Even though plants lack ears like most animals, they are capable of responding to sound vibrations and making physiological changes based on the signals they receive.
Our environment is filled with sounds, and throughout evolution, animals have developed different mechanisms to receive and utilize these sounds for their benefit. For humans, our ears serve as a specialized organ for sound perception. In contrast, certain animals, such as snakes, perceive sounds through their body surface.
However, there is another group of organisms that coexist with us in our world – plants. Is it possible for plants to perceive sounds as well?
Definition of Sound
Sound refers to the vibrations that propagate through a medium, such as air, water, or solid material. When animals detect these vibrations, their specialized organs for sound perception amplify and convert them into electrical signals. These organs, known as ear ossicles, are the smallest bones in the human body.
Sound is a type of vibration that can be detected by both animals and humans. (Photo Credit : maxpixel)
These converted electrical signals then travel to the brain through the auditory nerve and are processed in the auditory cortex, which is located in the temporal lobe.
The frequency of sound is measured in Hertz (Hz), while its intensity is measured in decibels (dB).
Can Plants Sense Sounds?
Plants may not have a brain, but that doesn’t mean they can’t interact with their surroundings. For example, sunflowers turn towards the sun, and Touch-me-not plants shrink upon physical contact. If plants can respond to light and touch, is it possible for them to respond to sound as well?
Studies investigating the effects of acoustics on plants have shown that plants do respond to sounds.
Studies have indicated that plants have the ability to perceive sound vibrations and react to them accordingly. Plants can detect sounds in two different ways. Firstly, they can directly sense vibrations, such as when a caterpillar is chewing on their leaves. The rhythmic pattern of the caterpillar’s chewing can be felt by the plants. Secondly, plants can also sense vibrations that travel through a medium, such as air or soil. They can detect the movement of water in the ground, as well as the buzzing of insects.
Researchers from the University of Missouri conducted an experiment where they recorded the chewing sounds of caterpillars as they ate leaves. They then played these sounds back to Arabidopsis plants. When exposed to the chewing sounds, the plants released certain chemicals, specifically glucosinolates and anthocyanin, which are known to protect plants from herbivorous attacks.
Interestingly, the plants only produced these chemicals in response to the chewing sounds. When exposed to the sound of wind or insect buzzing, the plants did not exhibit high levels of these same chemicals. This suggests that plants have a specific defensive reaction to the sounds produced by herbivores feeding on them.
Plants have unique reactions to the sounds made by insects, such as bees buzzing. Insects, especially bees, play a crucial role in pollination and the spread of plants. Researchers from Tel-Aviv University in Israel discovered that when they played the sound of bees buzzing to Beach Evening Primrose flowers, the flowers produced sweeter nectar within three minutes of hearing the buzz. The buzzing sound from insects stimulates the production of sweeter nectar in flowers.
Moreover, plants are even capable of sensing the sound of trickling water. Evolutionary biologists from the University of Western Australia observed that the roots of pea plants grow towards the sound of water. Plant roots serve as water sensors and use moisture gradients to navigate through the soil and reach areas with abundant water. The question is, how do plants know where to find water in the first place? The scientists proposed that plants can sense the sound of water in the soil, which guides them to the correct location. The roots of plants grow towards the sound of water.
Can Plants Hear Without Ears?
As mentioned previously, sound is a type of vibration. Humans perceive sound because our brain converts these vibrations into electrical signals. Snakes, however, sense sound differently. They feel vibrations through their skin, similar to a rhythmic touch.
Plants also have specific structural features that enhance their ability to perceive sound. The Evening Primrose flower, for example, is shaped in a way that amplifies the frequency of insect pollinator wing flaps.
The evening primrose flower has a shape that helps amplify the wing beat sound of insects. (Photo Credit : twenty20) Some plants have the ability to reflect sound to animals. In the dense forests of Central American Rainforests, there are two vine species that are pollinated by bats and have large dish-like leaves. These leaves serve as reflectors, bouncing the sound produced by the bats back to them. This echoing effect helps the bats locate these specific vines amidst the dense foliage of the forest. (Photo Credit : twenty20)
Summary
In conclusion, the ability of plants to perceive sound has evolved as a means to enhance their chances of survival and reproduction. Throughout their lives, plants are exposed to a range of sounds, including the buzzing of insects, the gentle flow of underground water, the destructive feeding of herbivorous predators, and the rustling of their own leaves and those of nearby plants in the wind.
Researchers have proposed that plants interpret these sounds as mechanical (such as roots gravitating towards the water) or metabolic (such as plants releasing chemicals or nectar) signals, rather than electrical signals like humans do.
Using Sound Frequencies to Improve Crop Yield
Specific sound frequencies have the potential to enhance crop yield. By utilizing sound frequencies within the 1 to 2.5 kHz range and with a volume of 90 dB, the germination rate of green beans can be notably increased.
There is no doubt that it has been firmly established that plants have the ability to perceive and react to sounds. Researchers are currently working on understanding the specific mechanism behind these responses, as well as investigating the impact of sound pollution on plants.