Abstract: We explored the seedlings growth and utilization and distribution characteristics of ¹⁵N and ¹³C in one-year-old potted Robinia pseudoacacia seedlings under different concentrations(0、0.15%、0.3%、0.45%)salt stress using the isotope tracer technology. The results showed that soil salt stress significantly reduced the relative high growth rate, relative ground diameter growth rate, root activity and carbon and nitrogen uptake. Specific root length and specific root surface area, root biomass ratio and root shoot ratio increased significantly. In different organs, the distribution rates of ¹⁵N and ¹³C in roots under salt stress were significantly higher than those of the control. Correlation analysis showed that the relative growth rates of ground diameter and seedling height were positively correlated with root vitality, stem biomass ratio, leaf uptake of ¹⁵N, stem ¹³C and leaf ¹³C, but negatively correlated with root biomass ratio and root-shoot ratio. The root biomass ratio and root-shoot ratio were significantly positively correlated with root ¹⁵N allocation rate, and negatively correlated with leaf biomass ratio, leaf ¹⁵N allocation rate and stem ¹³C uptake. Salt stress significantly inhibited the growth of Robinia pseudoacacia seedlings and significantly reduced the carbon and nitrogen absorption capacity. Carbon and nitrogen were preferentially allocated to roots, and the root biomass ratio and root-shoot ratio increased with the change of carbon uptake and nitrogen allocation rate. The allocation of root biomass and the regulation of carbon and nitrogen among organs of Robinia pseudoacacia seedlings are important ways for Robinia pseudoacacia seedlings to adapt to salt stress.

Key words: Robinia pseudoacacia, salt stress, ¹⁵N, ¹³C, absorption, distribution