The aim of this study was to evaluate the physiological responses and growth of Eucalyptus urophylla young plants, clone AEC0144, in hydroponic medium, in a completely randomized experimental design with five different ratios of NO3- and NH4+ (0/100, 25/75, 50/50, 75/25 and 100/0) and four replications. The NO3-/NH4+ ratios analyzed affected the initial growth of plants by changing the dry mass accumulation, Dickson quality index, SPAD index, and leaf macronutrient content. Plant growth was particularly favored by the 75/25 NO3-/NH4+ ratio, based on tissue expansion and dry matter accumulation. However, the NO3-/NH4+ ratios didn't cause significant change in some physiological aspects, such as net photosynthesis and nitrogen assimilation metabolism. The NO3-/NH4+ ratios affected the pH of nutrient solutions, nitrate reductase activity and plant nutritional status, but no visible symptoms of deficiency or excess of macronutrients were detected in the leaves.
woody plants; nitrogen; mineral nutrition