Soil Life

Soil Life are the thousands of species of macro- and microorganisms that live in the soil.

Prokaryotes
Many organisms living in the soil are prokaryotes, living organisms, including the domains Bacteria and Archaea, which lack "a unit membrane-bound nucleus" and usually lack other cell organelles as well. Unlike eukaryotes, the other major category of living organisms, some prokaryotes are able to fix atmospheric nitrogen.


 * "Despite the apparent, relative simplicity of prokaryotic cells, as a group they have the greater taxanomic and functional diversity. Globally, organic C in prokaryotes is equivalent to that in plants and they contain 10-fold more N. They also possess the most efficient dispersal and survival mechanisms. As a result, prokaryotes are of enormous importance in creating, maintaining, and functioning of the soil."

As prokaryotes are tiny - "several micrometers in length or diameter" - they exhibit a high surface area:volume ratio, "which explains, in part, the ability of prokaryotes to sequester nutrients at extremely low concentrations."

Antibiotic Production
Some prokaryotes can produce antibiotics. For example, certain species of Streptomyces produce the antibiotic Streptomycin, which "strongly inhibits a wide range of both gram-positive and gram-negative bacteria."


 * "Antibiotic production by soil bacteria, involving secondary metabolism, has been harnessed for decades for a wide range of medical applications. Although antibiotic production has long been linked with chemical defense, the factors determining antibiotic production in soil suggest that antibiosis occurs only when the supply of available carbon is high (Thomashow and Weller, 1991). These conditions are likely to be met in the rhizosphere, the zone around seeds (the spermosphere), and relatively fresh plant or animal residues."

There is some evidence that plants rely on the antibiotics produced by prokaryotes in their rhizosphere to protect them from pathogens.

Related Sourcewatch

 * Prokaryotes
 * Synthetic Fertilizer
 * Mycorrhizal Fungi
 * Plant Root Exudates

External Resources

 * Janice S. Snow, Misunderstanding Soil Ecosystems: How flawed conceptions of soil have lead to flawed U. S. land, water and climate policies, Masters Thesis, Tufts University, November 2009.
 * J. Prosser and Ken Killham. "Prokaryotes." In Soil Microbiology, Ecology, and Biochemistry, edited by Eldor A. Paul. Burlington, MA: Academic Press (Elsevier), 2007.
 * R. Larry Peterson, Hugues B. Massicotte and Lewis H. Melville, Mycorrhizas: Anatomy and Cell Biology (Ottawa: NRC Research Press, National Research Council of Canada, 2004).
 * Melissa J. Brimecombe, Frans A De Leij and James M. Lynch "Effect of Roots Exudates on Rhizosphere Microbial Populations," in The Rhizosphere: Biochemistry and Organic Substances at the Soil-Plant Interface., ed. Pinton, Roberto, Zeno Varanini, and Paolo Nannipieri (New York: Marcel Dekker, Inc, 2001).
 * Franci Martin, Silvi Perotto and Paola Bonfante, "Mycorrhizal Fungi: A Fungal Community at the Interface between Soil and Roots," in The Rhizosphere: Biochemistry and Organic Substances at the Soil-Plant Interface, ed. Pinton, Roberto, Zeno Varanini, and Paolo Nannipieri (New York: 2001).
 * Lynn Margulis and Karlene V. Schwartz, Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth, Third ed. (New York: W.H. Freeman and Company, 1997).