In this episode, Anja and Matthias take you on an underground safari through the hidden jungle of the soil. And they’ve won some excellent scientists as tour guides. You’ll hear from Diana Wall about a tiny worm that is so tough it even lives in Antarctica or hot deserts. Richard Bardgett introduces you to collembola, also known as springtails – tiny insect-like animals that can jump like crazy! Stefan Scheu and Maddy Thakur reveal which animals are considered the “wolves of the soil”, and Kate Scow delves into bacterial communities. How do all these organisms work together as a system, and why does this soil food web matter greatly to us as well?

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TRANSCRIPT

Soundscape “Transversal is a Loup” by Saša Spačal
 
Theme “Deep in the Soil” by Sunfish Moon Light
 
Anja Krieger
If you could choose to be one soil organism, which one would you want to be and why? 
 
Richard Bardgett
(Laughs) Well, yeah, that’s a very interesting question. But I have a very, very clear answer, I would definitely be a collembolan. It’s a very small, insect-like animal, it’s about sort of, just about visible to the naked eye. 
 
Diana Wall
I would like to be a nematode (laughs). And I think I would like to be my favorite nematode, which is dominant in the soils of Antarctica. And the reason is, that nematode is so tough. And it’s very beautiful, I think. 
 
Madhav (Maddy) Thakur
Soil is full with lives, full with a variety of lives. So I would choose many characters depending on the day, depending on my mood.
 
Kate Scow
Man, I just love them all!
 
Yong-Guan Zhu
In my opinion all these organisms are useful one way or another. We can’t say which is good, which is bad.
 
Anja
Welcome to Life in the Soil, a podcast by the plant, fungal and soil ecology lab at Freie Universität Berlin. I’m Anja Krieger, your host. In the first two episodes we explored the habitat beneath our feet, and visited the world of fungi. Now, we want to take you on an underground safari, to meet some of the other characters that live in this hidden jungle. We won some real experts as your tour guides – the soil biologists who study these little creatures. So hop onto our tiny jeep, and come along.
 
Vocoder sings “Life in the soil, the life in the soil”
 
And as always, I’m joined by my co-producer, soil biologist Matthias Rillig.

Matthias, there’s this huge and diverse community living in the soil. Maybe you can take us from the ones that most of us will know like an earthworm, down to the very, very tiny.
 
Matthias Rillig
Yeah, it goes from earthworms that you can hold in your hand, depending on if you like that, all the way to the tiniest of critters, like bacteria and archaea that are a few cubic micrometers. So super, super tiny, you know. I mean a millimeter, you know what that is, it’s like this one mark on your ruler, and then a thousand times smaller than that. That’s really what you’re talking about in terms of the microbes that are the vast majority of the organisms that live down there – I mean, in one gram of soil, you can have 10 to the eight bacteria. So that’s a one with eight zeros, an unimaginable number. And fungi – we give fungi often in meters because they are lines. So in one gram of soil – and one gram is really not very much, as much as can hold between your two fingers – so in one gram of soil you can have you know, up to 40 meters or up to sometimes even 100 meters of hyphae. This is only possible because they’re so tiny, so you can fit a lot of them in even the tiniest crumb of soil. And then everything in between, you know, protists, you have microarthropods, so collembola and mites and nematodes, enchytraeids, all the crazy critters and it’s incredibly diverse. And in the very top of the soil you also have algae, you know, but because there is no light down there, they sort of very quickly fade away. But that is an incredible diversity. That’s all in there in the soil, all interacting with each other, all forming part of the food web, which is one way to conceptualize and simplify the incredible diversity that’s in the soil.
 
Anja
I heard that it’s one of the most complicated that exists. Who eats whom in the soil, and why does that matter to us?
 
