Life in the soil food web

From soil engineers to microscopic partners

When you look at a handful of soil, how many different forms of life do you imagine are hidden inside it? Soil may appear quiet and lifeless from the surface at first glance, but beneath our feet lies a remarkably diverse community of organisms. From earthworms and insects that reshape the physical structure of soils to microscopic bacteria and fungi that drive chemical processes, soil supports an enormous variety of life forms. Together, these organisms interact with each other and with their environment, creating a complex living system known as soil biodiversity.

Soil biodiversity refers not only to the variety of organisms living in soils, but also to the ecological relationships they form across different habitats and landscapes. The FAO defines soil biodiversity as the diversity of life below ground and the ecological complexes these organisms form, including the interactions between organisms and their environments (FAO, 2020).

These organisms differ enormously in size, appearance, lifestyle, and ecological role. Some are visible to the naked eye, while others can only be observed with a microscope. Some create pathways through the soil, others recycle organic matter, some regulate populations of other organisms, and some form close partnerships with plants. Although each group has its own ecological role, they are connected through the soil food web and together contribute to the functioning and resilience of soils.

© Size classification of soil organisms by Tibbett, M., Fraser T.D. and Duddigan, S. (DOI). Photos originated from the Global Biodiversity Atlas. Credit: (Orgiazzi et al. 2016); Credit: B Jakabek, Y Eglit, M Shaw, H Segers, L Galli, A Murray, RR Castro Solar, T Tsunoda, S Franzenburg, D Hope, C Abbe, CC BY 2.5, no changes were made to the original image.

In this lesson, you will explore this hidden community, moving from the largest soil inhabitants to the smallest. Along the way, you will discover how organisms of different sizes and lifestyles interact, and how their combined activities keep soils alive.