How to Harness the Ancient Partnership between Forests and Fungi | Colin Averill | TED

So we know forests play an essential role in regulating the Earth's climate. However, most of what we know about those forests is actually based on things we can measure aboveground. So historically, ecologists like myself would come to this place, and we’d count the number of tree stems we’d find. We’d identify which species they are, and today we’d probably remotely sense features of this forest canopy from space. And all of this absolutely makes sense. Aboveground is where photosynthesis happens. Photosynthesis is how carbon and energy enter forests. Photosynthesis is how trees can remove carbon dioxide from the atmosphere. However, we also know most trees are limited in some way, by soil resources like water or nutrients. And to access those resources, trees have to build roots. And trees build an incredible amount of roots. So in some forests, there can be as much or more biomass belowground, in root structures, as aboveground, in stems and leaves. Decades of research have now made very clear that belowground ecology -- so what’s going on in the soil -- is really essential to understanding how these forest systems work. However, if you follow these root systems all the way out to their terminal ends, the finest tips in the root system, and you look closely -- I mean super closely, like, you’re going to need a microscope closely -- you discover a place where the tree stops being a plant, and starts becoming a fungus. So most trees on Earth form a partnership, or what scientists call symbiosis, with mycorrhizal fungi. So this, in my opinion, is one of the most remarkable images ever captured of these organisms. So in the background, at the top, you can see this dense network of fungal hyphae. These are essentially like roots, but for fungi, instead of plants. And in the foreground, you can see these incredible, multinucleated fungal spores, which look totally unreal, but absolutely are. These are the reproductive structures of the fungus. These have the potential to become entirely new fungal networks. Mycorrhizal fungi are essential to how basically all plants access limiting soil resources. There's actually evidence that when plants first made the evolutionary transition from living in water to living on land, they evolved this symbiosis before they even evolved roots. And so this partnership between forests and their fungi is ancient, and it stretches back hundreds of millions of years. However, these roots don't have to be just fungi. They can also be, for instance, bacteria. So these circular structures in this root network are called root nodules. They house symbiotic, nitrogen-fixing bacteria. And what these bacteria do is actually convert nitrogen gas in the atmosphere into plant-usable forms, and in turn, they nurture plant growth. And the complexity of soil biology just keeps going. So these root symbionts are embedded in an even more complex network of free-living bacterial and fungal decomposers, and archaea and protists, microscopic soil animals, viruses... The biodiversity of soil communities is astonishing. We now know a handful of soil can easily contain over 1,000 coexisting microbial species. And so all of this, this is the soil microbiome. This is the forest microbiome, this is the ecosystem microbiome. So breakthroughs in DNA sequencing technology have finally turned the lights on belowground. DNA has allowed us to see these microbial communities in unprecedented detail, and, only recently, at unprecedented scales. Yet despite these breakthroughs, I'd argue we still don't know the answers to seemingly simple questions, like this

"What does a healthy forest microbiome look like?" We're far closer to answering a question like this for people than we are for plants. The Human Microbiome Project has really led in this area. So the human body is a microbial ecosystem. Each of us houses an incredibly biodiverse community of bacteria in our gut, and that has a profound impact on our health. This was discovered by medical microbiologists using DNA sequencing to characterize which bacteria live in hundreds of people's bodies. And importantly, also noting health features of those same people. So, are they sick? And if so, with what? What's their blood pressure, their digestive health, their mental health? And by combining all of that information, those microbiologists could begin to identify combinations of bacteria linked to health and disease. And these analyses became a road map for the development of human microbiome transplant therapies, which is essentially ecosystem restoration, but for your gut microbiome. And these therapies are now on the road to market to treat some of these diseases today. And so drawing from this work, my team asked, "What would it look like to take the Human Microbiome Project approach, but apply it to the forest?” What could we discover about the forest carbon cycle? Could we identify places where we could actually do belowground microbial restoration, and, in the process, combat climate change? Over the past three years, we’ve been working with forest scientists across Europe to do exactly that. In each of these locations, scientists have been documenting forest health for decades. And so, we asked our forest research partners to go out to each of these forests and collect a small sample of soil, which they then shipped back to our lab in Zurich so we could extract and sequence DNA, which allowed us to understand which microorganisms, and particularly fungi, live in each of these forests. And then finally, we used statistics and machine learning to relate which microorganisms live in a forest to a really important forest health metric: tree growth rate and carbon-capture rate aboveground. Now, once we controlled for the environmental drivers of tree growth -- so how warm and wet each of these places is, as well as other variables we know control background site fertility -- we discovered that particularly which fungi colonize the roots of these trees is linked to threefold variation in how fast these trees grow, how fast they remove carbon dioxide from the atmosphere. So put another way, these correlations imply that you could have two pine forests, sitting side by side, experiencing the same climate, growing in the same soils. But if one of them was colonized by the right community of fungi on its roots, it could be growing up to three times as fast as that adjacent forest. And furthermore, these patterns were not driven by the presence of particularly high-performing species or strains, but instead, they were driven by biodiverse and completely different communities of fungi. And so these fungal signatures are super exciting to us

