Influence of iron availability on nutrient consumption ratio of diatoms in oceanic waters

Abstract

The major nutrients (nitrate, phosphate and silicate) needed for phytoplankton growth are abundant in the surface waters of the subarctic Pacific, equatorial Pacific and Southern oceans, but this growth is limited by the availability of iron1,2,3,4,5. Under iron-deficient conditions, phytoplankton exhibit reduced uptake of nitrate6 and lower cellular levels of carbon, nitrogen and phosphorus7. Here I describe seawater and culture experiments which show that iron limitation can also affect the ratio of consumed silicate to nitrate and phosphate. In iron-limited waters from all three of the aforementioned environments, addition of iron to phytoplankton assemblages in incubation bottles halved the silicate:nitrate and silicate:phosphate consumption ratios, in spite of the preferential growth of diatoms (silica-shelled phytoplankton). The nutrient consumption ratios of the phytoplankton assemblage from the Southern Ocean were similar to those of an iron-deficient laboratory culture of Antarctic diatoms, which exhibit increased cellular silicon or decreased cellular nitrogen and phosphorus in response to iron limitation. Iron limitation therefore increases the export of biogenic silicon, relative to nitrogen and phosphorus, from the surface to deeper waters. These findings suggest how the sedimentary records of carbon and silicon deposition in the glacial Southern Ocean8 can be consistent with the idea that changes in productivity, and thus in drawdown of atmospheric CO2, during the last glaciation were stimulated by changes in iron inputs from atmospheric dust.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Figure 1: Results of in vitro iron-enrichment experiment in the Southern Ocean (64.2° S, 140.7° E; Jan. 1995).
Figure 2: Nitrate versus silicate concentration in the seawater culture of Antarcticdiatom Chaetoceros dichaeta.

References

  1. 1

    Martin, J. H. & Fitzwater, S. E. Iron deficiency limits phytoplankton growth in the north-east Pacific subarctic. Nature 331, 341–343 (1988).

    ADS  CAS  Article  Google Scholar 

  2. 2

    Martin, J. H. et al. Testing the iron hypothesis in ecosystems of the equatorial Pacific. Nature 371, 123–129 (1994).

    ADS  CAS  Article  Google Scholar 

  3. 3

    Coale, K. H., Fitzwater, S. E., Gordon, R. M., Johnson, K. S. & Barber, R. T. Control of community growth and export production by upwelled iron in the equatorial Pacific Ocean. Nature 379, 621–624 (1996).

    ADS  CAS  Article  Google Scholar 

  4. 4

    Martin, J. H., Fitzwater, S. E. & Gordon, R. M. Iron deficiency limits phytoplankton growth in Antarctic waters. Glob. Biogeochem. Cycles 4, 5–12 (1990).

    ADS  CAS  Article  Google Scholar 

  5. 5

    de Baar, H. J. W. et al. Importance of iron for phytoplankton blooms and carbon dioxide drawdown in the Southern Ocean. Nature 373, 412–415 (1995).

    ADS  CAS  Article  Google Scholar 

  6. 6

    Price, N. M., Ahner, B. A. & Morel, F. M. M. The equatorial Pacific Ocean: Grazer-controlled phytoplankton populations in an iron-limited ecosystem. Limnol. Oceanogr. 39, 520–539 (1994).

    ADS  CAS  Article  Google Scholar 

  7. 7

    Green, R. M., Geider, R. J. & Falkowski, P. G. Effect of iron limitation on photosynthesis in a marine diatom. Limnol. Oceanogr. 36, 1772–1782 (1991).

    ADS  Article  Google Scholar 

  8. 8

    Kumar, N. et al. Increased biological productivity and export production in the glacial Southern Ocean. Nature 378, 675–680 (1995).

    ADS  CAS  Article  Google Scholar 

  9. 9

    Duce, R. A. & Tindale, N. W. Atmospheric transport of iron and its deposition in the ocean. Limnol. Oceanogr. 36, 1715–1726 (1991).

    ADS  CAS  Article  Google Scholar 

  10. 10

    Paasche, E. Silicon content of five marine plankton diatom species measured with a rapid filter method. Limnol. Oceanogr. 25, 474–480 (1980).