Matthias
Yeah, I think it is one of the longest food chains of any food web anywhere. You can imagine life in the soil being organized into these trophic levels. So at the base, you have bacteria and fungi. And then already there, it separates, because some organisms would prefer to eat on fungi, for example, collembola, certain nematodes. And then other organisms would prefer to eat bacteria, for example, protists, also certain nematodes, not so much microarthropods. And so you have these two, what are called energy channels by some people that are basically flows of matter, of carbon through this food web – of course, as an abstraction. And in the end, that goes to various levels, you know, nematodes, different nematodes, predatory nematodes, that eat other nematodes, mites that eat other organisms, and then it goes to the top, the top level, the top predator is predatory mites. And so you can visualize each of these levels as a trophic level. And having omnivory in the food web means that organisms don’t adhere to this strict ordering of trophic levels, but will feed across trophic levels – that’s been shown to be very important for stability. But really, this food web is incredible! And it doesn’t get that much attention, like in an ecology textbook, you will not find it, you will find the food web, you know, like grass-cow-tiger, but you don’t see one of the most amazing food webs on Earth. And we should care about that food web because this is how our litter gets recycled and made and how nutrients are being unlocked for use by plants. So the entirety of the food web, basically one of the functions that it has, from our perspective of the ecosystem. Of course, this is not some is not a service that the food web does, this is just what comes out in the end of all these feeding interactions, is nutrients are being transformed from an organic form to an inorganic form, it’s called mineralization. And these nutrients are then available for plants to take up – otherwise we would, you know, drown in a heap of trash everywhere, because nothing gets recycled.
 
Sound Walking on Leaves
Music – Calisto by Blue Dot Sessions
 
Anja
You’ve probably seen some of the bigger animals that live in soil – the earthworms, centipedes, ants, termites, or the beetles. But what about collembola, mites or bacteria – some of these other organisms Matthias just mentioned? I have to admit, when he told me their names, I could not really picture them. I guess they’re as different from each other as a fish is from a cat or a dog. But it’s not like everybody’s posting cute pictures of them. They’re just too small, and not very fluffy. To appreciate them, we need to zoom in closer – and open our hearts to a whole new world of life. Like nematodes. If you have never heard about them: these tiny worms are one of the most abundant groups of microfauna in the soil. I had no clue, but nematodes are everywhere – even in the most unlikely of places,such as the dry valleys of Antarctica. 
 
Diana Wall
And that’s a large area, that is just like time stopped. And there’s lots of soil, but no plants and no flying around bugs or…it looks like Mars, it looks like nothing would be alive.
 
Anja
This is Diana Wall, a soil ecologist at Colorado State University. She has travelled to one of the most far-off places in search of life in the soil. Now, I always thought of Antarctica to be completely covered in snow, but in fact there are these snow-free valleys. The temperatures there are way below freezing, the landscape is dry and barren. Just grey rubble and sand. And yet, a few organisms have evolved strategies to cope and make this uninviting place their home. And on top of that simple food web sits a microscopic worm called Scottnema.
 
Diana Wall
But what is really cool about it is its survival. The way it survives those Antarctic harsh winters, is by going into anhydrobiosis, this life without water and it shuts down its metabolism. And it’s like the fountain of youth, you know! Okay, I’m shutting everything down. I’m hibernating like a bear. My metabolism isn’t going. When we get the Antarctic summer, which is about six weeks, and conditions are better and a little warmer, and I have a little water, I will rehydrate and move through soil particles and see what’s there and what’s different. And I will find my bacteria and my food. And then I’ll go back to anhydrobiosis when the weather gets be-…that way, you live forever! This nematode has all these genes to help it turn on, turn off in case there is change in the environment. And I think that that is really remarkable!
 
Anja
Other nematodes can do that too. Researchers were able to revive some of these tiny worms after decades of this state of suspended animation! Nematodes make up a lot of the biomass in soil. And they also live in other places. Different kinds of roundworms can be found in the oceans, in rivers, in great depths and on high mountains.
Over a hundred years ago, a wise nematologist called Nathan Cobb beautifully imagined how the Earth would look like with nothing but nematodes:

Music – Verdigris by Blue Dot Sessions 

Narrator Kevin Caners
“If all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes. The location of towns would be decipherable, since for every massing of human beings there would be a corresponding massing of certain nematodes. Trees would still stand in ghostly rows representing our streets and highways. The location of the various plants and animals would still be decipherable, and, had we sufficient knowledge, in many cases even their species could be determined by an examination of their erstwhile nematode parasites.”
 
Anja
To really see a nematode, you need a microscope. They’re tiny tubes basically – just as small as your eyelash. And they’re transparent, so you can see all their body parts. Scientists are able to tell them apart based on their mouthpieces, Diana told me.
 
