Rapid urbanization and increasing land scarcity have made urban agriculture and efficient space utilization critical directions in modern agriculture. Ougan, a fruit tree valued for both its economic and ecological benefits, holds significant promise for dwarfing cultivation techniques. In this study, a root-irrigation method was used to apply paclobutrazol at various concentrations (200, 500, 1000, 1500, and 2000 mg/L) to Ougan seedlings, with a control group for comparison. Growth parameters include an average daily increase of plant height, stem girth, new branches, and new branch girth, as well as physiological indices such as leaf SPAD values, leaf nitrogen content, net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, and transpiration rate, were measured during both spring and summer growth periods. The results demonstrate that PBZ exerts a distinct concentration-dependent regulatory effect on Ougan growth: higher concentrations significantly inhibited plant height while promoting increases in stem diameter, with several parameters exhibiting a unimodal response. Short-term (spring) PBZ application enhanced certain photosynthetic parameters, such as net photosynthetic rate and stomatal conductance; however, prolonged exposure (summer) resulted in a decline in photosynthetic efficiency and overall leaf physiological status. Through comprehensive evaluation using principal component analysis and PLS-SEM, the 500 mg/L PBZ treatment was identified as achieving the optimal balance between growth inhibition and the maintenance of photosynthetic and nutritional status, closely approximating the ideal dwarfing effect. This study elucidates the complex regulatory effects of PBZ on the growth, photosynthesis, and carbon assimilation of Ougan through natural climate, providing robust technical parameters and theoretical support for future dwarf cultivation practices. These findings facilitate the development of dwarf fruit trees into bonsai vegetation, demonstrating significant horticultural application potential.

The reduction of chemical fertilizers is a management practice gradually being adopted in long-term fertilized soils. However, the effects of chemical fertilizer reduction on soil health have remained underexplored in orchard systems. Through a two-year field experiment, we investigated how the reduction of chemical fertilizers affects soil chemical properties, the soil quality index (SQI), and fruit yield and quality. The results indicated that chemical fertilizer reduction significantly increased soil pH and organic matter, while it decreased the available nitrogen and phosphorus contents in 2022 and 2023. The reduction of chemical P fertilizer enhanced the availability of Si, S, Mn, and Cu, while it had no impact on the availability of Mo, Fe, and B. Chemical fertilization reduction did not decrease fruit yield and quality, except for the 1/3N treatment. Moreover, the SQI for the N and 2/3N treatments was higher. The random forest model demonstrated that SQI and soil pH were the most important driving factors regulating fruit yield in response to chemical fertilizer reduction practices. Our study suggests that the appropriate reduction of chemical fertilizers can enhance SQI and the availability of micronutrients without decreasing fruit yield and quality, which may have direct implications for soil health.