September 2022

Abstract

Even though Acacia mangium is able to perform Nitrogen Biological Fixation (NBF), seedlings are grown under N-fertilizer application during the initial stages of seedlings. The hypothesis tested herein is that the N supplying for Acacia seedling until the establishment of the symbiosis relationship is a required practice to enhance seedlings growth, N accumulation and Nitrogen Use Efficiency (NUE). In this sense, the goal of this study was to evaluate the implications of increasing N rates on Acacia seedlings' growth and nutritional status in earlier stages of growth. The study was performed along four months in greenhouse with increasing N rates (0, 50, 100 and 200 mg dm -3 ) applied in pots. Plant parameters evaluated included: collar diameter, height, number of leaves, shoot and root dry matter. Plant nutritional status was evaluated through N content in leaves and NUE at the end of the trial. Findings herein showed that increased N rates applied enhanced all plant parameters, as follow: height (+53%), coller diameter (+43%), number of leaves (+70%) and shoot (+52%) and roots (+68%) dry matter production. Overall, increasing N rates promoted linear increasing on plant growth. Moreover, the N rates applied also improved the N content into the leaves, stem and roots in 55, 41 and 82%, respectively. The NUE was enhanced from 1.7 to 3.9 g mg -1 and plant dry matter was correlated with N content (r = 0.88). The findings herein indicate that N uptaken by plants was efficiently converted into dry matter. The high-N rates promoted higher N accumulation in roots (leaves>roots>stem) with a reduction in N fluxes, while N-low rates increased N fluxes and a reduction of N accumulation in roots (leaves>stem>roots) was observed. Based on our results, the N supplying during Acacia seedlings' earlier stages, when seedlings are not able to perform NBF, was a promising strategy to increase plant growth as well as enhancing NUE by plants.