Recent news headlines reveal that plants scream in ultrasound when scientists cut their leaves. We can’t hear these sounds, but they’re there, and we can record them.
Media erroneously reported that as beyond doubt proof that plants, just like animals, communicate through sounds. They said that plants warn each other about danger through ultrasound screams and, most importantly, feel pain and an aversion to the pain.
But what does this actually mean? Let’s dive into the study published in “Cell,” a well-reputable journal that wouldn’t publish just anything. The study is great, and the problem isn’t in the study but in how it is reported in the media.
Do plants scream?
First, what did the researchers do, and what did they find? The researchers grew tomato and tobacco plants in a controlled environment and recorded the ultrasound that plants emitted during drought or when their leaves were cut. So far, so good; no one disputes that plants emit sounds. It’s been shown before.
Next, they trained an AI model to discriminate between sounds. They found out that, eventually, it could classify different sounds and understand what kind of stressor the plant was experiencing and also, in the case of drought, how intense it was.
This brings up various scenarios about plant communication. If the sounds under each stressor are different, it could potentially mean that these are forms of communication. But is it so?
How do plants “scream,” and what happens if we “listen”?
The researchers propose that the likely mechanism is vapor bubbles bursting in the stem. The stem changes shape and volume when it dries, and the air escapes from those cavities when cut.
This explains why sounds emitted at each condition are discernible, but I wouldn’t dismiss this as a form of communication. Similarly, one could say that animals don’t really “scream,” just that the air is rapidly escaping their lungs and travels through the trachea, making sounds.
The authors of the study don’t mention communication here. They state that it could lead to developing game-changing monitoring of plant conditions in greenhouses by recording the sounds they emit.
Place recording devices in a greenhouse or on a field, attach an AI that “listens” to these sounds, and you have an early warning system that the soil is too dry. It could save water since you can only water plants when they “tell” you to.
Given that about two-thirds of water usage accounts for irrigation in agriculture, this could potentially lead to enormous savings with great environmental impact. That was the point of the study, according to the authors.
Do plants communicate stress to each other?
You might ask, but do other plants respond to these “screams”? Unfortunately, this study didn’t investigate that. But could a plant do something about it if its neighbor “screams” about drought? It’s possible.
Plants have many defenses against drought, such as opening and closing their pores to conserve water, growing deeper roots or thicker cuticles. They can also change their physiology through altered gene expression, growing more oils, which can be broken down to create water when it is in deficit or even enter a dormant state with reduced growth (learn how plants grow here).
These are measurable outcomes, so I can easily imagine an experiment, growing plants in separate pots, next to each other. Would the plants in a well-watered pot change their physiology when grown next to a plant that’s experiencing drought?
This particular study didn’t look into that, but others have. One study (among many) found that plants under normal conditions respond to con-specifics growing in a neighboring pot under drought stress by conserving water and showed signs of oxidative stress. However, the authors of this study suggest that volatiles produced by stressed plants are the main mechanism of this interaction and they don’t mention “screams.”
Again, this doesn’t necessarily mean conscious communication. We also get sick when we taste something rotten. It doesn’t necessarily mean that the rotten thing is trying to warn us.
Another question: do plants even have the ability to “listen” to these screams? Plants don’t have ears, but they can sense vibrations. It’s been shown that noise pollution can hinder their growth, so they could potentially sense the noises emitted by other plants. Potentially.
Plants are more complex than we might think
Overall, however, the findings suggest that plants are more complex than we generally assume. Indeed, their experience of pain and emotions would be strikingly different from ours or other animals’. Yet, to say that they don’t experience any, we can’t know for sure.
On a similar note, animal behaviorist Frans da Wall, in his book “Mama’s last hug,” reminds us that even though we cannot speak about plant sentience or their crying out of pain, science has a long history of treating animals the same — as simple stimulus-response machines that don’t feel pain or emotions.
So, let this serve as a reminder that the inner world of plants shouldn’t be underestimated. While the study exploring “screams” that plants emit when stressed doesn’t necessarily mean that they actually scream, it’s a significant finding with potential applications in environmentally friendly agriculture.