Halophytic resilience in extreme environments: adaptive strategies of Suaeda schimperi in the Red Sea's hyper-arid salt marshes

<i>Suaeda schimperi</i>, a halophyte native to the Red Sea’s hyper-arid salt marshes, thrives in its extreme conditions (high salinity, minimal rainfall, and elevated temperatures). However, its adaptive tolerance mechanisms to these harsh conditions remain unclear. Herein, we investigated its growth responses and physiological mechanisms after short (5 days after treatment; DAT) and long-term (15 DAT) exposure to 0, 100, 200, and 400 mmol NaCl. Moderate salinity (200 mmol NaCl) enhanced growth, inducing 103.2% (5 DAT) and 40% (15 DAT) higher leaf biomass and 43.33% and 59.6% higher root biomass, respectively, compared to non-saline conditions. Deviation from moderate salinity reduced growth and disrupted ion balance, lowering K⁺, raising Na⁺, and increasing the Na⁺/K⁺ ratio, particularly under high salinity. The moderate salinity-enhanced growth was associated with increased chlorophyll, glycine betaine, glutathione, betacyanin, and betaxanthin, as well as higher antioxidant enzyme activity (polyphenol oxidase, peroxidase, catalase, ascorbate, and peroxidase) at 5 DAT. At 15 DAT, sugar accumulation and unsaturated fatty acids increased, while malondialdehyde and saturated fatty acids decreased. These findings reveal multiple adaptive strategies that support <i>S. schimperi’s</i> physiological stability under extreme environments and highlight its significance in ecological restoration and breeding salt-tolerant crops under escalating soil salinisation and climate change.