Soil is the foundation of terrestrial ecosystems because it supports plant growth, stores water and nutrients, provides habitats, and enables nutrient cycling. As plants form the first trophic level, most terrestrial food webs ultimately depend on soil.
This is Topic 5.1 Soil and is core content for SL and HL.
How Soil Supports Terrestrial Ecosystems
Soil is a dynamic system with inputs, outputs, storages and flows. Inputs include dead organic matter and weathered minerals; outputs include eroded material, leached minerals and gases released during decomposition.
| Soil function | Importance to terrestrial ecosystems |
|---|---|
| Medium for plant growth | Anchors roots and supplies water and mineral nutrients. Plants obtain carbon mainly as carbon dioxide from the atmosphere. |
| Water storage | Retains water for plants, while infiltration and percolation influence runoff and groundwater recharge. |
| Nutrient cycling | Decomposers transform dead organic matter, releasing mineral nutrients that producers absorb. |
| Habitat provision | Supports bacteria, fungi, earthworms and other organisms, increasing biodiversity and decomposition. |
| Carbon regulation | May act as a carbon sink, store or source, depending on organic inputs and decomposition. |
These functions connect soil to the wider ecosystem. Greater plant productivity provides biomass for herbivores and higher trophic levels, while decomposers return nutrients to the soil. Soil degradation can therefore reduce productivity, biodiversity and ecosystem resilience.
China's Loess Plateau is a named example. Severe erosion reduced soil fertility and agricultural productivity, but terracing, revegetation and grazing controls helped restore soils, vegetation and local livelihoods. This demonstrates the environmental, social and economic dimensions of soil conservation.
A common misconception is that soil is inert “dirt.” Soil is a living, interacting system shaped by biological, chemical and physical processes.
Exam Technique
For an explain question, link each soil function to an ecological consequence rather than merely listing functions. Use precise systems terminology and connect soil degradation or conservation to productivity, biodiversity, sustainability and human well-being.