Page 613 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

18.1
SOIL ORGANISMS
Soil organisms range in size from land mammals that burrow into the ground, such as badgers, prairie dogs, and voles; to earthworms that ingest and secrete soil; to microscopic organisms that break down organic matter. The actions of these living organisms help maintain soil fertility.
Moles can cause extensive soil disturbances.
[Hector Ruiz Villar/Shutterstock.] [Background photo: DJTaylor/Shutterstock.]
Plant litter:
The remains of plants, from leaves and stems to tree trunks, accumulate on the surface and as they decay, gradually add organic matter to the soil.
Plant roots:
Plant roots provide channels for water and air movement within the soil; these channels remain intact even after the root decomposes. The area around plant roots is biologically active and contains nutrients from root secretions and sloughed off root cells.
Root nodes
Some bacteria live on root nodes, where they “fix” nitrogen so that it can be taken up by plants.
Mammals:
Mammals cause mechanical disturbances that mix soil, a process known as bioturbation.
Insects and other invertebrates:
A wide range of insects, including ants and beetles, inhabit soil, along with spiders, mites, and many other invertebrates. All contribute to soil-forming processes.
Earthworms:
Earthworms increase soil porosity, breaking up organic matter and then recycling soil aggregates to new locations (upward or downward in the soil column) by ingesting and secreting soil material.
Fungi:
Fungi have threadlike extensions (called mycelia) that extend beneath the soil surface and bind soil particles together.
Nematodes
Microorganisms:
Describe: How do earthworms affect soil?
Soil bacteria, and other microorganisms such as protozoa (single-celled organisms) and nematodes (non-segmented roundworms), help to break down the remains of organisms in the soil or release wastes other organisms can use.
GEOquiz
Visit the Study Area in MasteringGeographyTM to explore biological activity in soil.
Visualize: Study a video of Soil Moisture Active Passive mission. Assess: Demonstrate understanding of biological activity in soil (if assigned by instructor).
1. Compare: How are the effects of mammals and plant roots on soil similar? How are they different?
2. Explain: Explain three ways in which organisms improve soil fertility.
Adiverse collection of organisms inhabit soil environments (GIA 18.1). Organisms play a vital role in soil-forming processes, helping to weather rock both mechanically and chemically, breaking up and mixing soil particles, and enriching soil with organic matter from their remains and wastes.
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geosystems in action 18 BiOlOgiCAl ACTiViTy iN SOilS