For the past few weeks, I’ve been hearing over and over about this new discovery that stressed plants make sounds.
Sometimes my two dogs jump up at the same time and bark to let me know that they heard something (that I obviously didn’t hear)… Coincidence? I don’t think so!
The Scientific Study
I often say that my plants talk to me. They show it when things are not going well: spots, loss of tone, coloring… But we now know that they also emit ultrasounds to lament.
I imagine my rather limp plant screaming in a very high-pitched voice: «I’M THIIIIIIIRSTYYYYYYYY!!!”… And inevitably, my scientific mind wonders: do animals hear? What is the purpose of these sounds? Are they all equivalent according to the type of stress or the type of plant? What a cacophony, it must be in the forest in full drought!
I’ve consulted the scientific article at the source of this discovery because by reading the different texts, I realized that the journalists did not all grasp the same information… And I want to know if my dogs really hear my plants!
Here’s some information taken directly from the article in question.
1. How Do Plants Make Sounds?
It’s long been known that plants under stress (not from school or work, but from environmental stress such as lack of water or light) can emit vibrations. These are obviously minimal and are caused by pressure changes in the plant.
As for airborne sounds (sounds are vibrations that travel through the air), it’s likely that they would also come from pressure changes in the channels of the plants. Think of a flute, or a balloon: they don’t produce the same sounds depending on the force of the air (pressure), or on the “outlets” of that air. These changes in pressure create vibrations that are audible. Think of a vibrating guitar string.
2. How Can You Hear These Sounds?
Our human ears unfortunately cannot. At the same time, I wouldn’t want to hear all my plants lamenting the mistreatment they receive.
These sounds don’t carry very far. During the study, microphones were positioned a few dozen centimeters away from the plants. Moreover, the sounds are in a frequency inaudible to the human ear (a bit like the ultrasounds of bats).
I would have liked to tell you more about decibels and hertz, but after reading the article, as well as the Wikipedia page on decibels, I have to admit that I don’t understand any of these sound calculations!
Let’s just say that the sounds are too high and too low for the human ear. You need special microphones to record these sounds, computer programs to modify and amplify them so that you can hear them (or rather see them thanks to the sound curves) and, obviously, be an expert in the field!
3. Who Hears These Sounds (What Are They For)?
Very good question! What is the use of “saying”: OUCH! SOMEBODY HAS CUT A BRANCH!
Here, we are in the world of assumptions. The study was able to show that plants make different sounds depending on the species and the nature of the stress (in this case, drought or cutting). However, some hypotheses make a lot of sense.
Some moths that can hear these sounds might use them to choose the right tree to lay eggs in. Indeed, a stressed tree might be a less good choice: they want a healthy host to put their babies in!
Also, plants may react to sound to protect themselves from drought. If a neighbor is short of water and we perceive his stress, we manage not to lose our own water unnecessarily and we slow down his transpiration (yes, plants breathe and transpire!).
I remember hearing about a tree that emitted pheromones when it was nibbled by an animal. It warned its neighbors, who sent a compound into their leaves to present an unpleasant taste and protect themselves. Maybe there is a similar influence with sounds?
I really hope for a future study on why plants have developed this mechanism and what is its role in nature, but for now, knowing that it exists is a good start!
The authors of the article would like to see this knowledge used one day, for example to understand plants in the field or in greenhouses in order to increase productivity, or to identify stress early on. They discovered that the plant emits sounds faster and faster depending on the intensity of the stress. Why wait for our plant to get low? As soon as it makes sounds, hop! A little water!
What to Do With All This?
For the moment, not much. It’s a great discovery, but it’s still too early to say that we understand plants. Too few species have been tested and we can never be sure that the experiment gave false results since it is the only one documented so far. It’s still really cool!
The article mentions that the sounds emitted by plants (between 20 and 100 kilohertz (kHz)) can be detected by many mammals and insects at a distance of 3 to 5 meters.
As these sounds are emitted in the spectrum audible by cats and dogs (which hear up to 60 and 50 kHz respectively), I like to believe that (even if I know nothing about sounds) they can hear them. Humans, on the other hand, can’t hear above 20 kHz.
Does your dog have a favorite tree to pee on? Maybe they have great conversations together!
Does your cat always roll around in your spider plant? Maybe he likes his cries of pain! (Cats are sadists, what do you expect?)
We’re a long way from knowing everything about our surroundings, so why not make some wild guesses?