1. Freshwater Algae Growth Associated with Iron Fertilization Yang Zhang

2. 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.

3. Previous Research

4. 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. 407:695-702

5.  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

6. The maximum growth rate was observed at 20° C (optimal temperature) for both Fe-replete and Fe-stressed cells. 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. 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. This is because the enzyme activity is Fe and temperature co-dependent. The degree of Fe-dependence: NRA>P>ETS The degree of Fe-dependence: NRA>P>ETS The degree of temperature-dependence: ETS>P>NRA The degree of temperature-dependence: ETS>P>NRA ---Isal Kudo, Makiko Miyamoto, et.al. 2000. Combined effects of temperature and iron on the growth and physiology of the marine diatoms. J.Phycol. 36:1096-1102

7.  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

8. 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.

9. Culture strategy OECD recommended fresh water algae culture medium (Fe excluded) Mineral slatsContent (mg/L)Mineral saltsContent (mg/L) NH4Cl15H3BO30.185 MgCl212MnCl20.415 CaCl218ZnCl23 ×10-3 MgSO415CoCl21.5×10-3 KH2PO41.6CuCl210-5 Na2EDTA0.1Na2MoO47×10-3

10. Culture strategy Different Fe levels of fertilization Series012345 Fe level (nM) 00.150.31.53.015

11. Setup of the experiment

12. Results and discussions…

13. Algae composition in the community

14. Algae Growth V.S Iron Level

15. Algae composition evolution Series 0—Fe limited

16. Algae growth—series 1, 0.15 nM Fe

17. Algae composition evolution Series 1—0.15 nM Fe

18. Algae growth--Series 2, 0.3 nM Fe

19. Algae composition evolution Series 2—0.3 nM Fe

20. Algae growth—series 3, 1.5 nM Fe

21. Algae composition evolution Series 3—1.5 nM Fe

22. Algae growth—series 4, 3 nM Fe

23. Algae composition evolution Series 4—3.0 nM Fe

24. Algae growth—series 5, 15 nM Fe

25. Algae composition evolution Series 5—15 nM Fe

26. Drawbacks of my experiment No sterilization No replicates No consideration of temperature dependence

27. 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.

28. Thanks! Any questions?