Catalyst with Shayle Kann - The fungus among us

Episode Date: June 29, 2023

More than a third of the world’s current greenhouse gas emissions from fossil fuels go through underground networks of fungi, according to a new peer-reviewed study in Current Biology. That’s a whopping 13 gigatons of carbon dioxide equivalents per year. Mycorrhizal fungi act as a symbiotic partner of plants, seeking out nutrients and bringing them back to the plants’ roots. In return, they accept carbon in the form of carbohydrates—which they then lock away in the structure of the fungi. This symbiotic relationship is nothing new to scientists; what’s surprising is the magnitude of carbon stored. But how permanent is this sink? And what can we do to support fungi as a nature-based climate solution? In this episode, Shayle talks to Dr. Heidi-Jayne Hawkins, lead author of the new paper and research director at Conservation South Africa.  They cover topics like: The evolutionary history of mycorrhizal fungi  The mechanics of fungal carbon storage, which boosts carbon storage by 5-20% more than plants alone What we can do to support conditions for fungi to absorb carbon Open questions about the permanence of the storage Recommended Resources: Current Biology: Mycorrhizal mycelium as a global carbon pool Catalyst is a co-production of Post Script Media and Canary Media. Support for Catalyst comes from Climate Positive, a podcast by HASI, that features candid conversations with the leaders, innovators, and changemakers who are at the forefront of the transition to a sustainable economy. Listen and subscribe wherever you get your podcasts. Catalyst is supported by Scale Microgrids, the distributed energy company dedicated to transforming the way modern energy infrastructure is designed, constructed, and financed. Distributed generation can be complex. Scale makes it easy. Learn more: scalemicrogrids.com.

from the studios of PostScript Media and Canary Media. I'm Shail Khan, and this is Catalyst. You've got this whole other extension of the root system, which is an additional sink, you can call it, for the CO2. So it's not just going down into the plant, leaves and roots, but it's also additionally going into the fungal body. So what would happen, you know, if there was no fungus? Well, you would still have CO2 drawdown, but it presumably wouldn't be as much.

The vast underground fungal network that partners with plants to take up over a third of global fossil fuel emissions. Science is so cool. When utilities need flexible capacity they can count on, they turn to Energy Hub. Energy Hub works with more than 170 utilities, coordinating over 2.5 million devices to manage 3.4 gigawatts of flexibility built for the moments when utilities can't afford uncertainty. Energy Hub builds and operates virtual power plants that utilities actually stake their grid planning on, coordinating EVs, batteries, thermostats, and more through a single platform built for utility scale.

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Listen to Critical Capital on Spotify, Apple, or wherever you get your podcasts. I'm Shail Khan. I invest in revolutionary climate technologies at energy impact. partners. Welcome. All right, so here's the headline. There is an underground network of fungi that partner with plants that results in about a 13 gigaton pool of carbon sequestration underground. That's equivalent to about 36% of the annual emissions from fossil fuels in the world. It's a crazy figure, I think, and it's from this new academic study that I found absolutely fascinating. Maybe you already know this, but I for one, had no idea that much of the phosphorus and nitrogen fixation in plants actually comes from this symbiotic relationship that they have with these fungi, who essentially go out and hunt for nutrients on behalf of the plant well beyond its root structure. Stepping back, one of the things that I find most fascinating about the way that climate tech is evolving is that there are these communities of people working really hard at strengthening or hacking these massive natural systems that are a part of the global carbon.

system, which we've thrown out of equilibrium via human activities over the past century or so. A good example of this that I think more and more people are paying attention to is the ocean, which of course is this massive store of CO2 and has a bunch of different ways to potentially capture even more. Soil, of course, is another one. But when you hear about soil carbon, or at least when I do, you almost never hear about the role of fungi, which apparently is a mistake. Sometimes a piece of science is just so fascinating you want to spend.

an hour really understanding it, or at least I do. And this podcast is my excuse. So here we go. So let's figure out what's happening here. And also, I think more relevant to the types of conversations we like to have, like, is this a pathway to global scale atmospheric carbon abatement beyond what we already see today? Is it, on the other hand, at risk, thanks to human activities? He's like, what is the impact of this 13-gagetone pool of carbon in fungi underground? My guest is Dr. Heidi Jane Hawkins, who is the lead author of the paper. She's also the research director at Conservation South Africa and is associated with the Department of Biological Sciences at the University of Cape Town.

