Prolonged artificial shade affects morphological, anatomical, biochemical and ecophysiological behavior of young olive trees (cv. Arbosana)

Light requirement in olive trees is the most important factor to ensure both olive production and oil quality. However, in the intensive and hyper intensive olive cultivation, problems of shading frequently appear. The objective of this work was to study the effects of reduced irradiance on growth, morphology, anatomy, physiology and some biochemical traits of young olive plants. Thus, an artificial shade (ca. 60%) was performed in young olive plants cv. Arbosana. Plant responses occurred to shade application may be classified as short- and long-term ones. Shoot growth was started to be affected 18 months after shading application, and after that date a total suppression of growth was observed. However, both leaf surface and leaf angle insertion were affected from the beginning of the experiment (3 months).Shaded leaves had higher area and lower thickness. Palisade and spongy parenchyma thickness were reduced in shaded plants. Stomatal density, net photosynthetic rate, stomatal conductance and transpiration rate were also reduced by shade. Shading induced a significant decrease in the concentration of chlorophyll alpha, beta-carotene, lutein and pigments within the xanthophyll cycle (VAZ). A significant decrease of fruits number was observed in shaded plants after one year of shading application, while with prolonged shade, a total absence of fruits were observed. In conclusion, the limitation of the amount of light intercepted by the olive canopy affects negatively most of studied parameters. Therefore, an adequate management of the olive canopy by applying adequate training and pruning programs or by the application of growth regulators will avoid shading problems with negative effects on vegetative growth and yield.