Carbon cycle is the simplest of all nutrient cycles. Its salient features are :

1. The reservoirs of carbon are : air( as Carbon dioxide), Water ( as dissolved carbon), earth's crust and ocean ( as bicarbonates) and  fossil fuels. 

2. Carbon dioxide is used by green plants for the process of photosynthesis and oxygen is released as a by-product. The fixed carbon enters the food chain and passed to herbivores, carnivores, decomposers. About 4 x 10¹³ kg of carbon is fixed in biosphere through photosynthesis annually.

2. CO₂ production and return to atmosphere.

(a) Carbon dioxide is released into the atmosphere by respiration of producers and consumers.

(b) It is also released by decomposition of organic wastes and dead bodies by decomposers by the action of bacteria and fungi of decay.

(c) Burning of wood and fossil fuels also produces C0₂.

(d) Volcanic eruptions and hot springs also release C0₂ into the atmosphere.

(e) Weathering of carbonate-containing rocks by the action of acids also add C0₂ to the atmosphere.