Photoinhibition

Photoinhibition is a decrease in photosynthetic efficiency that occurs when the amount of light energy absorbed exceeds the plant’s capacity to utilize and safely dissipate it. It can involve either a rapidly reversible reduction in the activity of the photosynthetic apparatus or chronic damage to the photosystems. The risk is increased not only by heat but also by cold, drought, and other factors that limit light utilization. Once the stress has subsided, a full return of photosynthesis to normal levels is not always possible. The risk can be reduced by gradually hardening off seedlings, maintaining a consistent watering schedule, and providing temporary shading when very intense light is combined with heat or drought.