Diana Wall
There’ll be some that have these stylets, like a hypodermic needle, that penetrate a plant root. But then there’s going to be a bunch of others that have a different kind of morphology. And they kind of suck in bacteria. And then there are ones that have a tiny little stylet, they can feed on fungi. And there’s some that have a little tooth and they’re predators and they feed on other nematodes and other tardigrades…
 
Anja
…yeah, those cute little water bears, which can also survive pretty extreme conditions. That is – if they don’t meet one of those hungry little worms in the soil. So nematodes have many different tastes, and each has their own set of tools to satisfy its appetite. And as always in nature, it’s not only about eating, it’s also about being eaten. Nematodes are a favorite food of mites, for example. Even fungi sometimes hunt nematodes. These little worms are super significant for the soil food web. But back when Diana started studying them, few people knew them. And those who did, often saw them as quote unquote problem worms. Because they’re also pretty successful parasites of plants and animals.
 
Diana Wall
You know, my uncle who was a farmer knew about nematodes, but he was the only person in my family who knew why I was studying nematodes. And he also would just say, oh, they cause a lot of disease, in my, you know, my crop of tomatoes or whatever. And so it was it was kind of like, you know, I was on one end of learning about the science and who they were and what they did, and how they affected the metabolism of plants. And then at the other end was my uncle who was just like, ugh, kill them all! You know? (Laughs) They’re really taking care of my crops in a bad way. And then I can’t sell the crop. 
 
Anja
Well as you know, that didn’t stop Diana. She was already on a mission to lobby for the little creatures in the soil.
 
Diana Wall
When I would go to meetings, ecology meetings or, you know, get with other disciplines, they would say, nematodes? Oh, there must be two talks here on nematodes. So I thought they were disrespecting nematodes, and I got very involved in…oh, well look, the people who talk about mites, you know, microarthropods, they also find that people aren’t that interested. So it seemed like every creature in the soil was being disrespected! Or maybe just there wasn’t enough knowledge to consider it as part of global biodiversity. And that really got me going on we need to consider all the biodiversity in soil and what it does for us.
 
Richard Bardgett
The activities of those organisms are what provides the nutrients on which the growth of plants depends.They are the activities which determine, for example, how much carbon is stored or released from the soil.They are the activities that determine whether nutrients are leached from the soils into waterways or whether they’re retained within the soil matrix or whether they’re released to the atmosphere as greenhouse gases. 

Theme Interlude

Anja
Another scientist who is raising attention for the biodiversity in soils is Richard Bardgett. He’s a professor of ecology at the University of Manchester in the United Kingdom.

Richard Bardgett
So all the biogeochemical transformations that actually occur within the soil, the cycling of carbon, the cycling of phosphorus, the cycling of nitrogen, depend upon those trophic interactions.
 
Anja
Richard has written this great book called “Earth Matters” that explores the significance of soil for our civilization. He’s also studied some of the tiny organisms in great detail. His favorite is a particular springtail – an animal that gets its name from its ability to jump. They can go so high, it would be like one of us jumping over the Eiffel Tower. We’ve already mentioned their scientific name – collembola.
 
Richard Bardgett
It’s a very small, insect-like animal. It’s about sort of, just about visible to the naked eye. And it’s quite dominant in the soil, so you can get something like 100,000 of them within a meter square all within the surface soil. And I guess I always like it, because it’s quite a charismatic organism. It’s one of the few animals in the soil that you can actually see.
 
Anja
Springtails can be colorful and really cute. While they don’t get quite as much attention as cats and dogs, you can actually find some really adorable pictures of them on social media. For example, the amazing images of Andy Murray who runs a website called chaosofdelight-dot-org. On his page there’s pictures of a springtail family called Onychiuridae. That’s the one Richard Bardgett’s favorite springtail belongs to, the one he studied for his PhD in the early ‘90s.
 
Richard Bardgett
So I used to do experiments where I presented them with different fungi, and explored which ones they preferred. And it’s quite amusing because I actually did these experiments under my bed in my house, so I spent a lot of time checking every six hours or so, where these little animals had gone, which fungi they were preferring. So I didn’t just live with them in my work environment, I also lived with them in my home.
 
