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Soil as an Ecological System

Soil as an Ecological System

By Ana Salazar Martínez

From an ecological point of view, the soil is the subsystem of terrestrial ecosystems where the decomposition process is mainly carried out, fundamental for the reobtaining and recycling of nutrients that ensure the other great vital process: production, which is clearly manifested for us in the epigeal subsystem.

The soil constitutes the surface layer of the earth's crust. It consists of rocks of different sizes, substances of organic origin, air, water and organisms. These elements are organized: the particles establish precise topographic relationships according to their size and this gives rise to the formation of spaces that communicate with each other as pores or channels and that can be filled with air or water. These spaces in turn house organisms, usually small, or parts of organisms, such as the roots of plants.


Soil formation is a complex process driven by forces such as climate (especially water availability and temperature), the original rock material, topography, and the organisms that use it as habitat. The result of the interaction of these elements with time, gives rise to characteristic units, arranged in strata called horizons, of different physical-chemical characteristics, which therefore allow to host different organisms according to their ecological requirements.

In soils, water drains by gravity, more or less easily according to the pore space they present, so that they represent an important step phase in the water cycle. According to its organo-mineral characteristics, it retains or releases compounds acting as a natural filter. It also retains water by capillarity allowing the existence of small aquatic organisms.

From an ecological point of view, the soil is the subsystem of terrestrial ecosystems where the decomposition process is mainly carried out, fundamental for the reobtaining and recycling of nutrients that ensure the other great vital process: production, which is clearly manifested for us in the epigeal subsystem.

On the other hand, from a broader ecological point of view, the soil serves as a refuge for a large number of consuming species that hide in anonymity in their pores and cavities. The biological diversity of the soil is very high and includes from bacteria to small vertebrates.

Most of the small ones (less than 2 mm) carry out their complete life cycle in this environment. These are the most unknown due to the difficulties of study: algae, bacteria, protozoa, fungi and small invertebrates, especially arthropods. Others pass on the ground only the stages of metamorphosis in which they are weakest, thus avoiding their predators, but their adult life passes in the epigeal or aerial subsystem: this is the case of numerous insects such as coleopterans or diptera.

Larger edaphic inhabitants (greater than 2 cm), such as large arachnids, small mammals and reptiles, use the soil mainly to build their burrows and protect their young.

A representative of the actinédid mite family, predators of small arthropods and their eggs in sclerophyllous forest mulch.
From an energy point of view, all these organisms are linked in complex trophic networks whose initial deposit of greater energy is the organic matter that comes from the aerial subsystem and that forms the "mulch" and that of the roots and their exudates, incorporated directly; leaves, trunks, fruits, branches, roots, corpses etc, are the main substrates for decomposition. This deposit is used by decomposers in general: bacteria and fungi that mineralize and produce the necessary change from organic to inorganic matter: from "useless residue" to "plant nutrient"; The rest of the organisms are divided between a great diversity of saprophages that fragment, mix and change the physical nature of organic matter, favoring its mineralization and a large set of predators that regulate the population sizes of their prey, influencing the speed of transfer of energy through this large network. As a special characteristic of this trophic web, matter resynthesized from organic remains, sooner or later to thicken the initial deposit due to death.

The growing human action on the planet also affects the soil, so that, at present, the management of this subsystem has become the key to its quality.

Today it is recognized that the soil fulfills five vital functions for the planet (Soil Quality Manual, USDA):

  • Sustain biological activity, diversity and productivity,
  • Regulate and partition water and solute flow,
  • Filter, drain, immobilize and detoxify organic and inorganic materials, including municipal and industrial waste,
  • Store and enable the cycling of nutrients and other biogeochemical elements and
  • Provide support to socio-economic structures and protection of archaeological treasures

The soil always works under the same natural laws; continues to maintain its internal organization plan, now reflecting in this plan, human intervention. Changes in the physical-chemical environment as a result of human activity (change of components due to garbage dumping, compaction by vehicular traffic, increased erosion due to deforestation, etc.) directly affect the habitat of edaphic organisms.


These modifications constitute interventions in the natural system and according to their quality (what is done), scale of space-time effect (in what magnitude, covering how much space and for how long) and the ability to return to the balance of the natural system, It will be the new organization that is established.

One of the components that quickly reflects these new conditions of change in search of the new balance are the edaphic organisms. Among them mainly the small arthropods, continuous inhabitants of the soil that have become good bio indicators of the quality of the soil and consequently the level of anthropic intervention.

This allows us to have interesting applications in the field of methodologies for evaluating natural resources and the impacts to which they are subjected.

Tyrophagus sp., A common mite in house dust and stored products. Its abundance in soil is an indication of anthropic intervention.

That is, by understanding the properties and relationships existing between the different components of natural edaphic systems, it is possible to conceive different tools that allow, for example, to evaluate the quality of soils with the perspective of qualifying the feasibility of a certain activity that is intended to be installed in it . It will also be possible to qualitatively and quantitatively characterize the impact produced by previous anthropic interventions.

These assessment tools are undoubtedly powerful, as they work with an aspect that is extremely sensitive to change, such as the myriad small organisms that quietly inhabit the ground under our feet.

* Doctor in Natural Sciences Ana Salazar Martínez
[email protected],
ProGeo - Independent Consulting Group. http://progeo.hypermart.net


Video: Video Lecture on Soil BiologyEcology (June 2021).