Responses of Mediterranean ornamental shrubs to drought stress and recovery

The aim of this study was to evaluate the differences in the mechanisms that are involved in the resistance of ornamental species to drought stress resulting from a regular suspension and recovery of thewater supply. Plants of five ornamental shrubs [Callistemon citrinus (Curtis) Skeels (Callistemon), Laurus nobilis L. (Laurus), Pittosporum tobira (Thunb.) W.T. Aiton (Pittosporum), Thunbergia erecta (Benth.)Anderson (Thunbergia) and Viburnum tinus L. ‘Lucidum’ (Viburnum)] were subjected to two consecutivecycles of suspension/rewatering (S-R) and compared with plants that were watered daily (C). The relativewater content (RWC), leaf water potential ( ), net photosynthetic rate (A), transpiration rate (E) and sto-matal conductance (Gs) parameters were monitored during the experiment. The five species that wereinvestigated exhibited different responses to drought stress. At the end of the experimental period, S-R treatment had no effect on dry weight in all species, except Pittosporum. In Pittosporum, drought stress reduced total plant biomass by 19%. Drought stress induced alterations in shrubs, including decreases in the shoot dry matter and increases in the root to shoot ratio, strongly affecting Callistemon and Pittosporum. All species adapted to water shortages using physiological mechanisms (RWC and water potential adjustment, stomatal closure and reductions in photosynthesis). Following rewatering, the species fully recovered and thus can be considered appropriate for green spaces in the Mediterranean environment. However, Laurus and Thunbergia seem to be less sensitive to drought stress than the other species.