There’s a crazy place beneath your feet, a jungle of sand, silt, and clay, of solids and pores. Some of the most diverse and overlooked communities on Earth live here, in a world unlike anything we know – completely dark, of tiny proportions, and full of surprises. Even the air and water aren’t the same. Soils and their inhabitants play a huge role for the overground world, from food security to climate change. What do scientists know about them, and how are they exploring soils? In this first episode of the Life in the Soil podcast, host Anja Krieger learns more about the soil habitat from soil scientists Matthias Rillig and Johannes Lehmann.

---

TRANSCRIPT

Sound “Transversal Is A Loop” by Saša Spačal

Theme “Deep in the Soil” by Sunfish Moon Light

Katie Field
All life and well-being depends on it. It’s where we grow our food. It’s where our leisure time is spent. It’s got critical implications for the planet’s climate regulation. It’s hard to imagine a component on Earth that is more important than soil and the biodiversity present within that soil.

Anja Krieger
Welcome to Life in the Soil, a podcast by the plant, fungal and soil ecology lab at the Freie Universität Berlin.

Richard Bardgett
We appreciate the atmosphere, we appreciate the quality of water and the importance of water. But generally, soil comes very low down on the agenda.

Yong-Guan Zhu
The soil biodiversity in many ways supports the Earth ecosystem.

Diana Wall
I think of it as this huge food web in the soil. And everything is interdependent and they’re working 24-7 – to give us clean water and clean air and to stop soil erosion, you know, by aggregating little particles.
­
Stefan Scheu
I mean without that all the more colorful above-ground world wouldn’t exist.

Toby Kiers
Microbes are really key to our fight against climate change. I mean, microbes adapt, and they do it much faster and more efficiently than anything humans can do. So to understand how we can protect our planet, we really need to understand this huge and undiscovered biodiversity below ground.

Matthias Rillig
It’s life! And we should care about it just because it’s there.

Theme vocoder imitates “Life in the Soil, life in the soil”

Anja Krieger
Thanks for tuning in to the very first episode of “Life in the Soil”, a new podcast series supported by the BiodivERsA research network. My name is Anja Krieger, and I’m your host. As an environmental journalist, I’ve learned quite a bit about oceans, climate and pollution. But the world of soil somehow escaped my attention. All I knew was that there’s this brown stuff with the creepy crawly critters and it’s somehow important for humans and the planet – but I didn’t really get why. That changed when I met Matthias Rillig, the biology professor who runs the soil laboratory here in Berlin. He gave me this irresistible pitch of what a cool and crazy world soil really is. And since few people know about it, we decided to make this podcast. Join us on our journey into the habitat beneath our feet – a special place, where fungi, earthworms, microbes and countless other organisms thrive and maintain the world as we know it. On our tour through tiny tunnels and pore spaces, you’ll get to hear from some of the best scientists exploring these unique ecosystems. So…let’s roll the tape!

Sound effects (dripping) from podcast theme by Sunfish Moon Light

Anja
Matthias, when we first spoke you introduced me into this architecture of soil, this habitat. Maybe you can tell our listeners a little bit about it.

Matthias
Yeah, soil has been called the most intensely 3D-structured environment. And I think that hits it just perfectly. So, soil is a combination of atmosphere, so air, the lithosphere, which is the rocks and the minerals, the hydrosphere, which is the water, and the biosphere, which is the organisms, its biodiversity, and their dead remains. And these four components that together form soil, they’re arranged in incredibly complicated ways. So soil, I like to think of it as an incredible internal surface area. So soil is just surface. And it’s surface because all these different components are bound together in aggregates and the pore spaces that remain in between them. The cool thing about soil aggregates is that they’re made by organisms. So fungi build them, bacteria, microarthropods, earthworms, of course, everybody contributes to the production of these aggregates. And these aggregates are the very architecture of soil, they determine the structure literally of the habitat. And that’s what made them so interesting to me, because it’s a physical structure, it’s like, if you will, it’s the architecture, it’s like the house, it’s the city. And really, these organisms make these structures in various ways, you know. Fungi make what’s been called a sticky string bag that maybe holds them together. And bacteria exude sticky substances that glue them together. And earthworms, of course, they’re doing this at a slightly different scale, they tunnel through soil, leaving behind biopores and smooshing soils together. To me, it’s the heart of what soil is all about, is soil aggregates and the structure of a soil. It’s the stage on which life in the soil is being played out on and it is in itself a product of life.

