Photosynthesis

Photosynthesis, primary production, carbon production or simply ‘production’ is the process whereby pigments such as chlorophyll a in plants and algae capture sunlight and covert it to organic matter and oxygen. Plankton generally has a Redfield molar proportion (e.g. C₁₀₆H₂₆₃O₁₁₀N₁₆P₁). Therefore photosynthesis by phytoplankton can be represented by the following reaction [1]:

106CO₂ + 16 NO₃^– + HPO₄^2- + 122H₂O + 18H⁺ + (solar energy, trace elements) = C₁₀₆H₂₆₃O₁₁₀N₁₆P₁ + 138O₂

A maximum photosynthetic rate (P-max) is attained when an increase in light level no longer causes an increase in production rate (Figure 1).

Figure 1. Pmax is the maximum photosynthetic rate. It is achieved at a certain light level for which any increase in light does not increase the production rate. However, a decrease may occur due to high light levels and is called photoinhibition (Contributed by Samantha Wellman, University of Newcastle).

1. Drever, J.I. 1982. The Geochemistry of Natural Waters, Prentice-Hall, Inc., Englewoods Cliffs, N.J., pp. 388.