Dong Zhang

Soil salinization severely constrains agricultural productivity and ecosystem sustainability. Suaeda salsa L. is a representative halophyte and demonstrates strong adaptability and potential for saline–alkali land restoration. To elucidate its physiological responses to salt stress, pot experiments were conducted under four salinity levels, namely CK (0 mM NaCl), LS (800 mM NaCl), MS (1600 mM NaCl), and HS (2400 mM NaCl), with 20 replicates per treatment, and the dynamics of endogenous hormone were analyzed using targeted metabolomics. The soil salinity levels were prepared by adding NaCl solutions of different molarities to achieve the desired salinity treatments. Results showed that low to moderate salinity (CK-LS: 0–800 mM) promoted growth performance, whereas higher salinity (HS: 2400 mM) significantly inhibited biomass accumulation, plant height, and stem diameter (p < 0.01). Salinity markedly affected nutrient accumulation in Suaeda salsa, with Na increasing up to 222%, K decreasing by 17–33%, Ca by 7–21%, Mg by 35–46%, and S by 45–56% across growth stages, while Fe remained unchanged. Under increasing salinity, stress-related hormones such as abscisic acid, jasmonic acid, salicylic acid, and indole derivatives were upregulated, while gibberellins decreased markedly. Zeatin and its derivatives showed significant increases under MS (p < 0.01). Correlation analysis indicated positive associations of abscisic acid and zeatin with growth traits, and negative correlations for gibberellins (R > 0.6). These findings suggest that Suaeda salsa adapts to saline conditions by modulating hormone-mediated ion balance, osmotic regulation, and defense metabolism, thereby optimizing growth and biomass allocation under salt stress.

Succulence is a key trait involved in the response of Suaeda salsa to salt stress. However, few studies have investigated the effects of the interaction between salt and drought stress on S. salsa growth and succulence. In this study, the morphology and physiology of S. salsa were examined under different salt ions (Na⁺, Ca²⁺, Mg²⁺, Cl⁻, and SO₄²⁻) and simulated drought conditions using different polyethylene glycol concentrations (PEG; 0%, 5%, 10%, and 15%). The results demonstrate that Na⁺ and Ca²⁺ significantly increased leaf succulence by increasing leaf water content and enlarging epidermal cell size compared to Mg²⁺, Cl⁻, and SO₄²⁻. Under drought (PEG) stress, with an increase in drought stress, the biomass, degree of leaf succulence, and water content of S. salsa decreased significantly in the non-salt treatment. However, with salt treatment, the results indicated that Na⁺ and Ca²⁺ could reduce water stress due to drought by stimulating the succulence of S. salsa. In addition, Na⁺ and Ca²⁺ promoted the activity of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), which could reduce oxidative stress. In conclusion, Na⁺ and Ca²⁺ are the main factors promoting succulence and can effectively alleviate drought stress in S. salsa.