The Effects of Nitrogen Application on the Growth and Key Physiological Characteristics of Gardenia jasminoides J. Ellis Seedlings

Five-month-old Gardenia jasminoides cuttings were used as plant material, with urea (46% nitrogen content) as the nitrogen source. Four nitrogen application treatments were established: T₀ (0 g/plant), T₁ (0.2 g/plant), T₂ (0.6 g/plant), and T₃ (1.0 g/plant), To investigate the effects of different nitrogen application rates on the growth, physiological characteristics, and photosynthetic performance of Gardenia jasminoides. Nitrogen application rates significantly affected the growth and biomass accumulation of Gardenia jasminoides. The plants exhibited a unimodal response curve, where growth parameters and biomass production initially increased then decreased with elevating nitrogen supply. The optimal performance was observed under T₂, which achieved peak increments in plant height (65.70 cm), ground diameter (8.88 mm), and leaf area (45.52 cm²). The soluble sugar content in Gardenia jasminoides leaves under T₂ (0.6 g N/plant) was significantly higher than other nitrogen application levels; nitrogen application rates had no significant effect on soluble protein content in Gardenia jasminoides leaves. All nitrogen application treatments significantly increased chlorophyll a, chlorophyll b, and total chlorophyll content in Gardenia jasminoides leaves compared to CK. Photosynthetic parameters in Gardenia jasminoides leaves showed a unimodal response to increasing nitrogen application, peaking under T₁ (0.2 g/plant) and T₂ (0.6 g/plant) before declining at higher N levels. Pearson correlation analysis revealed a significant positive relationship between plant growth parameters and leaf soluble sugar content in Gardenia jasminoides, The principal component comprehensive evaluation results indicated that the T₂ yielded the optimal overall performance in Gardenia jasminoides. The T₂ (nitrogen application rate of 0.6 g/plant) was the most favorable nitrogen fertilization regime for Gardenia jasminoides growth, under which the photosynthetic characteristics of the leaves were optimal, accompanied by increased accumulation of soluble sugars and chlorophyll, thereby promoting the overall growth of Gardenia jasminoides.