MICROORGANISMS AND GLOBAL CYCLES

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MICROORGANISMS AND GLOBAL CYCLES
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Biogeochemical Cycling

• Describes the movement and conversion of
  materials by biochemical activities throughout
  the atmosphere, hydrosphere and lithosphere
• Most elements subject to some degree of
  biogeochemical cycling, especially the biogenic
  elements

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Types Of Transformations

• Physical transformations
• Dissolution, precipitation, volatilization,
  fixation
• Chemical transformations
• Biosynthesis, biodegradation
• Combination of physical and chemical
  transformation

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What Drives Biogeochemical Cycling?

• Radiant energy of sun and
• Energy of reduced minerals
• The energy is absorbed, converted, stored and
  eventually dissipated ( i.E. Energy flows through
  the ecosystem)

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Reservoirs

• The various chemical forms of a particular
  element constitute reservoirs (pools)
• Global reservoirs relatively stable ito human
  history but undergo shifts during geological ages
• within habitats, elements occur in reservoirs of
  a distinct size. This size varies between
  habitats . Some forms accumulate, some are
  depleted

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Reservoir Size

• Reservoir size is NB parameter when considering
  possible disturbances to a cycling system
• If V1 ? V2, magnitude of change in both
  reservoirs will be equal but opposite, but
  relative changes will be different

V1
Pump
A
V2
B
Valve
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Global ecological problems associated with
cycling systems

• GLOBAL WARMING
• excess CO2 produced by human activity is building
  up in the atmosphere
• elevated levels of CO2 absorb increased amounts
  of radiation and cause warming

• ACID RAIN
• Nitrogen compounds such as nitric and nitrous
  oxide and sulfur compounds such as sulfur dioxide
  are converted to nitric and sulfuric acid and
  cause extensive damage to crops

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Global Reservoirs of Nitrogen

• atmosphere consists of 80 N2 lithosphere ? same
  amount of bound N. Unlimited amts of nitrates,
  but at depths unreachable by roots. In addition,
  N compounds usu very water soluble thus leach out
• Both large reservoirs not immediately available
  for plant/animal use

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Major Forms of Nitrogen in Biogeochemical Cycling

• NH4 and NH3 (ox) ammonium ion and
  ammonia
• organic N
• N2 and N2O N gas and nitrous oxide
• NO2- nitrite
• NO3- (red) nitrate

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The Nitrogen Cycle

• a

N2
Fixation
NH3
food
Plant protein
Urine
Animal protein
N2
Urea
bacteria
decomposition
assimilation
Denitri- fication
bacteria
Ammonia NH3
NO2-
NO3-
Nitrification
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Nitrogen Fixation

• N2? NH3
• Ammonia assimilated into amino acids
• Large amount energy required to break N?N bond
• Free living bacteria and symbiotic bacteria
  involved

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Ammonification

• decomposition of protein to ammonia
  (deamination/ mineralization)
• NH3 volatile - can be lost through vaporization
• Prokaryotes and fungi involved (mainly in the
  soil)
• Much is rapidly recycled to amino acids

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Nitrification

• Oxidation of NH3 to NO3- by nitrifying bacteria
  (aerobic chemolithotrophs)
• 2 step process NH3 oxidising bacteria produce
  NO2-, which is oxidised to NO3- by nitrite
  oxidising bacteria

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Control of Nitrification

• Nitrification is undesirable in agriculture
  why?
• Rate of nitrification high in soil with high
  protein content
• Nitrate readily assimilated by plants, but also
  readily leached
• Nitrapyrin used as nitrification inhibitor

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Denitrification

• Main means by which gaseous N2 is formed
  biologically
• Is the conversion of nitrates to N2 under
  anaerobic conditions
• Anaerobic respirers (e.g. Bacillus and
  Pseudomonas) use NO3 as an electron acceptor and
  reduce it NO3?NO2?N2

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Steps in Dissimilative Nitrate Reduction
(denitrification)

• Nitrate (NO3-)
• Nitrate reductase
• Nitrite (NO2-)
• Nitrite reductase
• Nitric oxide (NO)
• Nitric oxide reductase
• Nitrous oxide (N20)
• Nitrous oxide reductase
• Dinitrogen (N2)

To atmosphere
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Consequences of Denitrification

• Disadvantages
• Nitrate is a common (and costly) form of
  fertilizer so denitrification must be minimised
  in agricultural soils

• Advantages
• For sewage treatment, conversion of NO3-?N2 is
  beneficial as it reduces amt of available N thus
  minimizing algal growth