    ADS  CAS  Article  Google Scholar 

  11. 11

    Harrison, P. J., Conway, H. L., Holmes, R. W. & Davis, C. O. Marine diatoms grown in chemostats under silicate or ammonium limitation. III. Cellular chemical composition and morphology of Chaetoceros debilis, Skeletonema costatum, and Thalassiosira gravida. Mar. Biol. 43, 19–31 (1977).

    CAS  Article  Google Scholar 

  12. 12

    Hutchins, D. A. & Bruland, K. W. Iron-limited diatom growth and Si:N uptake ratios in a coastal upwelling. Nature 393, 561–564 (1998).

    ADS  CAS  Article  Google Scholar 

  13. 13

    Raven, J. A. The iron and molybdenum use efficiencies of plant growth with different energy, carbon and nitrogen sources. New Phytol. 109, 279–287 (1988).

    CAS  Article  Google Scholar 

  14. 14

    Brzezinski, M. A. The Si:C:N ratio of marine diatoms: Interspecific variability and the effect of some environmental variables. J. Phycol. 21, 347–357 (1985).

    CAS  Article  Google Scholar 

  15. 15

    Round, F. E., Crawford, R. M. & Mann, D. G. The Diatoms(Cambridge Univ. Press, 1990).

    Google Scholar 

  16. 16

    Paasche, E. The influence of cell size on growth rate, silica content, and some other properties of four marine diatom species. Norw. J. Bot. 20, 197–204 (1973).

    Google Scholar 

  17. 17

    Dugdale, R. C. & Wilkerson, F. P. Silicate regulation of new production in the equatorial Pacific upwelling. Nature 391, 270–273 (1998).

    ADS  CAS  Article  Google Scholar 

  18. 18

    Dugdale, R. C., Wilkerson, F. P. & Minas, H. J. The role of a silicate pump in driving new production. Deep-Sea Res. I 42, 697–719 (1995).

    CAS  Article  Google Scholar 

  19. 19

    Barnola, J. M., Raynaud, D., Korotkevich, Y. S. & Lorius, C. Vostok ice core provides 160,000-year record of atmospheric CO2. Nature 329, 408–414 (1987).

    ADS  CAS  Article  Google Scholar 

  20. 20

    Martin, J. H. Glacial-interglacial CO2change: The iron hypothesis. Paleoceanography 5, 1–13 (1990).

    ADS  Article  Google Scholar 

  21. 21

    Martin, J. H. in Primary Productivity and Biogeochemical Cycles in the Sea(eds Falkowski, P. G. & Woodhead, A. D.) 123–137 (Plenum, New York, 1992).

    Google Scholar 

  22. 22

    Mortlock, R. A. et al. Evidence for lower productivity in the Antarctic Ocean during the last glaciation. Nature 351, 220–222 (1991).

    ADS  Article  Google Scholar 

  23. 23

    Takeda, S. & Obata, H. Response of equatorial Pacific phytoplankton to subnanomolar Fe enrichment. Mar. Chem. 50, 219–227 (1995).

    CAS  Article  Google Scholar 

  24. 24

    Obata, H., Karatani, H., Matsui, M. & Nakayama, E. Fundamental studies for chemical speciation of iron in seawater with an improved analytical method. Mar. Chem. 56, 97–106 (1997).

    CAS  Article  Google Scholar 

Download references

Acknowledgements

I thank H. Ogawa, T. Usui, and S. Watanabe for shipboard assistance in processing nutrient samples; H. Obata for assistance in processing iron samples; K. Watanabe for Antarctic phytoplankton samples; and I. Koike, K. Kawaguchi, and M. Terasaki for their support during the cruises. My appreciation is also extended to the crew and officers of the RV Hakuho-maru.

Author information

Affiliations

Authors

Corresponding author

Correspondence to Shigenobu Takeda.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Takeda, S. Influence of iron availability on nutrient consumption ratio of diatoms in oceanic waters. Nature 393, 774–777 (1998). https://doi.org/10.1038/31674

Download citation

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.