GROWTH-RESPONSES OF TROPICAL DECIDUOUS TREE SEEDLINGS TO CONTRASTING LIGHT CONDITIONS

The growth responses of seedlings of Amphipterygium adstringens, Caesa lpinia eriostachys, and C. platyloba, species associated with undistur bed parts of the tropical deciduous forest in Mexico, and Apoplanesia paniculata and Heliocarpus pallidus, two gap-requiring pioneer species , were determined under contrasting light conditions in a growth chamb er experiment. The high (400 mumol m-2 s-1) and low (80 mumol m2 s-1) light treatments correspond to the light available in a medium size ga p and underneath the vegetation canopy in the deciduous forest during the rainy season, respectively. Following four destructive harvests th e biomass production, relative growth rate, root/shoot ratio, specific leaf area, net assimilation rate, leaf area ratio and light dependenc y were determined for all species. In the high light treatment all spe cies achieved higher relative growth rates and net assimilation rates than when growing at low light intensity. However, the two pioneer spe cies showed the highest light dependency and were the species more aff ected by the low light treatment in biomass production. The two Caesal pinia species showed similar growth responses, but C. platyloba was th e most shade tolerant species. Plastic adjustments in terms of the spe cific leaf area were more evident in the two pioneer species.