Freshwater Algae Growth Associated Freshwater Algae Growth Associated with Iron Fertilizationwith Iron Fertilization

Yang Zhang

• 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.

Previous ResearchPrevious Research

Increased iron supply leads to Increased iron supply leads to elevated marine phytoplankton elevated marine phytoplankton biomass and rates of photosynthesis biomass and rates of photosynthesis in surface waters, causing a large in surface waters, causing a large draw down of carbon dioxide and draw down of carbon dioxide and macronutrients and elevated macronutrients and elevated dimethyl sulfide levels. These effects dimethyl sulfide levels. These effects are due to the proliferation of diatom are due to the proliferation of diatom stocksstocks..

--Phillp W. Boyd, Andrew J. Watson et.al. 2000. A mesoscale --Phillp W. Boyd, Andrew J. Watson et.al. 2000. A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization. Nature. 407:695-702 iron fertilization. Nature. 407:695-702

Phytoplankton growth is simultaneously limited by the availability of both iron and light—co 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

• The maximum growth rate was observed at The maximum growth rate was observed at 20° C (optimal temperature) for both Fe-20° C (optimal temperature) for both Fe-replete and Fe-stressed cells.replete and Fe-stressed cells.

• Fe-stressed cells grew at half the growth Fe-stressed cells grew at half the growth rate of Fe-replete cells at 20° C.rate of Fe-replete cells at 20° C.

• This is because the enzyme activity is Fe This is because the enzyme activity is Fe and temperature co-dependent.and temperature co-dependent.

The degree of Fe-dependence: NRA>P>ETSThe degree of Fe-dependence: NRA>P>ETS

The degree of temperature-dependence: The degree of temperature-dependence: ETS>P>NRAETS>P>NRA

---Isal Kudo, Makiko Miyamoto, et.al. 2000. Combined effects of ---Isal Kudo, Makiko Miyamoto, et.al. 2000. Combined effects of temperature and iron on the growth and physiology of the marine temperature and iron on the growth and physiology of the marine diatoms. J.Phycol. 36:1096-1102diatoms. J.Phycol. 36:1096-1102

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 > Prokaryotic (Cyanobacteria)

Effeciency of siderophore complexed iron assimilation: Prokaryotic (Cyanobacteria) > 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. 400:858-861

• Previous research concerns exclusively on marine algae.

• Previous research didn’t 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.

Culture strategyCulture 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 1.5×10-3

KH2PO4 1.6 CuCl2 10-5

Na2EDTA 0.1 Na2MoO4 7×10-3

Culture strategyCulture 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

Setup of the experiment

Results and discussions…Results and discussions…

Algae composition in the community

Algae Growth V.S Iron Level

4.54.74.95.15.35.55.75.96.16.36.5

0 5 10 15 20

days

log

(to

tal

cell

s/m

l) 0 nM

0.15 nM

0.3 nM

1.5 nM

3 nM

15 nM

0200000400000600000800000

10000001200000140000016000001800000

0 5 10 15 20

days

tota

l cel

ls/m

l0 nM

0.15 nM

0.3 nM

1.5 nM

3.0 nM

15 nM

Algae composition evolutionSeries 0—Fe limited

0

10

20

30

40

50

60

70

80

0 2 4 7 9 12 14 16

algae 1

algae 2

algae 3

algae 4

Algae growth—series 1, 0.15 nM Fe

0200000400000600000800000

10000001200000140000016000001800000

0 5 10 15 20

days

tota

l cel

ls/m

l 0 nM

0.15 nM

Algae composition evolutionSeries 1—0.15 nM Fe

0102030405060708090

100

0 2 4 7 9 12 14 16

algae 1

algae 2

algae 3

algae 4

Algae growth--Series 2, 0.3 nM Fe

0200000400000600000800000

10000001200000140000016000001800000

0 5 10 15 20

days

tota

l cel

ls/m

l

0 nM

0.3 nM

Algae composition evolutionSeries 2—0.3 nM Fe

0

10

20

30

40

50

60

70

80

90

0 2 4 7 9 12 14 16

algae 1

algae 2

algae 3

algae 4

Algae growth—series 3, 1.5 nM Fe

0200000400000600000800000

10000001200000140000016000001800000

0 5 10 15 20

days

tota

l cel

ls/m

l 0 nM

1.5 nM

Algae composition evolutionSeries 3—1.5 nM Fe

0

10

20

30

40

50

60

70

0 2 4 7 9 12 14 16

algae 1

algae 2

algae 3

algae 4

Algae growth—series 4, 3 nM Fe

0200000400000600000800000

10000001200000140000016000001800000

0 5 10 15 20

days

tota

l cel

ls/m

l

0 nM

3.0 nM

Algae composition evolutionSeries 4—3.0 nM Fe

0

10

20

30

40

50

60

70

0 2 4 7 9 12 14 16

algae 1

algae 2

algae 3

algae 4

Algae growth—series 5, 15 nM Fe

0200000400000600000800000

10000001200000140000016000001800000

0 5 10 15 20

days

tota

l cel

ls/m

l

0 nM

15 nM

Algae composition evolutionSeries 5—15 nM Fe

0102030405060708090

100

0 2 4 7 9 12 14 16

algae 1

algae 2

algae 3

algae 4

Drawbacks of my experimentDrawbacks of my experiment

• No sterilization

• No replicates

• No consideration of temperature dependence

ConclusionsConclusions

• 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.

Thanks!Thanks!

• Any questions?Any questions?