Mapping underground fungal networks: Interview with SPUN’s Toby Kiers

All around her, scientists had their eyes set on studying flora and fauna that lived aboveground. But Toby Kiers’s interest always lay in the oft-overlooked biodiversity that existed beneath it.

It was the mysterious nature of the vast mycorrhizal fungal networks that so fascinated Kiers.

“It’s so alive, but humble and quiet,” Kiers, an evolutionary biologist and co-founder of the Society for the Protection of Underground Networks (SPUN), an organization that’s working to map mycorrhizal fungi around the world, told Mongabay in a video interview.

Mycorrhizal fungi, found in almost every soil system on the planet, have a crucial symbiotic relationship with plants. They live on plant roots and extract nitrogen, phosphorus and water from the soil for the plants. The plants, in return, feed carbon dioxide absorbed during photosynthesis to the fungi, which need it for their growth. As a result, a massive amount of CO₂ — more than 13 billion metric tons, according to a 2023 study — moves from plants to these fungal networks, making them a crucial tool in carbon sequestration.

But there’s more to it than meets the eye.

The movement of nutrients and carbon between plants and fungal networks is a calculated barter system in which the fungal networks allocate nutrients for plants based on how much they get in return. “We still don’t understand how they are doing it,” Kiers said. “It’s almost like watching the best poker players in the world play a game of poker.”

To understand more about these complicated networks, researchers at SPUN are deploying a wide array of technology, from remote sensing to imaging robots. Kiers said the technology has helped them get better insights on where fungal networks are distributed and how they move carbon underground. “As atmospheric carbon dioxide increases, it has become more and more urgent to not only identify where these carbon hotspots are across the Earth,” she said, “but to protect them because they will release a lot of carbon.”

Toby Kiers spoke with Mongabay’s Abhishyant Kidangoor about the crucial need to map fungal networks, the technology that’s aiding researchers, and the challenges they face in their work. The following interview has been lightly edited for length and clarity.

Mongabay: To start with, what got you interested in studying and working with fungal networks?

Toby Kiers: I was drawn to the underground because it was so unknown. There’s this idea that it’s so alive, but so humble and quiet. To study something so hidden really forces you to change your perception. I started working on these networks when I was 19, and I moved to an island in the middle of the Panama Canal called Barro Colorado Island. There was so much diversity in these tropical rainforests, but all the older scientists were studying this riot of organisms aboveground. But I was interested in what generated all that diversity belowground. I did my first experiment there and it was published in early 2000, almost 26 years ago.

Mongabay: What has the journey been like ever since?

Toby Kiers: I guess, ever since, the big aim has been to pioneer a new way of understanding life on Earth. But it’s been hard because fungi are completely invisible, and they are really the underdogs in the conservation world and even in the research world. They receive so much less funding. Mycology [the study of fungi] receives so much less funding than many other fields, and that’s been hard. From a scientific point of view, it’s also been a big challenge to get people to flip their perspectives and think that underground ecosystems are not just dirt, but actually where life begins.

But right now, we’re entering a really incredibly exciting time with all kinds of new emerging technologies, like remote sensing, machine learning, fungal sequencing and even robotics. So that’s how we can start really exploring the inner lives of fungi.

SPUN started out of frustration and from a desire to turn the data into impact. In academia, we are trained to publish papers and do good research, but we’re not trained to get the data out into the public eye. That was really frustrating to me. A lot of people become scientists because they want to make a difference. So we started SPUN in 2021 to make a difference with a very simple but audacious mission. And that’s to map the networks of mycorrhizal communities that regulate the Earth’s ecosystems and then advocate for their protection.

Mongabay: Why do you think this mission is more important now than ever before?

Toby Kiers: Fungi lie at the base of life on Earth. They really are key engineers of our ecosystems. One of the most important roles they play is to build soil and regulate the Earth’s climate. We know that soil stores about 75% of Earth’s terrestrial carbon. They also contain 59% of the Earth’s biodiversity. Most of our biodiversity is underground. All of this is really possible because of the infrastructure of the mycorrhizal networks built underground. I don’t think people quite understand the ubiquity of these fungi.

