The Earth’s Internet: How Fungi Help Plants Communicate

The internet connects more than half of the
world’s population through an invisible web of servers, computers,
and devices. It has changed our lives in countless ways by allowing otherwise separated people to
interact and by providing access to vast amounts of
information. But humans aren’t the only organisms on
the planet with an invisible interconnected network. While plants might seem like isolated, solitary
individuals, they’re capable of communicating with each
other, sometimes over considerable distances, all thanks to their special relationship with
fungi. Nearly all plant species we know of have a
mutually beneficial relationship with soil fungi called mycorrhizae. Mycorrhizae grow a network of small, branching
tubes, called a mycelium, that extends throughout the soil, including
inside of or around plant roots. And these allow the fungi to absorb nutrients
from the soil, like nitrogen and phosphorus, which plants
struggle to extract. So they basically barter: in exchange for
those hard-to-get nutrients, the plants trade the fungi carbon in the form
of sugars. And ultimately, together, both can thrive
when they otherwise wouldn’t. This symbiotic relationship between plants
and fungi was discovered in the early 1900s, but it
wasn’t until 1997 that we understood just how deep this underground
network goes. Ecologist Suzanne Simard had a hunch that plants weren’t just sharing nutrients
with fungi, but also with each other. To test her hypothesis, she and her colleagues infused trees in a
forest with a traceable, radioactive form of carbon, and later took samples from neighboring trees. And it turned out many nearby trees had the
radioactive carbon, too, proving that plants could send nutrients back
and forth to one another. Not only that, they seemingly distributed the nutrients where
they were needed most. Plants need light energy to turn carbon dioxide
and water into sugar and oxygen thanks to that magical process called photosynthesis. So those in shade have less sugar to go around. Simard found that these shaded, energy-deficient
trees ended up with more of the radioactive carbon than their sunbathing counterparts. So it’s basically the plant-fungi equivalent
of feeding the hungry. Continued research into these underground
networks, called Common Mycelium Networks, has revealed that plants are not only able
to gain access to more nutrients, they can also engage in sophisticated communication by “talking” chemically through mycelia. And, it turns out, they’re saying quite
a bit! Generally, any seedling that’s plugged into
the Common Mycelium Network, or CMN, has a higher likelihood of surviving. And plants that are “online” are generally
healthier, too. Researchers think this has to do with having
access to an early warning system. When a plant is attacked, it releases chemicals that tell nearby plants something bad is coming
their way. This communication happens with airborne compounds, but also through a CMN. And other plants heed this warning. For example, when tomato plants are connected
by a CMN, and one plant is attacked by a pest, nearby plants will activate their defenses
before the pest reaches them. Scientists are only just starting to understand how important these plant networks are. They’ve discovered that entire forests can
be interconnected, but like with our internet, connectivity throughout an ecosystem isn’t
evenly distributed. Older, larger trees are more connected, kind of like some servers in the human internet. These highly connected trees are called hub
or mother trees. They have big root networks that host a greater
diversity of mycorrhizal fungi, and that allows them to interact with a lot
of other plants. They do play favorites, though… Scientists have shown they can send ‘care
packages’ of extra nutrients to their kin to help them survive, which is
how they got the mommy moniker. And they also can help forests transition
during times of change. When they’re injured or dying, they release
a surge of carbon into the network which nurtures the next generation
of trees, even if they’re a different species. Of course, no internet is complete without
hackers. Some plants can claim territory and influence
community dynamics by sending toxins into the CMN. Black Walnuts will use these networks to release toxins into the soil, for example. Those that are immune to the toxins thrive,
while others struggle or die off. And harmful worms, parasitic plants, and fungi can find their way to the plants they target
by following chemical trails emitted by the mycorrhizae underground. It’s amazing to think that this chemical
information superhighway was right below our noses for eons and yet
we had no clue. But now that we can finally plug in, it might
just help us connect with the planet’s flora in much more constructive
ways. Knowledge of this interconnectivity is helping
improve our relationship to plants, including things like forest conservation
and agriculture. For example, preserving the highly connected
mother trees from deforestation ensures mycorrhizal fungal diversity, and helps forest regrowth happen more quickly. And farming in soil with a CMN means plants
can warn each other of invading pests, which may reduce the need
for pesticides. Like with the human internet, the internet
of the earth increases security, awareness, and knowledge for those connected
to it—including us. Thanks for watching this episode of SciShow! If you liked learning about plant symbiotic
relationships, you might like our episode on how plants recruit