Abstract:

In this study， we selected three typical Chenopodiaceae annuals （Bassia dasyphylla， Salsola ruthenica， and Halogeton arachnoideus） that grow in a typical desert-oasis ecotone in the Hexi Corridor and determined their responses to salt stress. We investigated the effects of different concentrations of salts （NaCl and NaHCO₃， 0， 50， 100， 150 and 200 mmol·L^-1） on their seed germination， seedling growth， and physiological characteristics. The results showed that： 1） Sodium salt stress significantly inhibited the seed germination and seedling growth of all three species. At the seed germination stage， the germination rate， germination power， and germination index decreased with increasing salt concentrations， but the seeds of all three species were able to recover germination after the removal of salt stress. At the seedling growth stage， the plant height， main root length， and fresh weight decreased with increasing salt concentrations. 2） The salts clearly affected the physiological characteristics of the three Chenopodiaceae annuals. As the concentration of the salts increased， the chlorophyll content of three plants showed a downward trend， while the malonaldehyde content showed an upward trend， and the free proline and soluble sugar contents initially increased and then decreased. Among these parameters， chlorophyll content was particularly important for seedling growth. 3） Under mild （50 mmol·L^-1） and moderate （100， 150 mmol·L^-1） salt stress conditions， the three plants adapted mainly through osmotic adjustment， and the contents of soluble sugars and free proline increased significantly to improve the water holding capacity and maintain normal plant growth through cell osmotic regulation. Under severe salt stress （200 mmol·L^-1）， the malonaldehyde content increased rapidly， chlorophyll decomposed more rapidly， osmotic adjustment was weakened， and there was a clear inhibitory effect of salts on plant growth. 4） In terms of individual adaptation strategies to severe salt stress， the three Chenopodiaceae annuals adapted to salt stress by reducing the distribution of resources to the roots and significantly decreasing the root∶shoot ratio. 5） Compared with NaCl， the alkaline salt NaHCO₃ had stronger negative effects on the three Chenopodiaceae annuals. In addition， there were significant differences in the salt tolerance of different species among different growth stages. The species were ranked， from most to least salt tolerant， as follows： H. arachnoideus>B. dasyphylla>S. ruthenica.

Key words: alkaline salt, neutral salt, Chenopodiaceae annuals, osmotic adjustment, growth tradeoff, growth stages