To explore the effects of different nitrogen application rates on the growth of transplanted seedlings of Phoebe neurantha (Hemsl.) Gamble cv. ‘Fengweinan’ Y.J. Fei, and to provide a theoretical basis for the efficient utilization of exogenous nitrogen in transplanted seedlings of this cultivar.

A pot experiment was conducted to compare the performance of one-year-old bare-root transplanted seedlings (L) and soil-root-ball transplanted seedlings (T) under five nitrogen application gradients: 0 (CK), 100 (ZN1), 200 (ZN2), 300 (ZN3), and 400 mg/plant (ZN4). The aim was to determine the optimal nitrogen application rate for transplanted ‘Fengweinan’ seedlings.

For bare-root transplanted seedlings (L), the total root length reaches its peak at ZN2, which is 81% higher than that of the control (CK). For soil-root-ball transplanted seedlings (T), multiple growth indicators are optimal at ZN3: plant height, ground diameter, total root length, and leaf length are significantly increased by 29%, 56%, 102%, and 103% compared with CK, respectively. The photosynthetic pigment content of both types of transplanted seedlings first increases and then decreases with the increase of nitrogen application rate. For bare-root transplanted seedlings, the photosynthetic pigment content is the highest at ZN2, and the basic photosynthetic parameters of the seedlings reach their maximum values, with net photosynthetic rate and transpiration rate significantly increased by 170% and 166% compared with CK, respectively. For soil-root-ball transplanted seedlings, the photosynthetic pigment content is the highest at ZN3, but the peaks of photosynthetic rate and transpiration rate appear at ZN4. Appropriate nitrogen application can increase the contents of soluble sugar, soluble starch, and organic nitrogen compounds, and enhance the activities of nitrogen metabolism enzymes. Excessive nitrogen application (under ZN4 treatment) leads to a 36% increase in root soluble protein content compared with ZN3, but decreases in soluble sugar, soluble starch contents, and nitrogen metabolism enzyme activities. Specifically, the soluble starch content in roots, total nitrogen in underground parts, and leaf nitrate reductase activity in the ZN4 treatment group are 28%, 7%, and 10% lower than those in the ZN3 treatment group, respectively.

Moderate nitrogen application promotes seedling growth by enhancing photosynthetic performance and carbon-nitrogen metabolism. The optimal nitrogen application rates for bare-root seedlings and soil-balled scedings are 200 mg per plant and 300 mg per plant, respectively.

Through an in-depth study of the leaf morphology of 10 species of Phoebe, to provide a theoretical basis for the identification and classification of Phoebe.

Through morphological observation combined with optical microscopy, scanning electron microscopy, and paraffin sectioning techniques, the taxonomic significance of leaf morphology, microscopic characteristics of leaf epidermis, and anatomical structure characteristics of leaves was deeply investigated.

1) The phenotypic traits of leaves exhibit significant differences. According to quantitative traits, they can be classified into four categories: extra-large leaves, large leaves, medium leaves, and small leaves. Within-species variation in leaf polymorphic traits with midrib above and below is stable. P. zhennan, P. bournei and P. hui present the morphological characteristics of the midrib being sunken on the upper surface and protruded on the lower surface. The backs of leaves, veins, and petioles of the 10 species all have hairs to varying degrees, with the most significant difference being the hairiness on the backs of leaves; 2) The anticlinal walls of the upper epidermis are straight to arched, and those of the lower epidermis are irregular and shallowly wavy. Stomata are only distributed on the lower epidermis. The stomatal morphology is similar among different species, but the stomatal density varies significantly, with the highest density in P. chekiangensis; 3) The cuticular ornamentation of the upper epidermis and the waxy ornamentation of the lower epidermis are diverse and differ among species. Epidermal hairs are distributed on the leaf epidermis of all species, all being unicellular hairs, and the density of epidermal hairs shows significant differences among different species; 4) The anatomical structure reveals that the leaves of the 10 Phoebe species are all bifacial leaves, composed of leaf epidermis, mesophyll tissue, and veins. The petioles are composed of epidermis, collenchyma, xylem, and phloem. There are significant differences in the palisade/spongy ratio, leaf thickness, and the distribution positions of mucilage cells among different species.

The leaf morphology and anatomical characteristics of the 10 Phoebe species are significantly different, which can provide important reference bases for the identification and classification of Phoebe.