Ambi/Sound of sieving machine by Matthias Rillig

Anja
So basically, these aggregates are the little crumbs you see in soil. Matthias showed me how the scientists test them in the soil lab. With a special machine, they softly tumble the aggregates in water. That way they measure the stability of the soil crumbs. The more stable they are, the better.

Matthias
When aggregates are not stable, what happens is what’s called erosion. You know, when aggregates are not bound together by these binding forces that are produced by organisms, then they fall apart into smaller pieces. And these smaller pieces can be moved by various forces in the environment, for example, by water. Or they can be entrained in the air and blown away, this is wind erosion. And that happens when soil is not stable, when the soil structure is not stable. So having a stable soil structure is important for avoiding erosional losses, one of the most severe problems facing soil on a worldwide basis, really. And when you’ve lost the soil, it can take a long time to form it again, I mean, depending on the soil, hundreds to thousands of years. But it can be lost in a heartbeat.

Anja
Soil erosion really has devastating effects, on so many levels. When fertile topsoil is eroded, it gets harder and more expensive for farmers to grow food and crops. Soil erosion can also lead to mudslides and floods and damage roads and buildings. Minerals and pollutants can wash out of the soil and impact the water quality in rivers and oceans.

Matthias
So that’s important. The other reason why soil aggregates are important is that inside of them, it’s really where carbon is being stored. Everybody’s interested in soil carbon storage, because that carbon is not in the atmosphere in the form of CO2, with its undesirable effects. But you know, soil is not stored… sorry, carbon is not stored in soil in the form of, you know, blocks. It’s stored in the form of organic matter, soil organic matter. And that soil organic matter becomes part of the structure of soil. So it’s built into these aggregates, really, this is what holds the aggregates themselves together. When you lose soil organic matter – and this has been documented very well in, for example, in North America, but when you lose soil organic matter, for example, when you till, so agricultural plowing, you knock open these aggregates by just physical force, then the soil organic matter that’s inside of these aggregates that’s basically physically protected by virtue of being inside of these aggregates is now open and exposed to the outside, for example, where it’s aerobic, rather than anaerobic in the inside of these aggregates among other things. And they can be attacked by the microbes and can be degraded.

Anja
When a healthy soil is disturbed this way, it can lead to a vicious cycle. Organic matter gets lost, and there are less binding agents to make new aggregates. That way, the rest of the organic matter also becomes more unstable, and the soil further degrades. So it’s really important to know what this soil organic matter really is, and how it can be protected. The first thing I thought about, was the leaves falling from the trees. But that’s not all, says Matthias.

Matthias
You know, this organic matter in soil used to be viewed as dead plant matter that’s maybe been slightly modified by microbes – that view has been changing in the last several years towards soil organic matter being more microbial product, so dead microbes or what’s called microbial necromass. So it’s the…

Anja
Huhhh…necromass!

Matthias
It’s a bit dark, I know. But soil organic matter, maybe actually, mostly dead microbes – that completely changed the way we view something as fundamentally important for soil like organic matter, that has really undergone a revolution, I’d say.

Sound walking on leaves by iamdylanavery on freesound.org under a CC-0 license

Anja
So imagine you step off the asphalt or stone into a park or forest, and are walking on an intricate architecture built by zillions of tiny soil organisms. It’s an underground landscape that also shapes what happens up above, in our world. To learn more, I called Johannes Lehmann. He’s a professor of soil science at Cornell University.

Johannes Lehmann
We are calling ourselves after soil organic matter and soils, right? We are calling ourselves “humans” and the word comes from “humus”, soil and soil organic matter. So we, our whole idea of humanity is linked to soil and soil organic matter, as nothing else in this world. And in contemporary terms, soil organic matter is still the most important aspect of soil fertility. If you want to do one thing to improve your soils, for producing nutritious and healthy and large amounts of food, you’re managing soil organic matter. If you want to improve water quality in your district, apart from avoiding soil pollution, you would manage soil organic matter. And now over the last five years or so we increasingly recognize that one wedge, one important aspect of mitigating climate change is restocking soil organic matter.