Here's Heidi. Heidi, welcome. Hi, Shail. Thanks for the invitation. I can't tell you how excited I am to talk about this. After reading your paper, I'm just like obsessed with it. So let's start by talking about mycorrhizal fungi, which is, I will admit, a term you helped me to learn how to pronounce nigh 10 minutes ago. Right. What is this type of fungus?

Well, first of all, it's amazing that somebody says they're excited about A, soil, and B, mycorrhizal fungi, because that doesn't happen a lot. see that you read the paper, so well done. But to your question, so mycorrhizal fungi, the word comes from the Greek, so myco means fungus and rhizor means root. So it literally means fungus root. And so they are fungus root fungi, which sounds odd, but what it means is that hardly a root on the planet is actually just a root. It's very often this associated And so what it is is a mutualistic partnership where the plants, where the threads of the fungi form this really close association with the root cells. They either go into the cells or they go around them.

And then from there, they spread out into the soil. So I don't know if you've ever looked at your bread mold closely, but it would generally radiate out and that's exactly what these fungi do and they've got really small thread like bits of their bodies so they can go into soil pores where roots can't access right so the image that I have in my head you can tell me if this is a literal correct image or if I've got it wrong is I plant a tree the tree grows roots then these fungi these mycorrhizal fungi wrap themselves basically around or even intertwined into the roots and then basically extend the root network. They go further out beyond where the roots go to access nutrients for the tree that the tree itself

would not be able to reach via its own root structure. Is that basically right? Yeah, that is right. So extending the root system is a really good way to put it. And, you know, it's all sorts of plants, not just trees. And I think the basis of the this is that the plants are getting something out of it, right, the nutrients and the water, but that it's this reciprocal exchange. That's really the nature of the partnership that the fungus, not being green and being underground and not being able to photosynthesize like a plant, that's what it's getting from the plant, is sugars for fuel.

My colleague on the paper, Toby Kier, she's actually really well known for putting this whole partnership into economic terms. So describing it as this reciprocal exchange where, like in our own economy, you can get cheaters. You can get fungi that give more than they take or take more than they give. And, you know, like with everything, it seems to depend. It depends on the partners involved. It depends on the resources available. And how tough the environmental conditions are, whether this exchange is equitable or not. Has it always been this way?

Did these microisyl fungi, did they evolve with co-evolve with the plants upon which they depend? or did they develop later? What do we know about the history here? Well, we know from the fossil record that by the time, plants moved out of an aquatic environment, so the sea, onto land, we know that this partnership already existed. So the fungi are really, really old,

how old exactly we don't know. But we know by about 450 million years ago that these, These fungi were definitely around. They were definitely colonizing plants. And then over time, that symbiosis, that mutualism has evolved and re-evolved and modified many, many different times so that you've ended up with quite a few different types of these mycorrhizal fungi.

And we think we know why this happened, because as you can imagine, if you're a an aquatic plant and you're in the sea and nutrients and water, nutrients and water are literally swimming around you. You don't really need a root system. But then getting onto land, you'd suddenly be faced with this quite harsh environment of a soil which is quite dry. The nutrients are somewhere in patches here and there. And the roots of the plants at that time would have been something like moss. I don't know if you've ever grabbed a handful of moss and turned it over. Of course you have.

But those root-like things that moss have are pretty similar to what those early plants would have had, which are really just holdfast. They weren't really very good at getting nutrients. or water. So that's where the fungus would have come in and, you know, go through the pores and of the soil and get that water and nutrients and deliver these to the plant. Okay, so these fungi have been around for at least 450 million years having this symbiotic relationship, generally a symbiotic relationship with plants. How prevalent are they today? Like, do we have a sense? sense of, is it everywhere? Is it in certain ecosystems? Is it some plants and not others? Is it everywhere? Like how, yeah, how ubiquitous is this type of fungus? Well, ubiquitous was actually the word I was going to use because they're on all continents

of the globe. And then with those plants, they're with 90% of plants on the globe. So it's, it's really prevalent and everywhere. It was a successful partnership in the past and it seems to continue to be a successful one. But you do get different types being more prevalent in different places. So one type of mycorrhizal fungus is called ectomicorizal, so ecto-micorizal. So they don't go into the root, but they tend to sort of sit around the root in a sheath. And that's really prevalent in forests. So if you've got, you know, pine and beach and birch, all sorts of conifers, conifers, but also other types of trees, they're really prevalent then in forests.

