Mitigação de estresse hídrico em mudas de Eucalyptus urophylla × E. grandis pela aplicação de regulador de crescimento

Abstract

Eucalyptus is one of the most important forest species in Brazil due to its high productivity and economic and environmental importance. However, water deficit is one of the main factors limiting seedling growth and survival. In this context, growth regulators such as paclobutrazol (PBZ) have been investigated due to their ability to induce morphological, physiological, and biochemical adjustments associated with stress tolerance. This study aimed to evaluate the effects of PBZ application on morphological, physiological, biochemical, nutritional, and survival responses of clonal seedlings of Eucalyptus urophylla × Eucalyptus grandis under different water availability conditions. The experiment was conducted in a greenhouse using a randomized block design with a factorial arrangement consisting of six soil water levels (0, 10, 20, 40, 60, and 80% of field capacity) and two PBZ treatments (with and without application). Growth parameters, stress intensity, photosynthetic pigments, osmoprotective compounds, leaf nutrient concentrations, and seedling survival were evaluated. PBZ application increased seedling survival under moderate water deficit conditions, particularly at 20 and 40% of field capacity, and delayed the progression of stress symptoms after irrigation suspension. The regulator reduced shoot height and leaf expansion, altered leaf number, and increased the Dickson Quality Index. Root dry biomass was enhanced mainly under moderate water deficit conditions. Regarding photosynthetic pigments, PBZ contributed to the maintenance of total chlorophyll under severe water stress, while chlorophyll a content was reduced regardless of water availability; carotenoid levels were not affected by PBZ application. Biochemical analyses showed that PBZ promoted the accumulation of proline, sucrose, and total soluble sugars under severe water restriction, whereas soluble protein content was reduced by PBZ. Leaf nutritional status was modulated by PBZ, with specific changes in macro- and micronutrient concentrations, including increased calcium, magnesium, and some micronutrients, as well as reduced sodium accumulation under certain water conditions. Overall, PBZ promoted physiological and biochemical adjustments that contributed to the acclimation responses of Eucalyptus seedlings to water deficit.