. Plants that are not stressed are usually silent.

In contrast, plants that are under stress make more noise, averaging about 40 clicks per hour depending on the type of plant. Dehydrated plants have a distinctive sound profile: they begin to click more often before there are visible signs of dehydration, intensify as the plant becomes more overdried, and decrease as it wilts.

The algorithm successfully distinguished between these sounds and even identified the types of plants that made them. Moreover, he did not limit himself to tomatoes and tobacco: other plants, including wheat, corn, grapes, cactus and shrubs, also made sounds.

For humans, the consequences of this are obvious: we can track the sounds made by thirsty plants and give them water before they become severely dehydrated. However, the question of whether other plants are able to perceive and respond to these sounds remains unexplored. Previous research has shown that plants can increase their resistance to drought in response to sound, making this question likely for further study.