Suaeda salsa adapts to high-salt environments through expanding vessel diameter, activating antioxidant enzymes and strengthening osmotic regulation

Halophytes have evolved various mechanisms to adapt to saline conditions. However, their morpho-anatomical changes, along with the root metabolic responses to increased salt stress in saline-alkali soils, remain poorly understood. This study aimed to elucidate the adaptive mechanisms of Suaeda salsa under four saline-alkali soil levels (non-saline; NS, lightly saline; LS, moderately saline; MS, and severely saline; SS) by analyzing their anatomical morphological traits, nutritional components, and root differential metabolites through a combination of imaging and metabolomics technologies. Results showed that increased salt stress markedly enhanced leaf succulence, root vessel diameter, and epidermal thickness. Compared to NS treatment, leaf perimeter increased by 11.48, 28.29 and 47.94 %, respectively; root vessel diameter increased by 11.07, 24.39 and 14.31 % (p < 0.05). Root epidermal thickness increased by 24.34 and 109.37 % in MS and SS treatments, compared to NS treatment (p < 0.05). High salt stress disrupted leaf chloroplast and mitochondrial membranes, as indicated by malondialdehyde (MDA) increases of 32.45, 73.36 and 112.96 % in LS, MS and SS treatments (p < 0.05). Antioxidant enzyme activities (catalase; CAT, peroxidase; POD, superoxide dismutase; SOD) significantly increased in LS, MS, and SS treatments by 49.25–71.89 %, 90.64–278.86 %, and 12.94–116.37 %, respectively (p < 0.05). Elevated soil salinity increased sodium/potassium (Na/K) ratios by 223–518 % in roots, 215–330 % in stems, and 303–524 % in leaves; sodium/calcium (Na/Ca) ratios increased by 99–180 % in roots, 842–1810 % in stems, and 1111–2901 % in leaves. Additionally, root metabolic pathways associated with galactose/alanine, aspartate, and glutamate were markedly enhanced, leading to the upregulation of L-aspartate, β-alanine, glycine, galactinol, glycerol, and galactonic acid. Consequently, halophytes highlight their robust adaptive mechanisms by substantial morphological, physiological, and metabolic adjustments in response to salinity stress.