Anja
The relationship between some soil scientists and the objects of their study can be pretty close. It turned out that Richard’s little springtails had a very diverse diet. They ate from the mycelia of seven species of fungi in the British grasslands. And of course, they prefered some fungi over others, just like you and me would. Thanks to researchers like Richard, science is gaining more and more insights into the soil food web. The importance of this web can’t be overstated. A intact soil food web leads to a healthy soil that in turn provides the basis human food production.
 
Music – Heliotrope by Blue Dot Sessions
 
Anja
If you could be one organism in the soil, which one would you want to be and why?
 
Maddy Thakur
(Laughs) Ehm, that’s a difficult question for a soil ecologist because soil is full with lives, full with variety of lives. So I would choose many characters depending on the day, depending on my mood.
 
Anja
Maddy Thakur is an Assistant Professor at the University of Bern in Switzerland.
 
Maddy Thakur
But if I have to pick one, I will go with a predator which I am always fascinated by, this is a group called predatory mites. And I’m always fascinated by them because they… I call them wolves of the soil, you know, because they do solitary hunting, they also do pack hunting and they just fascinate me – and their ecology is incredible with the kind of aggressive feeding they do in the soil attacking almost something which is three times bigger than it, it will still attack it. So yeah, I think if you give me the choice of picking one group of organism it would be predatory mites.
 
Anja
In our previous episode we looked into the friendly interactions of mycorrhizal fungi with plants, but soil can also be a vicious jungle!” These predatory mites are like the wolves of the ecosystem. They can look vicious, but they’re still very tiny. Predatory mites hunt all the other organisms we’ve mentioned so far – especially the tasty soft nematode worms and springtails. But in case there is nothing else, predatory mites can also hunt other mites. Like the oribatid or moss mites. But it’s a lot of effort. Mites know how to defend themselves.
 
Stefan Scheu
On the one side, because they are really very heavily sclerotised. And they do have special devices for example, to hide their legs. So no predator can kind of attack their legs. And then they also have poison glands. So if any predator comes they poison them.
 
Anja
Stefan Scheu is a soil ecologist working at the University of Göttingen in Germany. He’s fascinated by oribatid mites, but also many other species in soil.
 
Stefan Scheu
When you once really are educated and kind of guided into that below ground system, I think you can’t resist that it gets really fascinating.
 
Anja
Stefan’s favorite mites, the moss mites, look a bit like little beetles. You can find them in the leaf litter and the topsoil, especially in forests. There, they break down the organic matter and nibble on some fungi. But how do soil biologists even know what all these tiny animals feed on? Like, you can’t really shrink yourself and hang out behind a soil crumb to see what’s happening.
 
Stefan Scheu
Basically you are what you eat, in that respect that the lipids you ingest are ending up in your own lipid body without major changes. So if we analyze the lipid composition of your fat body, we can trace the origin of these lipids.
 
Anja
Lipid analysis is just one of the methods scientists use to better understand the tangled food web of the soil. But what’s clear is that at the base of it, there’s one major resource. And that’s the detritus, the dead stuff, that quote unquote smoothie of organic matter. 
 
Music – Ghost Byzanine by Blue Dot Sessions
 
Anja
We don’t yet understand why or how, but the biodiversity in soil is huge. And that gives us lots of choices to imagine what it would be like. Maddy described it perfectly:
 
Maddy Thakur
I think that’s, you know, the beauty of being a soil ecologist, that you if you really want to understand how the biology in soil works, there is so much sort of options for you to pick from. But on the other hand, you also want to have the overall view of, you know, what is happening. So on a day where you want to have a lazy day you would probably pick an animal like earthworm which is you know, which is slow, which is you know, moving around. When there is a rain you start to become more active, but on other days you are usually not as active as a predatory mite, for example. Some other days you would like to be probably a collembola. And collembola is so much fun to be because you can jump! You can jump like crazy if you’re a collembola. Or, or why not sometimes even become a microorganism(s) which really are the you know, the lifeblood of soil?
 
Anja
From earthworms to springtails to fungi and bacteria – soil is a living system. It’s not about individual organisms, it’s about the way they all interact.
 
