Syllabus Edition
First teaching 2015
Last exams 2025
Soil Ecosystems
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
Soil Ecosystems
Soil Ecosystem Succession
Soil ecosystems undergo changes over time through a process known as succession
Succession in this context refers to the predictable sequence of changes in the composition and structure of a soil ecosystem
The process of succession is influenced by factors such as climate, vegetation, and interactions between biotic and abiotic components
Primary Succession
Primary succession occurs in areas where soil development starts from bare rock where there is no organic matter
Pioneer species, such as lichens and mosses, colonise the bare substrate and begin the process of soil formation
These pioneer species are well adapted to harsh conditions and can tolerate low nutrient availability
As these pioneer species establish and grow, they begin to break down rocks and organic matter, contributing to the formation of the initial thin, nutrient-poor soil layer
Over time, the accumulated organic matter and the process of weathering lead to the development and deepening of the soil layer
This soil can be colonised by herbaceous plants and shrubs - these plants have slightly higher nutrient requirements compared to pioneer species and contribute to the further enrichment of the soil
As the soil becomes more fertile, it can support the growth of larger plants, such as trees
The establishment of trees marks the later stages of succession, known as climax communities, where the soil ecosystem reaches a stable state
Changes in Soil Characteristics
As succession progresses, there are significant changes in soil characteristics
Initially, the soil may be nutrient-poor and have a low organic matter content
However, as vegetation and organic matter increase, the soil becomes enriched with nutrients, organic compounds, and microbial communities
The soil structure improves, leading to increased water-holding capacity and better nutrient availability for plant uptake
Soil pH may also change as different plants and microbes affect nutrient cycling processes
Additionally, soil erosion becomes less of a risk as the soil becomes more stabilised and protected by vegetation
The general process of succession resulting in the creation of new soils
Fertile Soil and Nutrient Cycles
Fertile soil contains a diverse community of organisms, including bacteria, fungi, insects, and earthworms, that play essential roles in maintaining functioning nutrient cycles
Decomposers, such as bacteria and fungi, break down organic matter, releasing nutrients back into the soil
Nutrient cycling involves the movement of essential elements, such as nitrogen, phosphorus, and carbon, between living organisms, organic matter, and the soil
This cycling ensures the availability of nutrients for plants, supporting their growth and productivity
Resistance to Soil Erosion
A well-developed and fertile soil ecosystem is resistant to soil erosion (the process by which soil is transported away by wind or water)
The presence of vegetation, particularly deep-rooted plants, helps to stabilise the soil, preventing erosion
Soil organisms, such as earthworms, contribute to soil structure by creating channels and burrows that improve water infiltration and soil porosity, reducing the likelihood of erosion
The organic matter content in fertile soil enhances its ability to retain moisture, reducing surface runoff and erosion risks
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