Physiological and morpho-anatomical traits used as markers for the selection of drought tolerance of ornamental plants

Urban and peri-urban green areas are often characterized by the lack of irrigation systems, for lowering the management costs and during summer the ornamental plants are exposed to drought stress. There are many ornamental shrubs and suffrutex plants that have good tolerance to water stress. These plants have adapted their physiology and morphology to survive in the arid environments. In urban green planning, the selection of the adequate species is essential for the ornamental value of the areas. The identification of physiological and morpho-anatomical traits associated to drought tolerance, can be helpful for selection of suitable plant species in arid environment. Also due to the large number of species, there is often no information on the drought tolerance of ornamental plants. It is well known that the water loss occurs at leaves level through the transpiration. Drought-tolerant species have coriaceous leaves or are rich in trichomes or waxy surface. Most of these species are called xerophytic species, able to survive in environments with very low water availability. At physiological levels, drought-tolerant ornamental plants show high levels of abscisic acid a hormone related to stomata opening regulation. Other important biochemical changes are represented by the accumulation of proline, reducing sugars, sugar alcohols, mannitol, glycine-betaine, etc. At the molecular level, there is the activation of drought associated genes such as specific transcription factors, reactive oxygen species, associated genes or plant hormone-related genes. All these parameters can be used alone or in combination to screen ornamental species for their drought tolerance. The concentrations or the gene expression of these putative markers can be used for the ornamental plants' classification based on their drought tolerance degree. The drought tolerance degree associated matched with the pedoclimatic conditions of the project area can provide useful information for positioning the different species in the green urban area.