Can plants talk to each other? - Richard Karban

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Can plants talk to each other? It certainly doesn’t seem that way: They don’t have complex sensory or nervous systems, like animals do, and they look pretty passive. But odd as it sounds, plants can communicate with each other — especially when they’re under attack. Richard Karban explains how.

Lesson by Richard Karban, animation by Yukai Du.

Can plants talk to each other?

It certainly doesn't seem that way.

Plants don't have complex sensory
or nervous systems like animals do,

and they look pretty passive,

basking in the sun,

and responding instinctively
to inputs like light and water.

But odd as it sounds,
plants can communicate with each other.

Just like animals, plants produce
all kinds of chemical signals

in response to their environments,

and they can share those signals
with each other,

especially when they're under attack.

These signals take two routes:

through the air,

and through the soil.

When plant leaves get damaged,

whether by hungry insects
or an invading lawn mower,

they release plumes
of volatile chemicals.

They're what's responsible for the smell
of freshly cut grass.

Certain kinds of plants,
like sagebrush and lima beans,

are able to pick up on those
airborne messages

and adjust their
own internal chemistry accordingly.

In one experiment, sagebrush leaves
were deliberately damaged by insects

or scissor-wielding scientists.

Throughout the summer,

other branches on the same sagebrush plant

got eaten less
by insects wandering through,

and so did branches on neighboring bushes,

suggesting that they had beefed up
their anti-insect defenses.

Even moving the air from above
a clipped plant to another one

made the second plant
more insect-resistant.

These airborne cues increase
the likelihood of seedling survival,

and made adult plants produce
more new branches and flowers.

But why would a plant warn
its neighbors of danger,

especially if they're competing
for resources?

Well, it might be an accidental
consequence of a self-defense mechanism.

Plants can't move information through
their bodies as easily as we can,

especially if water is scarce.

So plants may rely
on those airborne chemicals

to get messages from
one part of a plant to another.

Nearby plants can eavesdrop
on those signals,

like overhearing your neighbor sneeze
and stocking up on cold medicine.

Different plants convey those warnings
using different chemical languages.

Individual sagebrush plants
in the same meadow

release slightly different sets
of alarm chemicals.

The makeup of that cocktail influences
the effectiveness of communication.

The more similar
two plants' chemical fingerprints are,

the more fluently they can communicate.

A plant will be most sensitive to the cues
emitted by its own leaves.

But because these chemicals seem
to be inherited,

like human blood types,

sagebrush plants communicate
more effectively

with relatives than with strangers.

But sometimes, even other species
can benefit.

Tomato and tobacco plants can both
decipher sagebrush warning signals.

Plants don't have to rely solely
on those airborne broadcasts.

Signals can travel
below the soil surface, too.

Most plants have a symbiotic relationship
with fungi,

which colonize the plants' roots
and help them absorb water and nutrients.

These fungal filaments
form extensive networks

that can connect separate plants,

creating an underground super highway
for chemical messages.

When a tomato plant responds to blight

by acitvating disease-fighting
genes and enzymes,

signaling molecules produced
by its immune system

can travel to a healthy plant

and prompt it to turn on
its immune system, too.

These advance warnings increase
the plants chance of survival.

Bean plants also eavesdrop
on each other's health

through these fungal conduits.

An aphid investation in one plant

triggers its neighbor to ramp up
production of compounds that repel aphids

and attract aphid-eating wasps.

If you think of communication
as an exchange of information,

then plants seem to be
active communicators.

They're sending, receiving,
and responding to signals

without making a sound,

and without brains, noses, dictionaries,
or the Internet.

And if we can learn to speak to them
on their terms,

we may gain a powerful new tool to protect
crops and other valuable species.

It all makes you wonder
what else are we missing?