Differential Resilience of Mediterranean Coastal Dune and Cliff Plants to Combined Salinity, Drought and Heat Stress: Implications for Coastal Habitat Management Under Climate Change

Mediterranean coastal dunes and cliffs are climate-sensitive ecosystems increasingly exposed to interacting stressors, including salinity, drought, and extreme heat. However, limited information is available on how projected shifts in the timing and intensity of these stressors affect actively growing coastal plants. This study evaluated the physiological and biochemical responses of Pancratium maritimum (dune geophyte) and Crithmum maritimum (cliff halophyte) to salinity (0.15 and 0.3 M NaCl), drought, and subsequent heat stress (40/30 °C) during vegetative growth. Stress treatments induced species-specific adjustments in osmolyte accumulation, ion homeostasis, and oxidative balance. In P. maritimum , high salinity significantly reduced photosynthetic pigment content and relative water status, with effects exacerbated by heat. Elevated oxidative damage markers indicated limited redox buffering capacity. Proline accumulation increased under moderate salinity combined with heat but declined at 0.3 M NaCl, suggesting a potential metabolic shift associated with stress-induced dormancy. In contrast, C. maritimum maintained pigment stability and water balance, sustained higher K⁺ retention, effectively regulated Na⁺ and Cl⁻ accumulation, and showed enhanced Ca 2+ mobilisation. Lower oxidative marker accumulation indicated more efficient redox control, although drought combined with heat imposed significant constraints. These contrasting biochemical and ionic regulation strategies reveal marked differences in stress resilience between Mediterranean dune and cliff specialists. The results indicate that climate-driven shifts in the timing and overlap of salinity, drought and heat stress may alter species performance during active growth, potentially reshaping the structure and stability of dune and cliff plant communities. These findings provide a physiological basis for anticipating vegetation responses and informing adaptive management of climate-vulnerable Mediterranean coastal habitats.