Physiological Adaptation of Three Wild Halophytic Suaeda Species: Salt Tolerance Strategies and Metal Accumulation Capacity

Understanding salt tolerance mechanisms in halophytes is critical for improving the world’s agriculture under climate change scenarios. Herein, the physiological and metabolic responses of Suaeda monoica, Suaeda vermiculata, and Suaeda schimperi against abiotic stress in their natural saline environment on the east coast of the Red Sea were investigated. The tested species are exposed to different levels of salinity along with elemental disorders, including deficiency in essential nutrients (N&P in particular) and/or elevated levels of potentially toxic elements. The tested species employed common and species-specific tolerance mechanisms that are driven by the level of salinity and the genetic constitution of Suaeda species. These mechanisms include: (i) utilization of inorganic elements as cheap osmotica (Na+ in particular), (ii) lowering C/N ratio (S. monoica and S. schimperi) that benefits growth priority, (iii) efficient utilization of low soil N (S. vermiculata) that ensures survival priority, (v) biosynthesis of betacyanin (S. schimperi and S. vermiculata) and (vi) downregulation of overall metabolism (S. vermiculata) to avoid oxidative stress. Based on their cellular metal accumulation, S. monoica is an efficient phytoextractor of Cr, Co, Cu, Ni, and Zn, whereas S. vermiculata is a hyper-accumulator of Hg and Pb. S. schimperi is an effective phytoextractor of Fe, Hg, and Cr. These results highlight the significance of Suaeda species as a promising model halophyte and as phytoremediators of their hostile environments.