Produzione primaria: differenze tra le versioni

{{T|lingua=inglese|argomento=ecologia|data=ottobre 2007}}

La '''Produzione primaria''' è la produzione di [[composti organici]] dalla [[Anidride carbonica|CO₂]] presente nell'[[atmosfera]] o in acqua che avviene principalmente mediante processi [[fotosintesi|fotosintetici]] o, in misura minore, [[chemiosintesi|chemiosintetici]].

 

 

==Produzione oceanica==

Contrariamente alla terraferma, negli [[oceano|oceani]] quasi tutta la produzione primaria è dovuta alle alghe e le piante vascolari apportano solo un piccolo contributo.

 

 

===Light===

The sunlit zone of the ocean is called the photic zone (or euphotic zone). This is a relatively thin layer (10-100 m) near the ocean's surface where there is sufficient light for photosynthesis to occur. For practical purposes, the thickness of the photic zone is typically defined by the depth at which light reaches 1% of its surface value. Light is [[attenuation|attenuated]] down the water column by its [[absorption (optics)|absorption]] or [[scattering]] by the water itself, and by dissolved or particulate material within it (including phytoplankton).

 

 

===Nutrients===

Mixing also plays an important role in the limitation of primary production by nutrients. Inorganic nutrients, such as [[nitrate]], [[phosphate]] and [[silicic acid]] are necessary for phytoplankton to [[synthesis]]e their cells and cellular machinery. Because of [[gravity|gravitational]] sinking of particulate material (such as [[plankton]], dead or faecal material), nutrients are constantly lost from the photic zone, and are only replenished by mixing or [[upwelling]] of deeper water. This is exacerbated where summertime solar heating and reduced winds increases vertical stratification and leads to a strong [[thermocline]], since this makes it more difficult for wind mixing to entrain deeper water. Consequently, between mixing events, primary production (and the resulting processes that leads to sinking particulate material) constantly acts to consume nutrients in the mixed layer, and in many regions this leads to nutrient exhaustion and decreased mixed layer production in the summer (even in the presence of abundant light). However, as long as the photic zone is deep enough, primary production may continue below the mixed layer where light-limited growth rates mean that nutrients are often more abundant.