Functional Trait Variability of Salicornia europaea L. Across Inland Saline Habitats: Integrating Shoot and Root Morphometrics with Soil Salinity and Trophic Status

<i>Salicornia europaea</i> is an extremely salt-tolerant annual halophyte. It occurs in coastal and inland saline habitats and is increasingly cultivated for food, nutraceuticals, and environmental remediation. This study examined whether inland populations from contrasting saline sites exhibit heritable differences in shoot and root morphology. Seeds from four isolated sites (Ciechocinek, Inowrocław, Salzgraben, and Soltauquelle) were grown at 0, 200, 400, and 1000 mM NaCl, and morphometric traits were quantified from digital images. Corresponding soil samples were also analyzed. A strong relationship was found between population origin and responses to salt stress. Optimal growth generally occurred at 200-400 mM NaCl. Shoot canopy area consistently best discriminated among populations. Inowrocław and Salzgraben performed best under extreme salinity (1000 mM), whereas Ciechocinek showed the weakest growth. Root analyses revealed a shift from radial expansion at moderate salinity to elongation at higher levels, with Salzgraben and Soltauquelle maintaining the longest roots. Soil analyses indicated substantial site differences: Ciechocinek had the highest salinity, resulting in the smallest trait development, Inowrocław was rich in Ca²⁺ and organic matter, while the German sites had lower salinity but higher pH and bicarbonates. These findings demonstrate population-specific adaptive strategies and soil-legacy effects, supporting targeted ecotype selection for saline agriculture and phytoremediation.