Acclimation to partial shading or full sunlight determines the performance of container-grown Fraxinus ornus to subsequent drought stress

Cultivation techniques in the nursery aimed to improve tolerance to abiotic stresses after planting in thelandscape may have great ecological value. Here we tested the hypothesis that the irradiance at whichplants grow in the nursery may impact on their responses to a subsequent drought stress. Measurementsof relevant morpho-anatomical, physiological and biochemical traits were conducted in Fraxinus ornus, amember of the Oleaceae family of increasing interest as an urban tree. Leaves developed under moderateshade displayed a lower ability to preserve water balance, thus suffering from a greater decline in netCO2assimilation than leaves acclimated to full sunlight, when subsequently exposed to drought stress.Shaded leaves also displayed an inherently lower capacity to dissipate excess radiant energy through non-photochemical quenching, thus suffering from greater oxidative damage than sun leaves under drought.These results indicate that sunlight irradiance at which container-grown ash trees grow in the nurserymay tightly affect the tolerance to subsequent drought stress. This may have great value for enhancingthe establishment of container-grown plants in the landscape, as fully leaved plants may suffer fromsevere drought stress during early stages of acclimation in the landscape.