Ecophysiology of the marine cyanobacterium Trichodesmium
The marine non-heterocystous cyanobacterium Trichodesmium is a major contributor to the marine nitrogen cycle and thus is important for parameterizations for nitrogen fixation in Ocean Biogeochemical Circulation Models. Published information on ecophysiological characteristics of Trichodesmium is summarized in a literature review. The most commonly applied nitrogen fixation measurement technique (Acetylene Reduction Assay) is improved by providing previously unavailable ethylene gas solubility coefficients that are required to accurately calculate nitrogen fixation rates. The role of temperature for diazotrophic growth of Trichodesmium is assessed and a future decline in the fixed nitrogen input by Trichodesmium within this century is predicted. Further, Trichodesmium growth and N2-fixation as a function of light intensity are assessed and synthesized in a simple numerical model to describe nitrogen input into seawater by Trichodesmium. Overall, this thesis contributes to the mechanistic understanding of nitrogen fixation by the marine non-heterocystous cyanobacterium Trichodesmium.