The first few “talking tree” papers quickly were shot down as statistically flawed or too artificial, irrelevant to the real-world war between plants and bugs. Research ground to a halt. But the science of plant communication is now staging a comeback. Rigorous, carefully controlled experiments are overcoming those early criticisms with repeated testing in labs, forests and fields. It’s now well established that when bugs chew leaves, plants respond by releasing volatile organic compounds into the air.
By Karban’s last count, 40 out of 48 studies of plant communication confirm that other plants detect these airborne signals and ramp up their production of chemical weapons or other defense mechanisms in response. “The evidence that plants release volatiles when damaged by herbivores is as sure as something in science can be,” said Martin Heil, an ecologist at the Mexican research institute Cinvestav Irapuato. “The evidence that plants can somehow perceive these volatiles and respond with a defense response is also very good.”
Plant communication may still be a tiny field, but the people who study it are no longer seen as a lunatic fringe. “It used to be that people wouldn’t even talk to you: ‘Why are you wasting my time with something we’ve already debunked?’” said Karban. “That’s now better for sure.” The debate is no longer whether plants can sense one another’s biochemical messages — they can — but about why and how they do it. Most studies have taken place under controlled lab conditions, so one of the major open questions is to what extent plants use these signals in the wild. The answer could have big implications: Farmers might be able to adapt this chatter, tweaking food plants or agricultural practices so that crops defend themselves better against herbivores. More broadly, the possibility that plants share information raises intriguing questions about what counts as behavior and communication — and why organisms that compete with one another might also see fit to network their knowledge.
Scientists are also exploring how the messages from these signals might spread. Just a few months ago, the plant signaling pioneer Ted Farmer of the University of Lausanne discovered an almost entirely unrecognized way that plants transmit information — with electrical pulses and a system of voltage-based signaling that is eerily reminiscent of the animal nervous system. “It’s pretty spectacular what plants do,” said Farmer. “The more I work on them, the more I’m amazed.”
Farmer’s study doesn’t mean that plants have neurons, or brains, or anything like the systems that animals use to communicate. We don’t do justice to them when we try to put their fascinating, alien biology into human terms, he said. But we may have dramatically underestimated their capabilities. As researchers begin to learn the language of plants, they are starting to get a whole new view of the leafy green world we live in.