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 d ecreasing duration of the lightfleck, and depends on photosynthetic in duction. Sun and shade leaves differ with respect to photosynthetic in duction. Shade leaves may become fully induced by a series of light pu lses, whereas photosynthetic induction of leaves from partial shade or full sun depends on continuous light. Additionally, shade leaves main tain a higher induction state over longer periods in dim light or dark ness than sun leaves. Both features are advantageous to shade leaves i n a highly dynamic light environment. We determined whether pioneer pl ants 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 eff ects of shade acclimation and successional position of spe cies on pho tosynthetic induction and LUE. Results from temperate and tropical rai n forests indicate a trade-off between leaf acclimation to shade and t he successional position of species. Light acclimation is important, b ut in deep shade, late-successional species maintain a higher inductio n state over longer periods than pioneer species.