Anja
The soil actually stores several times more carbon than the atmosphere and all vegetation combined. But despite these benefits, people didn’t really understand the nature of soil organic matter for a long time. It was thought to be a special substance, called “humus”. Well, according to Johannes, that stuff doesn’t really exist. It’s just a misunderstanding, rooted in history.

Johannes Lehmann
The beginning of soil science in the 1700s was marked by overcoming the inability to extract organic matter from soils. And when it started to get possible to remove organic matter from soil to have a look at it, it was really a mixture of everything that was in that soil and that really got us on the wrong track of thinking about what soil organic matter is, what it is composed of, and how it is created. We thought soil organic matter are humic substances that are very large molecules that are recalcitrant, because they are so large and that they accumulate because they are recalcitrant. And that view was really an artifact of our inability to look very closely into the soil, through the eyes of a microorganism. What can the microorganism see around it, and eat, and what is the microorganism doing there, what kind of wastes are they producing? And we were not able to do that, we were only able to look at the whole thing – that is as if, as if you are drinking a fruit smoothie that has banana, strawberry, and cherry in it. And you’re blending it all together. And then somebody asks you, without you knowing what a strawberry and a banana and a cherry is what’s in that fruit smoothie, it’s impossible, you cannot do that! And you think it’s a new fruit, that fruit smoothie, but it’s just three different fruit blended together.

Anja
Think of that fruit smoothie. Without a way to analyze and separate the different fruit, there’s no way to understand what it is made from. Soil scientists encountered a similar issue. They thought the whole organic matter was a special substance. But thanks to new tools and methods, they found out more. It turned out that the molecules were small, not large – and that they weren’t new, just a complex blend of substances already known. The scientists had found the recipe for the fruit smoothie.

Johannes Lehmann
Soil organic matter is really a smorgasbord of different compounds. It’s anything you can imagine is there, mixed together. And that makes it so complex. The diversity of compounds that are in the soil is staggering. And on top of that, the architecture of the soil is very complex. There are all these small pores, big pores, nooks and crannies. There’s a lot of materials around each corner and you don’t know what is around the next corner. It can be big particles, it can be small particles, they can be dissolved or they can be particulate. They can be big, they can be in a plant format or debris from other microorganisms – the entire environment changes all the time. It can be dry, it can be wet, it can be cold, it can be warm, an acidic pH, it can be alkaline, it can be nutrient rich or nutrient poor. So the soil environment is incredibly diverse and versatile and that makes it also very challenging for one organism to inhabit and explore it all. And therefore, we also have a huge diversity of life forms, whether it’s fauna, large earthworms, to very small bacteria, and everything in between. And all these organisms live very, very differently. And they have to, because the diversity of soils is so large that it gives rise to many different organisms to specialize on certain habitats in the soil.

Theme Music (Interlude Mix)

Anja
Imagine you’re one of these tiny creatures, living in a labyrinth of sand, silt or clay, crawling or swimming through the tiny tunnels and pores. The air around you is almost completely water saturated, 100% humidity – and there’s no wind to bring you fresh air. Carbon dioxide accumulates, and oxygen levels are low. Even the water is special. It’s all pretty strange, at least from our human perspective.

Matthias
All of these components are really quite special. You know, we are used to light and in soil, it’s always dark, it’s eternal darkness, except for maybe the top very few millimeters, whether it’s some light, where there’s some algae maybe growing there. But at any depth in soil, it’s completely dark. And it’s quiet because communication usually goes via chemical ways, so there is no singing. There may be some vibrations that some organisms can perceive. But it’s quiet, it’s dark, it’s moist. It’s really a totally different ballgame.

Anja
Reminds me of like a cellar or maybe even like what cavers would experience. You know, there’s these huge tunnel systems, cave systems that some people explore and I mean, I get claustrophobic just thinking about it.

Matthias
Me too!

Anja
But could we say that soil has similar structures, but just in a very smaller dimension?

Matthias
Well, I think it’s not a bad analogy. You know, there’s also these pore necks, where, you know, if there’s an opening that’s smaller than your body size, beyond that, you can’t get to – this is exactly what is the case with soil as well. Well, so maybe it’s not a bad analogy at all, to have sort of this labyrinthine tunnel system. In addition, though, you have additional complexity, you know, you have immense biodiversity populating those tunnels and running around trying to eat you, trying to collaborate with you, or competing with you. So, you know, it’s not just you and a bunch of fellow cave enthusiasts. And you know, there (are) incredible gradients. Soil is just full of gradients, gradients in everything, gradients in gases.

