Why it’s so hard to tell the age of a fungus

[MUSIC PLAYING] FLORA LICHTMAN: Hey, I’m Flora, and you’re listening to Science Friday. When you see a mushroom popping up from the forest floor, that mushroom is just the tip of the fungal iceberg for a vast world beneath the surface. But the nature of fungus makes it hard to answer some basic life questions, like, what exactly is one individual organism?

And how do you tell how old a fungus is when parts of it can recycle, regenerate, and grow again? Dr. Kristin Aleklett is trying to understand what fungi are doing in the world underground and tackle some of these questions. Hey, Kristin.

KRISTIN ALEKLETT: Hi. Nice to be here.

FLORA LICHTMAN: Thanks for being here. OK. So do we have a method for aging fungi? We have tree rings. Is there an equivalent for fungi?

KRISTIN ALEKLETT: No, not really, especially not one that works for all kinds of fungi, because– well, we have to remember is that there’s millions of species of fungi. And if you compare to animals, you wouldn’t maybe look at age in a chicken in the same way as you look at an age in an earthworm.

There are some ways that people have tried to estimate the age of fungi. One of the most famous examples, what they did was they looked at how a fungal disease spread between trees. And in that way, they could see that, OK. In a year, it got about one meter to another tree.

It’s the same. We can see, for example, these fairy rings that people see sometimes out in the forest. There has been actually people able to look at old satellite images to be able to see how much they’ve grown and for how long that ring has specifically been there.

But it’s not always that we have those kind of ground indicators for all kinds of fungi. In most cases, we’re not really able to track the mycelium underground throughout its life, so it’s really hard to know.

FLORA LICHTMAN: That’s really interesting. Those seem kind of crude methods, too. I mean, even just tracking a fungal disease– I mean, that tells you maybe how fast a fungus grows, but does that tell you much about how old it is?

KRISTIN ALEKLETT: Yeah. So what makes it even more tricky, you could say, is that they’re also constantly both growing and degenerating and disappearing, and some of them can even recycle themselves as they grow. So it’s really hard to have a visual measurement of exactly how old they are just based on their size.

FLORA LICHTMAN: Given those caveats, do we have a contender for what people might think is the oldest fungus among us?

KRISTIN ALEKLETT: Yeah. So there’s this one fungus that’s thought to cover 965 hectares of land in Oregon. Based on how fast they’ve seen this species spread between trees, they’ve then calculated that it could be as much as 8,650 years old.

FLORA LICHTMAN: Wow. I mean, 965 hectares puts us at 3.7 square miles. It’s huge. Just enormous.

KRISTIN ALEKLETT: Yeah. And they don’t even think that this is so uncommon. It could be similar ones in other forests. It’s just that we haven’t really been looking or doing these type of studies everywhere.

FLORA LICHTMAN: Yeah, they’ve been overlooked. I mean, how did you get interested in these questions?

KRISTIN ALEKLETT: So I mean, I’ve been always been really fascinated by fungi, I think, because I found that often teachers would go like, well, we don’t actually really this. And if you’re a biologist, and you kind have the mind of a researcher, when someone says, we don’t really know this, what you want to do is find out more.

So I’ve always been really fascinated by what’s going on with the fungi and how they live their lives, and it’s this kind of secret world underground, something that’s kind of been called a black box.

But in late years, we’ve been doing research, trying to make new methods to study soil organisms using microfluidic chip technologies, what looks like a microscope slide that we then have imprinted little channels in silicon.

And so it becomes like a little labyrinth, a little maze that’s enclosed, where we can get the fungal mycelium to grow in there. And then we can introduce them to things or challenge them with things and see how they respond and long they persist.

FLORA LICHTMAN: I mean, do they show signs of age?

KRISTIN ALEKLETT: So we recently did a study where we could see that there was a big difference between species in terms of how much they did this recycling of themselves, where some of them left a lot of empty mycelium left behind, where they had kind of withdrawn all the content of their hyphae.

And other ones kind of completely broke down the whole mycelium and then could reuse these material to build new hyphae. They didn’t waste anything. They didn’t leave any as much behind. So that’s really fascinating to see that it can be really different between different species that, to us, look like they’re living the same kind of life out in the forest.

FLORA LICHTMAN: But if you keep giving them nutrients and what they need, do they just keep going? Of course, we’re getting into deep questions about immortality and those topics. But do they slow down?

KRISTIN ALEKLETT: Yeah. So it’s a good question, because I think a lot of people are interested in this, whether fungi live forever or not. And I think people think more that this is possible than maybe what’s the case.

And I think I’ve seen some publications also saying that they’re actually having some struggles with this also in other applied settings where they want to have these fungal cultures growing forever and producing things for us, but they do sometimes see degeneration in the culture, so they don’t really how to explain it or why it’s happening.

But also, we don’t how old the cultures we have are. We maybe in what year it was isolated from nature, but we don’t how old it was already when we sampled it out in the field. There’s a lot of things that we haven’t maybe necessarily taken into consideration when it comes to fungi.

And this is really important, especially if we want to conserve fungi and make sure that they don’t go extinct. If we’re worried about species that are at risk, we need to know, how long does it take for them to get to an age of maturity? When do they start reproducing? Can they reproduce at all stages of their life? We don’t know these things.

FLORA LICHTMAN: It’s so fascinating. These questions feel like basic biology meeting these sort of deep philosophical questions. What is an individual? What is age? What does that really mean? Is that the appeal for you in part, or do you feel like you ever get lost in the sauce, the mushroom sauce?

[LAUGHS]

KRISTIN ALEKLETT: No, for sure. I think for me, because I also do research where we try to look at behavior of fungi. That is also kind of touching on the philosophical. Can we think about fungi as organisms that behave? And in order to understand some of that, I also kind of need to know what is old and what is young.

But I think ultimately, it’s just about trying to wrap your head around, what is it like to be a fungus? What does their world look like? What are they interacting with? Which problems are they running into? What does it take for a fungus to get 8,000 years old?

What is it that they have to adjust about their bodies, or their environment, or what they’re eating and who they’re interacting with to extend their life as long as possible? And there’s a lot of really unknown questions out there. And I think it’s super fascinating.

I want to be part of trying to answer those questions, because fungi are really everywhere, and they’re affecting more things than we think about in forests, in agriculture. They’re in the air. They affect health and prosperity of everything.

So if we want to be able to affect fungal lives, what they do and where they are, then we also need to understand how they function, and understanding their life histories is a big part of that puzzle.

FLORA LICHTMAN: That sounds fun.

KRISTIN ALEKLETT: Come join us.

FLORA LICHTMAN: I might. I’m tempted.

KRISTIN ALEKLETT: It’s not too late.

FLORA LICHTMAN: I’m tempted. Dr. Kristin Aleklett is a researcher at Lund University in Sweden. Thank you so much for talking to me today.

KRISTIN ALEKLETT: Thank you.

FLORA LICHTMAN: This episode was produced by Charles Bergquist and Dee Peterschmidt, and if you have questions, deep and existential or otherwise, give us a ring. 877-4-SCIFRI is our number. Thank you for listening. I’m Flora Lichtman.

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