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‘Amazon forests of the underground’: Why scientists want to map the world's fungi

“These fungal networks have been a global blind spot in conservation and climate agendas," said Toby Kiers, an evolutionary biologist and professor at Vrije Universiteit Amsterdam.
Image: mycelium network
High resolution image of mycelium network.Loreto Oyarte Galvez

Vast networks of microscopic, underground fungi serve a crucial role in Earth’s ecosystems — and there’s a lot we don’t know about them.

More than a quarter of Earth’s species live in soils underground, including the fungal networks that help store huge quantities of carbon, provide most plants with the majority of the nutrients they need to survive and allow the plants to receive important signals from others. 

Now, a team of scientists is launching a first-of-its-kind effort to map the world’s mycorrhizal fungi, a process they hope can identify fungal biodiversity for conservation, grow understanding of how these species interact within ecosystems and keep more carbon in soil. 

“These fungal networks have been a global blind spot in conservation and climate agendas. People haven’t woken up and realized there is this ancient life support form below our feet,” said Toby Kiers, an evolutionary biologist and professor at Vrije Universiteit Amsterdam, who co-founded SPUN, the Society for the Protection of Underground Networks

“We need to know where biodiversity hot spots are. Where are the Amazon forests of the underground?” Kiers said.

Most of these fungi are underground and too small to see without a microscope — but they are plentiful. A handful of soil contains networks of tubular fungi that would span 60 miles if they were stretched out, Kiers said. 

Confocal 3D-image of a fungal network with reproductive spores containing nuclei.
Confocal 3D-image of a fungal network with reproductive spores containing nuclei.Vasilis Kokkoris

Gardeners might recognize mycorrhizal fungi — pronounced my-core-eye-zal — as the white filaments that extend from the roots of trees and other plants, clinging to dirt clods like stringy, ancient hair. Combined in layers, they are massive networks of fungal threads called mycelium. 

Kiers described tangles of mycorrhizal fungi as a “continuous pipe system” that branches, fuses and flows with nutrients like nitrogen and phosphorus. 

“We follow them as if they are a river,” Kiers said, adding that the nutrients can flow in more than one direction.

The networks — which typically share a mutually beneficial relationship with the plants to which they connect — are fundamental to how forests and other ecosystems work. 

“The fungi massively extend the trees’ root systems,” said Colin Averill, a co-founder of SPUN and a senior scientist at ETH Zürich. Some help decompose dead plants and animals and recycle nutrients.    

The way scientists talk about the creatures can sound like fables. 

Without mycorrhizal fungi, plants might never have reached land. Hundreds of millions of years ago, all flora were aquatic until a partnership with mycorrhizal fungi allowed them to settle on land, Kiers said.

Plants can receive chemical signals through the networks, which helps them share resources, learn from neighbors about pests and get warnings about competitors, recent studies suggest. The pioneering work by Canadian scientist Suzanne Simard and others has upended the idea that trees are solitary competitors duking it out for space, water and sunlight in the forest. 

Instead, through fungal networks, “trees may really be cooperating as a family unit,” Averill said. More research is needed to better understand the nature of the relationships.  

SPUN aims to map the world’s fungal networks by using machine learning to identify where biodiversity hot spots might exist and then work with local scientists to collect samples in remote locations where they’ve never been gathered before. 

SPUN 2021
The team at the Society for the Protection of Underground Networks.Seth Carnill

The DNA of each fungus species within the sample will be extracted, sequenced and then mapped to its location, giving scientists a census of which species live where. Scientists plan to combine the information with data about the surrounding climate and vegetation coverage to better understand patterns in different ecosystems. 

The nonprofit organization, which recently received a $3.5 million donation from the Jeremy and Hannelore Grantham Environmental Trust, hopes to collect 10,000 soil samples over the next 18 months.

It’s work that couldn’t have been done without recent advances in genomic sequencing, which allows scientists to see the genetic makeup of these tiny species.

“We really didn’t have tools to see the diversity and types of organisms living underground,” Averill said. “Now it feels like we’re inside the soil.”

Microorganisms — including bacteria and fungi — play critical roles in the carbon cycle, and the ability to rapidly analyze what is living within soils offers a deeper understanding of our changing climate and possible solutions.

“It really is a frontier,” said Serita Frey, a microbiologist and professor at the University of New Hampshire who isn’t involved with the project. “That can’t really be overstated. There’s so much we don’t know yet about what goes on below ground.”

 Frey said the mapping project could help fill out scientists’ understanding of microbial communities and help target areas deserving of conservation. 

“This sort of mapping has been done for macro-organisms for a long time. The idea of mapping microorganisms is quite new and only something we’ve been able to do in the last five to eight years,” Frey said. 

As the world warms, understanding how mycorrhizal fungi and other microorganisms interact with soil could be crucial to slow down warming and adapt to a new climate. 

“We’re just coming to understand this outsized role microbes play in the global carbon cycle, which has important implications for climate and future climate,” Frey said. “How these microbes are managed is going to be really important.”

Fungi promote plant growth, which sequesters carbon in trees and other plant species. They also help bury and store carbon in the soil.

About 75 percent of terrestrial carbon is in soil, and the scientists want to keep it there by preserving these biodiversity hot spots.  

“We’ve got this amazing carbon sink,” Kiers said. “We can’t lose it.”

They are also exploring what tweaks to the system could promote more carbon absorption or cut down on fertilizer use in agriculture, which can have environmental costs. 

“There’s a threefold variation in how fast a tree grows, depending on which fungi is living in those soils,” Averill said. “Can we accelerate carbon capture in forests by manipulating which  mycorrhizal fungi live in the forest soil?”