Experimental evidence from Suaeda glauca explains why the species is not naturally distributed in non-saline soils

Euhalophytes are not naturally distributed in non-saline areas. However, the reason for this is unclear. Seed germination, seedling emergence and plant tolerance to salt were evaluated in the euhalophyte Suaeda glauca. One population occurs in saline soils (SS), and another has been cultivated in non-saline soils (NSS) for more than 20 years. A total of 500 mM NaCl had a greater adverse effect on seed germination and seedling emergence of brown seeds in S. glauca from NSS compared with those from SS. The seedlings grown from brown seeds collected from NSS were uniform and dwarf, but this was not the case for the seedlings from SS. The salt tolerance of seedlings from NSS did not significantly differ from those from SS, as judged by such factors as the shoot dry weight and contents of leaf Na⁺ and K⁺. The concentrations of phytohormones, such as abscisic acid, methyl jasmonate, gibberellin 3 and 4, zeatin riboside, brassinolide, indole acetic acid, and indole-3-propionic acid, in the leaves of seedlings from NSS were generally lower than those from SS under different concentrations of NaCl. In conclusion, salts are not strictly required for the growth of S. glauca. The reason why typical euhalophytes, such as S. glauca, are not found in non-saline areas is probably because the seedlings grown in NSS become dwarf and uniform, thus, weakening their ability to compete with glycophytes in non-saline habitats.