Salinity stress on three representative species from Mediterranean semifixed dunes: Assessment of salinity exposure and substrate conductivity data reveal variable response strategies and tolerance between species

Coastal ecotones can disrupt natural conditions, yielding intricate ecological contexts where salinity plays a variable role. The aim of this study was to assess the salinity effect on three species representatives of semifixed dune (Crucianella maritima, Helianthemum caput-felis and Teucrium dunense). Field data were collected to assess plant cover in semifixed dunes, ecotone with other coastal habitats, and artificial Posidonia oceanica wracks. Soil samples were collected, and conductivity measured. Then, experimental exposure to salinity was conducted with 6 seawater (SW) treatments (Control, 6.25 % SW, 12.5 % SW, 25 % SW, 50 % SW, 100 % SW). Flowering, gas exchange, chlorophyll fluorescence and enzymatic antioxidant measurements were conducted after two months of exposure. In the field trial, species presence varied depending on the habitat and was null on P. oceanica. The relation between conductivity and species abundance showed moderate tolerance for the three species. For C. maritima this relation was variable depending on the habitat. Experimental data suggest moderate tolerance with stress occurring at 25 % SW onwards. Gas exchange response to salinity was similar among species, but more drastic reduction in assimilation rate and larger decrease in water use efficiency was observed for C. maritima. Instead, photoinhibition occurred in H. caput-felis and T. dunense but was absent in C. maritima likely related to the fact that H. caput-felis and T. dunense activated catalase and superoxide dismutase enzymes, while C. maritima showed activation of glutathione-related enzymes. Malondialdehyde (MDA) increased in C. maritma and decreased for the other species indicating a more complex involvement of MDA under stress conditions. Flowering response to salinity was overall more resilient in T. dunense. Our results, based on field conductivity data and measurements of physiological, antioxidant, and reproductive traits, delineate specific tolerance differences and strategies towards salinity for Mediterranean semifixed dune species.