Forgetting to water your plants happens from time to time. Aside from wilting leaves, it may seem like there are no other signs that the flora is not doing as well as it could. Well, a study published in Cell suggests that plants do have a way of communicating when they are stressed—by emitting high-pitched sounds.
Don't feel bad if you've never noticed it though. These noises range between 20 and 100 kilohertz, making them inaudible to the human ear. Actually, only some animals, like bats, mice, and moths, are believed to have the ability to hear these plant sounds. Likewise, the study found that plants may also respond to animal noises from their surrounding environment. “Even if the emission of the sounds is merely a result of the plant's physiological condition, nearby organisms that are capable of hearing these sounds could use them for their own benefit,” the study says. “Moreover, we show that the emitted sounds carry information about the physiological state of the plant.”
So, what triggers these plant sounds? It seems like major stress, such as lack of water and having their stems cut, triggers some plants to produce 35 sounds per hour—compared to healthy, uncut plants which make only one sound per hour. The study measured these differences by placing tobacco and tomato plants in small containers accessorized with microphones and limiting the water intake as well as trimming the stems. Although the researchers couldn't hear anything, the microphones were able to detect faint sounds. “It is a bit like popcorn—very short clicks. It is not singing,” says Lilach Hadany at Tel-Aviv University.
Naturally, the researchers wondered how plants emit these strange noises. Although there is no conclusion yet, they theorize that it depends on their xylem, which is how a plant transports nutrients from its roots to its stems and leaves. If an air bubble forms inside these tubes and breaks, it could possibly produce a popping sound; however, this is still just a hypothesis that requires further study.
A study suggests that plants emit high-frequency sounds when they are stressed.
These sounds are inaudible to the human ear, though.
They can only be heard by certain animals like bats and mice.