图源｜Little Shop of Horrors
Don't think that the plants are quiet and silent when they get hit. In fact, our ears didn't hear their voices...
Written by | chestnut
Review | Clefable
When human beings are under pressure and have nowhere to release, they may run to an open place and shout hard, as if this can drain the backlog of emotions out of the body and dissipate into the air.
If a plant is under pressure to survive, it may not be realistic to think of running around. But even if it can't be easily moved, the sound it makes can still pass through the air and drift farther away.
Often, it is difficult for humans to hear these sounds on their own ears to think that plants are a group of silent beings. But scientists in the lab, with the help of equipment, collected sound waves from plants as they "shouted."
Of course, before that, researchers have to inflict some damage before they can force the plants to shout. So, what exactly did they do?
Hurt, scream
Itzhak Khait and his colleagues from Tel Aviv University in Israel set up two dilemmas for plants to capture their sounds, one is drought and the other is the stem being cut.
The contestants who take these tests are our more common plants, tomatoes and tobacco. Before the experiment began, they all grew healthily in moist soil. After the experiment began, the fate of the plants was different: some were never watered again, some were cut off from the stem, and some continued to live under normal conditions, which were the control group.
The source | original paper
The experiment was carried out in a soundproof box, and the radio equipment was placed 10 centimeters away from the plant, listening to what kind of sound the plant would make after it was damaged differently.
As a result, both plants subjected to drought stress and plants with severed stems made a lot of noise: the volume was about 65 decibels (usually the volume of two people talking face to face was about 60 decibels), the frequency was between 20,000 and 100,000 Hz, which was ultrasound.
The human ear can probably only hear sounds between 20 and 20,000 hertz, and this range shrinks as we age. Therefore, if you replace the radio device with a person, standing 10 centimeters away from the plant, it is unlikely to catch such a high frequency of "screaming".
These shouts came very frequently. Tomato plants under drought stress emit an average of 35 sounds per hour, compared to 11 for tobacco plants. When the stem is cut, tomato plants emit an average of 25 sounds in the next hour, compared to 15 for tobacco plants. In contrast, plants that have not suffered drought and have not been cut, only make occasional sounds, and are not measured on average once an hour.
So scientists believe that these ultrasounds are the reactions of plants when they are under pressure to survive. Of course, in addition to being dehydrated and cut, plants face many other pressures, and not every one of them can form a scream.
How does this sound come about?
Sound is nothing more than an object vibrating.
As early as the 1960s, scientists detected vibrations during plant droughts and believed that those vibrations were caused by cavitation. When there is a lack of water, in the xylem of the plant, the dissolved air in the water will form bubbles, and then the bubbles will continue to expand and even burst, which is a cavity phenomenon.
The cavitation phenomenon will redistribute the stress in the plant, and when the stress is concentrated in one part, it is possible to quickly release a large amount of energy: it is mechanical energy that is converted into sound energy, so this process is called "Acoustic Emission" (AE).
In a 1966 study, scientists detected vibrations on both the leaves and petioles of castor| Milburn & Johnson
Researchers more than half a century ago discovered that it was by detecting the waveform emitted by plants that it was vibrating. Nowadays, in industry, people often use the principle of acoustic emission to check whether a piece of material is defective. If multiple sensors are utilized, it is also possible to determine the exact location of the defect.
However, when using acoustic emission to detect a certain piece of material or a plant, it is usually necessary to connect the sensor directly to the object being measured. Therefore, in past studies, although scientists have captured the sounds of plants, the sound waves rely on the plant body itself to propagate and be received by the device, which cannot prove that the outside world also has the opportunity to hear those sounds.
But this time, the tel Aviv University research team placed the radio device 10 centimeters away, proving that the ultrasonic waves emitted by plants in the absence of water or cutting did indeed spread through the air. And this means that even if humans can't hear it, there may be other animals that can hear it.
Scientists say the ultrasounds they collected may also be heard from 3 to 5 meters away in many mammals (such as mice) and insects (such as moths). This is important for researchers.
There is a difference between ultrasound and ultrasound
The team found that although the plants emitted ultrasound during drought and when the stems were cut, there were some differences in the ultrasound emitted by the plants under two different pressures.
Specifically, they wrote a machine learning algorithm, or AI, that fed the AI the sound waves collected in both cases to help it train its ability to distinguish between arid and cut plants. After the training is completed, the accuracy rate of AI distinguishing between the two exceeds 70%.
This means that the sound waves emitted by arid plants are different from those emitted by plants with severed stems, which are different for AI. Ai can distinguish the difference between the two, and other animals may also be able to distinguish it when they listen.
Scientists say that if an insect that parasitizes a plant can hear a difference in the sound waves, it is possible to use this information to prevent itself from laying eggs on an arid plant. If there is an insect that feeds on a plant, its natural enemies can hear the difference in the sound waves, and they have the opportunity to run in the direction of the sound waves, catch more insects, and protect the safety of the plant.
Plants perceive sound| dopi: 10.3389/fpls.2018.00025
In addition, it's not just animals that can hear sounds. Past studies have shown that plants also have strong perceptual abilities, responding to many stimuli, including sounds, in addition to being responsive to touch (such as mimosa closing). If one plant is in a drought trap and another hears its screams, it is equally likely to trigger some mechanism to protect itself.
Of course, scientists still have a long way to go before these ideas are confirmed.
Original paper:
https://www.biorxiv.org/content/10.1101/507590v4.full
Reference Links
https://academic.oup.com/jxb/article/64/15/4779/460888
https://pubmed.ncbi.nlm.nih.gov/24557825/
https://www.newscientist.com/article/2226093-recordings-reveal-that-plants-make-ultrasonic-squeals-when-stressed/
https://www.frontiersin.org/articles/10.3389/fpls.2018.00025/full
This article is reprinted from Universal Science (ID: huanqiukexue) with permission, please contact the original author for secondary reprinting.