DIFFERENCES IN LIGHT ENERGY-UTILIZATION AND DISSIPATION BETWEEN DIPTEROCARP RAIN-FOREST TREE SEEDLINGS

The light environment within tropical rain forests varies considerably both spatially and temporally, and photon flux density (PFD) is consi dered to be an important factor determining the growth and survival of rain forest tree seedlings. In this paper we examine the ability of f our ecologically contrasting dipterocarps (Dryobalanops lanceolata, Sh orea leprosula, Hopea ne rvosa and Vatica oblongifolia) to utilise and dissipate light energy when grown in different light environments in lowland dipterocarp rain forest in the Danum Valley Conservation Area, Sabah, East Malaysia. Specifically we report (i) photosynthetic Light response curves and associated fluorescence characteristics, includin g quantum yield (Phi PSII) and non-photochemical quenching (qN) and (i i) the extent to which photoinhibition occurs when plants grown in eit her high or low light are exposed to short bursts of high PFD. When gr own in low light (artificial or forest shade) all four species had low light saturated rates of photosynthesis which were achieved at low PF Ds. In addition, values of Phi PSII and qN were similar over a range o f measurement PFDs. D. lanceolata and S. leprosula were also grown at high PFD and showed marked differences in their responses. S. leprosul a demonstrated an ability to increase its rate of photosynthesis and t here was a small increase in capacity to dissipate excess light energy non-photochemically at high PFDs. Partitioning of this qN into its fa st, photo-protective (qE) and slow, photoinhibitory (qI) components in dicated that there was an increase in qE quenching. In contrast, altho ugh D. lanceolata survived in the high light environment, greater rate s of photosynthesis were not observed and the plants showed a greater capacity to dissipate energy non-photochemically. Partitioning of qN r evealed that the majority of this increase was attributable to the slo wer relaxing phases.