CO2 and N2 fiaxtion and various release of dissolved nitrogen compounds by Trichodesmium IMS101 under the influence of different light intensities and different P sources.

Nurlaeli, Hilda (2011) CO2 and N2 fiaxtion and various release of dissolved nitrogen compounds by Trichodesmium IMS101 under the influence of different light intensities and different P sources. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 53 pp.

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Abstract

Biological nitrogen fixation is one of the most important processes in the marine environment since it is the only biological source of new fixed nitrogen to the global ocean. The imbalance between biological N2 fixation relative to the biological N2 lost from denitrifications and anammox leads to the possibility that the true rate of N2 fixation has been severely underestimated. Besides, one of the methods most commonly used to measure N2 fixation (the prior method of 15N2 tracer method) has been demonstrated to underestimate the true rate. Thus, the experiments conducted for this thesis provide an additional comparison between the prior method (15N2 gas bubble injection) and the revised method (15N2 enriched water). The results showed that N2 fixation rates measured with the revised method were approximately three times higher than with the prior method, resulting in N2 fixation rates high enough to balance growth rates of Trichodesmium IMS 101. Furthermore, additional experiments conducted only with the revised method, demonstrated the effect of different light intensities and P sources (Phosphate and methylphosphonate) in term of the mass balance, the C02: N2 fixation balance, and the released of recently fixed N2 as dissolved nitrogen compounds. Both C02 and N2 fixation rate were calculated from the isotopic ratio accumulated in the biomass measured using IRMS (Isotope Ratio- Mass Spectrometry). There was no influence of different light intensities on carbon and nitrogen fixation rates observed during the growth of the batch cultures of Trichodesmium IMSlOl. However, methylphosphonate seemed to influence the C02 and N2 fixation in Trichodesmium under high light conditions resulting in a higher biomass accumulation during the 15 days of the experiments. During the entire growth phases, the variation in the C02:N2 fixation rate of the specific rate (between 0. 7-1.4) can be explained by the physiological changes in the molar C:N ratio in the biomass. This mass balance was supported by the finding that there was no substantial amount of dissolved nitrogen compound from the filtrate samples. Dissolved inorganic nitrogen (N03-, N02-, and NH/) was very low to undetectable, while the concentration of dissolved organic nitrogen (DON) detected did not follow the pattern of particulate organic nitrogen (PON) accumulation. Thus, this low DON concentration was most likely not due to the release of recently fixed N2.

Document Type: Thesis (Master thesis)
Thesis Advisor: LaRoche, Julie
Keywords: Trichodesmium IMS101; C02 and N2 fixation; mass balance; light intensity; P sources; 15N2 tracer method; dissolved nitrogen compounds
Subjects: Course of study: MSc Biological Oceanography
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
Date Deposited: 19 Mar 2012 13:14
Last Modified: 07 Jan 2022 14:01
URI: https://oceanrep.geomar.de/id/eprint/14000

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