Scientists Observe Fungi Creating Complex Supply Chains

FLORA LICHTMAN: This is Science Friday. I’m Flora Lichtman. As the leaves start to pop out, it is natural to look up and admire the trees. But actually, there’s a lot of action happening underneath your feet. Beneath you is a complex network of fungal trade routes carrying essential nutrients to the roots of plants mined from the soil by fungus. It is a subterranean supply chain.

But how exactly do these complex networks form? How does the fungus decide where to ship which resources or where to build roads? Basically, how does a brainless thread make decisions? Here to help us leaf through these questions is Dr. Toby Kiers, professor of evolutionary biology at Vrije University in Amsterdam and executive director of the Society for the Protection of Underground Networks. Toby, welcome to Science Friday.

TOBY KIERS: Such an honor to be here.

FLORA LICHTMAN: OK, I read a quote from you that said, “this is the kind of research that keeps you up at night.” Please tell me why fungal networks keep you awake.

TOBY KIERS: Well, we really wanted to understand the inner lives of these fungi. We studied a group of network-forming soil fungi, and these are known as mycorrhizal fungi. And they’re really defined by their trading relationship with plants. And it’s not just some plants, but it’s 80% of all plant species form trade relationships with these mycorrhizal fungi. And you just have to think about what they do to create these trade infrastructures.

They have to actually grow out into the soil and create this very complex network to collect the resources. But then they have to evaluate where and when to transport those resources back to the roots. And then they have to collect payoffs for those resources. So that’s what I’m talking about, “staying up late at night.” How does an organism that has no central nervous system, no brain– how does it achieve that?

FLORA LICHTMAN: Well, OK, so take me underground. If I’m standing on my lawn in front of my garden or underneath a tree, what should I be imagining as happening beneath me?

TOBY KIERS: That is such an amazing question because this is what we’re trying to bring to light. So you can imagine a network growing, and it’s a very complex network with lots of different junctions. And this network, it’s sort of like an open tube, meaning that inside the network. There’s this flow of nutrients. All of the cellular contents in the network is flowing through this open pipe tube.

FLORA LICHTMAN: What’s flowing? What are the things that are actually– what are the packages going back and forth?

TOBY KIERS: Well, all the cellular contents, so all the mitochondria, the nuclei, but really, the nutrients, too. So the plants are feeding carbon to the fungi in the form of sugars and fats. And the fungi are collecting these through very intricate structures that actually penetrate into the root cell. So the carbon is flowing from the plant down into the network, and it has to go all the way to the growing tips to build more network.

But the network is also, at the same time, foraging and collecting resources like phosphorus and nitrogen and water and bringing that back all the way back to the plant root system. So if you think about these tubes, they actually have streams of nutrients moving in two directions simultaneously.

FLORA LICHTMAN: That sounds complicated, just physics-wise.

TOBY KIERS: That’s why we work with biophysicists because this is something they had never seen before. And that’s what’s so exciting about it is we really just have to visualize what they’re doing, test different hypotheses, and see how they react.

FLORA LICHTMAN: You built a robot to do some of this work. Tell me about the robot.

TOBY KIERS: So the robot is really cool. All of this happens underground, as you said, out of sight. So it’s nearly impossible to study. And that’s why we built a robot. And then we started imaging the network with this robot 24 hours a day. And so the robot, with this data, we could actually extract the physical topology of the network and give every junction in that network a unique number.

Now this is the crazy part. This allowed us to track about half a million of these nodes of these fungal highways at any given time. So we’re keeping track of the physical coordinates of the network. But then we zoom in at specific coordinates to look at the traffic flows within these highways and the traffic flows. That’s what I mean by the nutrients, the carbon, the water, the phosphorus all moving through that.

FLORA LICHTMAN: I mean, the videos are amazing that you produced with this robot.

TOBY KIERS: The videos were really exciting to make because I don’t think people imagine just how dynamic these systems are underground. And when we show these videos of the nutrient flows, these are in real time. So these flows are actually moving very fast and it’s very dynamic. So not only are the two streams going in, let’s say, antiparallel directions, so two directions at the same time. But sometimes, they switch directions. So a stream will be going very fast in one direction, and all of a sudden, it’ll switch directions and start going the other way.

FLORA LICHTMAN: OK, I think this gets to one of the essential questions– who’s making the decisions? How does a brainless thread make a decision?