And actually really don't occur with so many species, but they really occur in the northern hemisphere. in forests really intensively. And then you get other types called arbuscular, which are with almost every other type of plant, including crops. And I don't know how long you want me to go on for, but you get erychoid microisers. They occur with plants in heathlands,

including your blueberries and cranberries and crowberries. And you get orchid mikerizer, and they've really evolved quite a strange relationship with orchids in that some orchids actually depend on the mycorrhizor totally, both for their nutrients but also for their carbs. So they've kind of swapped the rolls around depending on the stage of the plant's life cycle. So this whole symbiosis has diversified a lot over the, you know, ensuing time. Right. Okay, so my presumption here is that the prevalence, the ubiquity, the existence,

the history of these micro isle fungi, and the relationship to plant life is, has been known, not to me, but certainly I suspect in your, in your world for quite some time, what's new is this new research that you've published, that relates to the magnitude of the role of this microisal fungi in soil carbon and soil carbon uptake. So high level, before we get into how big a deal it is, like what is the mechanism? So now we understand that we have these microisal fungi, they're extensions of a root network essentially, and they have the symbiotic relationship wherein they trade nutrients basically with a plant or a tree.

What happens with CO2? What is the role? What is the mechanism through which CO2 uptube? goes through these fungi. Right. So just to come back to what is known, it's been known for a long time that how the CO2 reaches, you know, into the fungus. It's just that we're the first to make a global estimate of the extent of this carbon pool. So, but to come back to your question, it's really all happening at the level of the root cells, but where it begins is.

with CO2 fixation by green plants. So they fix the CO2 into their leaves, and then that gets converted together with sunlight and water into sugars, and then that gets sent down to the roots and to the leaves and elsewhere in the plant. But where you've got this symbiosis, where you've got, it's almost like a handshake at the cellular level, where you've got the fungus either in or around the root cell,

and then you've got the root cell, and you've got this interface. And depending on the type of mycorrhizer, you'll have different layers there, but the point is you can have an exchange across that interface of the nutrients and water coming from the fungus, and then the sugars coming from the plant into the fungus. So what's the impact of that on CO2? I get that the CO2 is fixed by the plant and then convert it into sugars that extend down into the root network and throughout the plant itself. What's the impact on the CO2 uptake when there is that exchange with the microisyl fungi?

Right. Well, the CO2 drawdown is happening due to the plant. but because you've got this added sink, and I use the word sink in terms of carbohydrate physiology, we talk about sources and sinks, but you've got this whole other extension of the root system, which is an additional sink, you can call it, for the CO2. So it's not just going down into the plant leaves and roots, but it's also additionally being going into the fungal body, which can extend out quite a far away, and being built into the structure of the fungus. So what would happen, you know, if there was no fungus, well, you would still have CO2

drawdown, but it presumably wouldn't be as much. And, well, we know that it wouldn't be as much because, you know, under experimental conditions, you can grow plants without these fungi and you can or with them and then you can measure what the cost is in terms of CO2 that's now instead of being used in the plant is being sent to the fungus. So you can have a you can even have less you can have that the plant has got less carbohydrate available, but it still may grow better because the symbiosis is providing it with these other benefits, if that makes sense. So there's a cost, but there's also enough, usually enough of a benefit. So that's where the drawdown would come, that the carbon will be built into

the fungal body underground. And so the fungus is helping to bury and distribute the carbon. And I think you would have seen in a study what we're uncertain about is just how permanent that is, that drawdown. Which is, right, an issue with all things carbon in soil, which is talk more about. But you mentioned that sort of we know that a plant in the absence of this fungal network extending the roots would take up less CO2 than by adding the fungal network and allowing it to basically extend further out and fix some more CO2, or carbon, rather, in the soil via the fungal network. I'm sure this is highly variable, and it totally depends on the type of fungus and the type of plant and so on.

Is there a range, though? Like, is it a 10% boost in the CO2 uptake, a 2x boost? Is it, do we have no idea? Like, what do we know about how much additional CO2 uptake comes from this fungal network relative to a scenario where it didn't exist? So you can have a boost of the photosynthetic rate, and I haven't tried to put that into, okay, how many molecules of CO2 is that? But you can have a boost of 5 to 20% of the plant's photosynthetic rate, so amount of CO2 per meter squared per second. Virtual power plants are becoming a reliable way for utilities to manage capacity.

