| Based on work performed during EisenEx, we have developed several hypotheses to shed light on unsolved problems related to the interaction between Fe availability and prokaryotic community composition and activity. Based on the unexpected absence of shifts in the composition of bacterioplankton following Fe-enrichment at a concurrent major shift in the overall activity (leucine and thymidine incorporation, ectoenzymatic activity, diversity of beta-glucosidase) of the bacterioplankton, we will focus our research on factors potentially responsible for this peculiar pattern. We will combine recently developed, sensitive methods (zymography with capillary electrophoresis, microautoradiography in combination with catalyzed reporter deposition fluorescence in situ hybridization) to determine whether there are some more subtle shifts in the phylogenetic composition in the prokaryotic community not detectable by fingerprinting techniques such as T-RFLP. The activity pattern of the prokaryotic community will be closely linked to the dissolved primary production of phytoplankton under non-fertilized versus Fe-fertilized conditions. Virioplankton diversity will be related to prokaryotic diversity to determine the influence of Fe-repleted conditions on viral control of prokaryotic diversity. Overall, this study should result in a mechanistic understanding on the dynamics and interactions between DOM produced by phytoplankton and prokaryotic plankton and viruses under changing Fe concentrations as they occur also naturally in the Southern Ocean, despite the general Fe-depletion in this part of the world's ocean. |
