Take a bush walk, and you’ll find yourself immersed in a soundscape of chatter.
You may hear the birds joking with each other Because they feed on food, or swarms of insects sing potential partners.
But the quietest form of life is having some of the most lively conversations.
Trees may seem the kind to keep, but they are busy under your feet forming secret relationships with the vast networks of underground fungi.
Large, old trees rely on this “wide wooden web” to transport nutrients to their younger neighbours, while others use it to send chemical signals that warn. Trees close to looming threats, such as diseases and pests.
“Symbiosis is important for all aspects of plant growth, but also the diversity we see in our landscapes,” says Ian Anderson, a fungal ecologist at Western Sydney University.
It’s an arrangement of friends with benefits that’s been around for millions of years, says Tom May, a mycologist at Royal Botanic Gardens Victoria, but researchers are just beginning to unlock the secrets of how trees and fungi interact, particularly in Australian ecosystems. .
“It’s as challenging to boundaries as deep space – it’s deep in the soil.”
Roots that wear socks
If you can shrink yourself down and dive under the jungle floor, you’ll encounter a wonderland of miniature lifeforms that work hard to keep the ecosystem running.
Among the crowded moths and microbes, you’ll be surrounded by dozens of tree roots dressed in ghostly white “socks.”
These sock-like coverings are known as ectomorphs, and they are the most common symbiotic fungi found in forests.
Friendly fungi reach the soil with their filaments – long strands of cobweb that are thinner than a strand of human hair.
In the Northern Hemisphere, “fingers” of fungi make up an estimated 30 percent of forest biomass.
“There are kilometers of hyphae in just a handful of soil,” says Dr. May.
These bundles of hyphae – or fungi – are tasked with food shopping for their tree hosts.
When they branch into the soil, the hyphae releases special enzymes that convert hard-to-reach nutrients like nitrogen and phosphorous into forms that the tree can easily consume, says Dr. May.
“They steal their food.”
In exchange for their efforts to shed nutrients, host trees send their fungal partners a sugar and carbon check.And the which they produce from sunlight through the process of photosynthesis.
This gives the fungi the energy it needs to grow and clean every crevice in the soil for tree nutrients.
“There’s almost an economy,” says Jonathan Plett, a molecular mycologist at Western Sydney University.
Trees are generous hosts, providing a home to dozens of species of mycorrhizal fungi that each play a role.
“Some of these fungi are related to different trees of the same species, and sometimes they are related to different trees of different species,” says Dr. May.
“It’s very complicated.”
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Australia’s invisible friendships
Over the past two decades, most research exploring the relationship between fungi and trees has focused on ecosystems in the Northern Hemisphere, such as pine forests.
Studies from this side of the world have revealed that trees don’t just rely on rhizomes to take care of themselves.
One 2015 study found that drought-ravaged Douglas fir trees (Pseudotsuga menziesii) – which is native to North America – dumps its carbon and sends chemical stress signals to the nearby Ponderosa pine (Ponderosa pine) the trees.
But the conversations between the indigenous Australian trees and their fungi are still largely shrouded in mystery.
Over the past few years, Dr. Plett and his team have been researching the finer details of how the root fungi help eucalyptus trees thrive and communicate.
While the relationships between Australian trees and fungi share some similarities with their northern hemisphere counterparts, Dr. Plett notes some striking differences.
First, his experiments showed that the Australian root fungus had evolved to absorb some heat.
Dr. Plett found that root fungi from the northern hemisphere do not adapt well when exposed to temperatures above 25 degrees, making their tree partners vulnerable as a result.
“They either die or stay hibernating and just kind of sit there… no longer help the plant,” he says.
It’s a different story for the Australian fungus, which continues to thrive in temperatures of up to 37 degrees.
“They love it,” says Dr. Plett.
“If you think about the Australian environment…they have been very hot for long enough that they have somehow adapted to it.”
Dr. Plait and his team also found that eucalyptus trees are not quite as loyal to their fungal partners as Northern Hemisphere tree species, which tend to stick to the same type of mycorrhizal fungi for life.
