Exogenous Sodium and Calcium Alleviate Drought Stress by Promoting the Succulence of Suaeda salsa

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 SO₄^2-) 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 SO₄^2-. 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.