Calcium : Magnesium Ratio Affects Environmental Stress Sensitivity in the Serpentine-Endemic \u3ci\u3eAlyssum inflatum\u3c/i\u3e (Brassicaceae)

Plants endemic to serpentine soils are adapted to harsh environmental conditions typical of those soils, particularly, low (\u3c1) calcium (Ca) : magnesium (Mg) ratios. We compared survival of two perennial Alyssum species native to Iran under experimental manipulations of Ca : Mg ratio, including when Ca : Mg ratio was varied under conditions of high ammonium concentration and heat stress. Alyssum inflatum is a serpentine endemic capable of nickel (Ni) hyperaccumulation, whereas A. lanceolatum is found on non-serpentine soils and is not known to hyperaccumulate Ni. We grew plants of both species under four Ca : Mg ratios (0.4, 2, 20, 40) and tested survival when plants were exposed to elevated ammonium levels (0, 1 and 4 mM) and heat stress (control conditions vs a 5-h 36°C treatment daily for 5 days). Alyssum lanceolatum was more tolerant of Ca : Mg ratio variation (100% survival in all treatments), whereas A. inflatum survival was maximum at Ca : Mg = 2, reduced at Ca : Mg = 0.4, and very low for Ca : Mg ratios of 20 and 40. Alyssum lanceolatum also tolerated ammonium and heat stress, whereas survival of A. inflatum declined at higher Ca : Mg ratios when subjected to both stresses. We conclude that at higher Ca : Mg ratios, the serpentine endemic has reduced tolerance for these environmental stresses and may be more susceptible to human-driven climate change-associated stressors than the non-serpentine species