IRA FLATOW: This is Science Friday. I’m Ira Flatow. One of the most extensive networks for sharing information and moving around essential goods is hidden from us. Yeah, it’s right below our feet. You might have heard of it. It’s the wood wide web. See what I did there? I’m talking about the fungal networks that connect trees and plants to one another. Scientists are starting to untangle what these fungal connections look like and how fungi respond and are affected by climate change, and what that means for the entire forest ecosystem.

This is something I really want to talk about with my next guest. He’s here to walk us through this mycological maze. Christopher Fernandez is a post-doctoral associate in plant and microbial biology University of Minnesota in Minneapolis. They call it the U over there, right, Chris?

CHRISTOPHER FERNANDEZ: That’s right.

IRA FLATOW: Welcome to Science Friday.

CHRISTOPHER FERNANDEZ: Thanks for having me, Ira.

IRA FLATOW: Even though we can’t see it, fungi play an important role, right? When it comes to trees and plant ecosystems. Can you take us through a bit of fungi 101? What do fungi fungi provide for plants.

CHRISTOPHER FERNANDEZ: Absolutely, yeah. So the organisms that I study are called mycorrhizal fungi. So these are fungi that are really important for the plant nutrition. Basically, these fungi colonize the finest roots of plants and provide access to nutrients that would otherwise be unavailable for direct plant uptake. So plant root activity is directly dependent on these kinds of associations.

And so about 90%– we’re saying these days– of plant species actually has one of these types of mycorrhizal associations. So there are two basic types of mycorrhizal associations are arbuscular mycorrhizal fungi, which are really common in grassland-type ecosystems and prairies and tropical forests. And then, there are ectomycorrhizal fungi, which are really important in temperate and boreal forests. And those are the organisms that I work with.

IRA FLATOW: Which ones do we see on our lawns and in the backyards on trees?

CHRISTOPHER FERNANDEZ: Yeah, so it would depend. If it’s a mushroom forming fungus, then it is a ectomycorrhizal fungus. Or it could be a saccharo cerevic fungus that just is decaying soil organic matter.

IRA FLATOW: There are also free living fungi?

CHRISTOPHER FERNANDEZ: Yeah, and they depend on carbon and nitrogen and phosphorus that exists in soil organic matter. And they break down that soil organic matter to obtain those resources. Whereas, mycorrhizal fungi, they acquire nitrogen and phosphorus and trade that– those nutrients to the plant in exchange for carbon.

IRA FLATOW: Is it true that the largest organism in the world is a fungus?

CHRISTOPHER FERNANDEZ: That is true, yeah. That would be an Armillaria species out West– in Oregon, I believe. Yes. And that is supposedly very, very large– acres.

IRA FLATOW: Which fungi are populating my sourdough bread?

CHRISTOPHER FERNANDEZ: Those would be yeast, primarily. So those are free living single-celled fungi.

IRA FLATOW: How many different fungal species does the average tree have, let’s say, associated with it?

CHRISTOPHER FERNANDEZ: In the systems that I work in, which are temperate and boreal forest, trees can have dozens of different fungal species colonizing their root system. It’s quite common to see 50, 60 different fungal species colonizing a single tree host.

IRA FLATOW: Wow. Fungi like the microbiome of the forest, it sounds like.

CHRISTOPHER FERNANDEZ: Yeah, absolutely. Just like you and I have our own microbiomes associated with our bodies, these trees have their own associated microbes including mycorrhizal fungi as well as some other bacteria and other things.

IRA FLATOW: So you’re saying that different types of forests have different types of fungal networks there.

CHRISTOPHER FERNANDEZ: Depending on which systems you’re looking at, they have completely different sets of fungal associates. Yeah.

IRA FLATOW: So if you planted a tropical tree in a conifer forest would it be able to tap in and use these different fungi in the soil?

CHRISTOPHER FERNANDEZ: Probably not. So most tropical trees– not all, but most tropical trees are arbuscular mycorrhizal associates. So they tend to form these mycorrhizal associations with a different set of symbiote. So these are quite different in terms of their functionality as well as their phylogeny. So they’re very different.

IRA FLATOW: I didn’t know that. So if I dig up the soil in my backyard, am I disturbing a ecosystem that’s taken decades, centuries to form?

CHRISTOPHER FERNANDEZ: Probably not. So where we dwell, usually, those soils are pretty disturbed anyway. Unless you’re living in a forest system, you’re probably not causing any more disturbance to those soils or anything that would be traumatic.

IRA FLATOW: Like with most things, climate change is affecting these fungal communities, correct? What changes are you and other scientists observing here?

CHRISTOPHER FERNANDEZ: So here in Minnesota, we have a system– an experiment set up by Dr. Peter Reich in 2008 It was also at the University of Minnesota. It’s called Be Forewarmed. And basically, the experiment is warming and excluding precipitation in these forest plots that have different boreal and temperate hosts planted together. And there’s been a lot of research on aboveground responses to climate change– these climate change treatments.

