The biospheric carbon cycle is primarily concerned with the atmospheric gas carbon dioxide, its incorporation into organic matter by photosynthesis, and its subsequent release by the respiration of all biota. Carbon also occurs in the earth,s rock predominantly as calcium and magnesium carbonates. These compounds are largely organic in origin.
Nitrogen cycle is not entirely edaphic but most has an atmospheric component linked to the soil by nitrogen fixation and denitrification. Nevertheless plants obtain most of their nitrogen from soil as nitrate or ammonium ions, former being more important.