Abstract: Secretohalophyte Atriplex canescens is a C₄ perennial shrub with excellent resistance to salinity and drought. Our previous study showed that the transport of excessive Na⁺ into leaf salt bladders and contribution of the elevated Na⁺ concentration to leaf osmotic potential (Ψ_s) improves water status of plants and is a primary strategy in salt tolerance of A. canescens. The external application of 100 mmol·L^-1 NaCl can substantially stimulate the growth of A. canescens. To investigate whether NaCl could help to alleviate deleterious impacts of osmotic stress on the growth of A. canescens, five-week-old seedlings were subjected to two osmotic stress levels (-0.2 and -0.5 MPa) induced by D-sorbitol in the presence or absence of an additional 100 mmol·L^-1 NaCl. It was found that under osmotic stress, the addition of NaCl obviously improved the growth of A. canescens. Leaf relative water content was increased, net photosynthetic rate was enhanced and significantly more negative Ψ_s was induced. Furthermore, exogenous NaCl significantly increased Na⁺ concentration in stem, leaf tissues and leaf salt bladders as well as enhancing the Na⁺ contribution to leaf Ψ_s, with little adverse effect on K⁺ accumulation in stem and leaf tissues. In addition, the content of free proline and betaine in plants was significantly increased in the presence of NaCl under osmotic stress, and their contributions to leaf Ψ_s were significantly increased by additional NaCl under osmotic stress. This suggests that compatible solutes, in addition to functioning as protectants, are also involved in osmotic adjustment to further alleviate the deleterious impacts of osmotic stress. In summary, the appropriate concentration of NaCl does effectively alleviate the adverse impacts of osmotic stress on the growth of A. canescens.

Key words: Atriplex canescens, halophyte, osmotic stress, NaCl, osmotic adjustment