Primary productivity is the rate at which autotrophs produce biomass using an external energy source and inorganic carbon. Secondary productivity is the rate at which consumers gain biomass from absorbed and assimilated food.
This distinction belongs to IB ESS subtopic 2.2, Energy and biomass in ecosystems, and is HL only.
The Mechanism
Primary productivity occurs in producers such as plants, algae and phytoplankton. Photoautotrophs transform light energy into chemical energy through photosynthesis, while chemoautotrophs use energy from exothermic inorganic chemical reactions.
Secondary productivity occurs in consumers. A consumer ingests organic matter produced by other organisms, but some is egested as faeces and some absorbed energy is released through cellular respiration. Only the portion incorporated into new consumer biomass contributes to secondary productivity.
Both are rates of biomass production, commonly expressed using units such as .