Leaf water status, physiological behavior and biochemical mechanism involved in young olive plants under water deficit

Abstract

Changes in leaf relative water content (RWC), water potential (Ψw), transpiration rate (E & Tsp), stomatal conductance (gs), maximum quantum efficiency of PSII (Fv/Fm), total chlorophylls, carotenoids, proline and soluble sugars were investigated in young Moroccan olive varieties (‘Moroccan Picholine’, ‘Menara’ and ‘Haouzia’) grown in pots under three water regimes (well-watering, moderate stress and high stress). The water treatment was applied at different growth stages during three growing seasons (2015, 2016 and 2017). Results from ANOVA analyses showed that all parameters were found to be mainly under the impact of the water regime and growth stage. In fact, the severe stress led to significant reductions in Ψw, gs, E and Tsp by more than 24%, but also in RWC, Fv/Fm and total chlorophylls with percentages lower than 15%. In contrast, water shortage activated the accumulation of proline and soluble sugars by about 13%. Among growth stages, the bud development displayed the highest levels for RWC, Ψw, gs, E, Tsp and Fv/Fm, and the lowest ones for proline and soluble sugars, whilst, the opposite was observed during the fruiting stage. Although the impacts of variety, growing season and interactions were of minor extents, we observed some significant differences. In fact, the young olive trees belonging to 'Moroccan Picholine' have shown more resistance to water stress, especially during the 2017 season. Principal component analysis (PCA) showed that 92% of the total observed variability was explained by the first two principal components, and allowed a good discrimination among the tree water regimes and the five growth stages. In addition, positive relationship was established between proline and soluble sugars, which were found negatively associated with the remaining parameters.