Abstract: [Objective] This study investigated the salt tolerance of seedlings of two blueberry (Vaccinium corymbosum) cultivarsunder different NaCl concentrations, to reveal the mechanism of salt adaptation, and to provide basis for the selection and rational cultivation of salt tolerant blueberry cultivars.[Method]Two cultivars (the northern highbush blueberry ‘bluecrop’ and the southern highbus blueberry ‘O'Neill’) were selected as testing materials. The two-year-old cutting seedlings were treated with NaCl concentrations of 0, 100, 200, and 300 mmol·L^-1 for 40 days in apot experiment, respectively. Subsequently, the dry matter accumulation, leaf damage, and the variation of ions (Na⁺, K⁺, Ca²⁺, Mg²⁺ and Cl^-) contentwere analyzed. The accumulation, transportation and distribution of these ions in different organs were investigated.[Results] The results can be summarized as 1) The dry weight gradually reduced in all organs of both cultivars with the increase of NaCl concentration. The dry weight of "bluecrop" did not significantly decrease in low salt concentration (100 mmol·L^-1) but the reduction became more remarkably with high salt concentration (200-300 mmol·L^-1) treatments. The dryweight of ‘O'Neill’ under the NaCl treatment was significantly lower than that of the control. The salt stress index (SI) of ‘bluecrop’ and ‘O'Neill’ increased with the increase of NaCl concentration, and the SI of the former was lower than that of the latter. 2) For both blueberry cultivars under salinity stress, the content of Na⁺ and Cl^- in all organs prominently increased, whereas the content of K⁺ in all organs, Ca²⁺ and Mg²⁺ in roots, and Mg²⁺ in stem decreased. Moreover, the accumulation of Na⁺ and Cl^-in leaves was more efficient than that in stem and roots. Comparing the salt-treated seedlings with the control of the two cultivars respectively, the content of Ca²⁺ in stem of ‘O'Neill’ did not significantly differ between them, but salt-treated ‘bluecrop’ was obviously higher than the control. For both species, the contents of Ca²⁺ and Mg²⁺ in leaves exhibited insignificant changes under salt stress. Comparisons were performed for these two cultivars, the contents of Na⁺ and Cl^-in stem and leaves of ‘O'Neill’, and the content of Cl^- in roots of ‘O'Neill’ was higher than that of ‘bluecrop’, but the content of Mg⁺ in all organs of ‘bluecrop’ was higher than that of ‘O'Neill’. 3) Under salt stress, the K⁺/Na⁺,Ca²⁺/Na⁺ and Mg²⁺/Na⁺ ratios of two cultivars considerably decreased compared with the control. Higher ionic ratios could be observed within the leaves of ‘bluecrop’ compared to ‘O'Neill’ under high salt concentrations. 4) Undersalt stress, the ion selective transport capacity from root to stem for both cultivars was substantially enhanced compared to the control, whereas the transport capacity from stem to leaves and from root to leaves of both cultivars was less facilitated than that in the control. More specifically, transport capacity from root to leaves (S_K⁺,Na⁺ and S_{Mg²⁺,Na⁺}) exhibited higher values for ‘bluecrop’ compared to ‘O'Neill’.[Conclusion] The low salt stress has little effect on the growth of ‘bluecrop’ seedlings but a significant effect on that of ‘O'Neill’. However, high salt stress have adverse effects on both blueberry cultivars seedlings. Under salt stress, accumulation of Na⁺ and Cl^- is less in ‘bluecrop’ compared to ‘O'Neill’, whereas the content of Mg²⁺ in all organs of ‘bluecrop’ is higher than that of ‘O'Neill’. Moreover, the capabilities of maintaining the balance of ions in the plant and ion-selective transportation of K⁺ and Mg²⁺ from root to leaves of ‘bluecrop’ are better than that of ‘O'Neill’, which can be used to explain why ‘bluecrop’ exhibits a stronger tolerance to salt than "O'Neill".

Key words: NaCl stress, Vaccinium corymbosum, ion homeostasis, absorption, growth