Dr. L. Deegan, www.dryas.mbl.edu/research/clue/default.htm The nitrogen cycle Used by permission

Nitrogen is cycled through air, water and and change them into nitrogen gas (N2). soil, undergoing many transformations Denitrification is an anaerobic process, made possible by the actions of taking place when no oxygen or specialized bacteria. extremely low concentrations of oxygen are available. Denitrification also The term “organic nitrogen” is used to requires a source of carbon. describe a nitrogen compound that had its origin in living material. Nitrogen is Nitrogen gas is very plentiful and makes found in protein and urea which is a up about 80 percent of the earth’s byproduct of protein digestion. When a atmosphere (oxygen accounts for plant or animal dies or an animal slightly less than 20 percent). excretes waste, organic nitrogen is released. Anammox bacteria are unique in their ability to convert ammonium and nitrite Bacteria use various forms of nitrogen to directly to nitrogen gas without the need survive and in the process convert for oxygen or a carbon source. organic nitrogen into ammonia (NH3) or + ammonium (NH4 ), a process called Atmospheric nitrogen gas becomes a ammonification. source of nitrogen for plants, but it must first be processed into a usable form, a The addition of oxygen allows different function again performed mostly by bacteria to convert ammonium to nitrite bacteria. The bacteria combine nitrogen - (NO2 ), and still other bacteria to change with hydrogen to produce ammonia - the nitrite to nitrate (NO3 ) during which they then convert further using nitrification. The need for oxygen enzymes to make their own organic defines nitrification as an aerobic compounds. An example is the process. Rhizobium bacteria that lives in legume plant root nodules. Plants can also Denitrification happens when other absorb nitrate or ammonium ions from bacteria take the nitrites and nitrates the soil via their root hairs.