Fungi: the invisible force protecting our planet

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1:50In the center of the Pacific Ocean, between Samoa and Hawaii, there's a tiny speck of land. So people say that Palmyra Atoll is the most remote island on Earth. The island has no permanent inhabitants. There's only infrastructure for research, so it's all scientists all the time. Scientists like Dr Toby Kears. When she visited, she was stunned by the abundance of life on the island, including the absolutely ginormous coconut crabs. They can be as wide as about a metre across. They actually hunt and they climb trees and they have an incredible sense of smell. And so you can't leave any equipment out at night or they'll actually steal it and bring it into their burrows.

2:39Palmyra is also known for its incredible seabird populations. Calls from colonies of red-footed boobies and sooty terns fill the air. It's so loud that you need to shout. But there's something far quieter and less conspicuous that lies at the heart of the atoll's ecosystem. When you're there, you really start to see the underground very differently because there's so much going on down there below the surface. Toby and her team have just published the first global map of mycorrhizal fungi, the planet's incredible underground network which supports plant life above ground. According to some estimates, they draw down 13 billion tonnes of CO2 into soil systems every year.

3:27There's so much subterranean fungi that, stretched out, it would reach from the Earth to the Sun 750 million times. times. And Palmyra offers an ideal case study for the role these mycorrhizal networks are playing and how they can help us to restore landscapes across the globe. So today, a trip to an atoll in the middle of the ocean and what it can teach us about the fungi quietly engineering the natural world.

4:04I'm The Guardian's science editor, Ian Sample, and this is Science Weekly.

4:13When we go and visit Palmyra Toll, there are many things that you have to do, including freezing all of your clothes before you arrive on the islands. This is to make sure that you're not bringing any invasive species. And then once you're there, you actually freeze your clothes every morning before you head out to the smaller atolls. And you're digging these frozen clothes out of a freezer chest, putting them on, doing a whole day of fieldwork, and then coming back to the main island, taking those clothes off, freezing them again, and the whole thing starts the next morning. Toby is a professor at the Free University in Amsterdam and executive director of the Society for the Protection of Underground Networks, or SPUN, an organisation that aims to map and protect mycorrhizal fungi.

5:02When she and her team visited Palmyra, frozen clothes were just one small part of the island experience. At night, there were so many crabs covering the ground that you couldn't take a step without touching one. So you kind of had to shuffle your way across the ground to make sure that you didn't hurt any organisms. The water also brought something new. So imagine all of these small atolls that are connected by water, but you can't ride the boat directly up to them. So as scientists, you'd bring up your boat as closely as you can, and then you start wading and sort of waste high water depending on the tides.

5:44Now the sharks don't see very many humans, so they're very curious. So these are just reef sharks, and they kept telling us, they're not going to hurt you. But they're definitely curious enough that they'll come up and brush against you. So for somebody that has spent her life on land collecting fungi, interacting with these sharks was really surprising. The cacophony of bird calls, equipment stealing, mega crabs and curious sharks make Palmyra sound like an untouched wilderness. But it's actually an ecosystem that suffered decades of damage. The introduction of rats which ate seabird eggs and the seedlings of the native pisonia trees caused plenty of destruction.

6:27But it was another arrival that conservationists are still tackling to this day. Coconut palms. After taking root in the 1850s, they quickly spread across the atolls. It's been a big problem because the seabirds don't like to nest in the crowns of the coconut palms, they much prefer Pisonia. These Pisonia trees are known to create a very sticky substance. And when seabirds land on it, especially in sort of masting years when they're making lots of seeds, then the birds actually get stuck and they can no longer move. And so you can have these situations where the birds are sort of hanging off the trees because they've died, because they're not able to move anymore, to fly away.

7:14And they start to decompose. And all of those nutrients go to the base of the tree. So it's called a bird-eating tree. Despite the Pisonia trees sometimes eating the birds, they're the favoured nesting site. That makes them a critical part of the island's ecosystem because with a lot of birds, you get a lot of bird poo. They can be considered keystone species because life on these atolls is incredibly dependent on those seabirds and them having a good place to nest because the seabirds leave guano that's incredibly rich in nitrogen and phosphorus and potassium. And those are the nutrients that fuel the entire island.

7:55The nutrients are also leaking out into the marine environment. And you have plankton, for example, and they benefit also from this bird guano. And the coral reefs benefit from the fishes that feed on the plankton. So you have this very tight nutrient cycling. The introduction of the coconut palm disrupted this cycle. Organisms have evolved an extreme dependence on each other because it's such a remote island. So there's even more interdependence among these species. And so if you lose one particular species, then there's huge negative cascading effects for the others. Remove one and the rest falls apart.

8:38So since 2019, there was like this massive effort to remove coconut palms. And I think so far about 1.5 million have been removed.

8:54Toby, now these efforts are underway to restore the native Personia grandest trees to Palmyra. And this is where your research comes in, because your team has been looking at a crucial element that has so far been missing, right? Well, we were invited to Palmyra Atoll to start mapping the underground fungi of the atoll. They call this team fungi. It's like a SWAT team. And our job was to understand how Pisonia trees are able to survive on this incredibly hard, nutrient-poor coral rubble. Now, a lot happens underground that a lot of people are not aware of. And in the case of this very special rainforest tree called Pisonia, we were interested in documenting their mycorrhizal fungal partners.

