Effects of salt stress on the growth and physiology of Apocynum venetum

Apocynum venetum is a typical native halophyte in the saline-alkali areas of North China. It increases the utilization efficiency of saline-alkali land owing to its high salt tolerance and economic value. We conducted a pot experiment to analyze the growth and physiological response of A. venetum under different soil salinity (3.0, 6.0, and 9.0 g·kg⁻¹) to clarify the effects of salt stress on the growth of A. venetum. The results showed that the increase in soil salt content significantly decreased the branch length and biomass of A. venetum. In addition, the fresh weight, dry weight, and water content of the whole plant, as well as the leaf water potential, net photosynthesis rate (P_n), and stomata conductivity (C_i), significantly decreased (P < 0.05) under salt stress. Under salt stress, Ca²⁺, Na⁺, and Cl⁻ contents of the leaf increased, whereas K⁺ content and the K⁺/Na⁺ ratio significantly decreased (P < 0.05). The root proline content of the plant under salt stress was significantly higher than that of the control plant. These results suggest that the growth of A. venetum was inhibited by salt stress. In mild saline soil, the growth of A. venetum decreased significantly, but the changes in physiological parameters were not significant. In moderately saline soil, Na⁺ accumulation and osmotic adjustment substances in the leaf increased. Although A. venetum survived in the heavily saline soil, the growth was slow. These results may provide a reference for the cultivation of A. venetum in coastal saline lands.