Nitrogen is essential to all living things. Most of the nitrogen that exist on earth is found in the atmosphere as a gas. Although nitrogen gas makes up about 78 percent of the atmosphere, neither plants nor animals can use nitrogen in that form. We inhale nitrogen with every breathe we take, but the unused portion is exhaled. Nitrogen cycles between the living and nonliving parts of the ecosystems.
All consumers get nitrogen-containing compounds in the things they eat and all foods can be traced back to the producer. Producers get their nitrogen-bearing compounds for the soil or water in which they grow. Nitrogen gas is present in the soil, dissolved in water. Living in the soil or in the roots of certain plants are nitrogen-fixing bacteria. They convert nitrogen to a form they or other organisms can use. Nitrogen fixers convert nitrogen gas to ammonia, which can be used to synthesized proteins and other nitrogen-containing compounds.
Decomposers in the soil breaks down the complex organic compounds in dead plant and animal bodies. They use the energy in those compounds and convert them to simpler substances. The main nitrogen containing substance is ammonia. Ammonia is a gas, and some of it escapes into the atmosphere. However, it also dissolves immediately in water. In watered soil, ammonia reacts chemically with hydrogen ions to form ammonia ions which is absorbed by the roots of plants. It is then built into living material again by plants. The nitrogen gas gradually escapes back into the atmosphere, and the cycle of nitrogen is complete.