THE VARIATION IN LEAF STRUCTURE OF SEEDLINGS IN THE FAMILIES
DIPTEROCARPACEAE, CLUSIACEAE, AND MYRTACEAE UNDER DIFFERENT LIGHT ENVIRONMENTS
B M P Singhakumara1, H K Gamage1, P M S Ashton2
1 Department of Forestry and Environmental Science, University
of Sri Jayewardenepura, Nugegoda.
2 School of Forestry and Environmental Studies, Yale University, New Haven,
Light has been characterised as the most important environmental factor
that affect the leaf structure of tree seedlings in tropical rain forest
in South and Southeast Asia. Many studies have been carried out on leaf
structure of early-successional and late-successional species and also
among the species within the same successional status. These studies have
helped in creating a clear understanding of ecological distribution in
relation to each species. The present study examined the leaf structure
of six canopy tree species that are considered to be relatively shade
tolerant in lowland rain forests in Sri Lanka.
Seedlings of Dipterocarpus zeylanicus, D. hispidus (Dipterocarpaceae),
Mesua ferrea, M. nagassarium (Clusiaceae), Syzygium firmum and S. rubicundum
(Myrtaceae) were grown in different controlled environmental shelters
that simulated a range of light environments found in the ground storey
of the rain forest. Two treatments exposed seedlings to different duration
of full sunlight. These simulated the groundstorey Photosynthetic Photon
Flux Density (PFD) that were comparable to the centres of about 200 m2
and 400 m2 canopy openings. Three other shelters exposed seedlings to
uniform diffuse light conditions that simulated amounts and qualities
of radiation similar to that of the forest understorey (PFD 50, R:FR ratio
0.46; PFD 350, R:FR ratio 0.97; PFD 800, R:FR ratio 1.05). A control light
treatment proved full sun light quality (PPFD 2000, R:FR ratio 1.27) for
the seedling growth.
The attributes measured were thickness of leaf blade, upper and lower
epidermis, palisade mesophyll and number of layers, and stomatal frequency.
Results show that Syzygium species have highest in leaf blade, palisade
cell thickness and stomatal frequency followed in order by Mesua>Dipterocarpus.
This suggests that Syzygium species are more light tolerant but less in
drought tolerance. The thickest upper and lower epidermis in Dipterocarpus
reveal that they are more efficient in water use. Syzygium and Dipterocarpus
exhibit rows in palisidae mesophyll when exposed to full sun. These findings
elucidate some of the relationships between leaf anatomy and the species
ecology across the forest topography.
Department of Forestry and Environmental Science,
of Sri Jayewardenepura,Sri Lanka. 1995-2000. All rights reserved.