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Many comparative studies have showed interspecific differences in physiological,
anatomical and morphological traits of plants. These aspects may be combined, and
interactively influence the establishment of tree seedlings under natural conditions.
However, few studies have combined these aspects (physiology, morphology and growth
performance) at the whole plant level. This study examined the seedling growth
performance and leaf level anatomical, physiological and morphological differences in
relation to species successional stage and mature tree crown position within a range of
simulated shade environments. The findings of this study are important for developing
silvicultural guidelines for restoration and sustainable management of tropical rain forests.
For this study, three canopy species, four subcanopy species, seven under storey
species, and six pioneer species were selected. All coexist in the rain forest of southwest
Sri Lanka. Seedlings were grown for two years in replicated shade houses which were
designed to create shade treatments that represented a range of light quantity
( photosynthetic photon flux density (PPFD) and quality (red: far red ratios) found within
the Sinharaja forest. Seedling height and mortality were recorded at three months intervals.
After one and half years of seedling growth, leaf photosynthesis and stomatal conductivity
were measured and leaf cross sections taken, for anatomical measurements. Digital graphs
of leaves were taken for leaf morphology measurements. After two years of growth,
seedlings were uprooted and dried at 80°C and dry mass recorded for root, stem and leaves. Mass ratios (Mass of plant part divided by total mass) were calculated for leaves (LMR),
roots (RMR), and stem (SMR). Results showed significant differences in seedlings of
climax and pioneer species in growth morphology, leaf physiology, and anatomy. Pioneer
species have higher plasticity values for seedling growth (height increment, root collar
diameter increment, total dry mass, stem mass ratio, root mass ratio), leaf anatomy (leaf
blade thickness, upper epidermis, lower epidermis) leaf physiology (net photosynthesis,
stomatal conductance) and leaf morphological characters (leaf number, specific leaf area,
and stomatal density) in relation to variation in shade. This study also revealed that
patterns of various seedling growth, leaf anatomical, .morphological, and physiological
attributes that were related to the mature tree canopy position of the seedlings. Canopy
species showed higher plasticity values for height increment, leaf mass ratio, upper
epidermis, net photosynthesis, leaf dry mass, leaf area and specific leaf area. Subcanopy
species had higher plasticity values for root collar diameter, total dry mass, stem mass ratio,
root mass ratio, palisade layer thickness and lower epidermis. Understorey species showed
the lowest plasticity values for most of the measured attributes. It can be concluded that
medium shade (350 umolmis') and light shade (800 Ilmolm-2s-1) favour the optimum
growth of most of the species studied ..
