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Alleviating Phosphorus Limitations in a Future Acidified Ocean

Paper Reviewed
Spungin, D., Berman-Frank, I. and Levitan, O. 2014. Trichodesmium's strategies to alleviate phosphorus limitation in the future acidified oceans. Environmental Microbiology 16: 1935-1947.

Writing as background for their work, Spungin et al. (2014) say that "the diazotrophic cyanobacterium Trichodesmium spp. is an important player in global biogeochemical carbon and nitrogen cycles and provides 25-50% of the geochemically derived N2 fixation in oligotrophic tropical and subtropical areas," citing the studies of Capone et al. (1997), LaRoche and Breitbarth (2005), Mahaffey et al. (2005) and Bergman et al. (2012). They also note that "laboratory studies of Trichodesmium spp demonstrate that elevating pCO2 from current concentrations of ~400 µatm to the ~900 µatm forecast for the next 100 years leads to higher N2 fixation rates, and enhanced growth and biomass accumulation," citing Hutchins et al. (2007), Levitan et al. (2007, 2010), Ramos et al. (2007) and Kranz et al. (2009).

In further exploring the subject, Spungin et al. set out to examine the combined effects of phosphorus (P) limitation and atmospheric CO2 enrichment on T. erythraeum IMS 101 cultures in a study where they measured nitrogen acquisition, glutamine synthetase activity, carbon (C) uptake rates, intra-cellular Adenosine Triphosphate (ATP) concentration and the pool sizes of related key proteins, where the two CO2 concentrations tested were 400 and 900 µatm and the two P concentrations were 0.5 and 50 µM.

With respect to their findings the three Israeli researchers report - among a large number of other related things - that the cell-per-day growth rate of T. erythraeum at 0.5 µM P was enhanced by 41% when going from 400 to 900 µatm CO2 at 0.5 µM P and by 57% at 50 µM P. Spungin et al. state that their results suggest several possible cellular mechanisms by which Trichodesmium could adapt to predicted changes in pCO2 and P availability in future oceans. They conclude, for example, that "by modifying its metabolic and physiological characteristics, Trichodesmium in the future oceans could maintain inputs of new nitrogen to the upper mixed layer of oceanic waters even in P-limited areas." And they further suggest that "this behavior may extend Trichodesmium's dominance in the acidified ocean ... and possibly increase its contribution of new N and C to these regions." Thus, once again, we have another example of a marine organism that will likely benefit from so-called ocean acidification.

References
Bergman, B., Sandh, G., Lin, S., Larsson, J. and Carpenter, E.J. 2012. Trichodesmium - a widespread marine cyanobacterium with unusual nitrogen fixation properties. FEMS Microbiology Reviews 37: 286-302.

Capone, D.G., Zehr, J.P., Paerl, H.W., Bergman, B. and Carpenter, E.J. 1997. Trichodesmium, a globally significant marine cyanobacterium. Science 276: 1221-1229.

Hutchins, D.A., Fu, F.-X., Zhang, Y., Warner, M.E., Portune, K., Bernhardt, P.W. and Mulholland, M.R. 2007. CO2 control of Trichodesmium N2 fixation, photosynthesis, growth rates, and elemental ratios: implications for past, present and future ocean biogeochemistry. Limnology and Oceanography 52: 1293-1304.

Kranz, S., Sultemeyer, D., Richter, K.-U. and Rost, B. 2009. Carbon acquisition by Trichodesmium: the effect of pCO2 and diurnal changes. Limnology and Oceanography 54: 548-559.

LaRoche, J. and Breitbarth, E. 2005. Importance of the diazotrophs as a source of new nitrogen in the ocean. Journal of Sea Research 53: 67-91.

Levitan, O., Rosenberg, G., Setlik, I., Setlikova, E., Grigel, J., Klepetar, J., Prasil, O. and Berman-Frank, I. 2007. Elevated CO2 enhances nitrogen fixation and growth in the marine cyanobacterium Trichodesmium. Global Change Biology 13: 531-538.

Levitan, O., Brown, C., Sudhaus, S., Campbell, D., LaRoche, J. and Berman-Frank, I. 2010. Regulation of nitrogen metabolism in the marine diazotroph Trichodesmium IMS101 under varying temperatures and atmospheric CO2 concentrations. Environmental Microbiology 12: 1899-1912.

Mahaffey, C., Michaels, A.F. and Capone, D.G. 2005. The conundrum of marine N2 fixation. American Journal of Science 305: 546-595.

Ramos, B.J., Biswas, H., Schulz, K., LaRoche, J. and Riebesell, U. 2007. Effect of rising atmospheric carbon dioxide on the marine nitrogen fixer Trichodesmium. Global Biochemical Cycles 21: 1-6.

Posted 15 October 2014