Anja
What is a gradient? I don’t even know.

Matthias
So, it’s a difference in concentration along space. For example, next to a root you have a lot of CO2 because that root respires. Further away from that root, you have less CO2. And so that gradient contains information. Organisms utilize that information. For example, fungi, our pet fungi, arbuscular mycorrhizal fungi, they can sense CO2. So if there is no CO2 around, they won’t bother sporulating typically. And so organisms exploit these gradients for information. But if you have even a gradient in something like a gas, then you can imagine there (are) gradients in just about everything as well, especially solutes, like nutrients or toxic compounds, or info chemicals. And you know, soil organisms have to navigate these gradients, that’s their source of information. Because they don’t have sight since it’s dark, it’s pointless to have good eyes where there’s no light anyway, so it’s all chemical, chemical gradients what these organisms have to sort of make use of in terms of environmental information.

Anja
The inside of a crumb of soil can be completely anaerobic, without any oxygen, for example. So we humans would die. But there are many organisms in soil that can replace oxygen with something else, like nitrate, to survive. In soil, conditions can switch radically from one corner to the next.

Matthias
So that the inside of an aggregate is completely anaerobic, the outside surface and even a couple hundred micrometers away you have full oxygen partial pressure. And that is the most, almost the most important part about the environment in soil is that you can have completely contradictory processes occurring in the same tiny volume of soil.

Anja
So soil is not just one, but many different worlds in super small dimensions. Another really strange phenomenon is called Life at Low Reynolds number.

Matthias
So that means everything around you is incredibly viscous. Even air becomes viscous, when you are really, really tiny. That’s really hard to imagine, it’s so radically different from our experience of the world as macroorganisms. You know, it’s like when our experience of the world is, you know, determined by when we throw a ball, that ball will fly for a while and then eventually fall down. But if you are a microbe and you stop moving your flagella, you instantly stop. It’s like in you there’s no coasting. You know, it’s a crazy world. For example, when a mushroom fruiting body in the gills of the mushroom, when they shoot out a spore. That spore basically hits air like it’s a thick, gooey substance. So it doesn’t fly very fast, even though they have to shoot it out with all their might, and basically it just stops in midair and falls down. It’s because there is no inertia. Everything just stops immediately when you are that small, even like growing out of a droplet of water is impossible, because the surface tension of water is such a strong force for you when you’re so small that you cannot overcome it. Which is why organisms have, you know, evolved all kinds of ways around it. Like they produce surfactants, otherwise they couldn’t grow out of a droplet of water. And you have to if you are in soil, you grow outside and into droplets of water all the time. Like if you’re a fungus.

Anja
The conditions for life in the soil are really weird. They almost sounds alien, like something that could only be possible on the surface of another planet.

Sound from Antares Cygnus NG-14 launch

Announcer: T Minus 15 Seconds

Anja
But it’s right here on Earth.

Announcer: T Minus 10

Anja
And that’s why Matthias and his lab took part in an international mission to send soil into space.

Announcer: 5, 4, 3, 2, 1

Matthias
Yeah, this has always been my dream.

Sound from launch
Announcer: Engine Start and Lift Off. The S.S. Kalpana Chawla takes flight sight set on the International Space Station.

Matthias
I just love the idea of examining what would happen to a living soil when there is no gravity. We simply can’t do it on Earth. There is no way to make gravity go away here. I mean, you could put things in a centrifuge or so – but it’s not convincing. So if you want microgravity, of course there’s little gravity in space, but if you want microgravity conditions, you got to go into space. And so this is the first time that living soil is in space under microgravity conditions. And so, of course, we are not interested per se in what happens under microgravity, we’re interested in finding out what actually happens here under conditions of gravity by switching it off. Just like what we do with other factors. If we want to know what nitrogen does, we take nitrogen away and see what happens. And here we want to know what gravity does. So we have to take gravity away, the only way to do that is in space. And so there’s living soil now in the International Space Station. And yeah, we’re just interested in how soil processes respond to that. For example, how soil aggregates are being formed when there is no gravity. How will this work? We don’t even know how this process works down here, actually, nobody knows how a soil aggregate really is being formed by the action of microbes – which is astonishing. We don’t know that. But here we could find out if there’s no gravity, does it still work? Or gravity has absolutely no influence whatsoever and these things up there will happily form aggregates also under conditions of microgravity. And how will biodiversity respond to it? Will fungi for example, be much less likely to deal well with things floating around because they’re a collection of lines. If I was a collection of lines, I would not like stuff floating around. On the other hand, if you are a bacterium and you are just attached to some surface, what do you care? I mean, maybe to them, it doesn’t make any difference at all. I mean, I doubt that, but it maybe makes less of a difference than if you’re filamentous organism. And it’s like just a complex system with all that biodiversity in there, and it’s the air, the soil atmosphere, the water – how will the water behave? I think it’s just a cool question to ask yourself. What role does gravity really play in the way soil works and its biodiversity.

