Effects of combined application of compound fertilizer and biofertilizer on the growth of Phoebe bournei seedlings and non-structural carbohydrates

To investigate the effects of different fertilization treatments on the growth and physiology of Phoebe bournei seedlings, and to provide a theoretical basis for developing scientific fertilization strategies to cultivate high-quality seedlings that are both tall and robust, thereby improving afforestation survival rates.

Two-year-old Phoebe bournei seedlings were used as experimental materials. A factorial design was employed with four compound fertilizer levels (0, 4, 8, 16 g per seedling) and four bio-fertilizer levels (0, 5, 10, 20 g per seedling), forming 16 treatment combinations. Seedling height, ground diameter, biomass, chlorophyll content, soluble protein content, as well as soluble sugar and starch contents in various plant parts (leaves, branches, roots) were measured. Multiple comparisons and correlation analysis were used to systematically study the effects of fertilization on seedling growth and NSC accumulation and allocation.

Fertilization significantly promoted the growth of Phoebe bournei seedlings. Treatments T6 (4 g compound fertilizer + 10 g bio-fertilizer) and T7 (4 g compound fertilizer + 20 g bio-fertilizer) showed the most pronounced increases in seedling height, ground diameter, and biomass. The medium fertilizer group overall exhibited the best comprehensive promotion effect, resulting in seedlings with suitable height-to-diameter and shoot-to-root ratios, while maintaining high seedling quality indices and overall growth coordination. Therefore, the combined application of 4-8 g compound fertilizer combined with 10-20 g biofertilizer is recommended to achieve both quality improvement and efficient NSC accumulation in Phoebe bournei seedlings. Correlation analysis indicated widespread correlations among seedling height, ground diameter, soluble protein, chlorophyll, biomass, and NSC contents in different parts. Main effect analysis revealed that compound fertilizer had a strong main effect, enhancing most indicators including seedling height, ground diameter, total biomass, and seedling quality index. Bio-fertilizer had a relatively weaker main effect but was particularly prominent in promoting NSC accumulation in roots and branches.

The combined application of compound fertilizer and biofertilizer is recommended to balance rapid growth and NSC accumulation in Phoebe bournei seedlings, shorten the growth cycle, and enhance stress resistance. This study provides support for supplying high-quality seedlings for the establishment of Phoebe bournei plantations and the restoration of wild populations.