Effects of Combined Application of N, P and K on the Content of Endogenous Hormones of Leaves in the Seedlings of Osmanthus fragrans var. aurantiacus

According to an orthogonal experimental design using L9(3³), 3 factors (nitrogen, phosphorus, and potassium fertilizer) were set at 3 levels (N application rates of 0, 5, and 10 g per plant; P₂O₅ application rates of 0, 2, and 4 g per plant; KCl application rates of 0, 3, and 6 g per plant). The experiment on 'Pucheng Dangui' seedlings involved 2 rounds of nitrogen, phosphorus, and potassium combinations with a 30-day interval. The enzyme-linked immunosorbent assay(ELISA) method was used to measure the content of 4 hormones indole-3-acetic acid(IAA), abscisic acid(ABA), gibberellic acid(GA₃), and zeatin riboside(ZR) in the leaves after 60, 120, 180, and 240 days of the second fertilization. The results showed that N₅P₀K₃ treatment significantly increased the content of IAA, ABA, and ZR, reaching their peak values at 240 days after fertilization(139.90, 157.79, and 14.86 ng/g, respectively). Compared to the control group(CK), these levels increased by 101.52%, 36.79%, and 73.08%, respectively. N₅P₂K₆ treatment significantly increased the content of GA₃, reaching its highest value(13.57 ng/g) at 240 days after fertilization, which was 97.71% higher than the CK group. N₅P₀K₃ treatment significantly increased the ABA/GA₃ and ZR/GA₃ ratios, while significantly decreasing the ABA/IAA and ZR/IAA ratios. The effects of nitrogen and potassium factors on the content of IAA, GA₃, ABA, and ZR differed significantly, while the phosphorus factor only showed a significant difference in the content of GA₃. The combined application of nitrogen, phosphorus, and potassium had a significant impact on the endogenous hormone content and homeostasis in the leaves of 'Pucheng Dangui' seedlings. Based on variance and range analysis, the optimal fertilization scheme to increase leaf IAA, GA₃, and ZR content was N₅P₂K₆, while the optimal scheme to increase leaf ABA content was N₅P₀K₃.