The primary nutrient source for primary producers is sunlight, which they utilize in the process of photosynthesis. These organisms, primarily plants and phytoplankton, convert sunlight into chemical energy by synthesizing glucose from carbon dioxide and water. This process not only provides energy for the primary producers themselves but also supports the entire food web by serving as the base of the energy pyramid. Additionally, nutrients like nitrogen and phosphorus from the soil or water enhance their growth and productivity.