Morphoanatomical characteristics of leaves of Anacardium othonianum seedlings subjected to different nitrogen doses under hydroponic conditions

Nitrogen is an essential nutrient that plants generally require in large amounts. Knowing the nitrogen dose that stimulates primary and secondary metabolic pathways is important for the management of nitrogen fertilisation in plants in general; however, this information is still unavailable for seedlings of the cerrado cashew tree. Based on the hypothesis that the availability of nitrogen for Anacardium othonianum Rizz. seedlings can affect can affect the development of anatomical structures, as well as the synthesis of secondary metabolism compounds in leaves, an experiment was conducted to determine the qualitative and quantitative anatomy this tissue collected from plants of this species subjected to N doses of 0, 2.5, 5.0, 7.5, 10.0, 12.5, and 15.0 mmol L-1 in nutrient solution and evaluated the effect at 30 and 90 days after transplanting (DAT). The largest leaf morphoanatomical changes were observed under the doses of 0 and 15.0 mmol L-1 of N. The lowest stomatal density being observed in the plants exposed to an N dose of 15 mmol L-1. The level of flavonoids was not influenced by the availability of N in the solution; however, the absence of nitrogen directly affected the accumulation of phenolic compounds, alkaloids and polysaccharides present in the leaves, whereas the doses of 7.5, 10.0 and 12.5 mmol L-1 were essential to stimulate the presence of this latter compound in cerrado-cashew-tree seedlings maintained in nutrient solution. Regarding the epochs of evaluation, effect was observed only for the thickness of the adaxial epidermis. These data confirm the hypothesis that the leaf anatomy as well as the accumulation of secondary metabolism compounds in leaves of A. ohonianum can be modified because of the availability of N to the plant.