Leaf physiological and anatomical responses of Lantana and Ligustrum species under different water availability.

Understanding the plant characteristics that support tolerance to water stress is important in choosing plants in arid or semi-arid environments, such as the Mediterranean. In particular, leaf characteristics can affect the response of plants to water stress. In order to understand how plants with different leaf features can overcome water stress, four water regimes were adopted on two species that are widespread in the Mediterranean environment, Lantana camara and Ligustrum lucidum. The four treatments were: control (C), in which the pot substrate moisture was maintained close to water container capacity (WCC), light deficit irrigation (LDI) irrigated at 75% of WCC, moderate deficit irrigation (MDI) at 50% of WCC, and severe deficit irrigation (SDI) at 25% of WCC. To better understand the action mechanisms, the trial was repeated twice (from January to May, and from May to September). Morphological, anatomical and physiological data were measured to identify the action mechanisms. Water deficit significantly decreased the biomass accumulation in both species during the experimental growth period. In Lantana, significant variations in total leaf area and leaf number were registered between C and SDI, while in Ligustrum, the differences were significant only for total leaf area. The water deficit treatments reduced the leaf thickness especially in Ligustrum. In both species, photosynthesis reduction was related to stomatal closure. Ligustrum showed a higher variability among treatments indicating a faster and more efficient response to water limitations compared to Lantana, as also demonstrated by the lower biomass reduction in the most severe water stress treatment.