Photosynthesis of Canopy Tree Species in a Sarawak Rain Forest

Abstract

The specific characteristics of photosynthesis of canopy tree species and other key tree species in Sarawak rain forest were studied with reference to the light adaptation mechanism. The change of the light-photosynthesis curve according to the light gradient from the upper canopy to the forest floor was compared among canopy species, lower layer species, and gap species. Shorea fallax and Dipterocarpus pachyphyllus were selected for the canopy species. Mallotus leptophyllus and Elaeocarpus beccarii for the lower layer species, and Macaranga triloba and Macaranga winkleri for the gap species. The saturation rate of the photosynthesis in canopy species increased with relative light intensity (RLI) and the initial gradient increased with decreasing RLI. They can shift the light photosynthesiscurve from the seedling to the canopy tree, and they can adapt to both shaded and exposed environment. The seedlings can survive on the shaded forest floor with performing the high initial gradient. When they reach the canopy surface, they can perform high values of photosynthetic production by the high saturation rate and strong sun light. The canopy species successfully adapted to the changes of the light environment throughout their life. Both the saturation rate and the initial gradient in lower layer species decreased in the darker environment. They cannot shift the light- photosynthesis curve like canopy species in the darker environment. But they keep the higher light saturation point even in the dark environment. They can respond immediately to strong light of the sunflex and perform high photosynthetic production. This suggests their survival under canopy may depend on the sun flex. The saturation rate in gap species decreased with decreasing RLI but the initial gradient did not increased. They can perform high photosynthetic rates at exposed environment but cannot survive in the shaded environment.