Discriminação isotópica do 13C e nutrição com cálcio e boro em clones de eucalipto submetidos ao défice hídrico

• Autor(a) principal: Barros Filho, Nairam Félix de
• Data de Publicação: 2014
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1669
• topic: Eucalipto - Nutrição; Carbono - Isótopos; Cálcio; Boro; Déficit hídrico; Eucalyptus - Nutrition; Carbon - Isotopes; Calcium; Boron; Water deficit; CNPQ::CIENCIAS AGRARIAS::RECURSOS FLORESTAIS E ENGENHARIA FLORESTAL::SILVICULTURA::NUTRICAO FLORESTAL

The expansion of eucalyptus plantations in Brazil have occurred mainly to areas of savanna, where soils have low fertility and climate is characterized by long dry seasons. The main symptoms observed are usually tip die back, as a result of B deficiency, followed by sprouting and/or desiccation of leaves from the base to the top of the trees, impairing growth and survival. The use of drought tolerant clones and mineral fertilizers has been the strategy used by forest companies as an attempt to minimize the risk of losses and to increase forest productivity. The selection of genotypes is a slow process and often does not define the mechanisms responsible for tolerance to drought. The 13C isotope discrimination ( ) and its relation to the survival and growth of plants have been suggested as an alternative method to select drought tolerant genotypes. Recent studies have shown the importance of B and Ca in tolerance to different types of stress, including water. Explanations of the function of these two nutrients in water stress tolerance and the development of methods that allow faster and safer selection of eucalypt genetic material to water requirement are needed. Thus, this study aimed to verify the influence of Ca and B tolerance of eucalypt clones to water stress, from the physiological parameters, along with the nutritional efficiency and growth and to establish relations between 13C, survival and growth of eucalyptus clones and rainfall in the northern region of Minas Gerais State, Brazil, to identify genotypes well adapted to conditions of low water availability. In the countryside, trees of 6 clones (i144, i224, i063, i182, 2486 and 3216) were measured and samples of leaves and bole wood collected for the determination of 13 C isotope discrimination ( ). Tree diameter and height were measured annually from the fifth year as well as the percentage of affected trees (PAA) by water stress. The results showed a positive correlation between growth and rainfall and between and growth, except for one of the clones. Despite the existence of a negative correlation between and PAA, the use of to select eucalypt for drought tolerance needs a better understanding. In the greenhouse two clones, a susceptible (i042) and a tolerant (i144) to water restriction were cultivated in a modified Clark solution during 14 days. After this period, the seedlings were subjected to the presence or absence of Ca and or B during 14 days. After the 30th day, gradual water restriction was imposed with PEG 6000, in 50 % of plants, reducing the water potential sequentially to -0.16, -0.65 and -1.00 MPa, in intervals of seven days. At the time of application of PEG, dry matter and gas exchange of the plants were determined. Differences were observed between the two clones in the total gas exchange and dry matter, and these differences were dependent on water stress and Ca and B nutrition. In the susceptible clone, B was more important in the mitigation of water stress while in the tolerant clone Ca was relatively more important than B, which may be linked to the function of Ca in the activity of the oxidative stress enzymes.