9:39Now, mycorrhizal fungi, it's a very special class of organisms that form a trade partnership with plants. The plants provide carbon to the fungi and in return, the fungi provide nutrients. So you were there to map the fungi on the island. How did you do it? You're going out on these atolls, often hiking between atolls in sort of waist high water, and going and setting up grids where then you core the soil and you extract what's underground, both in the native forest stands, but also in places where there were invasive palms. And that gets taken back to a lab where you extract the fungal DNA and start to understand which fungal partners are there.

10:23And we were asking whether these Pisonia trees, these very important keystone species, depended on mycorrhizal fungi to survive in such an extreme place. Right. And so as part of this mapping, you were trying to figure out what role the fungi is playing in supporting the Pisonia trees. What did you find? Well, can you guess? I mean, we found that fungi are critically important to the survival of the Pisonia trees. we found that 100 % of the sample trees were associated not with just only generally mycorrhizal fungi, but a very specific type of mycorrhizal fungi called tomentella. Now, tomentella is what we call an ectomycorrhizal fungi.

11:05It's sometimes called a crust fungi or a patch fungi. And we found it associated with every tree that we tested. So what role are the tomentella fungi playing in their partnership with the trees? Do we have an understanding of what they're doing? There are these very extreme nutrient conditions around these Pisonia trees. So either there's no nutrients because it's too sandy or it's all coral rubble, or all of a sudden there's this huge pulse of nutrients, which in many cases can almost be toxic. There's so much nutrient availability at once. And so when you think about what these Tometella mycorrhizal fungi are doing, it's almost like they have superpowers because they allow the tree to survive when there's very little nutrients but they also can feed the nutrients to the plant and survive when there's a huge pulse of nutrients and so yes we know now that the pisonia trees very much depend on these mycorrhizal fungi.

12:03This close partnership between pisonia and tomentella fungi is important. The fungi can survive the extreme conditions created by the seabirds as they nest and drop guano down to the ground, recycling the nitrogen, phosphorus and potassium to make it available for the trees. And what about those metre-wide equipment-stealing crabs? They're part of this intimately connected web too. Another key finding of this work was that crabs are important for fungi, and that's because they burrow. So we did an experiment where we tested for fungal diversity inside crab burrows and then in control holes that we would dig ourselves.

12:46And we found significantly higher fungal diversity inside the crab burrows. The crabs are actually helping the fungi disperse across these atolls.

12:59Coming up, fungi's critical role in the survival of our ecosystems.

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14:36So Toby, how does this knowledge that you're building on Palmyra, how does that really help you with restoring the biodiversity there? So first, we have to understand that these coconut palms, they don't associate with the appropriate type of fungi that are needed to restore the Pisonia forests. We know that Pisonia forests depend on Tometella fungi. And we know that the tomentella are present within, let's say, 100 meters of a Pisonia tree. But the further you get away from the trees, that just drops off into a point about 250 meters where the fungi just don't exist anymore. And so what that tells us is that we can now design experiments where seedlings can be planted even closer to the Pisonia trees themselves so they have access to this critical fungal resource.

15:27The Pisonia trees have an intimate, interdependent relationship with the Tometella. If you want to restore the trees, you have to think about the fungi. It's a principle that could be applied across all kinds of restoration projects. It also reveals how important fungi are for keeping existing ecosystems thriving. Scientists from Toby's organisation, Spun, have now created a global map of mycorrhizal fungi so that the health of these networks can be monitored and restored. I think just like our guts have a microbiome, soils have a microbiome. And they're very, very complex and not at all the same.

16:09I think people are always surprised to learn that about 59 % of all species on Earth live underground. And that's what creates these complex microbiomes. So I think recent studies, they've really explored the use of soil microbiome transplants as a method to ensure that native fungi are co-inoculated with native plant seedlings. And introducing soil microbiomes from native ecosystems, it really has been shown to improve restoration success. So I was part of a team that did a meta-analysis of 80 experiments, and it found that native soil transplants can increase biomass by more than 60 % across diverse ecosystems.

16:50More often than not, we don't know the exact role of each fungal species, nor exactly how they work together. I think this is really the frontier science. But we've made progress, especially in lab studies, where we can start to manipulate the abundance of particular individual fungal strains and start to understand their individual contributions. But this is really why mapping fungi is so important. And so presumably this means we should be putting more effort into protecting and conserving fungi. Well, that's why we started Spun, to map these mycorrhizal communities and advocate for their protection.

17:27And that's because fungal biodiversity is just not included in climate and conservation agendas to the level that it should be. There's still so much unknown about fungal biodiversity, and it really represents a library of solutions to so many problems that the world faces today. And yet the amount of resources going into fungal research is so far below other types of research. And so a big question for us is how can we get people to start paying attention to this critical biodiversity below ground? We know that there's a problem. We know that the destruction of these networks increases global warming, it accelerates biodiversity loss, it disrupts nutrient cycles.

18:13And so now the question is, what exactly do we do about it? We always talk about flora and fauna, but we need to start talking about flora, fauna and funga, which is the third kingdom, the kingdom of fungi.

18:32Toby, thank you very much Thank you so much, such a pleasure Thanks again to Dr. Toby Kears You can read about the Spun team's new global map of fungi networks on theguardian.com And that's it for today This episode was produced by Madeline Finley The sound design was by Joel Cox and the executive producer was Ellie Burie. We'll be back on Thursday. See you then.

19:07This is The Guardian.