Figure 5
(a) (Left) Chemostat competition study between marine, nitrogen-fixing Cyanothece sp. and a non-nitrogen-fixing Synechococcus species (source: Department of Aquatic Microbiology, University of Amsterdam). (Middle) Schematic drawing of a chemostat. (Right) At high nitrate levels, the nitrogen-fixer (Cyanothece) is competitively excluded by the non-nitrogen-fixer (Synechococcus). Symbols are measurements; lines are model predictions (after Agawin et al., 2007). (b) (Left) Study in Winogradsky column microcosms. (Middle) Schematic of the vertically layered structure of a mature Winogradsky column. Principal microbial types are found in different layers, their ecological activities and the associated core chemical reactions are illustrated. As a result opposing gradients of sulphide and oxygen develop. (Right) Microbial activity leads to a transient drop in redox potential in the overlying water, and a long-term drop in the sediment, at high levels of added cellulose (‘high C’). Low levels of added cellulose (‘low C’) induce only a short-term reduction in redox potential.
