Effects of light environment and successional status on lightfleck use by understory trees of temperate and tropical forests.

Utilization efficiency (LUE) of lightflecks by leaves increases with decreasing duration of the lightfleck, and depends on photosynthetic induction. Sun and shade leaves differ with respect to photosynthetic induction. Shade leaves may become fully induced by a series of light pulses, whereas photosynthetic induction of leaves from partial shade or full sun depends on continuous light. Additionally, shade leaves maintain a higher induction state over longer periods in dim light or darkness than sun leaves. Both features are advantageous to shade leaves in a highly dynamic light environment. We determined whether pioneer plants and late-successional species differ in photosynthetic induction dynamics and LUE during the establishment phase when both plant types are growing in the shade of the understory. We also determined the effects of shade acclimation and successional position of species on photosynthetic induction and LUE. Results from temperate and tropical rain forests indicate a trade-off between leaf acclimation to shade and the successional position of species. Light acclimation is important, but in deep shade, late-successional species maintain a higher induction state over longer periods than pioneer species.