It’s not just that some plants form partnerships, but 80-90% of all plant species. These networks are crucial for the exchange of nutrients flowing upward to the plant communities. And then, of course, the carbon which is flowing downward into the soil. So they’re really helping regulate the carbon dioxide in the atmosphere.

Mongabay: How did you map fungal networks before this technology came into the picture?

Toby Kiers: It was really what we call black box research. We didn’t really know what was going on. My work in Panama was so simple in many ways, because we were digging up soil from under one species of tree and then testing in the greenhouse how other species of trees reacted to that soil. And then looking physically at the root systems under a microscope by staining the fungi to see if there was fungal colonization and how much there was.

We just knew that these root systems were chock-full of fungi. So we want to know what are these networks controlling? And how is it that something that’s so invisible can cause the seedlings to grow at such a different rate? So I think that’s where it started. It was very simple experiments like just moving soil around in the greenhouse and trying to understand what we’re doing.

And then it started getting more and more sophisticated. For example, in 2011, we published our first paper after finding that these fungi can discriminate among their plant partners so that they’re able to choose where to send the phosphorus depending on how much carbon they’re getting from different plants. So that was a different technique where we started labeling carbon and phosphorus and watching the trade. We knew that plants can discriminate among which fungi they choose, but we found that fungi can also choose where they allocate their resources. That really changed the trajectory of the field where we could bring the root systems and the fungi into the lab and start to track resource exchange across the partners.

Mongabay: Could you tell me how recent technologies have helped make your work easier?

Toby Kiers: We started using a technique called quantum dots, which allows you to attach these bright fluorescent particles to phosphorus in different colors. So you could do all kinds of experiments to actually watch where and when the fungi traded because the phosphorus would be labeled in different colors. So that got us to 2019, where we published a paper looking at how these networks deal with inequality, like how they deal when there’s rich patches and poor patches of nutrients. We started to learn that these networks are actually quite sophisticated, and that they are not just passive accessories of plants, but instead they are really dynamic and powerful actors that have very sophisticated trade strategies where they’re moving the phosphorus to places across the network where plant demand is higher so they can get more carbon. The real interaction there is how much phosphorus they give for how much carbon.

But we still didn’t understand how they were doing it. It’s almost like watching the best poker players in the world play a game of poker. Imagine you set up the cards and then one partner wins this interaction but you don’t understand how they’re playing it.

So we built an imaging robot to understand the processes across time rather than when it starts and ends. We collaborated with our colleague Dr. Tom Shimizu of the AMOLF Biophysics Institute, who started building these imaging robots that allowed us to start tracking how the fungi build their networks across space and time.

Mongabay: Could you walk me through how these imaging robots work?

Toby Kiers: Picture a giant box. It has to be very dark because these fungi grow underground, and so it has to have a very specific illumination system. Basically, it’s a microscope that scans across these fungal arenas where the fungus is growing, and it takes these high-resolution images every two to four hours. It then stitches all of the images together and allows us to follow every single node of every single network that’s growing at any time. If you think of that as a fungal highway, we’re tracking about a half a million fungal nodes across an experiment to try to understand these supply chains between the plant and the fungi.

We are tracking about 500,000 individual numbers at any given time, and that is all stitched together. We can zoom in and actually quantify the traffic flows within the fungi because these fungi are translucent. You have to imagine an open pipe with this really dynamic river running through it. But the river is running in two directions at the same time: one river is going upstream and the other half of the river is going downstream. The carbon helps the tips of the fungi to grow. Carbon is the source of their energy, and it’s what builds the fungal body. So that’s being transported to the growing tips, and then the fungi are collecting phosphorus and nitrogen and water and moving that in the opposite direction up to the plant.

