The overwhelming majority of the primary production on Earth comes from photosynthesis. Plants, algae, and bacteria fix carbon by capturing energy from the sun (or inorganic nutrients, in the case of chemosynthesis) and using that energy to convert carbon dioxide into carbon compounds that can then be used by higher trophic levels.
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Net primary production (NPP) varies by latitude and type of biome.
The FACE (free air CO2 enrichment) experiment studied the response of plants to elevated atmospheric CO2 concentrations.
Primary production in aquatic systems is limited by light (which is limited by depth) and by the availability of different nutrients, depending on the type of system.