The Biogeochemical Cycles
Idealized
diagram of the
geologic cycle,
which includes
the tectonic,
hydrologic, rock
and
biogeochemical
cycles.
© 2003 John Wiley and Sons Publishers
Ecosystem
• Biotic and
abiotic
components are
required for
proper
ecosystem
functioning.
Nitrogen Cycle Vocabulary
Nitrification
• N2 Nitrogen
Denitrification
• NH3 Ammonia
Nitrogen fixation
• NH4+ Ammonium Ion
Decomposition
• NO2- Nitrite
Absorption
Consumption
• NO3- Nitrate
• N2O Nitrous Oxide
Fig 4.5 Periodic table of the elements.
© 2003 John Wiley and Sons Publishers
Vocabulary
Nitrification- Chem rxn that converts Ammonium (NH4+)
to Nitrate (NO3-) and Nitrite (NO2-)
Denitrification- Chem rxn that converts Nitrate and
Nitrite ions into Nitrogen gas (N2 ) and Nitrous Oxide
(N2O)
Nitrogen fixation- Conversion of N2 from atmosphere into
ammonia and ammonium ions for plants and animals
Decomposition- Plants and animals decompose and break
down supplying the soil with Nitrogen
Absorption- Plants absorb nitrogen from the soil
Consumption- Animals eat plants that have nitrogen in
them
Nitrogen (N2) in atmosphere
Absorption
by plants
Denitrifying
bacteria
Denitrification
Amino acids
and proteins in
plants and animals
Consumption
Nitrogen
fixation
Detritus
Nitrogen-fixing
bacteria in root
nodules of legumes
Nitrates
(NO3–)
Detritivores
Nitrifying
bacteria
Nitrifcation
Decomposition
Nitrogen-fixing
bacteria in soil
Nitrogen
fixation
Ammonium (NH4+)
Figure 36.16
Nitrogen Fixation
Convert N2 from atmosphere to a
usable form: NH4+1 or NO3-1
Ammonia or Nitrate
Three methods of Nitrogen Fixation:
1. atmospheric fixation by lightning
2. biological fixation by certain microbes alone or in a symbiotic relationship with
plants
Nitrogen Fixation
continued…
• The nitrogen cycle relies heavily on bacteria
• Nitrogen is plentiful in the atmosphere as N2
– But plants cannot use N2
• Various bacteria in soil (and legume root
nodules) convert N2 to nitrogen compounds that
plants can use
– Ammonium (NH4+) and nitrate (NO3–)
Nitrogen fixation by lightning
Nitrates are produced
by forest fires and
lightning.
Nitrogen fixation by bacteria
• Atmospheric nitrogen
(78% of atmosphere) is
chemically fixed by
bacteria to ammonium
(NH4+1) , which is used
by plants as a fertilizer.
Nitrogen cycle
Critical Thinking Issue – How are Human Activities
Affecting the Nitrogen Cycle?
Effects of increased use of
nitrogen fertilizer:
• Increased nitric acid in soil:
• Leaching of magnesium and potassium
• Increased aluminum levels
• Plant root damage
• Changes in microbe communities
• Fish kills
• Eutrophication of water bodies
• Nitrates in drinking water
© 2003 John Wiley and Sons Publishers
The Nitrogen Cycle
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N Cascade
A single atom of nitrogen can have sequential effects in various parts of the
environment after it has been converted from non-reactive N2 to a reactive form
during energy or food production.