Poster: Ecophysiology

Abs # 40: Leaf physiology and shade-tolerance of tropical rainforest tree seedlings

Presenter:	Gamage, Harshi K, gamagehars@student.vuw.ac.nz
Authors	Gamage, Harshi K (A) (B)  Singhakumara,  BMP (B)   Ashton, Mark S (C)
Affiliations:	(A): School of Biological Sciences, Victoria Uni. of Wellington, New Zealand (B): Dept. of Forestry & Env. Sciences, Uni. of Sri Jayewardenapura, Sri Lanka (C): School of Forestry & Env. Studies, Yale University, USA

This study aimed to identify: (i) leaf physiological differences (photosynthesis, stomatal conductance and nutrients) among closely related Syzygium species; and (ii) to correlate those differences with Syzygium spp. shade-tolerance. Seedlings of four Syzygium species (S. firmum, S. makul, S. operculatum, S. rubicundum) in the family Myrtaceae, were selected for the study, that, when taken together represented a wide range of shade-tolerance. Seedlings were grown for two years under six different shade treatments (95%, 82%, 50%, 0% of shade, long periods of full sun=6h d^-1, short periods of full sun=2h d^-1) at the research station of the Sinharja World Heritage Site, Sri Lanka. All species increased their rate of photosynthesis with decreasing shade. However, stomatal conductance and leaf nutrient content (N, P, K, Ca, and Mg) were greatest in the 95% shade treatment. Comparison across species revealed that the shade-intolerant Syzygium rubicundum and S. operculatum were highest in their photosynthesis rates in full sun treatment while S. makul, an intermediate species in shade-tolerance was highest in the 50% shade treatment. The very shade-tolerant species, S. firmum, had the highest photosynthesis rates in 85% shade treatment. Syzygium operculatum exhibited the greatest stomatal conductance and leaf nutrient content followed in decreasing order by S. rubicundum, S. makul, and S. firmum. Findings support the notion that measures of photosynthesis and stomatal conductance rates are good indicators of differences in shade-tolerance among Syzygium species.