Role of Endogenous Hormone Dynamics in Regulating the Development of Suaeda salsa L. Under Salt Stress

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.