Machilus thunbergii Siebold & Zucc. is recognized as an excellent tree species for landscaping and shelter forest. Excessive drought can affect the changes of physiological and biochemical substances in plants. However, little is known at present regarding the drought stress of M. thunbergii seedlings. In this paper, matrix water content, the anatomical structure of leaves, relative water content of leaves, and physiological characteristics index of leaves under droughting stress were dynamically observed. Droughting stress led to the wilting of M. thunbergii leaves, gradual closure of stomata on leaf epidermis, increases in stomatal density, gradual loosening of leaf cell structure arrangement, a thickening in leaf palisade tissue, and reductions in spongy tissue. Droughting stress caused the relative water content of the cultivation substrate to decline, the cultivation substrate reached the moderate drought level, and the seedlings began to die. Droughting stress led to the destruction of activity and balance of the leaf protective enzyme system, excessive accumulation of free radicals, the destruction of enzyme structure and function, and the production of lipid peroxidation product MDA. Droughting stress reduced the relative water content of leaves as a whole, the content of osmotic adjustment substances proline and soluble protein continued to decline, and a large number of electrolyte leakage in cells, causing serious damage to seedlings.

Introduction: As a native tree species in China, Machilus thunbergii is highly responsive to nitrogen fertilization. However, 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 aimed to investigate the effects of topdressing with different nitrogen fertilizers on the growth and nitrogen metabolism of M. thunbergii seedlings, with the goal of providing a scientific basis for optimized nitrogen fertilization management in M. thunbergii cultivation. The study used 3-year-old M. thunbergii seedlings as the material, and the fertilization rate was 3 g per seedling. The experiment was conducted in a one-way randomized block design with four treatments, including the control treatment and three nitrogen fertilizer treatments: urea (amide nitrogen fertilizer), ammonium sulfate (ammonium nitrogen fertilizer), and sodium nitrate (nitrate nitrogen fertilizer). From the start of the experiment, the branch and leaf morphology, the height growth, and the basal diameter growth of the seedlings in each treatment were monitored periodically. The activities of the nitrogen-metabolizing enzymes, such as nitrate reductase, glutamine synthetase, glutamate synthetase, and glutamate dehydrogenase, in the leaves were also measured. At growth cessation, all treatments were evaluated for biomass production, root morphological characteristics, and total nitrogen content in different plant parts (i.e., roots, stems, and leaves). Results: Due to the high nitrogen content in the cultivation substrate, the application of the 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 the overall height and diameter growth compared with the control, the timing and the intensity of these effects varied. For instance, the urea treatment initially showed less inhibition, whereas the sodium nitrate treatment consistently exhibited the strongest inhibitory effect throughout the experiment. Similarly, the promotion of nitrogen metabolism enzyme activity by the different fertilizers also displayed distinct temporal patterns, with peaks occurring at different measurement points. All nitrogen treatments increased the nitrogen content in the root, stem, and leaf parts, but decreased the nitrogen translocation efficiency of M. thunbergii seedlings. All nitrogen treatments increased the nitrogen accumulation in the roots and stems of seedlings. Urea treatment enhanced foliar nitrogen accumulation, whereas both the ammonium sulfate and sodium nitrate treatments reduced foliar nitrogen accumulation. Conclusion: All three nitrogen treatments significantly influenced both the growth and physiological indices of M. thunbergii seedlings. While generally enhancing the nitrogen metabolism and accumulation, improper selection of fertilizer types or excessive application rates elevated the tissue nitrogen concentration, inducing phytotoxic effects that ultimately inhibited seedling growth. In this research, sodium nitrate had the greatest toxic effect on M. thunbergii seedlings, followed by ammonium sulfate and urea. Among the nitrogen fertilizers tested, urea proved superior at an application rate of 3 g per plant for 3-year-old M. thunbergii seedlings.

The narrow crown, a distinct form of canopy architecture and a specialized phenotypic expression of branch angle traits in woody plants, significantly influences key physiological processes such as photosynthesis, transpiration, and biomass accumulation. This phenotype holds substantial application value in forestry production. This article aims to elucidate the biological traits and formation mechanisms of the narrow-crown phenotype in woody plants by analyzing the contributions of plant hormones, their related genes, and specific key genes to the formation and determination of branch angles. Furthermore, the review explores applications of the narrow-crown phenotype in timber forestry, orchard production, breeding of new ornamental woody varieties, and forest tree genetic improvement. Finally, we summarize recent advances in research on narrow-crowned woody plants. On this basis, the future research directions of woody plants with narrow-crown phenotype were prospected, in order to provide reference for promoting the study of branching angle formation of woody plants and the production and application of woody plants with narrow-crown phenotype.

Grafting is the primary vegetative propagation technique for ornamental crabapple, and rootstock–scion compatibility critically determines graft healing efficiency and seedling quality. Selecting suitable rootstocks is essential for the popularization of new crabapple cultivars, yet the healing performance of the newly bred cultivar Malus ‘Huabiao’ grafted onto different local Malus rootstocks remains unclear. This study evaluated graft compatibility for M. ‘Huabiao’ grafted onto three rootstocks (M. hupehensis, M. robusta, and M. baccata) through histological observation and dynamic detection of soluble sugar, soluble protein, and tannin during graft healing. The results indicated that M. ‘Huabiao’/M. hupehensis and M. ‘Huabiao’/M. robusta achieved higher survival rates (80.0% and 83.3%, respectively) and complete vascular reconstruction within 28 days, whereas the M. ‘Huabiao’/M. baccata combination exhibited a lower survival rate (63.0%) and obvious healing lag. All combinations showed consistent physiological variation trends, while the M. baccata group maintained higher soluble sugar content, greater protein fluctuations, and significantly elevated tannin levels (p < 0.05). Physiological substance accumulation was closely correlated with healing performance, with higher soluble sugar and protein levels associated with better wound recovery, and excessive tannin accumulation correlated with retarded tissue regeneration capacity. Distinct healing asynchrony was observed among combinations, with incomplete vascular connection detected in the M. baccata group at day 28. This study confirms that M. hupehensis and M. robusta are superior compatible rootstocks for M. ‘Huabiao’, and the dynamic levels of the three physiological indices can serve as potential indicators for evaluating crabapple graft compatibility.