What we did was we tracked the way that they built this supply chain, this carbon-to-phosphorus supply chain. We found that the fungi create a lace-like network. It looks like lace, and it’s so beautiful, and it moves the carbon outward in a wave-like formation. The fungi are controlling the flow, the speed of the traffic and the width of these highways as needed, to maximize how they grow.

Mongabay: What have been the challenges in doing this work?

Toby Kiers: Technically, it has been quite hard to be able to tag carbon and quantify it inside the networks. There’s a massive amount of carbon that’s underground, and these networks are a key entry point of carbon into global soils. But we really need to understand what triggers the fungi to increase these carbon flows. I think that’s a really big challenge. What controls how the fungi move the carbon? What controls how much of the carbon stays belowground? How do we work with fungi so that they can create this infrastructure to keep the carbon belowground?

We think of these networks as one of Earth’s circulatory systems, but people are not paying attention. So I think the other challenge is not just understanding the precise carbon dynamics of how the fungi move them and how much carbon stays belowground, but getting people to understand the importance of the fungi in climate. That’s a really big deal. As atmospheric carbon dioxide increases, it has become more and more urgent to not only identify where these carbon hotspots are across the Earth, but to protect them because they will release a lot of carbon, and they’re going to be hard to rebuild if we need to rebuild this infrastructure.

Mongabay: What does the future look like for SPUN? What can I expect to hear from you in two to five years?

Toby Kiers: We work with a massive network of underground explorers all over the world. There are 137 explorers to whom we’ve given grants to start mapping the mycorrhizal networks in their local ecosystems.

In January of 2026, we started another program called Underground Advocates. This is based on the fact that simply having data is just not enough. It needs to be turned to action. We live in a world where the direct connection between science and action is largely missing. We launched this Underground Advocates program to actually have scientists working directly with legal scholars to translate their data into action. The idea is to mobilize these expanding fungal databases to actually influence legal actions to support different fields like conservation, restoration, climate action and even land rights. The actions are going to be very locally led and scientifically grounded, but they can be supported by this legal network.

Fungi allow us to reimagine the world and offer new ways of tackling the biodiversity and climate crises. But we need to move fast to protect them. We’re really missing key biodiversity hotspots by focusing only on aboveground communities. I think now we understand the importance of restoring plant communities, but we need to restore native plants with their native fungi, and that’s really going to be a big future push.

Banner image: Toby Kiers co-founded the Society for the Protection of Underground Networks (SPUN) where researchers are working to identify and map underground mycorrhizal fungal networks. Image courtesy of Tomás Munita/SPUN.

Abhishyant Kidangoor is a staff writer at Mongabay. Find him on 𝕏 @AbhishyantPK.

Citations:

Hawkins, H., Cargill, R. I., Van Nuland, M. E., Hagen, S. C., Field, K. J., Sheldrake, M., … Kiers, E. T. (2023). Mycorrhizal mycelium as a global carbon pool. Current Biology, 33(11), R560-R573. doi:10.1016/j.cub.2023.02.027

Kiers, E. T., Lovelock, C. E., Krueger, E. L., & Herre, E. A. (2000). Differential effects of tropical arbuscular mycorrhizal fungal inocula on root colonization and tree seedling growth: Implications for tropical forest diversity. Ecology Letters, 3(2), 106-113. doi:10.1046/j.1461-0248.2000.00126.x

Kiers, E. T., Duhamel, M., Beesetty, Y., Mensah, J. A., Franken, O., Verbruggen, E., … Bücking, H. (2011). Reciprocal rewards stabilize cooperation in the mycorrhizal symbiosis. Science, 333(6044), 880-882. doi:10.1126/science.1208473

Whiteside, M. D., Werner, G. D., Caldas, V. E., Van’t Padje, A., Dupin, S. E., Elbers, B., … Kiers, E. T. (2019). Mycorrhizal fungi respond to resource inequality by moving phosphorus from rich to poor patches across networks. Current Biology, 29(12), 2043-2050.e8. doi:10.1016/j.cub.2019.04.061

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