To investigate the differences in the response of Euscaphis japonica and Euscaphis konishii seedlings to salt stress, providing a theoretical basis for the development and utilization of plants in the genus Euscaphis.

The growth differences between seedlings of the two tree species were compared under different concentrations of neutral salt (NaCl) and alkaline salt (NaHCO₃). Key metabolites and metabolic pathways related to salt stress response were identified using liquid chromatography-mass spectrometry (LC-MS) technology.

Salt stress significantly inhibited the seedling height, ground diameter increment, and biomass of both tree species. These indicators gradually decreased as the salt concentration increased. The negative effects of NaHCO₃stress on the seedlings of both species were significantly greater than those of NaCl stress. Metabolomic analysis revealed that salt stress significantly altered the metabolism of Euscaphis japonica and Euscaphis konishii seedlings. Under NaHCO₃ treatment, the total number of differentially accumulated metabolites (DAMs) and the number of downregulated DAMs in Euscaphis japonica seedlings were higher than those under other treatments. In contrast, the total number of DAMs in Euscaphis konishii seedlings under NaCl treatment was lower than that in Euscaphis japonica, but the number of upregulated DAMs was higher. The DAMs in both species under salt stress were primarily composed of phenylpropanoids, polyketides, organic acids and derivatives, lipids and lipid-like molecules, organic oxygen compounds, and organic heterocyclic compounds. These DAMs were significantly enriched in three metabolic pathways: phenylpropanoid biosynthesis, flavonoid biosynthesis, and riboflavin metabolism. Specifically, the differences in the accumulation of metabolites related to the phenylpropanoid biosynthesis and flavonoid biosynthesis pathways reflected the variability in how the two tree species responded to different types of salt stress.

The two species exhibited different metabolic response strategies under salt stress, with the phenylpropanoid and flavonoid biosynthesis pathways closely associated with the mechanisms by which Euscaphis japonica and Euscaphis konishii seedlings respond to salt stress.