Emergência, crescimento inicial e características fotossintéticas de Pterogyne nitens Tul. sob condições contrastantes de luz

Abstract

In tropical forest environments, changes in light intensity provide a highly heterogeneous environment, directly influencing the growth, survival and distribution of arboreal individuals in different strata. Thus, the work aimed to evaluate the effect of light availability on the initial establishment and physiological characteristics of Pterogyne nitens Tul. (Fabaceae). The study was conducted in an external area of the Biological Sciences Sector Elinsmar Adorno, from the Center for Agricultural, Environmental and Biological Sciences at UFRB, located in the municipality of Cruz das Almas, BA. To assess seedling emergence, 120 seeds per treatment were placed in trays with washed sand equally distributed in two treatments with variations in light intensity: shadow (SO), under 30% solar radiation condition, and full sun (PS), under condition of 100% of the solar radiation. The variables analyzed were: percentage of mergency (% E); emergency speed index (IVE); mean emergency time (TME) and mean emergency speed (VME). For growth analysis, the seedlings were standardized by height of the aerial part and transplanted to plastic pots containing substrate. After a period of 137 days, the effect of light on gas exchange, on the chlorophyll a fluorescence emission and on the content of chloroplast pigments was evaluated. The experiment was conducted completely at random with one species, two levels of irradiance and a variable number of repetitions per treatment and the results were subjected to analysis of variance at 5% probability. The emergence of seedlings of P. nitens showed a statistical difference between treatments. Plants subjected to artificial shading (SO) showed higher values of height (H), leaf area (AF), minimum fluorescence (Fo), regulated dissipation Y (NPQ) and levels of chlorophyll b (Chl b), carotenoids (Carot) and total chlorophylls (Total). Whereas, plants subjected to direct solar radiation (PS) showed higher values of liquid assimilation rate (TAL), CO2 assimilation (A), stomatal conductance (gs), transpiration (E) and effective quantum yield Y (II). The light regime influenced all the physiological parameters evaluated, indicating that young P. nitens plants have phenotypic plasticity, that is, they were able to change their physiology and morphology according to the light regime.