The cycling of elements in an ecosystem is called

Concept — Matter, unlike energy, is not lost from an ecosystem. The atoms of every essential element exist in a fixed supply and are used over and over: they move out of the non-living reservoirs of the earth — the atmosphere, water bodies and soil or rock — into living organisms, and later return to those same reservoirs. A pathway that carries an element repeatedly through both the living compartment (bio-) and the earth compartment (geo-) is termed a biogeochemical cycle: 'bio' for the organisms, 'geo' for the earth reservoirs and 'chemical' for the element in transit.

Applying it here — Follow carbon through any ecosystem:

1. Carbon dioxide of the atmosphere is fixed into organic compounds by green plants during photosynthesis.

2. That fixed carbon passes to herbivores and then to carnivores as one organism feeds on another.

3. Respiration by producers and consumers returns a part of the carbon to the air as carbon dioxide.

4. Decomposers break down dead bodies and excreta, releasing the remaining carbon back into the soil and the atmosphere.

The same closed loop through organisms and earth reservoirs runs for nitrogen (fixation, assimilation, ammonification, nitrification, denitrification), for phosphorus (rock weathering, soil, organisms, sediment) and for water. Because every such loop passes through both the living community and the physical earth, the whole class of cycles is named after both.

Contrast the neighbouring terms —

• Geochemical cycle — element movement among the earth's non-living reservoirs such as crust, mantle, ocean and atmosphere, studied as part of geochemistry.

• Geological cycle, also called the rock cycle — the conversion of rock material among igneous, sedimentary and metamorphic forms over geological time.

• Chemical cycle — a general chemistry term for any repeating reaction loop in which a substance is consumed and then regenerated.

Hence the cycling of elements in an ecosystem is called biogeochemical cycles. Remember also their two standard classes: gaseous cycles such as carbon, nitrogen and oxygen, whose main reservoir is the atmosphere or the hydrosphere, and sedimentary cycles such as phosphorus, sulphur and calcium, whose main reservoir is the earth's crust.