LEAF ANATOMICAL RESPONSES TO LIGHT IN 5 TROPICAL MORACEAE OF DIFFERENT SUCCESSIONAL STATUS

We characterized the leaf anatomical characteristics and maximum assim ilation rates of five neotropical Moraceae of different genera and suc cessional positions. Plants were grown under different light levels an d transferred to high light, simulating canopy openings. Total blade t hickness increased with irradiance among all species, and thicker blad es were developed when plants were switched. However, blade thickness, and the extent to which it was modified, was independent of the speci es' successional position and did not predict photosynthetic performan ce. Palisade thickness was a good predictor of maximum photosynthetic rate, but only on a species-specific basis. Overall, leaf thickening w ith increasing irradiance was associated more with structural than wit h photosynthetic changes. The early successionals Cecropia obtusifolia and Ficus insipida exhibited similarly high photosynthetic plasticity and acclimation values, but differed in their leaf anatomical traits. The late successional Poulsenia armata produced the most anatomically plastic leaves, but failed to acclimate either anatomically or photos ynthetically when transferred to higher light levels.