Nitrogen is an incredibly versatile element, existing in both inorganic and organic forms as well as many different oxidation states. The movement of nitrogen between the atmosphere, biosphere, and geosphere in different forms is called the nitrogen cycle (Figure 1), one of the major biogeochemical cycles. Similar to the carbon cycle, the nitrogen cycle consists of various reservoirs of nitrogen and processes by which those reservoirs exchange nitrogen (note the arrows in the figure). (See The Carbon Cycle module for more information.)