Gross primary production (GPP) is the total amount of carbon dioxide "fixed" by land plants per unit time through the photosynthetic reduction of CO2 into organic compounds. A substantial fraction of GPP supports plant autotrophic respiration (Ra), with the remainder allocated to the net primary production (NPP) of plant structural biomass in stems, leaves, and fruit, carbohydrates such as sugars and starch, and, to a much lesser extent, volatile organic compounds used in plant defense and signaling.
