Before the evolution of vascular plants, non-vascular plants likely played a more significant role. On the land, almost all primary production is now performed by vascular plants, with a small fraction coming from algae and non-vascular plants such as mosses and liverworts. See also: Terrestrial biological carbon cycle Note that a distinction is sometimes drawn between "production" and "productivity", with the former the quantity of material produced (g C m −2), the latter the rate at which it is produced (g C m −2 yr −1), but these terms are more typically used interchangeably. In terrestrial ecosystems, mass of carbon per unit area per year (g C m −2 yr −1) is most often used as the unit of measurement. As such it is available for consumption by herbivores.īoth gross and net primary production are typically expressed in units of mass per unit area per unit time interval. Net primary production is available to be directed toward growth and reproduction of primary producers. As noted, it is equal to the difference between the rate at which the plants in an ecosystem produce useful chemical energy (GPP) and the rate at which they use some of that energy during respiration. Net primary production is the rate at which all the autotrophs in an ecosystem produce net useful chemical energy. The remaining fixed energy (i.e., mass of photosynthate) is referred to as net primary production (NPP). Some fraction of this fixed energy is used by primary producers for cellular respiration and maintenance of existing tissues (i.e., "growth respiration" and " maintenance respiration"). Gross primary production (GPP) is the amount of chemical energy, typically expressed as carbon biomass, that primary producers create in a given length of time. Gross primary production and net primary production Consumption of primary producers by heterotrophic organisms, such as animals, then transfers these organic molecules (and the energy stored within them) up the food web, fueling all of the Earth's living systems. These relatively simple molecules may be then used to further synthesise more complicated molecules, including proteins, complex carbohydrates, lipids, and nucleic acids, or be respired to perform work. In both cases, the end point is a polymer of reduced carbohydrate, (CH 2O) n, typically molecules such as glucose or other sugars. The following two equations are simplified representations of photosynthesis (top) and (one form of) chemosynthesis (bottom):ĬO 2 + H 2O + light → CH 2O + O 2 CO 2 + O 2 + 4 H 2S → CH 2O + 4 S + 3 H 2O Regardless of its source, this energy is used to synthesize complex organic molecules from simpler inorganic compounds such as carbon dioxide (CO 2) and water (H 2O). The main source of this energy is sunlight but a minute fraction of primary production is driven by lithotrophic organisms using the chemical energy of inorganic molecules. Primary production is the production of chemical energy in organic compounds by living organisms. Ecologists distinguish primary production as either net or gross, the former accounting for losses to processes such as cellular respiration, the latter not. In terrestrial ecoregions, these are mainly plants, while in aquatic ecoregions algae predominate in this role. The organisms responsible for primary production are known as primary producers or autotrophs, and form the base of the food chain. Almost all life on Earth relies directly or indirectly on primary production. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through chemosynthesis, which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. Provided by the SeaWiFS Project, NASA/ Goddard Space Flight Center and ORBIMAGE. As an estimate of autotroph biomass, it is only a rough indicator of primary-production potential, and not an actual estimate of it. Global oceanic and terrestrial photoautotroph abundance, from September 1997 to August 2000.
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