The auditory capacities of plants

Researchers demonstrate that plants have sensory abilities. Indeed, these would be capable, in the same way as any living being, of analyzing their environment and perceiving odors and sounds.

It is in such a perspective that a study was conducted by Israeli researchers from Tel Aviv University, then published in 2018 in the journal bioRxiv. This study highlights the auditory capabilities of plants by hypothesizing that they may respond to the buzzing of bees.

Plant hearing

Desmodium gyrans or Codariocalyx motorius is a sensitive tropical plant famous on the web for its ability to move to the beat of music. This has earned it the nickname "semaphore plant" or "dancing plant". Although this phenomenon is still not scientifically explained, it seems to confirm the ability of plants to pick up sounds.

In addition, recent studies suggest that some species may be sensitive to sound signals. Crawley University researcher Monica Gagliano, for example, found in 2012 that corn roots grow more around a sound source with a frequency of about 200Hz. A team from S. Mancuso's lab also noticed that some plant roots orient themselves toward water based on the water's noise. Nevertheless, the study by Prof. Lilach Hadany and Dr. Yuval Sapir of Tel Aviv University really confirmed some theories on the subject.

According to this study, plants do have the ability to hear, which would give them an evolutionary advantage. The researchers reported their observations on the evening primrose (Oenothera drummondii). This is a wild plant that grows in the parks of Tel Aviv. They subjected 650 plants of this species to different noises. This allowed them to discover that they temporarily produce sweeter nectar to attract pollinators.

Sensitive to the buzzing of bees

In 2018, the study led by Prof. Lilach Hadany shows thatbiennial evening primrose responds to the rustling wings of bees and butterflies that collect its pollen. In effect, the plant increases the sugar concentration of the nectar from its flowers for three minutes. This would cause the bee to stay longer on the flower, thus increasing its chances of pollination, but also attracting more insects of the same species afterwards. However, the reaction of the plant depends strongly on the frequency of the buzzing sounds, as demonstrated by Lilach Hadany's team by exposing it to different sounds. These included silence, recordings of honeybees at a distance of 10 cm and computer-generated sounds at low, medium and high frequencies.

The results were significant. Plants exposed to silence showed no increase in the sugar concentration of their nectar. The same was true for those exposed to medium (34 to 35 kH) and high frequency (158 to 160 kH) sounds. Those exposed to buzzing sounds (0.2 to 0.5 kH) and low frequency sounds (0.05 to 1 kH) produced a sweeter nectar. Thus, it seems clear that evening primrose has auditory capabilities.

Lilach Hadany's team has made a few hypotheses about this ability of plants to respond to the buzzing of pollinating insects. On the one hand, nectar production is demanding for plants, so they prefer to concentrate it during pollination periods to save this energy. On the other hand, the shape of the flowers is not only a function of its visual attraction, but also of its ability to capture and absorb sound.

The flower, the "ear" of the plant

In their experiments on the evening primrose, researchers at Tel Aviv University discovered that the plant's sensory sensors are located at its flower. The latter is able to perceive the vibrations produced in the air by the wings of pollinating insects and react to specific frequencies.

Researchers at Tel Aviv University moreover hypothesize that the shape of flowers is the consequence of a long evolution to capture sound signals more easily. This is why some flowers have concave or bowl shapes, making them look like satellite dishes. This would allow them to receive and amplify sound waves in order to react accordingly.

To prove their theory, the Tel Aviv University researchers performed the same experiments on plants that had one or more petals removed. As a result, they found that the flowers were less receptive to the buzzing of bees, meaning that the petals detect sound waves. They are, in a way, the "ears" of the flower. However, this may not be applicable to all plant varieties since this experiment was only tested in one family. Thus, it would be necessary to repeat the experiment on other plants.

According to an article by Hugo Struna, science journalist at Vigie Nature, published on France Inter, it would seem that plants have a multitude of vibration detectors. These would be distributed throughout their cells. Thus, it would be possible for plants to detect sound waves through their roots, as suggested by the study of Australian researcher Monica Gagliano in 2012.

It is therefore clear that researchers have yet to understand the auditory mechanism of plants, as well as its functioning. This is why the discipline of phytoacoustics is being approached more and more by scientists.

Sources:

https://www.ami-universite-telaviv.com/index.php/2013-05-26-08-41-51/recherche/sciences/biologie/972-les-fleurs-peuvent-entendre-les-insectes,-d-apr%C3%A8s-une-%C3%A9tude-de-l-universit%C3%A9-de-tel-aviv

https://fr.wikipedia.org/wiki/Codariocalyx_motorius

https://www.arkopharma.com/fr-FR/la-sensorialite-des-plantes-0