Eucalyptus genus is the most widely planted hardwood tree, which productivity and development are limited by low water availability. Plant drought tolerance can be managed by adopting strategies, such as the exogenous application of salicylic acid. The main objective of the present study was to assess whether the exogenous foliar salicylic acid application would ameliorate the damages of water deficit on Eucalyptus globulus plants. Plants were watered at 70% (well water) or 15% (water deficit) of field capacity and four concentrations of salicylic acid (0, 0.75, 2.5 and 5.0 mM) were applied. Water potential, total chlorophylls and carotenoids contents, chlorophyll fluorescence parameters, leaf gas exchange, malondialdehyde, total soluble sugars, starch and total phenols contents were measured. The global hormonal content was quantified by ultra-performance liquid chromatography–mass spectrometry and specific local dynamics of indolacetic acid and abcisic acid were detected by immunolocalization in leaves. A multivariate statistical approach was used to get an overview of the plant physiological status. E. globulus water deficit response included growth rate decline associated with reduced in both water potential and leaf gas exchange parameters. Plant water deficit defence strategies led to an increase in total chlorophylls and carotenoids contents, lipid peroxidation, phenols and total soluble sugars. Six from the 18 hormones detected increased in water deficit plants. Exogenous salicylic acid application improved water deficit tolerance of E. globulus by improving water potential with a positive impact in primary metabolism (photosynthetic rate, soluble sugars) but also in secondary metabolism and defence mechanisms (higher total phenols and less lipid peroxidation) in the highest salicylic acid concentrations. Also, changes in endogenous levels of abscisic and salicylic acids, gibberellins 4 and 7, and specific cytokinins were found in water deficit plants with salicylic acid application. Our results indicated that salicylic acid application could be a potential chemical priming strategy to ameliorate water deficit effects on E. globulus plants.
