Morphophysiological Behavior and Cambial Activity in Seedlings of Two Amazonian Tree Species under Shade

Variations in light intensity can lead to important anatomical and morphophysiological changes in plants. Aiming to increase knowledge about the Amazonian tree species, this study examines the influence of shade on the cambial activity and development of Parkia gigantocarpa Ducke and Schizolobium parahyba var. amazonicum (Huber ex Ducke) Barneby seedlings. Seedlings of the two species were grown in a nursery under four shade intensities (treatments): full sun, low, moderate, and high shade (resp., 0%, 23%, 67%, and 73% of shade, or 2000, 1540, 660, and 540 µmol·m−2·s−1) obtained with polyethylene screens. We measured plant height, stem diameter, biomass production, stomatal conductance (gs), transpiration (E), photosynthesis (A), and cambial activity (CA) (xylem, cambium, and phloem). Also, we calculated the Dickson Quality Index (DQI). The highest values of biomass production, gs,  E, A, and DQI, were found under full sun, in P. gigantocarpa, and under low shade intensity in S. parahyba. In both species high shade intensity reduced CA. We concluded that the CA and the physiological and morphological attributes work together, explaining the radial growth and increasing seedlings quality, which optimized efficient seedling production under full sun, in P. gigantocarpa, and under low shade intensity in S. parahyba