Autotrophs make these molecules by photosynthesis. To do so, they use available inorganic nutrients. As plants and animals decompose they also contribute to the pool of available inorganic nutrients. Some are stored in forms that are taken out of circulation, such as coal and petroleum. These materials are used to make organic compounds and incorporated into organisms.
Soil comes largely from weathering of rocks and erosion.
There is active exchange between these two pools. Heterotrophs release carbon dioxide by respiration. Carbon is stored in reserves as petroleum, coal, peat, etc. This effect also is due to increased fuel consumption. 3 - Bicarbonate is stored in large quantities in the ocean.