TOBY KIERS: Exactly. If that doesn’t keep people up at night, I don’t know what does. And that’s really where we’re just starting on this journey of figuring out how it works. Mycorrhizal fungi– what we started to learn through this work is that they use very simple local rules. These local rules allow them to prevent, let’s say, overbuilding. And when I talk about a local rule, it’s something as simple as when two roadways meet, they fuse. They physically connect those traffic flows of nutrients.

FLORA LICHTMAN: Every time they meet, they fuse.

TOBY KIERS: Exactly. Now what’s cool is that this actually confers two advantages. It removes dead end streets, which are really bad for supply chains, but it also improves the traffic flows across the network, so really efficiently moving the resources to and from the route.

FLORA LICHTMAN: What was your biggest aha from these findings?

TOBY KIERS: Ooh, that’s a good one. There were so many ahas during this project that I can’t even begin to list them. I think, for me, it was this idea that these organisms, they’ve been really shaped by natural selection for hundreds of millions of years. And to be able to physically observe these type of strategies is really incredible because we use as humans– we use AI to solve very complex problems. And so it started making us think, well, what can we learn from these living algorithms that we’re watching in real time.

FLORA LICHTMAN: Living algorithm– I like that. I mean, is it permanent carbon capture?

TOBY KIERS: So really, when we talk about carbon, no carbon is really permanent in that sense. So these fungi are important parts of the carbon cycle. But what we want to do is make a big enough sponge that they keep that carbon down under there for longer. And so, of course, the fungi are respiring. They’re using the carbon. Some of that is released. But the fungi also make these secondary compounds that are very hard to degrade. And so if the carbon goes into that form and really form these sticky substances that hold the soil together, then we can keep the carbon down underground longer.

FLORA LICHTMAN: Which, of course, is useful if you’re trying to draw CO2 out of the air.

TOBY KIERS: Exactly. So this is like the physical infrastructure that allows us to bring the carbon below ground. I mean, in many ways, we think of these networks as really one of Earth’s circulatory systems.

FLORA LICHTMAN: OK, I’m going to take a chance here and wade into deep thoughts territory.

TOBY KIERS: I’m ready.

FLORA LICHTMAN: So you can bat it away if you want. When you see these brainless tubes making decisions– and I know they’re following rules. They’re not making decisions. But does it make you think differently about sentience or intelligence or any of these sort of big, squishy ideas?

TOBY KIERS: I’m vigorously nodding my head because what we see is that, as a society, we are so concentrated on the brain as a way to process information. And I get goosebumps just thinking about other options for processing information and making decisions. And that’s what we’re seeing in real time is just how that can happen. And it really opens up, I think, a brand new field of research into how organisms without brains process information and how we can actually understand the strategies that they’ve evolved to solve complex problems.

FLORA LICHTMAN: I want to ask you about something else that I think is related. I remember when research bubbled up years ago that suggested trees communicate and cooperate through these fungal networks, and some people called it the wood wide web, and there was a ton of interest and also pushback about it. How do you think about that? And does your research help us understand that any better?

TOBY KIERS: There’s one really important issue to think about with what research has been done on trees and networks. And it’s really always taken a very plant-focused view, and that is, how do these plants– how are they using fungi to, let’s say, talk or get resources? And what we’re trying to do is actually turn that research on its head and ask a different question and say, what is in it for the fungi? What are the fungi doing? Where are they moving the resources?

FLORA LICHTMAN: The fungi-eye view.

TOBY KIERS: Exactly. So we’re really taking a fungal-eye view. And so it’s not that we’re weighing in so much on the research about what’s happening with trees and how they communicate, but we’re really trying to understand, from a fungal lens, why and how are they moving resources? And then if that happens to help the trees, fantastic. But first, we really have to understand that living infrastructure underground and how it grows and what benefits it as it grows.

FLORA LICHTMAN: You’re team fungi is what I’m hearing.

TOBY KIERS: I’m totally team fungi.

FLORA LICHTMAN: Toby, thank you so much for taking the time to chat with us today.

TOBY KIERS: It was really fun. Thanks so much.

FLORA LICHTMAN: Dr. Toby Kiers is the executive director of the Society for the Protection of Underground Networks. And you can check out a video of these fungal highways in action at sciencefriday.com/fungus. You don’t want to miss it. The videos are awesome. sciencefriday.com/fungus.

This is Science Friday from WNYC Studios.

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