Kate Scow
And I think what’s exciting is this like sense of community, which I also am very excited about among humans.
 
Anja
Kate Scow is a soil microbial ecologist. She works at the University of California, Davis in the Department of land, air and water resources.
 
Kate Scow
It’s what you gain by being in a community is what are all the different kinds of things that you can do. For example, somebody can break down a really complex, like a pollutant into simpler form that then you can use, right? And then help keep it degrading. Keep it going along the way. There’s a lot of that kind of mutualistic behaviour that is really exciting about being in communities.
 
Anja
Soil bacteria are often the most abundant group of microorganisms in the soil. They’re not only everywhere, they’re also able to consume almost anything. Every living being needs a food source and something to breathe with. So we humans, for example, break down glucose from sugars in our bodies, and breathe in oxygen.
 
Kate Scow
But what’s incredible about bacteria is they can swap out that glucose for a whole bunch of different kinds of other compounds.
 
Anja
So they can use metals in soil, iron and manganese, sulphur, hydrogen gas, organic fats and proteins, but also pollutants, like oil, gasoline, or organic solvents. And then if we look at the other side, bacteria can also swap out oxygen for all kinds of other compounds.
 
Kate Scow
So, they can breathe with like nitrate or they can breathe with an oxidised form of iron, or they can breathe with sulphates or CO2.
 
Anja
That gives bacteria an amazing capacity to survive in many different conditions. Like we talked about in episode 1, they can inhabit the insides of soil aggregates even if there’s no oxygen. And because the conditions in soil can change rapidly from one corner to the next, there’s many different niches for different kinds of bacteria to inhabit. That is immensely important for the entire system.
 
Kate Scow
Microbes are the eye of the needle through which carbon flows from like plant residues into stabilised soil organic matter. They are the agents, they’re the ones that are involved. And so there’s a lot of capacity to bring some of the CO2 in the atmosphere down into the soil by managing the microbes.
 
Anja
And the bacteria play a big role in this microbial action. They process the bodies of the previous generation, returning the nutrients that these bodies had borrowed for a while back to the system. They’re some of our most important natural waste managers. Like our gut microbiome helps us digest our food.
 
Kate Scow
Don’t think about microbiomes as only the organisms. But it also encompasses their theatre of activity. It’s them, but it’s all the things that they do.
 
Anja
To see them in action isn’t easy. Bacteria are even tinier than nematodes or fungi. You can extract some DNA and see who’s in there, dead or alive. You can offer up different conditions in a petri dish, and see who’s reacting. But you can’t really experience life as a microbe, to really witness their role in the whole system.
 
Kate Scow
There’s a movie about a trip into a human body where they shrank down really small and then roamed around the body. I mean, I would love to do that in the soil. And the thing is, I would have to be changing scale all the time and have to go down to like a micron, and then I’d have to blow up to 50 microns, and then maybe go down to point to, you know, to look at the different processes going on. I mean, that would be my dream. And that’s not even… I don’t know, if there’s any technology that can shrink me down to do that, so I can be chased by, you know, say a nematode or hide in the small pore, you know, next to another shivering little bacterium, waiting for the predator to go by, or be a victim of, you know, be stuck onto cation exchange, you know, assuming I’m positively charged and I got to pull myself off of that soil particle to be able to keep moving. And, you know, I mean, that’s my… that’s my dream, or I’d like to make a film about it.
 
Music – Theme by Sunfish Moon Light (Interlude mix by Anja)
 
Anja
So the soil food web is this complicated, messy, but also finely tuned system, this circus of life, where all these different organisms live and feed. And in the process of that they produce waste products that then can be used by other organisms and plants again. Taken altogether, the action of life in the soil determines how well plants can grow and how much of the carbon dioxide they catch from the air is stored underground. A healthy soil community also provides plants with water and nutrients. And on a global scale, soil impacts the entire Earth system. Basically, all nutrient cycles we and other species depend on are born in the soil – with only a few exceptions. And they’re run by the living organisms, the tiny chemists of the soil.
 
