In order to explore the growth and physiological response mechanism of Gleditsia japonica var delavayi seedlings under different ratios of nitrogen, phosphorus and potassium fertilization, and to establish the best fertilization technology scheme for Gleditsia japonica var delavayi seedlings, so as to provide theoretical basis for its seedling raising.

In this study, 2-month-old Gleditsia japonica var delavayi seedlings were used as the research object, The application rates for N₀, N₁, N₂, and N₃ are 0 g/plant, 2.8 g/plant, 5.6 g/plant, and 8.4 g/plant, respectively; for P₀, P₁, P₂, and P₃ are 0 g/plant, 0.7 g/plant, 1.4 g/plant, and 2.1 g/plant, respectively; and for K₀, K₁, K₂, and K₃ are 0 g/plant, 1.4 g/plant, 2.8 g/plant, and 4.2 g/plant, respectively. The effects of different nitrogen, phosphorus and potassium ratio fertilization on six physiological indexes of superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), proline (Pro), soluble protein (SP) and soluble sugar (SS) and three growth indexes of plant height, ground diameter and dry weight of Gleditsia japonica var delavayi seedlings were studied.

Compared with the control group, reasonable fertilization could significantly promote the growth and physiological activity of G. yunnanensis seedlings. Under the ratio of fertilization, the overall performance is the strongest dependence on P fertilizer; in the interaction effect, the PK interaction further confirmed the promotion effect of appropriate nitrogen fertilizer on seedling growth, the NP interaction may affect root development, and P fertilizer has a significant effect on ground diameter and dry weight distribution. Under physiological stress, the contents of MDA and SS increased significantly, while the contents of SOD, CAT, Pro and SP decreased. N₂K₁ (Medium nitrogen and low potassium) fertilization combination showed good results in many physiological indexes. N fertilizer can improve the antioxidant capacity and osmotic adjustment substance content of plants, and P fertilizer has a greater impact on SP. Except MDA and SS decreased first and then increased with the increase of N, P and K fertilization, the other indexes increased first and then decreased with the increase of N, P and K fertilization. Excessive fertilization (N₃P₂K₂, N₂P₃K₂, N₂P₂K₃) significantly inhibited seedling growth.

Reasonable fertilization can enhance the growth and physiological and biochemical processes of Gleditsia japonica var delavayi seedlings, and low nitrogen, medium phosphorus and low potassium (N₁P₂K₂) treatment is the best fertilization scheme for its seedlings. According to the fitted quadratic equation, the optimum nitrogen, phosphorus and potassium application rates of Gleditsia japonica var delavayi seedlings were 3.2 g/plant, 1.6 g/plant and 2.2 g/plant, respectively.