Objective This study aimed to investigate the effects of simulated nitrogen deposition and biochar application on flowering intensity of Torreya grandis and its physiological regulatory mechanisms, providing theoretical support for ecological adaptive management of T. grandis under nitrogen deposition scenarios.

Methods A 2 × 3 factorial experimental design was conducted on fruit-bearing T. grandis trees, with three nitrogen deposition gradients (0, 30, and 60 kg·N·ha⁻¹·a⁻¹) and two biochar gradients (0 and 40 t·ha⁻¹). Flowering intensity, leaf carbon-nitrogen metabolic indicators, and soil physicochemical properties were measured under each treatment to analyze the mechanisms and interactive effects of nitrogen deposition and biochar on flowering intensity.

Results ① Nitrogen deposition exhibited dose-dependent effects: compared with the control (CK), low nitrogen increased flowering intensity by 3.51%, while high nitrogen decreased it by 9.27%. Biochar application alone significantly increased flowering intensity by29.58% (p<0.05) and alleviated the adverse effects of high nitrogen. The combined high nitrogen + biochar treatment significantly increased flowering intensity by 19.34% compared to high nitrogen alone (p<0.05). ② Nitrogen deposition and biochar treatments significantly affected soil nutrient status. Biochar application under high nitrogen deposition significantly improved soil pH, alkali-hydrolyzed nitrogen, organic matter, and available potassium contents during both the flowering initiation period (November) and flower organ development period (March of the following year) (p<0.05). ③ Leaf nutrient analysis revealed that combined nitrogen deposition and biochar treatment significantly increased soluble protein content (by 50.69% under high nitrogen + biochar, and 78.59% under low nitrogen + biochar: p<0.05) and reduced starch content (by 62.64% and 34.91%, respectively, p<0.05) in November. In March, high nitrogen + biochar significantly increased soluble protein content by 19.59% (p<0.05), while low nitrogen + biochar significantly increased starch content by 19.79% (p<0.05). ④ Flowering intensity was significantly correlated with leaf soluble protein, soluble sugar contents, and soil pH and nutrient indicators (p<0.05), suggesting that carbon-nitrogen metabolism and soil pH regulation are key factors influencing flowering intensity.

Conclusion The effects of nitrogen deposition on flowering intensity of T. grandis are concentration-dependent, with moderate nitrogen deposition promoting flowering and excessive nitrogen deposition inhibiting it. Biochar effectively alleviates the negative impacts of nitrogen deposition and enhances flowering intensity by improving soil pH and regulating plant carbon-nitrogen nutrients. It is recommended to implement combined biochar and nutrient management during the critical flowering period (November to March of the following year) in areas with high nitrogen deposition to mitigate its adverse effects.