Anja
Could there be planets with life that have no soil?

Matthias
Well, I think that’s not the first question one would ask. The first question one would ask is, are there other planets with life? And I don’t know, I think the chances are pretty good. There is a recent paper by my colleague, Dirk Schulze-Makuch, who has thought about superhabitable planets – planets that are maybe able… somewhere out in the galaxy or the universe that are more able to support life than on Earth. Because why should Earth be the measure of all things? Maybe there’s other planets that have more life, more biomass, more crazy biodiversity. But I have a hard time imagining that that planet would not have soil – I mean, sure, there could be oceans that harbor life. If you can imagine an ocean planet. Ah, yeah, but I wish it had soil, of course. Yeah, it should have soil.

Theme Music by Sunfish Moon Light

Anja
This was episode 1 of Life in the Soil, a podcast series by the plant, fungal and soil ecology lab at Freie Universität Berlin. If you’d like to hear more, tune in again – we’re going to explore fungi, the food web, global change and sustainability in coming episodes.

I’m your host, Anja Krieger, and co-produced this episode with biologist Matthias Rillig and our story consultants from the lab, Stefanie Maaß and Moisés Sosa Hernández. Visit the lab online at rilliglab.org. Thanks to Johannes Lehmann for sharing his insights on soil organic matter. The theme music is by Sunfish Moon Light of Future Ecologies, cover design by Maren von Stockhausen, and sounds from Sasa Spacal. A huge thank-you to the Biodiversa research network for funding our production as part of the Digging Deeper project. Learn more at biodiversa.org.

If you enjoyed the show, share us on social, and subscribe, rate and review us wherever you find your podcasts. To get in touch, you can find Matthias as mrillig on YouTube, Twitter and Instagram. I’m anjakrieger on Twitter.

The research aboard the International Space Station is made possible by sponsorship by and collaboration with several organizations – find our partners listed in the episode description. Audio of the launch is by NASA.

Thanks for listening, and see you soon!

Vocoder sings “The Life in the Soil”­­­, end of audio.

FULL CREDITS

Credits

Produced by: Anja Krieger and the Rillig Lab rilliglab.org
Funded by: Digging Deeper / BiodivERsA https://www.biodiversa.org/
Voices in intro: Katie Field, Richard Bardgett, Yong-Guan Zhu, Diana Wall, Stefan Scheu, Toby Kiers
Story consultants: Stefanie Maaß, Moisés Sosa Hernández
Thanks for feedback: Madara Pētersone, Mendel Skulski and Florian Hintz

Cover art: Maren von Stockhausen http://marenvonstockhausen.de
Theme music: Sunfish Moon Light / Future Ecologies https://www.futureecologies.net
Additional Music: Particle by Dorian Roy
Sounds: Intro: Sasa Spacal, “Transversal Is A Loop”; leaves by iamdylanavery; rocket launch by NASA

The Digging Deeper project was funded through the 2015-2016 BiodivERsA COFUND call for research proposals, with the national funders Swiss National Science Foundation, Deutsche Forschungsgemeinschaft, Swedish Research Council Formas, Ministerio de Economía y Competitividad and Agence Nationale de la Recherche.

The research aboard the International Space Station is made possible by sponsorships of Norfolk Institute, Rhodium Scientific, the ISS U.S. National Laboratory, and NASA, with special grants from bio365, Deep Space Ecology, Rhodium Scientific, and the Zwillenberg-Tietz Foundation, and the support of Cornell University and Freie Universität Berlin.