A Model Ocean To Study Nitrogen Use

A review of: Bragg, J.G., Dutkiewicz, S., Jahn, O., Follows, M.J., Chisholm, S.W., (2010), Modeling selective pressures on phytoplankton in the global ocean, PLoS ONE, 5, 3, 9569

As our understanding and knowledge of marine microbes improves and increases, new ideas and hypotheses arise to further learn about this vast topic. However, one area that has proven difficult is in the development of a model approach capable of representing the numerous and complex processes that are present in the marine microbial systems. These processes include physical, biogeochemical and biological forces, which can influence such factors as microbial growth, population dynamics and ecological processes such as predation and species interactions. These processes are addressed in this study by the incorporation of a global numerical simulation to study marine pictophytoplankton for nitrogen use abilities. 

This model is created using the marine pictophytoplankton Prochlorococcus and Synechococcus which are dominant planktons in tropical and subtropical ecosystems respectively. Within each of these genera, are many ‘ecotypes’ consisting of populations with different habitats and nitrogen using abilities. Examples of these include some of the Synechococcus ecotypes abilities to use nitrate, nitrite and ammonium as nitrogen sources. Many Prochlorococcus ecotypes do not possess the ability to use nitrate. 

The results of this model show that tropical regions are often dominated by picophytoplankton and higher latitudes are dominated by large phytoplanktonic groups. All of the phytoplankton used in the model could originally use nitrate, nitrite and ammonium, however as the model ran, mutations occurred and produced three different types of phytoplankton, one unable to use nitrate (M1), the second unable to use nitrate and nitrite (M2) and the third was a ‘null mutant’ resembling the parent in all respects (M3).

The loss of nitrogen use abilities was witnessed to occur at different biogeographic regions depending on the organism. One of the main observations seen was the lack in abundance of the M2 mutants at higher latitudes, indicating that they were disadvantaged in these regions, this indicates that being able to use nitrogen in these regions is an extremely important ability. This results in a higher selective pressure against the M2 mutants due to the higher latitudes containing larger quantities of inorganic nitrogen.

This is a very important test regarding the ocean processes that involve marine microbes, due to the application of studying selective pressures on functional traits. The results found tend to highlight the importance of studying the physical, biogeochemical, ecological and evolutionary processes that affect microbes in the marine environment. As this is a model, there are many ways to make it a more comprehensive test, allowing for a vast amount of  further research in this area, particularly in that of the effects of differing latitudinal gradients on microbial functional traits. It also allows the marine environment to be studied in one go, which is vastly beneficial to the understanding how the differing populations of microbes survive and flourish.