Effect of Light Intensity on Photosynthesis

In plants, solar energy is converted into chemical energy by the complex process of photosynthesis. Crop production is strongly dependent on the photosynthetic rates. In higher plants, photosynthetically active radiation (PAR), the fraction of sunlight with wavelengths from 400 to 700 nm is harvested by the photosynthetic pigments of photosystems PSI and PSII. PAR intensity is an important factor that determines the rate of photosynthesis. Too high or too low PAR intensities adversely affect the photosynthetic machinery. At low light intensities above the light compensation point (LCP), photosynthetic rate increases proportionally to the light intensity and reaches a maximum. Generally, plants try to maintain photosynthetic efficiency under changing light intensities by balancing conversion of radiation energy and protecting any damage to photosynthetic apparatus by photoinhibition and repairing damage. Some of the photoprotective mechanisms to dissipate surplus energy are quenching of chlorophyll fluorescence, modification of light-harvesting and energy-transfer processes. Alterations in leaf anatomy and chloroplast movements regulate the amount of light absorption by enhancing light capture in shade conditions and preventing light absorption in excessive light conditions in order to maximize photosynthetic efficiency. Through a genetic, molecular, physiological, biochemical, and functional genomics approach, significant developments have been made in identifying genes and molecular mechanisms underlying the relationship of light intensity and photosynthesis. Understanding these mechanisms has a practical value in improving photosynthetic efficiency in crop species growing under differential light intensities.