Adaptative mechanisms to saline stress in ornamental shrubs

Chiara Cirillo [Dipartimento di Agraria, Università di Napoli Federico II]
Veronica De Micco [Dipartimento di Agraria, Università di Napoli Federico II]
Rosanna Caputo [Dipartimento di Agraria, Università di Napoli Federico II]
Stefania De Pascale [Dipartimento di Agraria, Università di Napoli Federico II]

This review provides a description of morpho-
anatomical, biochemical and physiological adaptive mechanisms implemented by ornamental plants to cope with salt stress. Ornamental nursery production is still highly water demanding, which roughly can match with limited availability of high quality irrigation water. Since the irrigation of ornamentals with saline or reclaimed waters may be an alternative, there is a strong need in increasing knowledge of the effects that salinity may exert on shrubs and perennial plants used as ornamentals. At high level of salinity, plants exhibit reductions in growth parameters such as dry biomass or leaf area due to osmotic- and ionicinduced stresses. Growth under saline conditions leads to uptake of Na+ and Cl- by plants, which can result in a nutritional imbalance due to the antagonism between nutrients and saline ions, with possible effects on the foliage. Salinity can affect water relations in plants and photosynthetic capacity by stomatal limitations. These negative effects can be counteracted by the plants through the accumulation of compatible solutes or osmolytes and the activation of the antioxidant machinery. Nevertheless, the performance of these mechanisms is sometimes not enough to avoid damage to the decorative and marketable value of ornamental species. In several plant species, the tolerance to NaCl is implemented through a series of adaptations to acclimate to salinity, including the increase in the root/canopy ratio and in the chlorophyll content, in addition to changes in the leaf anatomical traits. These changes allow plant to maintain the water status in order to limit water loss and protect the photosynthetic process, also preventing harmful effects of ion toxicity on leaves. Finally, we claim that, beside the opportunity of maximizing the sustainability of nursery production of ornamentals, a deeper knowledge of adaptive mechanisms to salinity of ornamental shrubs is still needed to achieve a better selection of species more suitable in landscaping and xeriscaping projects in arid and semi-arid areas of Mediterranean Basin.

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