Freshwater Algae Growth Associated with Iron Fertilization

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Freshwater Algae Growth Associated with Iron
Fertilization

• Yang Zhang

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• Iron-limitation hypothesis
• Photosynthesis by marine phytoplankton
  in the Southern Ocean and the associated uptake
  of carbon, is thought to be limited by the
  availability of iron. One implication is that
  larger iron supply to the region in glacial times
  could have stimulated algal photosynthesis,
  leading to lower concentration of atmospheric
  carbon dioxide. Similarly, it has been proposed
  that artificial iron fertilization of the HNLC
  (high nitrate low chlorophyll a) oceans might
  increase further carbon sequestration.

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Previous Research
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• Increased iron supply leads to elevated marine
  phytoplankton biomass and rates of photosynthesis
  in surface waters, causing a large draw down of
  carbon dioxide and macronutrients and elevated
  dimethyl sulfide levels. These effects are due to
  the proliferation of diatom stocks.
• --Phillp W. Boyd, Andrew J. Watson et.al. 2000. A
  mesoscale phytoplankton bloom in the polar
  Southern Ocean stimulated by iron fertilization.
  Nature. 407695-702

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• Phytoplankton growth is simultaneously limited by
  the availability of both iron and lightco
  limitation.
• The amount of cellular iron needed to support
  growth is higher under lower light intensities.
• Growth of small cells is favored under
  iron-limitation.
• ---William G. Sunda and Susan A. Huntsman. 1997.
  Interrelated influence of iron, light and cell
  size on marine phytoplankton growth. Nature. 390
  389-392

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• The maximum growth rate was observed at 20 C
  (optimal temperature) for both Fe-replete and
  Fe-stressed cells.
• Fe-stressed cells grew at half the growth rate of
  Fe-replete cells at 20 C.
• This is because the enzyme activity is Fe and
  temperature co-dependent.
• The degree of Fe-dependence NRAgtPgtETS
• The degree of temperature-dependence
  ETSgtPgtNRA
• ---Isal Kudo, Makiko Miyamoto, et.al. 2000.
  Combined effects of temperature and iron on the
  growth and physiology of the marine diatoms.
  J.Phycol. 361096-1102

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• The dissolved iron is overwhelmingly bound to
  organic ligands with a high affinity for iron.
• There are mainly two kinds of chelated iron in
  seawater Siderophore complexes and Porphyrin
  complexes.
• Efficiency of porphyrin complexed iron
  assimilation
• Eukaryotic gt Prokaryotic (Cyanobacteria)
• Effeciency of siderophore complexed iron
  assimilation
• Prokaryotic (Cyanobacteria) gt
  Eukaryotic
• Competition between prokaryotes and eukaryotes
  may therefore depend on the chemical nature of
  available iron complexes, with consequences for
  ecological niche formation and plankton community
  size-structure seperation.
• ---David A. Hutchins, Amy E.Witter. et.al. 1999.
  Competition among marine phytoplankton for
  different chelated iron species. Nature.
  400858-861

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• Previous research concerns exclusively on marine
  algae.
• Previous research didnt discuss the effect of
  different iron levels on algae growth.

• My research investigated to what extent the iron
  fertilization influence freshwater algae, and
  tried to find out the optimal iron level for
  freshwater algae growth.

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Culture strategy

• OECD recommended fresh water algae culture medium
  (Fe excluded)

Mineral slats Content (mg/L) Mineral salts Content (mg/L)
NH4Cl 15 H3BO3 0.185
MgCl2 12 MnCl2 0.415
CaCl2 18 ZnCl2 3 10-3
MgSO4 15 CoCl2 1.510-3
KH2PO4 1.6 CuCl2 10-5
Na2EDTA 0.1 Na2MoO4 710-3
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Culture strategy

• Different Fe levels of fertilization

Series 0 1 2 3 4 5
Fe level (nM) 0 0.15 0.3 1.5 3.0 15
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Setup of the experiment
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Results and discussions
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Algae composition in the community
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Algae Growth V.S Iron Level
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Algae composition evolutionSeries 0Fe limited
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Algae growthseries 1, 0.15 nM Fe
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Algae composition evolutionSeries 10.15 nM Fe
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Algae growth--Series 2, 0.3 nM Fe
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Algae composition evolutionSeries 20.3 nM Fe
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Algae growthseries 3, 1.5 nM Fe
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Algae composition evolutionSeries 31.5 nM Fe
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Algae growthseries 4, 3 nM Fe
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Algae composition evolutionSeries 43.0 nM Fe
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Algae growthseries 5, 15 nM Fe
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Algae composition evolutionSeries 515 nM Fe
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Drawbacks of my experiment

• No sterilization
• No replicates
• No consideration of temperature dependence

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Conclusions

• Not the more iron, the better for growth.
• The optimal Fe level for freshwater algae growth
  is around 0.3 nM. However, this will vary with
  temperature change.
• Different Fe levels will result in different
  composition of the community. Higher Fe levels
  will favor diatom bloom.

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Thanks!

• Any questions?

Any questions?