Fig. 55-14c
N2 in atmosphere
Assimilation
NO3–
Nitrogen-fixing
bacteria
Decomposers
Ammonification
NH3
Nitrogen-fixing
soil bacteria
Nitrification
NH4+
NO2–
Nitrifying
bacteria
Denitrifying
bacteria
Nitrifying
bacteria
The Terrestrial Nitrogen Cycle
• The pathway in which nitrogen moves through
the ecosystem
• Nitrogen is a component of amino acids,
proteins, nucleic acids (DNA), ATP
• The main reservoir of nitrogen (N2) is the
atmosphere, 78% . N2 gas must be converted to
other forms.
4 processes of the Nitrogen Cycle
• Nitrogen Fixation - process converts N2 into
• NH4+ (ammonium ions). Done by nitrogen fixing
bacteria found in soil or nodules on roots of legumes
• Examples of legumes: peas, beans, alfalfa, peanuts,
clover
• NH4+ by ammonification, and NH4+ is decomposed to
NO2- and often to NO3– by nitrification
• Nitrifying bacteria convert NH4+ in soils
• Plants absorb nitrates through roots
Bashan, Y. and Levanony, H. (1987)
Ammonification
• Breakdown of nitrogen compounds back into
ammonia products
Denitrification
• Conversion of NH4+, NO2-, NO3- back to
gas (bacteria do this).
N2