How do you calculate GPP (Gross Primary Productivity)?

Gross Primary Productivity (GPP) is calculated by measuring the total amount of energy that plants capture through photosynthesis in a specific area over a given period of time. This can be done by measuring the rate of carbon dioxide uptake or oxygen release, which are indicators of photosynthetic activity. GPP is an important metric for understanding the productivity of ecosystems and the flow of energy through food chains.