LEAF OPTICAL-PROPERTIES ALONG A VERTICAL GRADIENT IN A TROPICAL RAIN-FOREST CANOPY IN COSTA-RICA

Leaf optical properties (400-1,100 nm) were compared for four species of rain forest trees with crowns in understory, mid-canopy, and canopy positions to test whether optical properties change with light enviro nment. The species tested represent a spectrum of regeneration pattern s ranging from shade tolerant to light demanding. Overall, leaf optica l properties of the four species were similar. Differences in absorpta nce were small, but statistically significant among the species and po sitions along the canopy gradient. Species absorptance differences cor responded somewhat to shade tolerance; two of the shade species showed higher absorptance in lower light environments, while the sun species showed the reverse pattern. Specific leaf mass (leaf weight per unit area) and chlorophyll content per unit leaf weight also changed along the canopy gradient. Specific leaf mass was positively correlated and chlorophyll per unit leaf weight was negatively correlated with increa sing light environment. Consequently, the efficiency of absorption, as represented by the absorptance per unit leaf weight, increased as lig ht level decreased, largely due to changes in specific leaf mass. In c ontrast, efficiency of absorption per unit leaf chlorophyll was relati vely constant with light environment for the two species measured for chlorophyll.