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Growth, morphological, anatomical, and physiological responses of canopy species to varied light environments.

By Admin | January 7, 2009

Growth, morphological, anatomical, and physiological characteristics of seedlings of three canopy species; Artocarpus nobilis Thw., Litsea gardneri Thw. and Myristica dactyloides Gaertn. were compared with variation to the light regimes in lowland tropical rain forest, southwest Sri Lanka. Seedlings were grown under four stimulated light environments; deep shade (50molm-2s-1), medium shade (350molm-2s-1), partial shade (800molm-2s-1), and full sun (1200molm-2s-1) found in Sinharaja rain forest. Seedling height and mortality were recorded at three months intervals. After one and half years of seedling growth, leaf photosynthesis and stomatal conductance were measured and leaf cross sections taken for anatomical measurements. Digital photomicrographs of leaf sections were taken for leaf morphology measurements. After two years of growth, seedlings were uprooted and dried at 800C and dry mass recorded for root, stem, and leaves. Mass ratios were calculated for leaves, roots, and stem.
Results showed significant difference between shade treatments for seedling growth morphology, leaf physiology, and anatomy. Seedling mortality of study species were not affected by irradiance level except Litsea gardneri. Total dry mass of Artocarpus nobilis and Litsea gardneri grown in medium and partial shade were significantly higher than those in deep shade and full sun treatments. Species showed different growth and growth allocation pattern in different shade treatments. There were significant differences between dry mass allocation to leaves, stem and root for all study species. Lower root mass ratios were recorded in deep with more allocation to leaf and stem in treatments that had lower amount of shade. Leaf anatomy between canopy species differ in several important ways that help explain their shade tolerance. All species produced higher or thicker leaf attributes in full sun treatment compared to the deep shade treatment. Typical sun- shade morphological responses to decreasing shade levels included increased stomatal density, decreased leaf number and specific leaf area. Lowest values of net photosynthesis were recorded for seedlings grown in deep shade. Highest values were recorded for seedlings grown in intermediate shade treatment. Results indicate that light conditions between medium shade (350molm-2s-1) and partial shade (800molm-2s-1) are optimal for plant growth and should be considered in management and reintroduction effort for these species.

Bandumala S.H1, Singhakumara B.M.P2 & Ashton P.M.S3.
1Forest Department 2 Department of Forestry & Environmental science, University of Sri Jayawardenepura, Nugegoda, Sri Lanka
3 School of Forestry and Environmental Studies, Yale University, New Haven, U.S.A.

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