Morphological and physiological responses to shade in seedlings of Parkia gigantocarpa Ducke and Schizolobium parahyba var. amazonicum (Huber ex Ducke) Barneby (Leguminosae)

The present study aimed to evaluate the morphological and physiological responses and shade tolerance in two Amazonian tree seedling species under different shade intensities. Seedlings of P. gigantocarpa and S. parahyba were allocated to the following shade intensities: full sun, low, moderate and high (respectively, 0%, 23%, 67% and 73% of shade, or 2000, 1540, 660 and 540 mu mol(-2).s(-1)) obtained with polyethylene screens in a nursery seedling production. We measured the SPAD index, stomata conductance (gs), transpiration (E), photosynthesis (A) and biomass production. We also calculated the specific leaf area (SLA) and biomass allocation. The highest values of gs, E, A, and biomass production were found under full sun, in P. gigantocarpa, and at low shade intensity, in S. parahyba. In P gigantocarpa, the SPAD index (chlorophyll content) and SLA increased under increasing shade intensity; while in S. parahyba, the increase in shade intensity increased biomass allocated to leaves. Thus, as a strategy of its phenotypic plasticity, the studied species responded differently to shade intensity. Although P. gigantocarpa seedlings developed best under full sun and S. parahyba seedlings performed better under low shade intensity, both species survived the different shade intensities, being shade tolerant and adapted to reforestation programs.