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and by the institutions that connect them. I'm Alfred Johnson, CEO of Crux, the capital platform for the clean economy. Join me for my brand new show, Critical Capital, as I talk with people deploying capital, shaping policy and building projects. Together we unpack how risk is priced, how incentives are structured, and how progress is actually made. Listen to Critical Capital on Spotify, Apple, or wherever you get your podcasts. And then so the big conclusion from, your study, which is you said is sort of the first global estimation of how much of the

CO2 fixation in the world comes through this network, was that it was something like 36% of all fossil fuel emissions in the world extends through this network. So unpack that a little bit for me. Right. Like how do we get to such a big number? This is something that's actually tripped people up in, you know, Twitter. I see lots of comments about, oh, you know, you know, that sounds like really a lot. And then it gives the impression that somehow micro-risa are this massive carbon reduction mechanism. So I think if you take, you know, all the carbon that is in the soil, I did a little calculation a little bit earlier, and we come up with a massive amount if we express it in CO2,

equivalents, it's nearly 9,000. And our micro-risal pool is about 13 gigatons of CO2 equivalents. So you can see, if you express it as a function of the whole soil carbon sink, then it's really like 0.1%. And if we look at the forest sink, which is about nearly 1,500 gigatons of CO2 equivalents, then compared to that, our micro-irisal pool is about 1%. So I hope that sort of puts it in perspective. Whereas if we look at our emissions, yeah, it is 36% of that. I think, I think, Maybe what is difficult is thinking about additionality. This process is going on all the time regardless. It's not like we can somehow use Microrizer to additionally now draw down more CO2 than they are already.

the use of the energy-related emissions was just a way to give people a reference point. Like, how much, you know, CO2 is this? Because you can say a number like 13 gigatons of CO2 equivalents, and it is pretty meaningless to most people. So I hope that puts it into perspective. But, yeah, it is a lot. The number is big. Why, why? So, you know, point taken on the size of the sink, 13 gigatons, if you're thinking of it in the context of, yeah, exactly, what do we need to do to decarbonize, right? We emit 50 gigatons a year globally, roughly. So we're trying to get from 50 to zero. Here's a 13 gigaton sink. And, I mean, you said we can't use this to draw down more CO2. I'm curious why that is. You imagine that, all right, we've got a 13 gigatone sink here. If we do things, this is the,

issue with forestry and stuff like that as well, which is there's this gigantic sink, but we're affecting the size of that sink in both negative and positive ways. When we deforest, we're negatively affecting it. When we plant trees, we're positively affecting it. And so if you've got something on the scale of 13 gigatons, you know, if you can do something that either increases that by another giga ton or decreases it by another gigaton, then you're having a meaningful impact on our pathway to decarbonne. you don't think there's a way to, I don't know, creatively increase the, or is it a bad idea, I guess, from an ecosystem standpoint, to think about how to creatively increase either the presence of microizal fungi or its ability to uptake carbon?

Yeah, no, I definitely do. I mean, it is a meaningful carbon pool. And as we said in the paper, there's a lot of uncertainty around the number that we put to it. And it actually may be much larger, so we may have underestimated it because we only use that external part of the fungal threads that extend out into the soil, whereas you can have almost double the amount inside the plant. So we, on that side, may have underestimated it. On the other hand, we may have overestimated it because we don't know how permanent that 13 gigatons is. We don't know how dynamic it is. We need to know more about soil respiration. You know, the fungus is there as a living biomass. At some point it dies. Some of that gets stuck onto mineral particles of soil, which is quite a stable form of soil organic carbon. But some of it's going to be chewed up

by microbes during decomposition and go off again as CO2 into the atmosphere. So I'm just just saying that there's uncertainty there, but what we can do, I certainly think there's a lot. I was just meaning, I don't think it's so much about it being some kind of carbon reduction system that we can manipulate so much as it's about our behavior change so that we provide conditions that encourage the growth of these microisal fungi, so that they're They can continue to draw down CO2 as they've been doing for millennia. And, you know, there we're talking about all these, well, what's been going on for ages, but what's now called nature-based solutions.

