1. Nitrogen Fixation

• Reduces atmospheric nitrogen to ammonia (NH3)
• Prokaryotes 
• Also by lightning (small amounts)
• eventually all organisms depend on this process for nutrients

• Oxidation of ammonia (NH3) to nitrite (NO2) (toxic to most plants) then to nitrate (NO3) form that can move into plant roots) responsible for many agal blooms 
• Plants assimalate (NO3) and convert it to amino acids and proteins 

• Returns nitrogen to the atmosphere by converting (NO3) to N2

• Decomposition of organic nirogen back into ammonium ion 
• Carried out by bacteria and fungi
• Recycles large amounts of nitrogen to soil

• reservoirs, atmosphere, soil, assimilation, plant absorption, animal consumption, release, denitrification, detrivorous bacteria (ammonification