Crescimento, resposta fisiológica e bioquímica de mudas de Tachigali vulgaris L.G. Silva & H.C. Lima, em função de fontes e doses de nitrogênio.

Abstract

Knowledge of the nutritional requirements for seedling production is a key resource for the success of any planting program of forest species. In this context, nitrogen, among all the nutrients, is found in higher concentrations in higher plants and has proved limiting growth and forest production, however, there are few studies on the demand of this nutrient. Thus, this study aimed to evaluate the effects of applying sources and doses of nitrogen on growth, gas exchange and biochemical response in seedlings Tachigali vulgaris L.G. Silva & H.C. Lima. The experiment was conducted in a greenhouse of the Institute of Agricultural Sciences at the Federal Rural University of Amazonia in Belém, Pará, in the period from April to July 2015. The seedlings were grown in pots containing 3 dm-3 of soil, in a greenhouse. Nitrogen sources tested were urea [(NH₂)₂CO], ammonium sulfate [(NH4)2SO4], ammonium nitrate (NH4NO3) and calcium nitrate [Ca(NO3)2], in five doses of 0, 75, 150, 225 and 300 mg dm-3 , applied as a solution in four portions, 25, 50, 75 and 100 days after transplanting. The experimental unit consisted of a vase and a randomized block design (RBD) in factorial (4 x 5), corresponding to 4 sources and 5 doses, with four repetitions, totaling 80 vessels. The morphological characteristics and their relations, gas exchange and biochemical responses were analyzed at the end of the experiment. Most of the growth characteristics and gas exchange of T. vulgaris seedlings were positively influenced by nitrogen fertilization. As for the N sources used, the highest average height, stem diameter and dry weight of root were obtained with ammonium nitrate and calcium nitrate. The maximum dose used caused negative effect on morphological parameters, damaging the quality of seedlings, for all sources. The lower growth of cultivated plants exclusively N-NH4+ may be associated with lower photosynthetic activity of these plants, due to the negative action of this ion on stomatal conductance, which resulted in lower growth and biomass production. The reduction in the concentration of proteins with ammonium nitrate and calcium nitrate, may be related to the formation of reactive oxygen species (ROS), the excess NO3-, causing damage to the photosystems by inhibition of protein synthesis. The accumulation of amino acids in the leaf and root was positively influenced by the application of N, the maximum accumulation occurring with the source ammonium nitrate, in nearby doses of 225 mg dm-3. Growth of T. vulgaris seedlings is affected by the presence of both forms of mineral nitrogen (NO3-and NH4+) in the fertilizer, and the combination of both forms of N had the highest average activity of the enzyme nitrate reductase and greater increase in total chlorophyll content, in nearby doses of 225 mg dm-3.