So protecting natural environments so that you've got, you maintain that plant cover and then restoring areas in an ecologically. appropriate way, of course, because we all know about the tree-planting fiascos, I think, as part of carbon projects, planting things in the wrong place at the wrong time. But, you know, restoring natural systems so that you get that plant cover, which will enable those fungi to come back. Also, there's a lot to be done in agriculture, actually, because annual, you know, there's a whole suite of practices which have been done for ages, whether it's no-till, cover crops, using a diversity of crops, perennial crops, rather than annual crops.

And all these things have been done for different reasons, right, like to discourage erosion. But now they also serve, they've been put under the climate smart umbrella because there are ways in which, you know, by using cover crops or less disturbance of the soil, you can hope or you can model how much soil organic carbon you might gain or how much you might reduce loss. So that was actually sort of one question I was going to ask. and it relates to the permanence question that you've raised a couple times too. So do you think of the carbon that is sitting inside these micro-isol fungi as just part of the soil organic carbon sink? It's just one component of that broader sink. And is it then also true that basically all the things that we suggest that you should do

to make that sink more permanent and to avoid respirating a bunch of soil organic carbon would apply here as well? Yes, yes, definitely. So we're careful in the paper to call it a pool rather than a sink, just because a sink implies that it's something that is going to continue, going to increase, actually, over time. Like a mature forest stand, we expect that to be a sink because it's going to continue to draw down CO2. And we don't even call it a store. We're just calling it a pool. But yes, we see it as part of the soil organic carbon pool. And do we have any sense of, on the question of permanence, and you've said a couple times, sort of we don't quite know, but relative to the rest of soil organic carbon, is there any reason to think that this,

that the microasal fungi would be any different in terms of permanence? Possibly, because there's some evidence. It's just a few papers. the exudates from mycorrhizal fungi. So that's the small molecular weight fluid that's given off like sugars, amino acids, and plants do it too. But there's some indication that the exudates from mycorrhizal fungi might be even more important than root exudates in eventually ending up being in quite a stable carbon form. I was actually listening to one of your other podcasts about soil carbon

and the guy there was speaking about how our understanding of soil carbon has changed and how we now recognize that soil microbes can quite efficiently use these really small molecular weight, organic carbon, and quite rapidly fix them onto, or via the microbes, they can end up being bound to mineral particles, which is quite a stable form. And then there's other fractions in the soil as well, like leaf litter and dead roots,

and that may be somewhat more vulnerable to loss. So I think we're beginning to realize that microbes as a whole of which microizer are part are really important in the process of taking soil carbon that has just entered the systems, they're quite new carbon, and then fixing it onto soil minerals, which are then relatively stable. So it's not just about how much, but the quality of the carbon and then their involvement in it. So I think that's quite exciting. So in your mind, now knowing what we know or what we think we know about the magnitude of the carbon uptake through microizal fungi, Do you think it should change how we think about conservation programs or extensions of that, how we finance those programs, things like carbon credits for either forestry or soil? Like, should this be incorporated in a way that it has not been historically? Yes, I think there's a lot of exciting potential there because on the cards are various sorts of maps that we can use in conservation.

planning. So, you know, when you're planning a conservation area, you will usually look at where you've got high biodiversity. You might look at other things like where you've got high soil carbon and then try to make some decisions about, all right, this is a really important area we don't want to lose. And I think that the maps that are being developed at the moment by some of my colleagues, which are about fungal diversity, so diversity of these types of mycorrhizal fungi, but also we're hoping to get some maps, some global maps of the carbon that is in these fungi. And if we can overlay these together with those other areas, those other spatial layers, I think this just gives us another tool for land use planning.

and in the same way, if we are setting up some sort of carbon offsets project in conservation, then this is just another tool to help us decide, you know, where should we put our priorities? All right, Heidi. Like I said, I found this stuff really fascinating. I probably should have already known about it a little bit, but I didn't. So I appreciate you bringing it to my attention, and thanks also for chatting through it with me. No, of course. Thanks so much. Dr. Heidi Jane Hawkins is the research director at Conservation South Africa. She's also an honorary research associate at the University of Cape Town.

This show is a co-production of PostScript Media and Canary Media. You can head over to canarymedia.com for links to today's topics. Post-Crip Media is supported by Prelude Ventures, a venture capital firm that partners with entrepreneurs to address climate change across a range of sectors, including advanced energy, food and ag, transportation and logistics, advanced materials and manufacturing, and advanced computing. This episode was produced by Daniel Waldorf, mixing by Roy Campanella and Sean Marquand, theme song by Sean Marquand. I'm Shale Khan, and this is Catalyst.