🌱 Photosynthesis Light Response

Light-response hyperbola. Net assimilation A = (φ·I·A_max)/(φ·I + A_max) − R_d, where φ is the quantum yield (initial slope), I the PAR irradiance, A_max the light-saturated rate, and R_d dark respiration. At low light the leaf is light-limited (rate rises with I); at high light it is saturated and limited by CO₂ or temperature instead (Blackman's law of limiting factors). The compensation point is where A = 0 (photosynthesis just balances respiration); the saturation point is where extra light barely helps. Raising CO₂ increases A_max; temperature follows a bell curve with an optimum around 25–30 °C (C3) or higher for C4 crops.