Oligotroph

An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates of metabolism, and generally low population density.

The adjective oligotrophic may be used to refer to environments that offer little to sustain life, organisms that survive in such environments, or the adaptations that support survival. Etymologically, the word "oligotroph" is a combination of the Greek adjective oligos (ὀλίγος)^[1] meaning "few" and the adjective trophikos (τροφικός)^[2]) meaning "feeding".

Oligotrophic environments include deep oceanic sediments, caves, glacial and polar ice, deep subsurface soil, aquifers, ocean waters, and leached soils.

Examples of oligotrophic organisms are the cave-dwelling olm; the bacterium, Pelagibacter ubique, which is the most abundant organism in the oceans with an estimated 2 × 10²⁸ individuals in total; and the lichens with their extremely low metabolic rate.

Plant adaptations

Plant adaptations to oligotrophic soils provide for greater and more efficient nutrient uptake, reduced nutrient consumption, and efficient nutrient storage. Improvements in nutrient uptake are facilitated by root adaptations such as nitrogen-fixing root nodules, mycorrhizae and cluster roots. Consumption is reduced by very slow growth rates, and by efficient use of low-availability nutrients; for example the use of highly available ions to maintain turgor pressure, with low-availability nutrients reserved for the building of tissues. Despite these adaptations, nutrient requirement typically exceed uptake during the growing season, so many oligotrophic plants have the ability to store nutrients, for example in trunk tissues, when demand is low, and remobilise them when demand increases.

Oligotrophic environments

An ecosystem or environment is said to be oligotrophic if it offers little to sustain life. The term is commonly utilised to describe environments of water, ice, air, rock or soil with very low nutrient levels.

Oligotrophic environments are of special interest for the alternative energy sources and survival strategies upon which life could rely.

Antarctic

Lake Vostok, a freshwater lake which has been isolated from the world beneath 4 km (2.5 mi) of Antarctic ice for approximately 15 million years^[3] is frequently held to be a primary example of an oligotrophic environment.

Australia

The sandplains and lateritic soils of southern Western Australia, where an extremely thick craton has precluded any geological activity since the Cambrian and there has been no glaciation to renew soils since the Carboniferous. Thus, soils are extremely nutrient-poor and most vegetation must use strategies such as cluster roots to gain even the smallest quantities of such nutrients as phosphorus and sulfur.

The vegetation in these regions, however, is remarkable for its biodiversity, which in places is as great as that of a tropical rainforest and produces some of the most spectacular wildflowers in the world. It is however, severely threatened by climate change which has moved the winter rain belt south, and also by clearing for agriculture and through use of fertilizers, which is primarily driven by low land costs which make farming economic even with yields a fraction of those in Europe or North America.

South America

An example of oligotrophic soils are those on white-sands, with soil pH lower than 5.0, on the Rio Negro basin on northern Amazonia that house very low-diversity, extremely fragile forests and savannahs drained by blackwater rivers; dark water colour due to high concentration of tannins, humic acids and other organic compounds derived from the very slow decomposition of plant matter.^[4][5][6] Similar forests are found in the oligotrophic waters of the Patía River delta on the Pacific side of the Andes.^[7]

Ocean

In the ocean, the subtropical gyres north and south of the equator are regions in which the nutrients required for phytoplankton growth (for instance, nitrate, phosphate and silicic acid) are strongly depleted all year round. These areas are described as oligotrophic and exhibit low surface chlorophyll. They are occasionally described as "ocean deserts".^[8]

See also

• Oligotrophic lake
• Eutrophic lake
• Pelagibacter ubique, most abundant species on Earth and a streamlined oligotroph

References

1. ὀλίγος. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
2. τροφικός. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
3. "Race against time for raiders of the lost lake". Nature. 469 (7330): 275. 2011. doi:10.1038/469275a. PMID 21248808.
4. Janzen, D. H. (1974). "Tropical Blackwater Rivers, Animals, and Mast Fruiting by the Dipterocarpaceae". Biotropica. 6 (2): 69–103. doi:10.2307/2989823. JSTOR 2989823.
5. Sioli, Harald (1975). "Tropical rivers as expressions of their terrestrial environments". In Golley, F. B.; Medina, E. Tropical Ecological Systems/Trends in Terrestrial and Aquatic Research. New York: Springer. pp. 275–288. ISBN 0-387-06706-X.
6. German, Laura A. (2004). "Ecological praxis and blackwater ecosystems: a case study from the Brazilian Amazon". Human Ecology: An Interdisciplinary Journal. 32 (6): 653–683. doi:10.1007/s10745-004-6831-1.
7. Del Valle-Arango, Jorge Ignacio (2003). "Cantidad, calidad y nutrientes reciclados por la hojarasca fina en bosques pantanosos del Pacífico sur colombiano". Interciencia. 28 (8): 443–452. (Spanish)
8. "Study Shows Ocean "Deserts" are Expanding". NOAA. 2008-03-05. Retrieved 2009-07-17.

External links

• Special issue about Lake oligotrophication published in Freshwater Biology