THE EFFECTS OF SHADE ON THE GAS-EXCHANGE OF SEEDLINGS OF 4 TROPICAL TREES FROM MEXICO

This experiment was concerned with the ecophysiology of Brosimum alicastrum (Moraceae), Swietenia macrophylla (Meliaceae), Cedrella odorata (Meliaceae) and Cordia alliodora (Boraginaceae). Species from the secondary forest displayed higher maximal values of photosynthesis than those species normally found in primary forests. These species were also more sensitive to shade, ie maximal rates of photosynthesis were reduced to a greater extent when plants were grown in "shade'. Plants grown under "sun' conditions displayed enhanced dark respiration, higher values of photosynthesis and their rate of photosynthesis continued to increase above a photon flux density of 400 μmol m-2s-1. When plants were raised in "sun' conditions, their leaves contained more N (on a leaf area basis) and this was associated with an increased mesophyll conductance. The species differed from each other much more in their growth than in their rates of photosynthesis. Assimilate distribution may be more diagnostic of the ecological status of a species than its rate of assimilate production per area of leaf. -from Authors