Plant Roots Talk To Neighbors When Others Are Too Close for Comfort

Animals have a host of survival strategies when competition gets a little too fierce—fight, sabotage, or if nothing else, pack up and move to find a quieter piece of turf. But without the freedom to relocate when the going gets tough, plants have to be a little more creative in order to survive. One key strategy is picking up on what's going on in the world around them by paying attention to what their neighbors are doing.

That can even include responding to clues left behind after neighbors are gone, according to a new paper published in the journal PLOS ONE.

"If we have a problem with our neighbors, we can move flat," co-author Velemir Ninkovic, an ecologist at the Swedish University of Agricultural Sciences in Uppsala, told The Guardian, using the British term for an apartment. "Plants can't do that. They've accepted that and they use signals to avoid competing situations and to prepare for future competition."

One key sign that a plant is facing competition is when it notices its leaves are rubbing up against something. Conveniently, that's quite easy for researchers to mimic—in this case, they stroked plants with a soft make-up brush for one minute every three hours. That stressed the plants out, as if there were a competitor nearby that might absorb all its resources.

When plants think they have close neighbors, one key counter-strategy is to try to grow faster, especially above ground. It's the vegetative equivalent of a runner putting on a burst of speed during a race after noticing someone is catching up to them.

Plant roots on display at a French greenhouse. Vincent Kessler/Reuters

The researchers behind the study looked at two situations: In one, they touched plants and studied what neighbors did after they blocked off the ability of those plants to send signals above ground through gas chemicals. In the other, they used old growing medium from a plant that had been touched to house a new plant.

In both cases, the plants that hadn't been touched got the message that something was crowding out their neighbors and kicked their growth into high gear, showing that they had registered signals through just their roots.

That shows plants rely on their underground communication networks to understand the world around them—remember that next time you scoff at a plant.