Morphophysiological Dynamics of Young Individuals of Tree Species under Different Irradiance Conditions

Light is considered one of the most critical environmental factors in the initial establishment of plants. Thus, knowledge of the ability of species to acclimate to light environments allows for the most suitable selection for restoration of different sites. Casearia sylvestris Sw. is a species with important functional characteristics, with wide geographic distribution and described for its wide plasticity, being used as a reference for the present investigation. Thus, this study aimed to investigate the morpho-physiological changes of the species planted under different conditions: full sun, moderate shade, and closed canopy. We found that the plants altered their morphological and physiological characteristics with the variation of light intensity. Under higher light availability, the species responded with increased photosynthetic rates, stomatal conductance, transpiration, survival (100%), reduced specific leaf area, pigment reduction, photosystem II quantum yield. In the subsystem, the species modulates the photosynthetic apparatus, increasing chlorophyll concentration and specific leaf area, seeking to increase light capture, with a survival rate of 86%. The variables with the highest plasticity index and that contributed most to the acclimation process were predominantly physiological (transpiration, stomatal conductance, photosynthesis, and photochemical quenching), as confirmed by the plasticity index analysis, where the least plastic variables were stomatal density and specific leaf area (morpho-anatomical variables) and other physiological variables (total chlorophyll, water use efficiency, photosystem quantum efficiency). In order to obtain a higher growth rate and survival, the present study indicates that the species should initially be planted in environments with greater light availability, and it is essential to note that there was no water restriction or nutritional unavailability in the study. The species does not show physiological plasticity for different light environments, and cultivation is not indicated especially in understory with light restriction, since there may be and increased mortality and decreased growth of the species.