The Nitrogen Cycle
Oh, Yeah!
Nitrogen is important because it is essential for the formation of proteins
and nucleic acids (always think DNA)
Atmospheric nitrogen is REALLY stable. It’s chemical formula is N2 and is
triple bonded
5 steps in the Nitrogen Cycle
1. Fixation: the use of bacteria is important in fixing nitrogen -- the
breaking down of atmospheric nitrogen to ammonia (NH3) -- this can be done
through man-made processes -- lightning, volcanoes, combustion and many
aspects of industry and natural processes with the use of bacteria:
cyanobacteria (blue-green algae in water)
nitrogen fixing bacteria utilize an enzyme -- nitrogenase (ni-tra-gen-ace) to
split the bonds and attach the nitrogen to hydrogen. This only works in the
ABSENCE of oxygen so some bacteria have created a slime that coats the
areas on the roots of plants where they live -- remember that there is
oxygen in the soil that must be kept away from the bacteria in order for the
breaking apart of nitrogen to take place. Legumes (beans,peas, soy, peanuts)
use the bacteria Rhizobium that live in side nodules on the roots. The
relationship is mutalistic between the plant and the bacteria
2. Nitrification: Ammonia NH3 or Ammonium NH+4 (reaction with water) is
changed to Nitrate (NO-3) through the use of soil bacteria. This is a twostep process:
a) soil bacteria convert ammonia or ammonium to nitrite (NO-2)
b) different soil bacteria oxidize the nitrite to nitrate (NO-3)
The soil bacteria get energy from this mutualistic relationship
3. Assimilation: Plant roots absorb the nitrate and use it to form proteins
and nucleic acids within the plant. Animals absorb these proteins when the
plant is eaten or the animal that ate the plant is eaten.
4. Ammonification: Urine and Urea (birds and reptiles -- solid urine, usually
white in color) is the breakdown of nitrogen compounds in the body back to
ammonia and ammonium (one of the reasons why urine smells -- by the way,
about half of us can smell asparagus pee. The smell the you get after eating
the vegetable. This is do to the sulfur containing amino acids that break
down when you digest asparagus. It’s the same stuff that you find in a
SKUNK!) When urine and urea decompose the nitrogen is released back into
the environment as a ammonia. The decomposition is done by Ammonifying
bacteria.
5. Denitrification: The reduction of nitrate back to gaseous nitrogen.
Denitrifying bacteria reverse what nitrogen fixing bacteria and nitrifying
bacteria do by breaking the oxygen away from the nitrogen and eventually
return it to the atmosphere as it makes its way through the soil. The
bacteria that do this need an oxygen free environment and find this deep
down in the soil where there is little penetration of oxygen (even if the soil
is turned over through tilling.)