Plants are generally stationary; moreover, they supposedly cannot see, hear or produce sounds.
However, now, researchers are breaking some of these long known stereotypes. Apparently, it’s not that plants cannot hear or produce sounds. It’s just that we are not aware of them.
In two different studies published in the online archive of BioRxiv, researchers revealed that plants can hear the sounds of insects and react by sweetening their nectar to attract them for pollination. Also, some plants can produce high-pitched noises that are undetectable by human ears but can nonetheless be detected some distance away.
Sounds are very important to the survival of most creatures. With this, Lilach Hadany, Tel Aviv University researcher doubted if plants have acoustic abilities.
“Plants have plenty of interactions with animals, and animals both make and hear noises,” Hadany said to The Atlantic. “It would be maladaptive for plants to not use sound for communication. We tried to make clear predictions to test that and were quite surprised when it worked out.”
Flowers as Ears
If the plants can hear what are their ears? The answer is very simple—it is their flowers. The researchers chose to use flowers as their first subject as they are the key to pollination and plant reproduction. And they’ve hit jackpot.
To check if primroses could hear sounds, researchers did both lab and outdoor trials. In the laboratory, the plants underwent five sound treatments; silence, honeybee sound recordings, and computer-generated sounds in three different frequencies
During the silent treatment, where the plants were placed under glass jars to block vibration, there is no notable change in their sugar concentration. The results were the same when they used high-frequency (158 to 160 kilohertz) and intermediate-frequency (34 to 35 kilohertz) sounds.
However, when exposed to bee sounds (0.2 to 0.5 kilohertz) and other low-frequency sounds (0.05 to 1 kilohertz), the sugar concentration of the plants rose to up to 20 percent within three minutes.
To test if the flowers are the ones responsible for plant hearing, the researchers repeated the process on plants with some of their petals removed. And the result, the plants did not have a reaction with either bee sounds or other low-frequency sounds.
Communicating with Plants
If the plants can hear, could they also make sounds? One which can signal animals or maybe other plants from afar?
Previously researchers found that dry or damaged plants give off popping noises. But that could be hardly called communicational. The researchers had to put microphones in the stem to hear the sounds.
The team tested tobacco and tomato plants by putting them into soundproof areas with sensitive microphones. They found out that the plants emitted short ultrasonic sounds every few minutes. The sounds have a volume of 60 decibels from a distance of four inches.
Additionally, as if asking for help, the damaged plants produce sounds more frequently than healthy plants. The sounds they produce are also different.
With its high pitch, the sound cannot be detected by human ears. However, that cannot be said for the animals near the area. “Ultrasonic-sensitive creatures like moths and bats, going around a field, might be hearing lots and lots of sound,” Hadany said