Abstract
Potassium (K) is the most limiting nutrient for Eucalyptus growth, especially in regions with low availability of water and nutrients in soils. The K supply can be partially replaced by sodium (Na) in the osmotic control, activation of enzymes, stomatal complex, and maintenance of cell turgor among other non-specific functions. The aim of the study is to evaluate the partial replacement of K by Na and the mechanisms (biochemistry, physiological and morpho-anatomical) involved in the response of two eucalyptus genotypes with contrasting drought sensitivity. Growth, gas exchange (A, gs, E and WUE), leaf water potential (¨w), relative content of leaf water, concentration and nutrient accumulation in roots, stems and leaves, as well as its leaves remobilization by analysis in ¼-XRF, the leaf area, leaf isotopic composition of carbon (C) and nitrogen (N) (´13C and ´15N 0), the C / N leaf ratio, the K and Na use efficiency, and metabolomics. We will also analyze the concentration of abscisic acid (ABA), quantification of hydrogen peroxide, lipid peroxidation, superoxide dismutase activity, catalase, ascorbate peroxidase and guaiacol peroxidase activity. Morpho-anatomical aspects also will be evaluated such as the leaf tissues thickness (epidermis, leaf limb, palisade parenchyma, ultrastructural alterations of chloroplasts and starch grains, intercellular spaces), the stomatal density (SD) and total area of stomatal pores (SS) and the root and stem aspects (root diameter and stem morphology). It is expected the understanding of biochemical, physiological and morphoanatomical mechanisms to water deficit attenuation, as well as higher growth and gas exchange of plants supplied with K and Na. We stand out the low molecular solutes accumulation (sugars or amino acids), optimizing the osmoregulation during water stress, the increase of ABA levels, enzymatic activities and metabolic pathways associated with the elimination of ROS, which allows the faster stomatal closure and the relative water leaf content maintenance in contrasting Eucalyptus genotypes to drought. (AU)
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