From a biological point of view , a source of carbon is a Nutriment (sugar, fatty-acid, amino-acid…) providing carbon necessary to the constitution of new organic molecules (Anabolism).

From an ecological point of view , a source of carbon or source CO₂ is an element or a process on this releasing carbonic gas element in the atmosphere.

For example, the human activity produces gases with greenhouse effect by the use of fossil sources of carbon (coal, gas, oil).
In the same way, the decomposition of the dead vegetation releases from great quantities of carbone.
The vegetation is a source of carbon . By extension, the decomposition of the plants is also called source of carbon .

By opposition, one calls Puits of carbon a capturing element of carbonic gas. The process of capture is called Séquestration of carbon. Photosynthesis allows the capture of CO₂ by the plantes.
They are thus well of carbon (as well as sources at the time of their death), and photosynthesis is a mechanism of sequestration.