Oligotroph
Encyclopedia
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 "oligoptroph" is a combination of the Greek adjective oligos (ὀλίγος) meaning "few" and the adjective trophikos (τροφικός)) 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 bacterium, Pelagibacter ubique
, which is the most abundant organism in the oceans with an estimated 1027 individuals in total, and the lichens with their extremely low metabolic rate.
s, mycorrhiza
e 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.
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.
, a freshwater lake which has been isolated from the world beneath 4 km of Antarctic
ice for approximately 15 million years is frequently held to be a primary example of an oligotrophic environment.
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 fertilizer
s, which is primarily driven by low land costs which make farming economic even with yields a fraction of those in Europe or North America.
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 river
s; dark water colour due to high concentration of tannin
s, humic acid
s and other organic compounds derived from the very slow decomposition of plant matter. Similar forests are found in the oligotrophic waters of the Patía River
delta on the Pacific side of the Andes.
, the subtropical gyres north and south of the equator
are regions in which the nutrient
s 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".
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs
Copiotrophs
A Copiotroph is an organism that tends to be found in environments which are rich in nutrients, particularly carbon, and are the opposite to oligotrophs, which survive in much lower carbon concentrations....
, 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
Etymology
Etymology is the study of the history of words, their origins, and how their form and meaning have changed over time.For languages with a long written history, etymologists make use of texts in these languages and texts about the languages to gather knowledge about how words were used during...
, the word "oligoptroph" is a combination of the Greek adjective oligos (ὀλίγος) meaning "few" and the adjective trophikos (τροφικός)) 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 bacterium, Pelagibacter ubique
Pelagibacter ubique
Pelagibacter, with the single species P. ubique, was isolated in 2002 and given a specific name, although it has not yet been validly published according to the bacteriological code. It is an abundant member of the SAR11 clade in the phylum Alphaproteobacteria...
, which is the most abundant organism in the oceans with an estimated 1027 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 noduleRoot nodule
Root nodules occur on the roots of plants that associate with symbiotic nitrogen-fixing bacteria. Under nitrogen-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known as rhizobia...
s, mycorrhiza
Mycorrhiza
A mycorrhiza is a symbiotic association between a fungus and the roots of a vascular plant....
e 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
Turgor pressure
Turgor Pressure or turgidity is the main pressure of the cell contents against the cell wall in plant cells and bacteria cells, determined by the water content of the vacuole, resulting from osmotic pressure, i.e...
, 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 ecosystemEcosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
or environment is said to be oligotrophic if it offers little to sustain life
Life
Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not, either because such functions have ceased , or else because they lack such functions and are classified as inanimate...
. The term is commonly utilised to describe environments of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
, air, rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
or soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
with very low nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
levels.
Oligotrophic environments are of special interest for the alternative energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
sources and survival strategies upon which life could rely.
Antarctic
Lake VostokLake Vostok
Lake Vostok is the largest of more than 140 subglacial lakes found under the surface of Antarctica. The overlying ice provides a continuous paleoclimatic record of 400,000 years, although the lake water itself may have been isolated for 15 to 25 million years. The lake is named after the...
, a freshwater lake which has been isolated from the world beneath 4 km of Antarctic
Antarctic
The Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...
ice for approximately 15 million years is frequently held to be a primary example of an oligotrophic environment.
Australia
The sandplains and lateritic soilsLaterite
Laterites are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock...
of southern Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
, where an extremely thick craton
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...
has precluded any geological activity since the Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
and there has been no glaciation to renew soils since the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
. 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
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
and sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
.
The vegetation in these regions, however, is remarkable for its biodiversity
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
, which in places is as great as that of a tropical rainforest
Tropical rainforest
A tropical rainforest is an ecosystem type that occurs roughly within the latitudes 28 degrees north or south of the equator . This ecosystem experiences high average temperatures and a significant amount of rainfall...
and produces some of the most spectacular wildflowers in the world. It is however, severely threatened by climate change
Climate change in Australia
Climate change has become a major issue in Australia due to drastic climate events since the turn of the 21st century that have focused government and public attention. Rainfall in Australia has increased slightly over the past century, although there is little or no trend in rainfall in northeast...
which has moved the winter rain belt south, and also by clearing for agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
and through use of fertilizer
Fertilizer
Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...
s, 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 pHSoil pH
The soil pH is a measure of the acidity or basicity in soils. pH is defined as the negative logarithm of the activity of hydrogen ions in solution. It ranges from 0 to 14, with 7 being neutral. A pH below 7 is acidic and above 7 is basic. Soil pH is considered a master variable in soils as it...
lower than 5.0, on the Rio Negro basin on northern Amazonia
Amazon Basin
The Amazon Basin is the part of South America drained by the Amazon River and its tributaries that drains an area of about , or roughly 40 percent of South America. The basin is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela...
that house very low-diversity, extremely fragile forests and savannahs drained by blackwater river
Blackwater river
A blackwater river is a river with a deep, slow-moving channel that flows through forested swamps and wetlands. As vegetation decays in the water, tannins are leached out, resulting in transparent, acidic water that is darkly stained, resembling tea or coffee. Most major blackwater rivers are in...
s; dark water colour due to high concentration of tannin
Tannin
A tannin is an astringent, bitter plant polyphenolic compound that binds to and precipitates proteins and various other organic compounds including amino acids and alkaloids.The term tannin refers to the use of...
s, humic acid
Humic acid
Humic acid is a principal component of humic substances, which are the major organic constituents of soil , peat, coal, many upland streams, dystrophic lakes, and ocean water. It is produced by biodegradation of dead organic matter...
s and other organic compounds derived from the very slow decomposition of plant matter. Similar forests are found in the oligotrophic waters of the Patía River
Patía River
The Patía River is a river in southwestern Colombia. It flows over 400 kilometers to drain into the Pacific Ocean north of Tumaco. The Patía River is the longest river on the Colombian Pacific Coast. The last 90 kilometers is navigable by boat.-Geography:...
delta on the Pacific side of the Andes.
World Ocean
In the World OceanWorld Ocean
The World Ocean, world ocean, or global ocean, is the interconnected system of the Earth's oceanic waters, and comprises the bulk of the hydrosphere, covering almost 71% of the Earth's surface, with a total volume of 1.332 billion cubic kilometres.The unity and continuity of the World Ocean, with...
, the subtropical gyres north and south of the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
are regions in which the nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
s required for phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
growth (for instance, nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
, phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
and silicic acid
Silicic acid
Silicic acid is a general name for a family of chemical compounds of the element silicon, hydrogen, and oxygen, with the general formula [SiOx4-2x]n...
) are strongly depleted all year round. These areas are described as oligotrophic and exhibit low surface chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
. They are occasionally described as "ocean deserts".
See also
- Oligotrophic lake
- Eutrophic lake
- Pelagibacter ubiquePelagibacter ubiquePelagibacter, with the single species P. ubique, was isolated in 2002 and given a specific name, although it has not yet been validly published according to the bacteriological code. It is an abundant member of the SAR11 clade in the phylum Alphaproteobacteria...
, most abundant species on Earth and a streamlined oligotroph
External links
- Special issue about Lake oligotrophication published in Freshwater Biology