The challenge of the Mediterranean climate to plant hydraulics: Responses and adaptations

• Mediterranean plants are exposed to prolonged summer drought stress, requiring specific adaptations to survive.
• Embolism repair or ion-mediated compensation might help Mediterranean plants to cope with xylem cavitation.
• Small leaves in Mediterranean plants may guarantee high vein density, protecting from drought-induced hydraulic dysfunction.
• Climate change might surpass the capacity of Mediterranean plants to survive more intense or prolonged drought events.

Mediterranean-type biomes characterized by warm summers with a distinct drought period lasting from 2 up to 10 months occur in several world regions including the Mediterranean basin, S-California, Chile, S-Africa and SW-Australia. All these areas are covered by a peculiar and hyper-diverse vegetation dominated by evergreen trees and shrubs with small and coriaceous leaves. Drought adaptation of Mediterranean plants relies on different mechanisms including deep rooting patterns, avoidance or resistance of cavitation-induced embolism, compensation or repair of embolism-induced hydraulic damage. The complementarity and/or co-occurrence of these physiological traits in different species inhabiting Mediterranean biomes is probably the basis for high plant biodiversity in these fascinating habitats. Ongoing climate changes, leading to enhanced frequency and intensity of drought episodes in Mediterranean biomes, represent a major threat to future conservation of these fragile ecosystems, especially if future harsher climate conditions will overcome the drought resistance limits of Mediterranean plants. Current knowledge about drought resistance mechanisms as well as about processes leading to decline and death of woody plants under extreme climatic conditions is revised and directions for future research are suggested.