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 alter natural conditions, leading to complex ecological environments where salinity plays a varying role. This study aimed to evaluate the impact of salinity on three plant species typical of semifixed dunes: Crucianella maritima, Helianthemum caput-felis, and Teucrium dunense. Field data were gathered to assess plant cover in semifixed dunes, ecotones with other coastal habitats, and artificial Posidonia oceanica wracks. Soil samples were collected, and conductivity was measured. Subsequently, an experimental salinity exposure was conducted using six seawater (SW) treatments (Control, 6.25% SW, 12.5% SW, 25% SW, 50% SW, and 100% SW). Flowering, gas exchange, chlorophyll fluorescence, and enzymatic antioxidant activities were measured after two months of exposure.

In the field study, species presence varied depending on the habitat and was absent on P. oceanica wracks. The relationship between soil conductivity and species abundance indicated moderate salinity tolerance for all three species. For C. maritima, this relationship varied based on the habitat. Experimental data showed moderate tolerance, with stress becoming evident at 25% SW and higher. The response of gas exchange to salinity was similar across species, although C. maritima experienced a more significant reduction in assimilation rate and a larger decrease in water use efficiency. In contrast, photoinhibition SW-100 occurred in H. caput-felis and T. dunense but not in C. maritima, likely due to H. caput-felis and T. dunense activating catalase and superoxide dismutase enzymes, while C. maritima activated glutathione-related enzymes. Malondialdehyde (MDA) levels increased in C. maritima and decreased in the other species, suggesting a more complex role for MDA under stress conditions. Flowering response to salinity was generally more resilient in T. dunense.

Our findings, based on field conductivity data and measurements of physiological, antioxidant, and reproductive traits, highlight specific differences in salinity tolerance and strategies among Mediterranean semifixed dune species.