ABSTRACT
The existing inconsistent data on the irradiance needs of Brazilwood plants Paubrasilia echinata (Lam.) Gagnon,H.C.Lima and G.P.Lewis. can be explained by their phenotypical variations. While small-leaf morphotypes grows better in the shade, not tolerating environments with high irradiance, a recently discovered population of medium morphotype presents different behavior: better performance under direct sunlight and limited growth in the shade. In order to understand the physiological mechanisms of the medium morphotype in response to the available irradiance, this study was performed to characterize the oxidative stress metabolism, photochemical and biochemical photosynthesis efficiency, as well as anatomical adjustments of leaves of the medium morphotype of P. echinata under different intensities of irradiance. The analyses were performed at direct sunlight condition (2000 µmol m-2.s-1) and within a dense ombrophilous forest with 80% shading (192 µmol m-2.s-1). Growth, leaf anatomy, chloroplast pigments, photochemical (chlorophyll a fluorescence), and biochemical (gaseous exchanges) efficiency, soluble carbohydrates, and antioxidants were measured. The results showed that the higher efficiency in light energy uptake, paired with better photochemical performance and better CO2 fixation in plants under direct sunlight resulted in higher concentration of soluble sugars and growth. The energy that should have been used in photochemical and/or biochemical reactions of shaded plants was dissipated in the form of heat, re-emitted as fluorescence or translocated to the production of antioxidant defense compounds of the secondary metabolism. Therefore, the medium morphotype of P. echinata presents an ecological profile of sun-tolerant or pioneer species, and as such, it is recommended its planting in full sunlight. These results differ from previous studies on small morphotype of P. echinata and suggest the need for a taxonomic reconstruction of this species, which is essential to adequate management practices in Atlantic rainforest recovery programs.
Keywords:
Brazilwood; Gas exchange; Oxidation stress
