Soil contributes to biodiversity by providing habitats and niches for organisms, supporting plant growth, and recycling nutrients within ecosystems. This is core content for IB ESS SL and HL, Subtopic 5.1 Soil.
How Soil Supports Biodiversity
Soil is a dynamic system containing inorganic particles, dead organic matter, water, air and living organisms. Its organisms include bacteria, fungi, earthworms, insects and other decomposers, each occupying a particular niche.
Soil also supports above-ground biodiversity. It stores water and almost all essential mineral nutrients needed by plants; plants obtain carbon from the atmosphere, not the soil. A more varied plant community can provide food and habitats for a wider range of consumers and decomposers.
| Soil contribution | Effect on biodiversity |
|---|---|
| Provides habitats and niches | Different soil depths, pore spaces, moisture levels and pH conditions support different organisms. |
| Recycles nutrients | Decomposers break down dead organic matter, returning mineral nutrients that plants can absorb. |
| Supports plant growth | Water, nutrients and physical anchorage allow producers to establish, supporting food webs. |
| Creates varied conditions | Differences in soil texture, drainage and organic matter produce habitat diversity. |
| Builds ecosystem resilience | Diverse soil communities maintain decomposition and nutrient cycling when disturbance affects some species. |
A common misconception is that biodiversity means only the number of species. In ESS, biodiversity includes diversity at genetic, species and habitat levels; species diversity also involves both richness and evenness.
The Loess Plateau rehabilitation project in China illustrates the connection. Measures such as revegetation and erosion control reduced soil loss and helped restore vegetation and ecosystem functioning. However, soil management also has a societal dimension: land degradation can disproportionately reduce the food security and livelihoods of farming communities, creating an environmental justice issue.
Exam Technique
For an “explain” question, give linked cause-and-effect statements: soil provides water and mineral nutrients, which support diverse plant communities, which then create food and habitats for other trophic levels. Avoid merely listing soil components without explaining their effect on biodiversity.