Suitability of drought-preconditioning techniques in Mediterranean climate

Arid and semiarid ecosystems in the Mediterranean are under high risk of desertification. Revegetation with native well-adapted evergreen shrubs is desirable, but techniques for successful establishment of these species are not fully developed. Transplant shock is a key hurdle to plantation success. The application of a drought-preconditioning treatment during the last months of nursery culture is a potential technique for reducing transplant shock. This technique has been widely applied in boreal habitats and humid temperate areas. Three representative Mediterranean species (Pistacia lentiscus , Quercus coccifera , and Juniperus oxycedrus seedlings) were exposed to classic drought-preconditioning treatment consisting of reductions in the watering regime. The effects of preconditioning on seedling quality were assessed by cell water relationships (pressure-volume curves), minimal transpiration, leaf capacitance, chlorophyll fluorescence, and gas exchange. Moreover, seedlings were exposed to transplant shock (intense drought period) during which water potential (predawn and midday) and maximal photochemical efficiency were evaluated to establish seedling performance. Results showed that preconditioning did not affect cell water relationships and minimal transpiration in any of the three species. Preconditioned seedlings of P. lentiscus maintained higher water content during desiccating conditions as a consequence of an increase in leaf water content at full turgor. These changes allowed plants to maintain higher net CO2 assimilation rates and an elevated photosystem II status, facilitating an increase in drought survival. Preconditioning improved the performance of Q. coccifera and J. oxycedrus seedlings, but these two species were much less responsive than P. lentiscus seedlings. Finally, results suggest that sensitivity to drought preconditioning may be related to drought tolerance or avoidance strategy of each species. Drought-related strategies should be considered to optimize management scale preconditioning.