Final answer:
Autotrophs convert light energy into chemical energy, measured as gross primary productivity. The remaining energy after their metabolic needs, called net primary productivity, is what is available to the ecosystem.
Step-by-step explanation:
The amount of chemical energy that autotrophs produce from light energy during a given period of time is referred to as gross primary productivity. Photoautotrophs, such as plants, algae, and photosynthetic bacteria, utilize the sun's energy to create carbohydrates through photosynthesis. This process includes the production of ATP and NADPH, which are used in the Calvin cycle to catalyze the reduction of carbon, creating organic molecules such as glucose. However, not all the energy captured is available for growth and reproduction, as some is used for the organism's metabolism. The leftover energy after these processes is known as the net primary productivity, which is available to other organisms in the ecosystem.