Every other Friday, NHPR's Outside/In team answers a listener question about the natural world. This week’s question comes from Jenna in Cupertino, Calif.
How do plants communicate with each other? And how is this communication defined within the human world? Like, could it technically be considered talking?
How plants communicate
Plants are constantly sensing the world around them. They have special receptors that sense light, touch, and even gravity. And they have ways to communicate by releasing and sensing “volatile organic compounds."
“Plants don't have noses, but they are also extremely sensitive to chemicals in their environment,” said Richard Karban, who studies plant communication at the University of California Davis.
Anytime an insect munches on some leaves, or even when grass is mowed, those damaged tissues can release chemical compounds that signal danger to other nearby plants. According to Karban, when those plants catch a whiff, they raise their defenses by producing chemicals that reduce their own nutritional value, or that are toxic to insects.
Plants can also communicate underground through their roots, emitting chemicals that stop the root growth of other plants around them, as if to say: “Hey, I got here first!”
But plants can also be cooperative. In one study, researchers put pairs of plants close together in a lab. One plant in each pair was watered while the other was dehydrated to simulate stress from a drought. They found that if the two plants’ root systems were touching, then both plants would conserve water by closing the stomata (or pores) on their leaves. But if the two root systems weren’t touching, this didn’t happen.
But does any of this count as talking?
Karban said the best analogy for plant communication is to say that they’re eavesdropping on what’s happening to their neighbors. In other words, it’s more of a mechanical reaction than it is talking. There are chemicals in the air or the soil, and those chemicals set off some reaction in a plant that helps it survive and reproduce.
But recently a group of scientists recorded the sounds that tomato and tobacco plants make when they’re stressed, by dehydrating them, or cutting them.
These noises are ultrasonic — they’re outside the frequency audible to the human ear. But the research team was able to use an AI program to show that each plant, and each type of stress, produced unique sounds. And while we humans can’t hear them, theoretically bats, rodents and some insects could.
The big question is: can other plants respond to these sounds? A 2012 study suggests they can. Researchers showed that the roots of young corn plants would bend toward the sound emitted by other corn plants that are grown in water.
Some scientists do call this “talking.” Richard Karban still disagrees. Yet, it doesn’t seem to diminish the sense of admiration he has for plants.
“We’re learning that plants are in fact capable of really sophisticated behaviors,” he said.
Submit your question about the natural world to the Outside/In team. You can record it as a voice memo on your smartphone and send it to outsidein@nhpr.org or call the hotline, 1-844-GO-OTTER.
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