Indicadores fisiológicos do status de nitrogênio em plantas de eucalipto

• Autor(a) principal: Ferreira, Eric Victor de Oliveira
• Data de Publicação: 2013
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1647
• topic: Nutrição mineral; Diagnose; Eucalyptus; Mineral nutrition; Diagnosis; Eucalyptus; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO

Although nitrogen (N) is a nutrient required in large amounts by plants, the effects of its application on dry matter production for eucalyptus are divergent, also with nutritional differences among species of this genus. Leaf analysis is an auxiliary method for assessing nutritional status of plants, mainly for N, because the diagnosis of its availability for plants, based solely on soil analysis, is difficult due to the complexity of its soil reactions. Total N leaf concentration has been widely used for verification of possible deficiencies of this nutrient in plants. However, some limitations of its use with regard to this proposal have been reported. Hence, the objectives of this work were to assess alternative indicators of N status in substitution to total N for eucalyptus clones grown under different N availability, such as: chlorophyll, N-NH4 + and N-NO3 - concentrations, leaf N/P, nitrate reductase (NR) and glutamine synthetase (GS) activities, and chlorophyll readings by SPAD (Soil Plant Analysis Development). In addition, it was also evaluated the differential behavior of these clones regarding growth, mineral nutrition, and gas exchanges. In doing so, two experiments were carried out, one in the greenhouse and another in the field. The greenhouse experiment was a 2 x 6 factorial in a randomized complete block design consisting of two eucalyptus clones (VM-01 and I-144) and six doses of N (0, 0.74, 2.93, 4.39, 5.85 and 8.00 mmol L-1 of NH4NO3) in nutrient solution. The field experiment was a 2 x 2 x 2 x 3 factorial in a randomized complete design, with two seasons (dry and rainy), two regions (Pompeu and João Pinheiro-MG), two clones (VM-01 and I-144), and three positions of leaf sampling in the crown (base, middle, and apex). The concentrations of N-NH4 + (root) and N-NO3 - (root and leaf) well represented N status of clones in greenhouse; however, they did not show the same behavior in plants grown in the field. The N/P, chlorophyll, and SPAD readings had similar responses to N application (quadratic and square root models) in greenhouse, with the highest correlation coefficients (r) for the clone VM-01. Among different seasons, N/P and chlorophyll did not reflect the real soils N status in the field. SPAD readings were not considered good indicators of N status either, due to the clone that showed the highest readings (I-144) was the one with the lowest total N concentrations. Total N was also not the best indicator of N status, once it did not show the highest r in the greenhouse experiment. Nevertheless, of all indicators evaluated, it better represented the variations of soils N status in the different seasons under field conditions. Clone I-144 absorbed less N (and synthesized less protein), although it showed higher NR and GS activities with higher dry matter production, compared to VM-01, in greenhouse. The activity of these enzymes was negatively influenced by greater N supply, probably due to an inhibiting effect of NO3 - (substrate of NR) and NH4 + (substrate of GS) in high concentrations. Not only in greenhouse, but also in the field, the highest activities of NR and GS were associated with lower N availability in the cultivation medium of plants. The activity of these enzymes also showed negative correlation with leaf total N of the clones grown in greenhouse, mainly for NR. Clones showed differential behavior to N in solution, with VM-01 being superior in height and height/collar diameter and leaf concentrations of macro and of Cu, Fe, Mo and Zn. In the other hand, clone I-144 had greater production of root and total dry matter, root/shoot and collar diameter, as well as greater stomatal conductance (gs) and transpiration (E). Therefore, clone I-144, regardless of the lower total N leaf concentration, reduced and assimilated more N, which was converted in better growth, making it the more efficient clone in the utilization of this nutrient.