2.3 — Soil biodiversity
Life in the soil food web
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Microorganisms: The biochemical engine (µm scale)
Microorganisms include bacteria, archaea and fungi. Together, they form the foundation of the soil food web by decomposing organic matter and driving the cycling of carbon, nitrogen, phosphorus and sulphur. Without their activity, dead plant and animal material would only accumulate, nutrients would remain locked away, and many other soil organisms would lose their primary food source.
Different groups of microorganisms perform distinct functions. Saprotrophic fungi break down complex organic materials such as wood and leaf litter, including compounds like lignin that few other organisms can decompose. Bacteria and archaea transform nutrients into forms that plants and other organisms can use, and play key roles in processes such as nitrogen fixation and nitrification.
For a visual overview of the many ways microorganisms contribute to soil functioning in arable soils, see the first figure in this article by Hartmann (2022).
Many fungi also form close partnerships with plants. Mycorrhizal fungi grow around or within plant roots, extending their reach into the surrounding soil. In exchange for sugars produced by photosynthesis, these fungi help plants absorb water and nutrients, particularly phosphorus. This mutually beneficial relationship is among the most widespread and important symbioses in terrestrial ecosystems.
One of the most active zones in the soil is the rhizosphere - the thin layer of soil surrounding plant roots. Here, roots release sugars and other compounds that feed microorganisms, while microbes influence nutrient availability, plant growth, and overall soil health. Countless interactions between roots, fungi, bacteria, and soil animals take place in this busy underground neighbourhood every day.
Do you want to discover more about fungi and their hidden world? We recommend watching one or both of the following videos: the video “David Attenborough Encounters a Symbiotic Fungi! | Nature Bites” was produced by Nature Bites and lasts approximately 4 minutes. The second video is a documentary titled “The life of the forest. Fungi”, produced by Forest Film Studio, with a duration of approximately 37 minutes.