An oligotroph is an
organism that can live in an environment that offers very low levels of
nutrients
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excr ...
. They may be contrasted with
copiotrophs A copiotroph is an organism found in environments rich in nutrients, particularly carbon. They are the opposite to oligotrophs, which survive in much lower carbon concentrations.
Copiotrophic organisms tend to grow in high organic substrate condi ...
, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates of metabolism, and generally low population density. Oligotrophic environments are those that offer little to sustain life. These 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 olm or proteus (''Proteus anguinus'') is an aquatic salamander in the family Proteidae, the only exclusively cave-dwelling chordate species found in Europe. In contrast to most amphibians, it is entirely aquatic, eating, sleeping, and br ...
; the bacterium "
''Candidatus'' Pelagibacter communis", which is the most abundant organism in the oceans with an estimated 2 × 10
28 individuals in total; and the
lichens with their extremely low
metabolic rate.
Etymologically, the word "oligotroph" is a combination of the
Greek adjective ''oligos'' (ὀλίγος) meaning "few" and the adjective ''trophikos'' (τροφικός)) meaning "feeding".
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
Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
root nodule
Root nodules are found on the roots of plants, primarily legumes, that form a symbiosis with nitrogen-fixing bacteria. Under nitrogen-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known a ...
s,
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
Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall.
It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilibriu ...
, 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
Oligotrophs occupy environments where the available nutrients offer little to sustain life. The term “oligotrophic” is commonly used to describe terrestrial and aquatic environments with very low concentrations of nitrates, iron, phosphates, and carbon sources.
Oligotrophs have acquired survival mechanisms that involve the expression of genes during periods of low nutrient conditions, which has allowed them to find success in various environments. Despite the capability to live in low nutrient concentrations, oligotrophs may find difficulty surviving in nutrient-rich environments.
Antarctica
Antarctic environments offer very little to sustain life as most organisms are not well adapted to live under nutrient-limiting conditions and cold temperatures (lower than 5 °C). As such, these environments display a large abundance of
psychrophile
Psychrophiles or cryophiles (adj. ''psychrophilic'' or ''cryophilic'') are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from to . They have an optimal growth temperature at . They are found in ...
s that are well adapted to living in an Antarctic biome. Most oligotrophs live in lakes where water helps support biochemical processes for growth and survival. Below are some documented examples of oligotrophic environments in Antarctica:
Lake Vostok
Lake Vostok (russian: озеро Восток, ''ozero Vostok'') is the largest of Antarctica's almost 400 known subglacial lakes.
Lake Vostok is located at the southern Pole of Cold, beneath Russia's Vostok Station under the surface of the cen ...
, a freshwater lake which has been isolated from the world beneath 4 km (2.5 mi) of Antarctic ice is frequently held to be a primary example of an oligotrophic environment. Analysis of ice samples showed ecologically separated microenvironments. Isolation of microorganisms from each microenvironment led to the discovery of a wide range of different microorganisms present within the ice sheet.
Traces of fungi have also been observed which suggests potential for unique symbiotic interactions.
The lake’s extensive oligotrophy has led some to believe parts of lake are completely sterile.
This lake is a helpful tool for simulating studies regarding extraterrestrial life on frozen planets and other celestial bodies.
Crooked Lake is an ultra-oligotrophic glacial lake
with a thin distribution of
heterotrophic and
autotrophic
An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Work ...
microorganisms.
The
microbial loop plays a big role in cycling nutrients and energy within this lake, despite particularly low bacterial abundance and productivity in these environments.
The little ecological diversity can be attributed to the lake's low annual temperatures. Species discovered in this lake include ''
Ochromonas,
Chlamydomonas
''Chlamydomonas'' is a genus of green algae consisting of about 150 speciesSmith, G.M. 1955 ''Cryptogamic Botany Volume 1. Algae and Fungi'' McGraw-Hill Book Company Inc of unicellular flagellates, found in stagnant water and on damp soil, i ...
,
Scourfeldia,
Cryptomonas
''Cryptomonas'' is the name-giving genus of the Cryptomonads established by German biologist Christian Gottfried Ehrenberg in 1831. The algae are common in freshwater habitats and brackish water worldwide and often form blooms in greater depths ...
,
Akistrodesmus falcatus,'' and ''
Daphniopsis studeri'' (a microcrustacean). It is proposed that low competitive selection against ''Daphniopsis studeri'' has allowed the species to survive long enough to reproduce in nutrient limiting environments.
Australia
The sandplains and
lateritic soils of southern
Western Australia, where an extremely thick
craton
A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...
has precluded any geological activity since the
Cambrian
The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ( ...
and there has been no
glaciation
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
to renew soils since the
Carboniferous
The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carboniferous ...
. Thus, soils are extremely nutrient-poor and most vegetation must use strategies such as
cluster root
Cluster roots, also known as proteoid roots, are plant roots that form clusters of closely spaced short lateral rootlets. They may form a two- to five-centimetre-thick mat just beneath the leaf litter. They enhance nutrient uptake, possibly by chem ...
s to gain even the smallest quantities of such nutrients as
phosphorus and
sulfur.
The vegetation in these regions, however, is remarkable for its
biodiversity
Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') le ...
, which in places is as great as that of a
tropical rainforest
Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as ''lowland equatori ...
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
Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to ...