because they imply an opportunity to manage, and in many cases, actually rewild the forest fungal microbiome. So, for example, can we reintroduce fungal biodiversity into a managed timber forestry landscape? And in the process, can we make those trees grow faster? Can we make them capture more carbon in their tree stems and in their soils? Can we rewild the soil and combat climate change? And these aren't just rhetorical questions -- we've actually started doing this. So this is one of our field trials in Wales, in the United Kingdom. It’s run in collaboration with the charity there called the Carbon Community. It’s 28 acres, or 11 hectares, and it's set up as a block-randomized controlled trial. This is analogous to how you would run a drug trial, but in this case, it's for trees instead of people. And here, we do a pretty straightforward experiment. We either plant trees, business as usual -- which is just direct planting of seedlings into the ground -- or we plant trees, and at the moment of planting, we add a small handful of soil. But it's not just any soil. It's soil sourced from a forest our analyses have identified as harboring potentially high-performing fungi. So since we reintroduced microbial biodiversity into some of these sites, we've observed that where we actually did that, we've been able to accelerate tree growth and carbon capture in tree stems by 30 to 70 percent, depending on the tree species. Or put another way -- where we manipulated and rewilded the invisible microbiology of this place, we’ve begun to change how that entire place works. Now it's important to emphasize that we're really excited about these findings, but we also understand they're still early. We want to see many more large-scale field trials and many more locations with many more years of data. However, beyond just these carbon and climate outcomes, I think the most exciting thing here is that we can actually do this with wild and native and biodiverse combinations of microorganisms. And while we pointed this approach at forestry, in principle, this kind of science has the potential to generalize to all of our managed landscapes. We can begin asking questions like

"What does a healthy agricultural microbiome look like?" Thinking across both food and forest agriculture. And there's reason to think a biodiversity-first approach may be particularly powerful here. And that’s because the history of agriculture has been an exercise in reductionism. We've identified high-performing plant species, and then strains, and then we’ve selectively bred them, and now we genetically modify them. And finally, we plant those organisms out in vast monocultures. So a single plant species as far as you can see. And to be clear, this has produced very productive agroecosystems. But it's also produced ecosystems we’re coming to understand are remarkably fragile. Systems increasingly sensitive to extreme climate events, novel pathogens. Systems incredibly reliant on chemical inputs, we're coming to understand have really serious externalities. So we now have the data, computational tools and the ecological theory to start going the other way, to lean into biodiversity and complexity. And once we do, the question really becomes, by rewilding our soils, can we make our managed food and forest landscapes reservoirs of belowground biodiversity? And in the process, can we enhance yields and carbon capture and all the other services we ask of these ecosystems? I think there's a lot of reason to be incredibly hopeful here. And I think we also shouldn't be so surprised that these microscopic organisms have the potential for such enormous, ecosystem-scale effects. And that’s because we’ve known now, really for a long time, that forests are fungi. And they’re incredibly biodiverse communities of bacteria and archaea and protists and microscopic soil animals and viruses. Soil is the literal foundation of terrestrial ecosystems, and the microbial life that inhabits soil represents some of the most complex and biodiverse communities of life on Earth. For the first time, DNA sequencing is turning the lights on belowground. It’s allowing us to see these organisms in unprecedented detail and at unprecedented scales. Imagine studying plant biology, but you never really knew if you're looking at a sequoia tree or a sphagnum moss. And then, all of a sudden, you did. That's what's happening right now in global environmental microbiology. And so we should expect this revolution in our understanding of these microscopic organisms, and particularly fungi, to transform how we understand and how we manage our ecosystems in a foundational way. Thank you. (Cheers and applause)