Apple Leaf Photosynthesis in Alternating Light1

Photosynthetic rates of mature leaves of apple ( Malus domestica Borkh.) from field shoots were measured under high, low, and alternating light conditions (0.5 seconds at each level) in the laboratory. Photosynthetic rates in alternating light were consistently 85% of those recorded under continuous high light. Photosynthetic efficiency was substantially increased under alternating light conditions.