THE NITROGEN AND CARBON CYCLES IN NATURE. If we were to cremate the bodies of different living beings, we would see that the resulting ashes are surprisingly similar to one another: 95% percent of the time, they all break down into four elements sometimes referred to as the CHON acronym, namely Carbon, Hydrogen, Oxygen and Nitrogen. The Nitrogen Cycle. During the Nitrogen Cycle, plants absorb this element in the shape of nitrates and nitrites. Nitrogen Fixation. How is Nitrogen returned back to the environment. The fastest method of global carbon transfer by carbon dioxide in the atmosphere. Continuous actions of natural cycles.