Características fisiológicas e anatômicas foliares de Apuleia leiocarpa (Vogel) J.F.Macbr. (Fabaceae) em ambientes contrastantes de luz

Abstract

Abstract Plants are continuously subjected to different levels of irradiance, which influence their development and directly affect the stomatal opening, chlorophyll synthesis and, consequently, the net assimilation of CO2. Thus, the present study aimed to evaluate the physiological characteristics and leaf anatomy of Apuleia leiocarpa (Vogel) JFMacbr. (Fabaceae) in contrasting light environments. The seeds were sown directly in sandboxes and distributed in two treatments with variations in photon flux density (DFF): shade (SO), under artificial shading conditions by shade screen, and full sun (PS), under condition of 100% of solar radiation. The effect of different light treatments on seedling emergence, initial growth, daily course of CO2 assimilation and chlorophyll a fluorescence emission as well as chloroplast pigment contents and quantitative anatomical characteristics were analyzed. Although different light levels did not influence seedling emergence, the higher photon flux density of PS resulted in lower values of daily CO2 assimilation (Ai), maximum photosynthetic capacity (Amax) and effective quantum yield of FSII. (YII) which, in turn, contributed to the lower values of total biomass and relative growth rate (TCR) when compared to SO plants. These reductions were accompanied by an irreversible fall in the Fv/Fm ratio throughout the day, indicating the occurrence of oxidative damage to the light collecting complex and the photosystem II reaction center and, consequently, the occurrence of chronic photoinhibition. It was also observed that light treatments affected chloroplast pigment content and leaf anatomical characteristics, with increased chlorophyll content and leaf lamina reduction with reduced light availability. In summary, the results indicate that the different light environments, in which A. leiocarpa young plants were subjected, exhibit great influence on the establishment and initial growth of the species, triggering, on the one hand, the absence of physiological plasticity and, on the other, presence of morphological plasticity.