Effects of Combined Application of Nitrogen and Phosphorus on the Growth and Root Morphology of Phoebe bournei Container Seedlings

In order to investigate the effects of single fertilization and nitrogen-phosphorus dosing on the growth and root morphology of Phoebe bournei container seedlings, 8 treatments were set up, namely, control, low level nitrogen application, conventional nitrogen application, high level nitrogen application, phosphorus application, low level nitrogen + phosphorus, conventional nitrogen + phosphorus, high level nitrogen + phosphorus. The effects of different fertilization treatments on the growth and root morphology of P. bournei container seedlings were determined, and the differences between nitrogen and phosphorus fertilization and single fertilization were compared. The results showed that the seedling height, diameter, relative growth rate, biomass, and quality index of seedlings were better than single application of nitrogen in the case of nitrogen and phosphorus fertilization. With the increase of fertilizer application, the seedling height, ground diameter, relative growth rate of seedling height, and seedling quality index of P. bournei container seedlings showed a tendency of increasing and then decreasing, which reached the maximum under the conventional nitrogen + phosphorus application treatment. The accumulation of biomass in general showed a trend that the aboveground biomass was greater than the belowground biomass, and the underground portion, aboveground portion, and total biomass also showed the same trend of first increasing and then decreasing, and also reached the maximum under the conventional application of nitrogen + phosphorus, which were 0.34 g, 1.59 g, and 1.93 g, respectively. Under the single application of phosphorus, the root-crown ratio, total root length, surface area of root, root volume, and the average diameter of the root system were all better than single application of nitrogen and nitrogen-phosphorus combination. The root-crown ratio of P. bournei container seedlings reached a maximum of 0.43 under single phosphorus application, and the total root length, root surface area, root volume and average diameter of the root system also reached a maximum under this treatment, which were 309 cm, 119.98 cm², 4.03 cm³ and 1.28 mm, respectively, and 1.6, 3.36, 7.73 and 2.13 times higher than those of the control. Overall, reasonable fertilization had a significant promotion effect on the growth of P. bournei container seedlings, and the promotion effect of phosphorus on the growth of root system was very obvious. Too low fertilization would form a limitation on the growth of seedlings, while too high would cause inhibition, both of which were unfavorable to the growth of seedlings. Seedling height, ground diameter, relative growth rate of seedling height, biomass, and seedling quality index under nitrogen-phosphorus dosing were better than those under single application of nitrogen, and reached the maximum in the treatment of (nitrogen fertilization of 4760 mg/plant + phosphorus fertilization of 2000 mg/plant) as a whole; the root-crown ratio and root growth development under single application of phosphorus treatment were the best.