Question

What is the fate of incident solar radiation on plants? Explain with reference to PAR and net primary productivity also.

Answer 1

Of the incident solar radiation, about 30% is reflected back into space and 20% is absorbed by the atmosphere. Only about 50% reaches the earth as visible light - the photosynthetically active radiation (PAR). Plants utilise only about 1–5% of the total incident radiation (or 2–10% of PAR) for photosynthesis, i.e., gross primary productivity (GPP). The remaining PAR is dissipated as heat. After meeting respiratory losses, net primary productivity (NPP) is only about 0.8–4% of incident radiation (or 1.6–8% of PAR). This NPP is the food energy available to herbivores.