What is Soil?

Soil is everywhere. But what is it, really? Soil starts with rocks, but it is more than just broken rocks. When rocks break down, whether by water or wind, pure sand is created. Sand feels gritty, like sugar; it does not retain water, and almost nothing lives in it. Real soil is a mix of sand, which drains quickly; clay, which sticks together and holds water; and silt, which is a smooth, fine soil that holds some water and nutrients. Soil is also packed with organic matter, which is the broken-down remains of countless dead microbes, small animals like insects, and plants.

There are various types of soils, depending on the rocks they came from and the type of organic matter they trapped over time. Soils are good at holding water (like a sponge) and essential for plant growth, because plants get the nutrients they need from the soil. In turn, plants provide essential food and habitat for some animals. Soils change over time because they are continuously modified by the many organisms that inhabit them, including bacteria, fungi, worms, arthropods, and plants. Soils are alive and fragile. They can be affected by many things such as compaction, changes in the plants that grow in them, pollution, or global warming. Soils are an essential component of ecosystems, so we need to protect them from damage.

Soil Engineers

Among the many organisms that live in soils, earthworms, termites, and ants have a big impact and are thus called soil engineers. Earthworms dig tunnels and enrich the soil with organic matter. Some species of termites and ants build large, long-lived underground nests. The action of wiggling through and mixing the soil is called bioturbation [1]. Through bioturbation, soil animals move nutrient-rich soil particles from deep layers to the surface, where plants can use them. They also increase the amount of air between soil particles, and help water soak into the soil (Figure 1). Soil engineers can be compared to a gardener mixing soil with a shovel. The burrows of soil engineers can also be used by other organisms that help keep soils healthy, including microorganisms. The soils around large termite and ant nests are often richer than elsewhere, so lots of plants can grow there—even though some ants and termites feed on plants!

Benefits of Healthy Soils

Despite their small size, soil engineers are important for nature and for humans. Their presence helps beneficial bacterial activity and increases plant growth, which is valuable for the entire ecosystem because plants sustain many animals. Soil engineers are also important for agriculture, as richer soils can lead to larger and more sustainable harvests. Plants also contribute to carbon storage, which means removing the excess carbon dioxide (CO₂) from the air. Can you see why it is important to protect soils and the biodiversity they contain? But how will soil engineers and soils be affected by ongoing global warming?

Rising Temperatures Change the Game

The negative effects of global warming are easy to see, and they affect all of us. Our planet is surrounded by a blanket of air called the atmosphere. Humans have released large quantities of heat-trapping gases, through industrial and agricultural activities, which have made this blanket warmer. Humans also continue to cut down trees and reduce humid areas such as the peat lands and mangroves that naturally remove CO₂ from the air. The combined result is that the planet is getting warmer, and this causes big changes in nature [2]. The extra heat affects all ecosystems, habitats, and many species, including soil engineers. When the soil gets hotter and drier, the body temperatures of soil organisms can increase to a level that they cannot tolerate. Unlike us, these animals depend on the environment for temperature regulation—they cannot produce heat to warm themselves up or sweat to cool down.

Can Soil Engineers Avoid the Increased Heat?

Ants are usually less sensitive to rising temperatures and dryness than earthworms and termites are, so they may play an important role in keeping the soil healthy in a warmer future [3]—but all bioturbators are important.

Termites and ants may be exposed to high temperatures when they forage for food outside of the nest. To escape the heat, some species change the time of day when they go outside (Figure 2A). However, this may affect their success at collecting food, as they may encounter different prey and predator species. Ants and termites may also be exposed to warming when they are in their nest. Some species build large, complex nests that provide stable temperature and humidity thanks to a complex system of tunnels allowing ventilation, but many species dig shallower nests and are affected by warming. They try to escape the heat by relocating their nest to cooler places, such as in the shadow of a tree. Some species build their nests in association with plants, which help prevent nest overheating during the day and loss of heat at night (Figure 2B). Another way to escape the heat is by digging deeper nests or adjusting the configuration and the connections between the various chambers and tunnels (Figure 2C) [4]. New nesting behavior can alter the effects nests have on soils, such as changing how soil particles and nutrients are mixed up across soil layers and how water penetrates the soil, which can then affect soil quality in ways that influence plants.

Can Warming Affect Soil Quality?

Plants need healthy, porous, and moist soil to thrive (Figure 3A). When the soil becomes too dry, plants have trouble growing (Figure 3B). Rainwater can easily pass through porous soils, which is not the case with dry soils. If soil engineers are harmed by warming, soil quality will likely get worse. As we have described, warming and drying can also affect other important parts of the soil, such as soil organic matter, communities of microorganisms, and the way nutrients move through the soil. These changes can weaken soil structure and even increase the risk of erosion or compaction. When soil quality declines, plants struggle even more, which affects the animals that depend on plants and the predators that rely on plant-eating animals. This shows how one problem, like global warming, can trigger many others, such as soil degradation, creating a cycle of challenges for entire ecosystems.

Conclusion: Tiny Organisms, Big Effects!

Soils are vital for plants, which themselves support animal life. Organisms living in the soil, and soil engineers in particular, are crucial for soil health. These organisms may be small, but they are precious and play a big role in the functioning of our planet. So, protecting them is important! We can help to keep soil organisms healthy by using less energy, because energy production releases gases that increase global warming. Walking, riding a bicycle, and using public transport are good ways to decrease energy use. By combining the work of these incredible bioturbators with our everyday efforts, we may be able to create a powerful, positive impact to protect and preserve our planet.

Glossary

Compaction: ↑ When soil gets squished too much, making it hard for water, air, and roots to move through.

Soil Engineers: ↑ Animals like worms, ants, and termites that build tunnels and mix soil. These activities modify the soil structure, which often help plants and other animals.

Bioturbation: ↑ The action of moving and mixing soil particles.

Carbon Storage: ↑ The process of trapping carbon dioxide from the atmosphere in plants and soil, keeping it out of the atmosphere.

Biodiversity: ↑ The variety of life in a specific area, including animals, plants, fungi, and microorganisms.

Porous: ↑ Soil with tiny holes that let air and water move through easily.

Erosion: ↑ When wind or water washes soil away, leaving less soil for plants to grow.

Degradation: ↑ When soil loses its nutrients or becomes weak, then plants cannot grow well and soil animals have a hard time living on it.

Conflict of Interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We would like to acknowledge the agency that gave us the necessary resources to allow the study to be performed. RS thanks the SOUND (Sorbonne Université) initiative for funding support (Avec le soutien de l’Alliance Sorbonne Université dans le cadre du projet « SOUND – pour un nouvel engagement » financé par l’ANR au titre de France 2030 (ANR-22-EXES-0004).

AI Tool Statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

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