What is primary productivity? Why does it vary in different types of ecosystems?

Primary productivity is defined as the amount of energy accumulation in photosynthetic organisms, by the process of photosynthesis, as biomass or organic matter per unit area over a period of time. It varies in different types of ecosystems because of the different factors that influence it. For different ecosystems, plant species composition, and succession, their photosynthetic activity, availability of nutrients, availability of sunlight and precipitation, type of soil and a number of environmental factors, all differ and hence there's a variability seen in different ecosystems.