For too long, mankind has seen soils only as a support, whether for human construction or for agriculture. But the truth is that soils are one of the Earth’s most important living spaces. This abundance of life can be compared to the ocean depths and the canopies of equatorial forests. In fact, soils alone are home to 25% of the world’s biodiversity and they provide crucial ecosystem services. 🍄🦠 🐛

Against a backdrop of climate change and demographic growth, with almost 10 billion people expected by 2050 📈, one of the greatest challenges of our time will be to feed the planet by using our soils sustainably. What are the risks if soil organisms were to disappear, and what measures could we put in place to preserve them?

First, let’s look at what kind of organisms and how many we can find in soils.

Inhabitants

Soil organisms are generally classified into four groups according to their individual size:

• Macrofauna includes animals larger than 2mm. They include earthworms, larval and adult insects, myriapods, spiders, molluscs and crustaceans. 🐞🕷🐌
• Mesofauna are animals between 200 µm and 2mm. Springtails and mites are the two main representatives of this group. 🦗
• Microfauna, invisible to the naked eye, is made up of individuals between 10 µm and 200µm in size, which can live in the capillary porosity of the soil. Protozoa and nematodes make up the bulk of this microfauna. 🔬
• Soil microorganisms, extremely abundant and with great taxonomic and functional diversity, are mainly comprised by bacteria and fungi. 🦠

As for their density and number, we now know that in a few grams of soil (a teaspoon) we can find up to

• 100 million to 1 billion bacteria
• 1 to 3 meters of mycelium (fungi)
• A few million protozoa
• 1000 to 2000 nematodes
• 100 arthropods and insects
• 5 oligochaetes (earthworms)

The number and diversity of these organisms is as impressive as the biomass they represent. On 1 ha we can have around 1 tonne of bacteria 🧱, 1 tonne of protozoa 🧱, 3 tonnes of fungi 🧱🧱🧱and up to 5 tonnes of earthworms 🧱🧱🧱🧱🧱. That’s up to 10 tonnes of living organisms per ha!

But, what ecosystem services do they provide us?

Ecosystem services provided by soil biodiversity

Health

This abundance of biodiversity has many potential benefits for human health 💗🏥. For example, many soil-dwelling organisms have medicinal or antibiotic functions. These include antibiotic-producing soil bacteria, such as Bacillus, and fungi, such as Penicillium; the latter is famous for its application into the world’s first antibiotic, penicillin G 💊. Besides soil organisms, plant-soil interactions through plant roots provide us with widely-used therapeutic compounds such as aspirin, which comes from white willow and meadowsweet. 🌿💊 Today, 50% of small molecules marketed for medical treatment are extracted or derived from plants.

Provision

Soils provide us not only with foodstuffs🍎🥦, but also with firewood, building materials and textile fibers 🧶. Soil biodiversity is largely responsible for provisioning ecosystem services 🍄🦠 🐛 acting on several levels.

• Chemical role: Soil organisms have the capacity to consume🍴, decompose 🔪 and then transform dead organic matter (plants and animals) into plant-available nutrients ♻️. Once decomposed and transformed into assimilable nutrients, organic matter feeds plants, promoting their growth.🌱
• Physical role: Soil organisms also play a physical role in structuring the soil🧱. As they move through the soil to feed or find shelter, living organisms aerate the soil considerably. The cavities 🕳️ formed allow better root invasion, and facilitate the supply of water and oxygen. This creates a favourable environment for all subsoil life 🏞️.
• Biological role: Positive interactions 🔄 between soil organisms and certain plants ensure better provisioning. One example is mycorrhizal fungi, which not only provide better nutrition, but also better tolerance of pathogens and climate change, through a positive relationship called mutualism 🤝. Another example is Rhizobium bacteria🦠, which develops symbiotic interactions with many plants in the Fabaceae family🌿, enabling them to fix atmospheric nitrogen. Fabaceae therefore have access to an additional source of nitrogen, and are less dependent 🤝 than other plants on the availability of inorganic nitrogen in the soil.

Flood control and purification of water

Thanks to its structuring role, soil biodiversity helps to maintain a more porous 🕳️ layer of soil, allowing groundwater to infiltrate💧. This plays an important role in flood control 🌊🏠, especially when the soil is covered with vegetation 🌱. The plant cover limits the impact of water drops on the soil, thus limiting erosion and roughening. At the same time, roots allow for better water infiltration and storage 💾.

Another role of soil biodiversity in relation to water is that of purifying and reducing soil contaminants. Thanks to their natural functions and metabolism, soil microorganisms are capable of breaking down certain toxic compounds and contaminants originating from human activity, enhancing water and air purification🚰.

Carbon storage

In view of the European climate law 🌎📜, which commits the European Union to achieving climate neutrality by 2050, biodiversity and soil offer us an essential ecosystem service for mitigating climate change: carbon storage 🏭💾. Soil is the world’s largest carbon reservoir after the hydrosphere (it is larger than the atmosphere and forests combined). Part of the CO2 emitted into the atmosphere can be absorbed by plants🌿 and stored 🔒in soils over a long period thanks to microbial decomposition. In fact, it is estimated that a 0.4% annual increase in this storage capacity could offset the total of Earth’s CO2 emissions.

Unfortunately, soil biodiversity is under threat. From deforestation 🌳🔪to overexploitation of the soil through over-mechanisation 🚜 and misuse of plant protection products 🧪, but also monoculture 🌾🌾, soil artificialisation 🏢 and climate change🌡️ are all threats to a healthy, living soil 💔. So, what can we do to protect our soils and the biodiversity they contain? 🛡️🐞

There are plenty of ways to preserve our soils and their biodiversity. Besides raising awareness about soil biodiversity 📣, we need to promote technological innovation that will enable us to learn more about our soils and protect them more effectively 🔬. We also need to develop policies based on sustainable soil management 🏛️, and we need to change our land-use practices🚫🔄:

• Halt deforestation
• Limit soil artificialisation,
• Develop our landscapes through nature-based solutions, for example, by creating flood expansion zones with wetlands

Crucially important, we must review our agricultural practices 🌾 :

• Plant meadows
• Practice agro-ecological farming, in particular with conservation agriculture, leave no bare soil, multiply grassed strips/hedges, leave crop residues on the ground, considerably reduce the use of phytosanitary products, etc.

As consumers, we can also play a part by consciously choosing agricultural products that respect our soils and biodiversity 🛍️🤝.

Conclusion

Our soils are teeming with a rich diversity of life. These organisms play crucial roles that allow us to benefit from a wide array of essential ecosystem services. Unfortunately, this vibrant biodiversity is increasingly under threat. It is our responsibility to take decisive action to preserve and protect this invaluable natural wealth.

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