Figure 20.1 Gross primary productivity and net primary productivity. About 99 percent of solar energy is reflected by producers or passes through their tissues without being absorbed. Only about 1 percent is captured by photosynthesis for gross primary productivity (GPP). Of the total GPP, about 60 percent is used by producers for respiration. The remaining 40 percent is available to producers for growth and reproduction, which is known as net primary productivity (NPP).