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Who lives underground?


The soil is alive! The earth beneath our feet is filled with an amazing frontier of bizarre minuscule creatures of varied biology. While some people may find it hard to believe, our lives actually depend on these minuscule creatures living in the soil.

Some of the most important soil organisms include fungi, bacteria, protozoa, nematodes and arthropods. Individual species do not directly contribute to general soil health, it is rather the interactions between the many species that are important.

Who lives underground?


Bacteria   Importance to soil

Bacteria on root hair


Nitrogen fixation
Bacteria are the only organisms on earth that can fix atmospheric nitrogen into ammonia, the form of nitrogen that plants can absorb. These bacteria are often integrated into the plant tissues (e.g. roots) of legumes (e.g. clover, beans), and form symbiotic relationships in which both parties mutually benefit, i.e. plants get nitrogen produced by the bacteria and the bacteria gets a place to live and food (carbon) produced by the plant through photosynthesis.

  • Bacteria are tiny (can only be seen under light (x1000) or electronic microscopes) single- celled life forms.·
2. Cyanobacteria (photosynthetic bacteria) secrete a polysaccharide that binds and holds soil particles together.
  • Their numbers can exceed 1 thousand billion per gram of soil with over 20 000 different species.
3. The carbon cycle
Bacteria and fungi help produce carbon dioxide (CO2) from dead organisms so that plants can use it for photosynthesis.
  • The organelles that make energy for your body (i.e. mitochondria) and the site of photosynthesis on green plants (i.e. chloroplast) were originally free-living bacterial cells.
4. Nutrient cycle
Bacteria decompose dead organisms, freeing nutrient components that are trapped to make them available for other organisms.
  • There are more bacterial cells on a human body than body cells.
5. Bioremediation
Bacteria help clean up our wrong doings, such as oil spills, pesticides, and other toxic materials, by returning them to their natural state in the environment while adding much needed fertility to the polluted environment.


A special group of bacteria that forms branched thread like filaments and gives soil its distinctive scent.

The above graphics are by permission of Saskatchewan Interactive.

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Fungi   Importance to soil

Plant root covered with fungal hyphae

1. They decompose dead leaves and wood that cannot be broken down by bacteria.
  • The fungal lineage includes common mushrooms, rusts, smuts, puffballs, truffles, morels, moulds, and yeasts.
2. Fungi, both free-living and as a part of lichens (symbiotically associated fungi with algae or cyanobacteria, fungus and algae), contribute to soil stability by binding soil particles with hyphae (fungal cells).
  • They provide numerous drugs (e.g. penicillin), foods like mushrooms (i.e. fruiting bodies, which are reproductive structures that produce spores), anti-rejection drugs (e.g. cyclosporine) used for organ transplants, and air bubbles in bread, champagne, and beer.
3. Mycorrhizal fungi improve the host plant’s efficiency at obtaining nutrients and water while increasing the surface area associated with the plant root fungus, allowing the plant root more reach to explore the ground for nutrients and water.
  • Some fungi (i.e. mycorrhizal fungi) develop a symbiotic relationship with most plant roots except brassicas. Some plants can’t survive to maturity without the fungi and are referred to as mycorrhizal-obligates.

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Arthropods   Importance to soil

The male, large garden cobweb spider (Eriophora pustulosa)

1. Help aerate soil by mixing the soil.
  • Includes members of the phylum Arthropoda (presence of an exoskeleton and jointed legs), such as beetles, spiders, mites, millipedes and other invertebrates (no backbone).
2. Improve soil structure through their activities (consumption, digestion and excretion).
  3. Shred larger plant debris and mix it with soil microbes, assisting decomposition.
to top of page 4. Help spread beneficial microbes, control disease-causing organisms and regulate organism numbers by preying on them.
Protozoa   Importance to soil

1. Keeps bacterial communities growing by consuming vast numbers·
  • A group of microscopic animal-like, single-celled creatures that are present in large numbers near plant roots due to the abundance of food (i.e. bacteria and organic matter).
2. Provides nutrients to plant roots and stimulates the rate of decomposition through increasing bacterial activity, by excreting digested wastes.
  • Some protozoas tend to live inside the guts of other creatures, e.g. the protozoa Trichonympha lives inside the termite gut and helps break down wood (cellulose) from its food but the actual digestion of wood is done by the bacteria living inside the gut.

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