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. 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 bacterium "Candidatus Pelagibacter communis", which is the most abundant organism in the ocean (with an estimated 2 × 10²⁸ individuals in total); and 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 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.

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. The presence of excess nutrients overwhelm oligotroph's metabolic systems, which cause them to struggle to regulate nutrient uptake. For example, oligotroph's enzymes function well in low nutrient environments, but struggle in high nutrient environments.

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 psychrophiles 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, 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 the lake are completely sterile. This lake is a helpful tool for simulating studies regarding extraterrestrial life on frozen planets and other celestial bodies.