Effects of Different Nitrogen Treatments on the Growth and Nitrogen Metabolism of Machilus thunbergii Seedlings

Fenghou Shi^1*灏怡 冯¹晓菁 李¹亚楠 白²仪增 鲁^3*伯强 仝³于卉 张^2*

• ¹Nanjing Forestry University, Nanjing, China
• ²Shanghai Forestry General Station, Shanghai, China
• ³Shandong Provincial Center of Forest and Grass Germplasm Resources, Jinan, China

Machilus thunbergii is highly responsive to nitrogen fertilization, yet related studies are scarce. This research seeks to elucidate how different nitrogen fertilizers affect its growth and nitrogen metabolism across different growth stages, thereby determining the most suitable type and establishing a scientific foundation for its fertilization. Methods: This study aims to investigate the effects of topdressing with different nitrogen fertilizers on the growth and nitrogen metabolism of M. thunbergii seedlings. The 3-year-old M. thunbergii seedlings were used as the material, and the fertilization rate was 3g per seedling. The experiment was conducted in a one-way randomized block design with 4 treatments, including the control treatment and 3 nitrogen fertilizer treatments: urea (amide nitrogen fertilizer), ammonium sulfate (ammonium nitrogen fertilizer), and sodium nitrate (nitrate nitrogen fertilizer). Since the experiment began, the branch and leaf morphology, height growth, and basal diameter growth of seedlings in each treatment have been monitored periodically, and the activities of nitrogen-metabolizing enzymes, such as nitrate reductase, glutamine synthetase, glutamate synthetase, and glutamate dehydrogenase, in the leaves have been measured. At growth cessation, all treatments were evaluated for biomass production, root morphological characteristics, and total nitrogen content in different plant parts (roots, stems, and leaves). Results: Due to the high nitrogen content in the cultivation substrate, the application of different nitrogen fertilizers induced varying levels of fertilizer injury. Temporal analysis revealed that the growth inhibition was not uniform across stages. While all nitrogen treatments ultimately suppressed overall height and diameter growth compared to the control, the timing and intensity of these effects varied. For instance, urea treatment initially showed less inhibition, whereas sodium nitrate treatment consistently exhibited the strongest inhibitory effect throughout the experiment. Similarly, the promotion of nitrogen metabolism enzyme activity by different fertilizers also displayed distinct temporal patterns, with peaks occurring at different measurement points. Conclusion: All three nitrogen treatments significantly influenced both growth and physiological indices of M. thunbergii seedlings. Among the nitrogen fertilizers tested, urea proved superior at the application rate of 3 g per plant for three-year-old M. thunbergii seedlings.