Matthias
Really all of these organisms just earn a living in their own specific way that you know, to us fits together into what appears like a cycle, like a nutrient cycle – like the nitrogen cycle, but also the phosphorus cycle. And of course, the carbon cycle, those are all cycles. And they are driven very much by soil organisms. And of course, the soil is fed in the end with carbon via photosynthesis – photosynthesis from the plant, then takes this carbon out of the atmosphere and pumps it below ground, of course, primarily to its roots. But because of all the organisms that sit in the roots, it gets quickly translocated into the soil. And of course, roots are not tight systems, the roots are constantly leaky, they’re leaking carbon by their very construction into the soil. This is a huge amount of carbon that’s input into soil, anywhere from 4 to 70% of the carbon that’s fixed in photosynthesis, so huge! This is the engine that drives that soil. And of course, then in the end, when plants die, they are litter aboveground and belowground, of course, we only see the aboveground litter, the leaves that fall down in the fall. But this also happens below ground, you just don’t see it. That is also another pathway of crop input. And all of this drives that motor in the soil that feeds that entire food web, because the basis of the soil food web is actually dead organic matter, primarily. This is why it’s called a detrital food web. So based on detritus, it’s really quite different from all the food webs that you may have generally heard of, and that are usually depicted in ecology textbooks, because the beginning of that food web is dead stuff on which then bacteria and fungi grow and then all the rest. But the driving force of all of that is plant growth.
 
Anja
So let’s do the elevator pitch. If you met a billionaire, or a millionaire, let’s say, and you have the chance to convince them that they would invest a substantial amount of money into soil biodiversity, what would you tell them?
 
Matthias
Well, first of all, get me into that elevator (laughs)! Yeah, there’s plenty of reasons to care about soil biodiversity, biodiversity in its own right. Maybe first and foremost: It’s life! And we should care about it just because it’s there. Irrespective of what it does for us, what perceived, quote unquote, services it may provide to us. And I guess if I had a billionaire there, uhm, I wonder… so I mean, I would probably tell them that soil biodiversity in its entirety is like an army of chemical factories. There’s always new reports on a new class of antibiotics being discovered from soil organisms. I mean, this is not by chance, it’s because the diversity is just so high! It’s because you have this reservoir of biodiversity in there, and of course, just almost by chance alone, there’s going to be something in there that produces something of interest. So it could be something that makes plants grow better, that protects plants from some adverse impacts of the environment. So it’s just…you could think of it as, as also a reservoir of chemical compounds. That’s a very utilitarian view of things, I prefer more the valueing-them-for-the-life-that-they-are. And to learn from it understand how it works, why it’s all there, how it interacts, what are the networks? I mean that is why I would value biodiversity in its own right.
 
Music – Theme by Sunfish Moon Light
 
Anja
This was episode 3 of Life in the Soil with Matthias Rillig, and me, Anja Krieger. Huge thanks to our guests Diana Wall, Richard Bardgett, Stefan Scheu, Maddy Thakur and Kate Scow, to the BiodivERsA network which funds our series – and to you, for listening. If you enjoy our series, leave us a 5 star review on iTunes, and share this podcast with your friends.

Diana and Richard are founding members of the Global Soil Biodiversity Initiative. They were among the 300 scientists who contributed to a United Nations report on the global state of soil biodiversity. Together with the European Commission the GSBI has also published a beautiful Global Soil Biodiversity Atlas, which you can order or download for free.

This is a Rillig Lab production. Stefanie Maaß and Moisés Sosa Hernández contributed as story consultants to this episode. The theme music is by Sunfish Moon Light, additional music and sound by Blue Dot Sessions and Sasa Spacal, and cover art by Maren von Stockhausen. The quote on nematodes was read by Kevin Caners, host of The Elephant, my favorite climate podcast.

In the next episode, we’re taking a deeper look into how soil scientists are exploring the underground. So stay tuned, and see you soon!

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

FULL CREDITS

Produced by: Anja Krieger and the Rillig Lab
Funded by: Digging Deeper / BiodivERsA
Story consultants: Stefanie Maaß, Moisés Sosa Hernández
Thanks to feedback: Madara Pētersone, Florian Hintz

Cover art: Maren von Stockhausen
Music: Sunfish Moon Light / Future Ecologies, Blue Dot Sessions
Sounds: Sasa Spacal, “Transversal Is A Loop”,  leaves by iamdylanavery

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.