Objective This study aimed to elucidate the mitigating effects and regulatory mechanisms of exogenous salicylic acid (SA) and abscisic acid (ABA) on Buddleja alternifolia seedlings under salt stress, in order to provide theoretical and technical support for the cultivation of this species in saline-alkali areas.

Method Seedlings of B. alternifolia 'Ningxia Zihua' were used as experimental materials. Salt stress was induced by applying 1.2% Na₂SO₄ under hydroponic conditions. Foliar sprays of SA at 0.2, 0.5, and 1.0 mmol/L and ABA at 25, 50, and 100 μmol/L were then applied. A salt-free control (CK1) and a salt-stressed control (CK2) were also included. After two weeks, the activities of antioxidant enzymes, contents of osmotic adjustment substances, photosynthetic parameters, and chlorophyll fluorescence parameters were measured in the leaves. Principal component analysis (PCA) was used for dimensionality reduction, and the mitigation effects were comprehensively evaluated using the membership function method.

Result Salt stress caused significant damage to the seedlings. Compared with CK1, the CK2 group showed significant increases in superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities by 93.96%, 235.97%, and 96.57%, respectively; malondialdehyde (MDA) content increased by 132.99%; net photosynthetic rate (Pn) decreased by 33.88%; and the maximum photochemical efficiency of photosystem Ⅱ (Fv/Fm) and effective photochemical efficiency (Fv'/Fm') decreased by 6.82% and 19.74%, respectively, indicating severe damage to the membrane and photosynthetic systems of the seedings. Exogenous SA and ABA exhibited concentration-dependent mitigation effects, with low to medium concentrations enhancing stress resistance. The best effect was observed with 50 μmol/L ABA: compared with the CK2 group, SOD, POD, and CAT activities increased significantly by 16.94%, 43.50%, and 17.24%, respectively; soluble sugar (SS), soluble protein (SP), and proline (Pro) contents increased by 18.13%-54.01%; MDA content decreased by 28.32%; and Pn and Fv/Fm increased by 35.22% and 4.88%, respectively, indicating notable recovery of photosynthetic and photochemical efficiency. PCA extracted three principal components with a cumulative contribution rate of 94.10%, among which antioxidant factors accounted for the highest proportion. The membership function evaluation further confirmed ABA 50 μmol/L as the optimal treatment.

Conclusion Both SA and ABA can alleviate salt stress by activating the antioxidant system, enhancing osmotic adjustment, and restoring photosynthetic function. Among the treatments, foliar application of 50 μmol/L ABA showed the strongest mitigation effect and can be recommended as a core technique for the cultivation of B. alternifolia in saline-alkali regions.