Ambiguous controls on simulated diazotrophs in the world oceans

Nitrogen fixers, are microorganisms that fix nitrogen from the air, making it available for ecosystems. It is known that they grow rather slowly so that they are easily taken advantage of by fast-growing algae – unless there is a lack of bioavailable nitrogen. This is when their unique property of “fixing” the nitrogen from the air comes into play. Surprisingly, nitrogen fixers in the ocean often fix more nitrogen than they need themselves –  a property that still puzzles researchers, because it ultimately reduces their typical habitats, which are characterized by a lack of bioavailable nitrogen. The novel study, recently published in the Journal Nature Scientific Reports examines other more complex regulatory mechanisms that can give diazotrophs advantages. A series of model simulations illustrates the potential importance of predators and different nutrient limitations. This illustrates considerable uncertainties (up to sign changes) in projections of nitrogen fixation. 

Cyanobacteria blooms in the Baltic Sea

Blue-green algae (or cyanobacteria)  form regularly massive blooms in the Baltic Sea – especially in late summer. The bacteria can produce toxins and add bioavailable nitrogen fixed from the atmosphere to the already over-fertilized system. In the presented study, high-resolution model data from the Baltic Sea were combined with various observations. Simulated currents were used to trace the origin of blooms and to analyze water properties during bloom formation. The results of the study are surprising in that the blooms develop in the open Baltic Sea instead of, as might be expected, near the coast. This indicates that complex interactions between the different phytoplankton species may be at play and that hypotheses about simple direct relationships to the nutrient composition of the seawater should be considered with some caution.