Download The Nitrogen Cycle

The Nitrogen Cycle
Why is nitrogen important?
• Its an essential part of many biological
molecules.
• Proteins
• Nucleic acids (DNA)
• Chlorophyll
• Adenosine triphosphate (ATP:
chemical energy)
Where is nitrogen found?
• In the air (78% of the air is nitrogen gas)
• The nitrogen in the air is not useful as a
direct nitrogen source for most organisms.
It is to tightly bonded to itself (N2)
• The nitrogen in the air must be fixed, or put
into a compound that can be used by most
organisms.
• The nitrogen that is usable by most
organisms is found in the soil or in other
organisms.
Step 1: The fixation of
nitrogen
• Pure nitrogen (N2) is converted into
ammonia (NH3) and ammonium (NH4)
compounds by specialized bacteria.
• Most of these nitrogen fixing bacteria
live on the roots of certain plants
(nitrogen fixers).
• Legumes (beans and peas) and
alders to name a few.
Step 2: Nitrification
• A team of bacteria convert the
ammonia or ammonium to
nitrates(NO3-).This process is called
nitrification.
Step 3: Assimilation
• Nitrates, ammonia and ammonium are
absorbed by plants through roots.
This is called assimilation.
• The nitrogen in these compounds is
used to make proteins and other
biological molecules in the plants.
• Animals get nitrogen when they eat
plants or other animals that have
eaten plants.
Step 4: Ammonification
• The nitrogen in organic compounds is
put back into the soil as ammonia or
ammonium when organisms produce
waste or die.
• This is also done by bacteria.
Step 5: Denitrification
• Nitrates in the soil are converted back
to pure nitrogen by bacteria.
Human influences on the
nitrogen cycle.
• Fertilizing crops with nitrogen based
fertilizers, which then enter the soil
and water.
• Ranching, during which livestock
wastes are released in unnatural
concentrations into the soil.
• Sewage and septic systems leach into
rivers and groundwater.
More human impacts:
• Nitrogen additions to the soil can
lead to changes that favor weeds
over native plants, which in turn
reduces species diversity and
changes ecosystems. Research
shows that nitrogen levels are
linked with changes in grassland
species, from mosses and lichens
to grasses and flowers.
More human impacts:
• Nitrogen oxides react with water to
form nitric acid, which along with
sulfur dioxide is a major component
of acid rain. Acid rain can damage
and kill aquatic life and vegetation,
as well as corrode buildings,
bridges, and other structures.
More human impacts:
• Adding large amounts of nitrogen to
rivers, lakes, and coastal systems results
in eutrophication, a condition that occurs
in aquatic ecosystems when excessive
nutrient concentrations stimulate blooms
of algae that deplete oxygen, killing fish
and other organisms and ruining water
quality. Parts of the Gulf of Mexico, for
example, are so inundated with excess
fertilizer that the water is clogged with
algae, suffocating fish and other marine
life.
Nitrogen is a limiting factor
• Under natural conditions, the amount
of available nitrogen in a stream limits
the growth of many organisms like
algae.