And we are interested in understanding how those changes cascade below ground and influence communities. And what we’re finding is that the networks that are formed between these different plant hosts are starting to degrade. So the communities are shifting from those that have– just species that have extensive, long-lived mycelium in the soil, to those that are weedy. They don’t produce a lot of mycelium. They shift a lot of resources to reproduction rather than exploration in these structures.

Basically, we’re hypothesizing that this is going to result in the breakdown of these really important networks.

IRA FLATOW: This doesn’t sound good.

CHRISTOPHER FERNANDEZ: No. No, it does not. These networks are quite important for plant nutrition, right? So we think that this will ultimately affect seedling recruitment. So seedlings are really dependent on the established common mycorrhizal networks, we call them, for being connected and tapped into an established network and having access to nutrients provided by those networks.

And so we think that this might alter how seedlings are recruited in the future.

IRA FLATOW: So the trees– the population of trees may go down because the fungus is doing something different than it used to.

CHRISTOPHER FERNANDEZ: Right, exactly. Instead of providing these really important benefits in terms of nutrition, maybe those won’t be there in the future.

IRA FLATOW: There is research out there that some fungi play a role in drought tolerance in trees. How does that happen?

CHRISTOPHER FERNANDEZ: Yeah, so there’s a lot of interesting work coming out of Cathering Gehring’s lab down at Northern Arizona University showing that some of these ectomycorrhizal symbiotes that have evolved in these really droughty environments have abilities to basically help the plant tolerate increased drought stress. Those are very different fungi than some of the fungi that you see here in Minnesota or higher latitude systems that have not evolved to tolerate those challenges with water stress. But they are out there.

IRA FLATOW: If you know that fungi– they’re beneficial or do better in the face of climate change, you know there are certain fungi that do better. Can you give a tree a fungal probiotic– an inoculation, so to speak, to help it out?

CHRISTOPHER FERNANDEZ: That’s certainly a strategy that could be explored. Today, I don’t think there’s a whole lot of research that would suggest that can be done immediately. But that is something that can be explored for sure. Cenococcum, the species of fungi that I’m interested in, actually is known for its ability to tolerate drought stress. But it doesn’t really– it’s not really abundant in a lot of these communities.

And we don’t really see it go up in abundance with– when we increase warming and drought stress in our system here in Minnesota. So it gets complicated.

IRA FLATOW: I know that fungi are also important in carbon sequestration. How will climate change affect this?

CHRISTOPHER FERNANDEZ: 20% to 30% of net primary productivity, that is the amount of carbon that plants pull down from the atmosphere and fix into biomass, is allocated below ground to mycorrhizal fungi. So that’s a significant flux into the soil. So the turnover of that mycorrhizal biomass that is produced from carbon allocation from this plant is important in terms of potential for carbon sequestration.

So what we’re seeing is that with warming and a drought, at least here in our system, the photosynthetic capacity of these hosts are declining significantly. And we think that their ability to allocate carbon below ground to mycorrhizal fungi is also being inhibited. It’s kind of like a sinking ship, right? So the fungi are attached to these hosts and are dependent on that carbon. And those fungi are really– thought to be really important in terms of the ability to sequester carbon in soil. So it’s quite troubling.

IRA FLATOW: Will fungal species that are better adapted to higher temperatures, are we going to see them start to dominate the forests under climate change and determine which trees grow in an area?

CHRISTOPHER FERNANDEZ: Yeah, so perhaps. Yeah, we’re seeing not so much drought tolerant species but drought avoiders. So these are weedy fungi, again, that invest a lot in reproduction rather than biomass in the soil. So instead of producing biomass they can tolerate droughty or warmer soils, they’re just avoiding those times of the year, right? And they’re growing when there is moisture available and reproducing really quickly. And then, just kind of dying off.

IRA FLATOW: I know we’ve already certified you as a fungi geek. And there’s probably nothing you don’t know about fungi. But what are the big questions? What more do you want to know about fungi and the role they play in these forest ecosystems?

CHRISTOPHER FERNANDEZ: We’re just scratching the surface on what we know about these fungi. We just have the ability for about 10 years to actually observe these fungi in situ with high throughput sequencing. So for the longest time, we couldn’t actually study them very effectively.

So we’re just now beginning to piece together patterns from these data sets. So what I’m particularly interested in is understanding functional diversity. So what are the traits that these different fungi have? What is their effect on their performance in ecosystems? So are there traits that confer tolerance to certain stressors? What are the traits that are really important for accessing nutrients?

And how did those traits, then, affect these ecosystem level processes? So basically, we’re just now being able to actually observe these things in the environment.

IRA FLATOW: Well, we’ve run out of time. It’s been quite informative. I want to thank you, Christopher Fernandez, postdoctoral associate in plant and microbial biology University of Minnesota in Minneapolis. Thank you for telling us all about the fungus among us.

CHRISTOPHER FERNANDEZ: Thank you, Ira.

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