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
Soil pH is a measure of the acidity or basicity (alkalinity) of a soil. Soil pH is a key characteristic that can be used to make informative analysis both qualitative and quantitatively regarding soil characteristics. pH is defined as the ne ...
lower than 5.0, on the
Rio Negro basin on northern
Amazonia
The Amazon rainforest, Amazon jungle or ; es, Selva amazónica, , or usually ; french: Forêt amazonienne; nl, Amazoneregenwoud. In English, the names are sometimes capitalized further, as Amazon Rainforest, Amazon Forest, or Amazon Jungle. ...
that house very low-diversity, extremely fragile forests and savannahs drained by
blackwater river
A blackwater river is a type of river with a slow-moving channel flowing through forested swamps or wetlands. As vegetation decays, tannins leach into the water, making a transparent, acidic water that is darkly stained, resembling black tea. ...
s; dark water colour due to high concentration of
tannin
Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.
The term ''tannin'' (from Anglo-Norman ''tanner'', ...
s,
humic acids 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
The Patía River () is a river in southwestern Colombia. It flows over to drain into the Pacific Ocean north of Tumaco. The Patía River is the longest river on the Colombian Pacific Coast. The last is navigable by boat.
Geography
The Patía ...
delta on the Pacific side of the Andes.
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
Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolubl ...
,
phosphate and
silicic acid
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
) are strongly depleted all year round. These areas are described as oligotrophic and exhibit low surface
chlorophyll
Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to ...
. They are occasionally described as "ocean deserts".
Oligotrophic soil environments
The oligotrophic soil environments include agricultural soil, frozen soil, ''et cetera''.
Various factors, such as
decomposition, soil structure,
fertilization
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
and
temperature, can affect the nutrient-availability in the soil environments.
Generally, the nutrient becomes less available along the depth of the soil environment, because on the surface, the organic compounds decomposed from the plant and animal
debris
Debris (, ) is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, as in geology, large rock fragments left by a melting glacier, etc. Depending on context, ''debris'' can refer to ...
are consumed quickly by other microbes, resulting in the lack of nutrient in the deeper level of soil.
In addition, the metabolic waste produced by the microorganisms on the surface also causes the accumulation of toxic chemicals in the deeper area.
Furthermore, oxygen and water are important for some metabolic pathways, but it is difficult for water and oxygen to diffuse as the depth increases.
Some factors, such as soil aggregates, pores and extracellular enzymes, may help water, oxygen and other nutrients diffuse into the soil.
Moreover, the presence of mineral under the soil provides the alternative sources for the species living in the oligotrophic soil.
In terms of the agricultural lands, the application of fertilizer has a complicated impact on the source of carbon, either increasing or decreasing the organic carbon in the soil.
''
Collimonas'' is one of the species that are capable of living in the oligotrophic soil.
One common feature of the environments where ''
Collimonas'' lives is the presence of fungi, because ''
Collimonas'' have the ability of not only hydrolyzing the
chitin produced by fungi for nutrients, but also producing materials (e.g., ''P. fluorescens'' 2-79) to protect themselves from fungal infection.
The mutual relationship is common in the oligotrophic environments. Additionally, ''
Collimonas'' can also obtain electron sources from rocks and minerals by
weathering.
In terms of polar areas, such as Antarctic and Arctic region, the soil environment is considered as oligotrophic because the soil is frozen with low biological activities.
The most abundant species in the frozen soil are
Actinomycetota
The ''Actinomycetota'' (or ''Actinobacteria'') are a phylum of all gram-positive bacteria. They can be terrestrial or aquatic. They are of great economic importance to humans because agriculture and forests depend on their contributions to soi ...
,
Pseudomonadota,
Acidobacteriota
Acidobacteriota is a phylum of Gram-negative bacteria. Its members are physiologically diverse and ubiquitous, especially in soils, but are under-represented in culture.
Description
Members of this phylum are physiologically diverse, and can be ...
and
Cyanobacteria, together with a small amount of archaea and fungi.
Actinomycetota
The ''Actinomycetota'' (or ''Actinobacteria'') are a phylum of all gram-positive bacteria. They can be terrestrial or aquatic. They are of great economic importance to humans because agriculture and forests depend on their contributions to soi ...
can maintain the activity of their metabolic enzymes and continue their biochemical reactions under a wide range of low temperature.
In addition, the DNA repairing machinery in
Actinomycetota
The ''Actinomycetota'' (or ''Actinobacteria'') are a phylum of all gram-positive bacteria. They can be terrestrial or aquatic. They are of great economic importance to humans because agriculture and forests depend on their contributions to soi ...
protects them from lethal DNA mutation at low temperature.
See also
*
Oligotrophic lake
The Trophic State Index (TSI) is a classification system designed to rate water bodies based on the amount of biological productivity they sustain. Although the term "trophic index" is commonly applied to lakes, any surface water body may be ind ...
*
Eutrophic lake
The Trophic State Index (TSI) is a classification system designed to rate water bodies based on the amount of biological productivity they sustain. Although the term "trophic index" is commonly applied to lakes, any surface water body may be ind ...
* ''
Pelagibacter ubique
"''Candidatus'' Pelagibacter", with the single species "''Ca.'' P. communis", was isolated in 2002 and given a specific name, although it has not yet been described as required by the bacteriological code. It is an abundant member of the SAR11 ...
'', most abundant species on Earth and a streamlined oligotroph
References
External links
* Special issue abou
Lake oligotrophicationpublished in ''Freshwater Biology''
{{modelling ecosystems
Edaphology
Aquatic ecology
Limnology