Nutrient Cycling

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Nutrient Cycling
Nutrients elements required for development,
maintenance, and reproduction by
organisms. Nutrients used by Plants and
Animals Plants C, O, H obviously needed for
photo. But also Nitrogen (N), Phosphorus (P),
Sulfur (S) for making amino acids Magnesium for
chlorophyll. Total of 14 essential minerals for
plants. Animals C, O, H, N, sodium, chlorine,
potassium, phosphorus, magnesium, calcium, etc.
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Nutrient Cycling
Energy is said to flow because it is eventually
lost from the biosphere as heat. Nutrients are
said to cycle because they remain in the
biosphere and continue to be recycled.
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Biogeochemical cycles, e.g., carbon
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Fig. 19.4. The carbon cycle.
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Nitrogen Cycle
Nitrogen fixation converts gaseous nitrogen
(N2) to a form usable by organisms, (ammonia NH3
and ammonium NH4). Mineralization conversion
of amino acids in organic matter to
ammonia. Nitrification the oxidation of ammonia
to nitrites (NO2) and nitrates (NO3). Denitrificat
ion the reduction of nitrates to gaseous
nitrogen (N2).
Atmosphere 79 N2
organisms nitrogen-fixation NH3, NH4
Consumers
Uric acid, body parts
Decomposers mineralization
Producers Amino acids
Soil NH3, NH4
Bacteria Nitritification NO2, NO3
bacteria Denitrification N2
Water
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Fig. 19.3. The nitrogen cycle.
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Decomposition

• Decomposition the breakdown of organic matter
  accompanied by the release of carbon dioxide and
  other inorganic compounds.
• Mineralization, conversion of nutrients from
  organic to inorganic form, takes place during
  decomposition.
• Rate in terrestrial systems is significantly
  influenced by temperature, moisture, and chemical
  compositions.

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Fig. 19.5. Decomposition of Fraxinus
Angustifolia leaves at wetter and drier sites in
Spain.
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Decomposition in Temperate Woodland Ecosystems

• Gallardo and Merino found differences in mass
  loss by the target species reflected differences
  in the physical and chemical characteristics of
  their leaves.

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Hubbard Brook Experiment Results
1. Inputs and outputs of nutrients are small
relative to those recycled within the system. N
- added via ppt (6.5kg/ha/yr), fixation (14
kg/ha/yr). Loss to streams (4 kg/ha/yr). So
system holds on to N tightly. Stream output is
only 0.1 of total organic N in watershed. 2.
Overall export of nutrients from harvest
watershed was 13 times control. 3. Because
reduced transpiration led to 40 increase in
runoff and higher leaching. Mostly due to plants
not being there to uptake all the soil N released
via decompsition.
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Ag and Forestry Effects on Nutrient
Cycling Removing biomass transports nutrients
elsewhere. Lack of vegetation prevents nutrient
uptake and retention by plants allowing higher
rates of leaching. Soil disturbance causes
erosion, loss of soil and organic matter, and
associated nutrients. Site prep like burning
leads to loss of nutrients to the
atmosphere. Fertilization leads to concentration
of nutrients in water bodies and pollution
problems.
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Forestry and Ag practices for keeping
Nitrogen. 1. Keep residual vegetation between
crops (or rotations) to uptake and hold nutrients
and make system less leaky. 2. Maintain soil
organic matter to reduce leaching of
nitrites. 3. Favor N fixing organisms via cwd,
lichens, early succ plants, cover crops. 4.
Manage amount and timing of irrigation. 3.
Control timing of fertilization to maximize crop
uptake. 4. Use vegetative ecotones to control
runoff.