Soil Fauna and Bioturbation

Soil fauna are the animals of the soil, from microscopic nematodes to earthworms and termites, whose feeding and burrowing fragment residues, mix the soil, and shape its structure and porosity.

Definition

Soil fauna are the invertebrate and other animal inhabitants of the soil; bioturbation is the mixing, burrowing, and reworking of soil and its materials by these organisms.

Scope

This topic covers the diversity and functional groups of soil animals, their roles in fragmenting and processing organic matter, and bioturbation, the biological mixing and reworking of soil. It complements soil microbiology by addressing the larger organisms that physically engineer the soil.

Core questions

• What are the main groups and functional roles of soil animals?
• How do soil fauna fragment and process organic residues?
• How does bioturbation mix soil and create pores?
• Why are organisms like earthworms called ecosystem engineers?

Key concepts

• Soil micro-, meso-, and macrofauna
• Earthworms, termites, and ants
• Litter fragmentation and comminution
• Bioturbation and soil mixing
• Casts, burrows, and biopores
• Soil food web interactions

Key theories

Soil fauna as ecosystem engineers

Larger soil animals such as earthworms, termites, and ants physically restructure the soil by burrowing, casting, and mound-building, creating pores and aggregates and redistributing organic matter in ways that strongly influence soil function.

Faunal control of decomposition

Soil animals fragment plant litter, mix it with mineral soil and microbes, and graze on microbial populations, accelerating decomposition and nutrient release beyond what microbes achieve alone.

Mechanisms

Microfauna and mesofauna such as nematodes, mites, and springtails graze on microbes and shred litter, while macrofauna such as earthworms ingest soil and residues, mixing them and producing nutrient-rich casts and stable aggregates. Burrowing creates large continuous pores that enhance infiltration and aeration, and the constant reworking redistributes organic matter through the profile, accelerating decomposition and building structure.

Clinical relevance

Soil fauna improve soil structure, infiltration, aeration, and nutrient cycling, and serve as indicators of soil health; practices that conserve them, such as reduced tillage and residue retention, enhance these benefits, while their loss signals and worsens soil degradation.

History

Charles Darwin's 1881 study of earthworms was among the first to quantify how soil animals form and rework soil, estimating the vast amounts of earth that worms pass through their bodies. Modern soil ecology has extended this to a detailed understanding of faunal functional groups and their roles as ecosystem engineers and drivers of decomposition.

Key figures

• Charles Darwin
• Eldor A. Paul
• Nyle C. Brady

Seminal works

• darwin1881
• brady2016
• paul2015

Frequently asked questions

Why are earthworms good for soil?

Earthworms ingest and mix soil and organic residues, producing nutrient-rich casts and stable aggregates, and their burrows create channels that improve infiltration, drainage, aeration, and root growth, which is why they are often used as indicators of healthy soil.

What is bioturbation?

Bioturbation is the biological mixing and reworking of soil by organisms such as earthworms, termites, ants, and burrowing animals; over time it blends horizons, moves organic matter and minerals, and helps build and maintain soil structure.