【Objective】In recent years, atmospheric nitrogen deposition in southeastern China has become increasingly severe, raising significant concerns about its ecological impacts. To systematically investigate the combined effects of external nitrogen input and biochar addition on the Torreya grandis plantation ecosystem, this study focused on the interactions among soil nutrient status, microbial community functional characteristics—particularly carbon source metabolic utilization capacity—and nutrient dynamics in plant leaves and fruits. A multi-factor-controlled experiment was designed to clarify the synergistic effects of different nitrogen fertilizer and biochar application patterns on soil physicochemical properties, microbial activity, tree nutrition, and fruit quality. The findings aim to provide a theoretical basis and practical guidance for scientific fertilization and sustainable management of T. grandis plantations.【Method】The experiment followed a completely randomized block design with six treatment combinations: N0BC0 (control, no nitrogen or biochar), N0BC1 (biochar alone at 20 t/hm²), N0BC2 (biochar alone at 40 t/hm²), N30BC0 (nitrogen fertilizer alone as NH₄NO₃ at 30.0 kg/(hm²·a)), N30BC1 (30.0 kg/(hm²·a) NH₄NO₃ with 20 t/hm² biochar), and N30BC2 (30.0 kg/(hm²·a) NH₄NO₃ with 40 t/hm² biochar). Throughout the trial, soil physicochemical properties—including organic carbon, total nitrogen, total phosphorus, available phosphorus, available potassium, and pH—were systematically monitored and analyzed. Soil microbial biomass carbon and microbial community metabolic function activity were assessed using Biolog ECO microplate analysis. Leaf samples and mature fruits were periodically collected to determine nutrient element content (nitrogen, phosphorus, potassium, magnesium, etc.) and fruit quality indicators (soluble sugars, soluble proteins). All data were processed using statistical methods such as analysis of variance and multiple comparisons to identify significant differences among treatments.【Result】(1) The results showed that nitrogen fertilizer application alone (N30BC0) significantly increased soil organic carbon content, leaf magnesium accumulation, and fruit soluble sugar concentration, but also significantly reduced leaf potassium content, indicating that while nitrogen input promoted carbon sequestration and certain nutrient uptake, it may pose a risk of potassium nutritional imbalance. (2) Biochar application alone (N0BC1 and N0BC2) generally improved soil nutrient status, leaf nutrition, and fruit quality, but significantly suppressed the overall metabolic activity of the soil microbial community, possibly due to biochar adsorption of microorganisms or alterations in the micro-environment. (3) Regarding the interaction between nitrogen and biochar, the low-biochar nitrogen combination (N30BC1) significantly enhanced soil nutrient content, microbial metabolic activity, and carbon source utilization efficiency compared to low-biochar alone (N0BC1), but reduced soil microbial biomass carbon. The high-biochar nitrogen combination (N30BC2) significantly increased soil total phosphorus, fruit soluble protein content, and leaf ratio of N to P compared to high-biochar alone (N0BC2). (4) Comparing the two combination ratios, the N30BC1 treatment outperformed N30BC2 in terms of soil nutrients, leaf nutrition, and microbial metabolic activity, and exhibited a significantly lower mass ratio of leaf N to P, suggesting that combining nitrogen fertilizer with a lower biochar application rate is more conducive to maintaining plant nutritional balance.【Conclusion】In summary, both nitrogen fertilizer and biochar application alone can improve soil fertility and promote plant growth in T. grandis plantations to varying degrees. However, their combined effects involve complex synergistic and antagonistic interactions. Based on a comprehensive evaluation of multiple indicators, the combination of 30.0 kg/(hm²·a) ammonium nitrate nitrogen fertilizer with 20 t/hm² biochar (N30BC1) not only significantly enhances T. grandis fruit quality but also better balances soil ecological function and plant nutrition. This approach represents an optimized management strategy for coordinating yield, quality, and plantation sustainability, and is recommended for demonstration and application in practical production, taking into account specific site conditions.