ECOPHYSIOLOGICAL RESPONSES OF MEDIUM MORPHOTYPE OF Paubrasilia echinata (Lam.)Gagnon,H.C.Lima and G.P.Lewis RAISED UNDER FULL SUNLIGHT AND NATURAL SHADE

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.

Lower oxidative damage and cell wall loosening, mediated or not by auxin, as part of the tolerance mechanism of Paubrasilia echinata morphotypes in the shade and full sun

“…The highest A values for SM under the shade and for MM in the full sun condition confirmed the tolerance of the first morphotype to the shade (Mengarda et al 2009) and of the latter morphotype to full sun (Gama et al 2019). The inhibition of A in SM in the full sun condition, and of MM and LM in the shade can be explained by the oxidative action of free radicals on the RuBisCO pathway under these stress conditions (Thach et al 2007).…”

“…The highest values of growth (height, total dry mass, relative growth rate-RGR, and net assimilation rate-NAR) and net carbon assimilation rates (A) of the SM were found in the shaded condition, and of the MM were observed in the full sun, confirming the shade-tolerant habit of the former morphotype (Mengarda et al 2009) and the sun-tolerant habit of the latter (Gama et al 2019). These results also reinforce the concept that sun-tolerant and shade-tolerant species are generally recognized by their higher growth and photosynthesis rate under intense and low solar irradiance, respectively (Finegan 1984;Swaine & Whitmore 1988;Whitmore 1991).…”

“…The A inhibition of the morphotypes in photo-inhibitory treatment can also be explained by the lower photochemical efficiency of photosystem II (F V /F M ). Thus, the photo-inhibitory conditions may have affected the fluorescence of chlorophyll a, and, consequently, limited the reducing power required for CO 2 fixation in the RuBisCO pathway, in the three morphotypes, under these stress conditions (Gama et al 2019) as suggested by the lower intercellular CO 2 concentration-Ci and instantaneous rate of carboxylation (Φc) of SM under the full sun condition, and of MM and LM in the shade.…”

“…The most abundant, reactive and stable reactive oxygen species is hydrogen peroxide-H 2 O 2 (Choudhury et al 2017), a potent lipid peroxidation agent detected by the increase of malondialdehyde-MDA (Asada & Asada 1999) in plants under stress situations. Under such oxidant conditions, including low and intense solar irradiance, the excess of H 2 O 2 may affect photosynthesis (Liu et al 2016) resulting in growth inhibition by limiting the amount of photoassimilates (Gaburro et al 2015;Portela et al 2019;Gama et al 2019). The H 2 O 2 can also affect growth by blocking the auxin synthesis (Kurepin et al 2007;Gong et al 2014), which promotes cell expansion and stem elongation (Sofo et al 2004;Baroniya et al 2014;Kataria et al 2014).…”

“…These three morphotypes also differ in their early growth habit. The small morphotype has been considered as shade-tolerant (Mengarda et al 2009) and the medium morphotype as sun-tolerant (Gama et al 2019). The criteria used by these authors to classify the morphotype habits were based on the irradiance that offered the best growth and photosynthesis condition for each morphotype.…”