As seedlings, eucalyptus mates with arboreal root fungi – a group that typically prefers crops and herbs over trees.
But like teens drifting away from childhood friends, eucalyptus turns into an outgrowth of fungi as they get older.
“Eucalyptus is one of very few hosts that does this,” says Professor Anderson.
Because mycorrhizal fungi typically sustain plants in nutrient-poor soils – a key feature of Australian landscapes – Professor Anderson suspects they give eucalypt trees a good start in life so they are ready to meet their long-term partners.
“It’s another peculiarity of the indigenous Australian ecosystem.”
Proteins as passwords
But not all underground fungi are interested in making friends with trees.
For example, the Australian honey mushroom (armillaria lotopoballina) It is the main cause of root rot in eucalyptus trees, and it can spread from tree to tree like underground wildfires.
So how can trees distinguish between friend and foe?
The answer lies in small molecular differences. Dr. Plett discovered that when root fungi encounter the roots of a tree, they secrete special proteins that can open Tree root cells without sounding alarm bells.
If the circulation of nutrients is like a conversation between trees and fungi, proteins are the language the rhizomes use to “talk” to the tree’s immune system, says Dr. Plett.
“This is what allows the fungus to actually rush to the root without the plant killing it.”
Some species of fungi will go so far as to maintain a love affair with selected trees.
Earlier this year, Dr. Plett and colleagues reported evidence of a fungus called . pisolithus microcarpus Manipulates gene activity in roots of flooded gum trees (Eucalyptus grandis).
When this fungus colonizes the roots of the gum tree, it releases small particles of genetic material that control the production of certain proteins – a strategy more common among disease-causing fungi.
Dr. Plett and his team found in the lab that the fungus had donated some of these genetic scraps to it The roots of the host tree, which helps it form a lasting bond with its woody partner.
But it wasn’t a one-sided relationship. The researchers also found that seedlings with fungal microRNA particles in their roots pulled more nutrients from the soil than those without.
The study showed that the mushrooms gave the trees some genetic modifications that boosted their immune response and their ability to process nutrients.
The perfect match for the makeover
While eucalyptus seedlings are often inoculated with mycorrhizal fungi before they are grown in the wild, the results are lost and bleak.
Some seedlings grow strong and vigorous, while others struggle to establish themselves, even if their roots are wrapped by the same type of rhizome fungus.
Part of the problem is that not all fungi – even those of the same species – are willing to share the fruits of their labour, hoarding some of the nutrients they collect.
This may be due to subtle genetic and metabolic differences between individuals, Dr. Plett says.
“Different types of fungi colonize different types of trees, just as we are attracted to certain people and not to others.”
By solving the mystery of how trees depend on fungi to thrive and communicate, Dr. Plett hopes to identify the most compatible partnerships between trees and fungi — a boon for the nursery industry and bush regeneration efforts.
And while trying to play a matchmaker is hard work, the payoff can be huge.
Dr. Plett estimates that inoculating eucalyptus and pine seedlings with appropriate mycorrhizal partners can reduce fertilizer use by up to 40 percent, and even help store more carbon underground.
Getting that delicate balance is also important for restoring out-of-control landscapes, such as cleared farmland.
For example, in soils with abnormally high levels of nitrogen and phosphorous, some trees shed their mycorrhizal partners because they meet their nutritional needs elsewhere, says Dr. May.
But independent living has its downsides.
“[The trees] You don’t get all the other benefits, like protection from disease.”
Dr May says that given that nearly 50 species of Australian fungi are now on the International Union for Conservation of Nature’s (IUCN) Red List of Threatened Species, categorizing native fungi and understanding their role in Australia’s forests is more important than ever.
This means turning our attention to the underworld instead of the sky.
“It’s interesting how people are really captured by star cataloging…there’s nothing going on in space that we need to worry about,” says Dr. May.
“But if we don’t step in here and understand what we have, it could be gone in 50 years.”