Nutrient Cycle

1. Nitrogen Fixation


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

2. Nitrification

  • 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 

3. Denitrification

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

4. Ammonification

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

Words to Know

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