Respostas ecofisiológicas de plantas jovens de Bertholletia excelsa Bonpl. sumetidas à fertilização em plantio homogênio

Abstract

The success of forest plantations depends, among other factors, on knowledge about the silvicultural aspects of species. Brazil nut (Bertholletia excelsa Bonpl.) has demonstrated potential to form homogeneous stands and agroforestry systems due to its excellent features, but there are many gaps in knowledge about the physiology of this species. This work was carried out to investigate the responses of growth, photosynthesis, water and nutritional status of young plants of B. excelsa under different fertilization treatments, especially nitrogen, growing in homogeneous stands. The treatments were: T0 (control), T1 (Ca + Mg), T2 (Ca + Mg + K + micronutrients) and T3 (Ca + Mg + micronutrients + K + N). Besides the analysis of soil fertility, were measured: height, diameter at ground level, leaf gain and leaf gain index, leaf area, specific leaf area and dry mass, as well as leaf nutrient content, nutrient use efficiency, gas exchange, leaf water potential, pigment contents and chlorophyll a fluorescence. Regarding the growth in height and diameter at ground level, T0, T2 and T3 showed similar results, with average monthly growth of 3.0, 3.1 and 3.4 cm month-1, respectively. T2 and T3 stood out for biomass, T3 leaf gain exhibited was two times higher compared to T0 and T1. The addition of N to T3 individuals allowed greater investment in leaf tissue, with average values of leaf area of 114.2 cm², value 53, 43 and 35% higher than T2, T1 and T0, respectively. There was no difference between treatments for specific leaf area. As for nutrient content, the highest concentrations of N were found in T3, while the higher Ca and Mg were observed in the T1, Ca levels were five times higher than those found in T3. There was no difference in P concentrations among treatments. T3 was more efficient in the use of N, P, Ca, Mg and Zn, while T2 was more efficient in use of Fe and K. Photosynthesis rates estimated ranged between 9.0 and 10.6 mmol m-2 s-1. There was no difference between treatments for dark respiration, stomatal conductance and transpiration. The highest values of water use efficiency and intrinsic water use efficiency were observed in T0. The measured predawn leaf water potential ranged from -0.29 (T3) and -0.26 (T1) MPa and at midday ranged from -2.7 (T1) and 1.7 (T3) MPa. The content of chlorophyll a (0.91 mmol g-1) and carotenoids (0.54 mmol g-1) were higher in treatment T0 and there was no difference in content of chlorophyll b between treatments. The chlorophyll content index showed the same results. Analyzes of chlorophyll a fluorescence revealed no differences between treatments for initial, maximum and variable fluorescence, with values of Fv / Fm ratio lower for T3. From this results, it can be inferred that young plants of B. excelsa growing in homogeneous plantations in limed soil with the addition of micronutrients and mineral nitrogen answered regarding the biometric aspects, except for liming that were not efficient with respect to biometric variables. Additionally, it is concluded that nitrogen fertilization showed direct reflexes, with increases in nutritional status and photosynthetic rates of young plants of B. excelsa. However, no differences between treatments in transpiration, stomatal conductance, dark respiration and chlorophyll contents, were found. Besides that, fertilization had no influence on energy use and dissipation.