Growth, Chlorophyll Fluorescence, and Mineral Nutrient Content of <italic>Pseudolysimachion nakaianum</italic> under Different Nitrogen Fertilization Levels

Background and objective: This study aimed to determine the optimal nitrogen fertilization level for <i>Pseudolysimachion nakaianum</i> by examining growth, mineral nutrient content, and chlorophyll fluorescence responses under different nitrogen application rates.Methods: Seedlings of <i>P. nakaianum</i> were transplanted, and nitrogen was applied at rates of 0, 2.5, 5, 10, and 20 kg·10a⁻¹. Plant height, number of leaves, leaf length and width, number of lateral branches, and fresh and dry weights of shoots were measured to evaluate growth. In addition, mineral nutrient contents in leaves and chlorophyll fluorescence parameters were analyzed.Results: Nitrogen application at 10-20 kg·10a⁻¹ significantly increased plant height, leaf length and width, number of leaves, number of lateral branches, and fresh and dry weight of shoots. Regression analysis between nitrogen fertilization levels and growth indicated that the optimal nitrogen rate was approximately 15–20 kg·10a⁻¹. As the nitrogen fertilization level increased, nitrogen and phosphorus contents in the leaves increased, whereas potassium content decreased. Compared with the control, plants treated with 10–20 kg·10a⁻¹ nitrogen showed higher Fv/Fo, Fv/Fm, Pi_ABS, ETo/ABS, and ETo/TRo values and lower ABS/RC and DIo/RC values, indicating that photochemical efficiency and energy utilization capacity were maintained at a stable level.Conclusion: <i>P. nakaianum</i> shows high sensitivity to nitrogen deficiency, which markedly reduces growth and photosynthetic function. Nitrogen application at 15–20 kg·10a⁻¹ effectively promoted growth and enhanced photosynthetic performance. Therefore, 15–20 kg·10a⁻¹ can be proposed as an appropriate nitrogen fertilization standard for <i>P. nakaianum</i>.