Environmental Variability and Its Control of Productivity

Focusing on the cyanobacteria and microalgae which globally are responsible for the bulk of aquatic photosynthesis, this chapter addresses the main abiotic factors controlling biosynthetic processes within cells and therefore the elemental and macromolecular composition of photoautotrophs in balance with the environment. It explores the main nutrient requirements in relation to their capacity to limit photosynthesis and cell growth in nature. Although required to perform oxygenic photosynthesis, the ionic forms of these elements have been, and are generally, ubiquitous and in quantities unlikely to exhibit depletions able to limit algal productivity. Nutrient availability is said to exert a bottom–up control on phytoplankton cell growth and productivity. The elemental stoichiometry of phototrophs is linked to their macromolecular composition, that is, cellular architecture and biochemistry, at the phylum level. When applied to the water column, certain conditions can be recognized, based on the availability of light and nutrient resources.