[Light energy utilization and dissipation in seedlings of three tropical rain forest tree species with different...

In this study, the light energy allocations between photochemical reactions and heat dissipation in the seedlings of three tropical rain forest tree species were investigated under three light regimes (100%, 25% and 8% of full sunlight) by using chlorophyll fluorescence technique. These tree species are Anthocephalus chinensis (Rubiacease), a pioneer species, Pometia tomentosa (Sapindaceae), a canopy climax species, and Horsfieldia tetratepala (Myristicaceae), a sub-canopy climax species. Under the same light levels, A. chinensis had a higher maximum photosynthetic rate (Pmax) and maximum electron transport rate (ETRmax) than P. tomentosa and H. tetratepala. From the light response curves of light energy allocations, all test species had a decreased fraction of light energy allocated to photochemical reactions, while the fraction of light energy allocated to heat dissipation was increased with light intensity. The fractions of light energy allocated to photochemical reactions and heat dissipation were negatively correlated with very high significance. Compared to other two species, A. chinensis allocated more light energy to fractions of photochemical reactions, and had weaker and unsaturated heat dissipation. But, when growing under 100% sunlight, this species had less excess light energy to be used for photosynthesis, so that, it did not suffer from photoinhibition. In contrast, more light energy was allocated to fractions of heat dissipation in both P. tomentosa and H. tetratepala seedlings. Growing under 100% sunlight, these two species received more excess light energy, which caused photoinhibition. Our results support the idea that light requirements for the regeneration of three tropical tree species under different ecological habits are related to their characteristics of light energy utilization and dissipation.