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13.5. The soil as an ecosystem

The soil as an ecosystem

The soil is a thin natural layer located in the superficial part of the earth's crust, made up of fragments from the decomposition of the bedrock.

The atmospheric agents (temperature, rain, wind, ice, etc.) and the action of living beings contribute to the formation of the soil, which will then be sustenance of many species animals and vegetables.

Soil components

The soil is made up of:

  • Inorganic matter: Fragments of rocks and minerals from the alteration of the rock, in addition to the water and air that fill the gaps that remain between these minerals.
  • Organic matter: Many living things such as bacteriafungi, vegetableswormsants, etc., and remains of undecomposed organisms and humus (decomposing organic remains).

Soil formation processes

The process of soil formation begins when a mother rock, located on the earth's surface, is exposed to weathering by the action of geological and climatic agents (water, ice) that alter the rock and decompose it. From then on, some microorganisms such as bacteria, lichens and mosses, taking advantage of the loose rock material remains, implant and colonize the rock. Some of these living things can take root and alter rock. When they die, their organic matter decomposes and affects the rock as well. After these first colonizers other animals will appear andmore complex plants that will make the layer of alteration located on the rock increase. From there, the soil horizons will form.

Soil horizons

The soil is divided into different layers called horizons in which the different materials that compose it are arranged:

  • Horizon 0 is the upper layer, made up of plant and animal remains. Its color is dark because it has a lot of humus.
  • Horizon A (from  washing  or  leaching). Its color is clear because the infiltrated water dissolves the mineral salts and carries them further down.
  • Horizon B (of  precipitation).  In this horizon, the precipitation of the mineral salts washed in the horizon A occurs.
  • Horizon C: It has fragments and remains of the bedrock.
  • Bedrock. Undisturbed rock, splitting which, when weathered, the soil was generated.

Horizontes del suelo

Hridith Sudev Nambiar [GFDL or CC BY-SA 3.0], via Wikimedia Commons

Living things that live on the ground are fundamental to all ecosystems. In the soil there is the interaction between the biological, atmospheric and hydrological systems. These organisms are responsible for the nutrient cycle, since they regulate the dynamics of soil organic matter, carbon retention and the emission of greenhouse gases. They also modify the physical structure of the soil and the water regimes, improving the efficiency in the access of vegetation to soil nutrients.

The soil is very fragile and, since it is the basis of all ecosystems, it is important to maintain it by avoiding contamination, erosion, and everything that could lead to its destruction.

Interactive activity: Analysis on desertification.

Answer in your notebook

13.7.- What would happen if the soil of an ecosystem is destroyed? Propose some measure to protect it.

This topic is also covered in other courses

This topic is also covered in other courses:


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.