## 3 Results and Discussion
### Regional Differences in Soil Nutrients  
The soil nutrient analysis results (Figure 5) revealed distinct characteristics across the 13 tea garden regions. The soil pH values ranged from 4.45 to 5.16, with 92.31% of the tea gardens meeting the criteria for high-quality fertility tea gardens, indicating optimal conditions for tea tree growth. Notably, the XN tea garden exhibited a pH of 4.45, which is below the threshold of 4.50, suggesting potential soil acidification issues. Total nitrogen (TN) content varied between 0.78 and 6.10 g/kg, with 84.61% of the tea gardens conforming to high-quality fertility standards. However, the MN and MA tea gardens exhibited TN levels classified as grade III. Available nitrogen (AN) content ranged from 54.67 to 214.67 mg/kg, with 61.54% of the tea gardens meeting high-quality fertility standards. The remaining gardens were distributed as follows: BKN, XN, and BS at grade II, and MN and MA at grade III, indicating generally sufficient soil nitrogen content across all sites. Total phosphorus (TP) and available phosphorus (AP) contents were measured at 0.13-0.77 g/kg and 0.83-6.75 mg/kg, respectively, with both parameters falling within grade II to III levels. Total potassium (TK) content ranged from 0.61 to 2.58 g/kg, with 69.23% of the tea gardens meeting high-quality fertility standards. The remaining gardens BKN, XN, PS, and WLS exhibited TK levels at grade II, accounting for 30.77% of the total. Available potassium (AK) content varied between 33.33 and 403.67 mg/kg, with 61.54% of the tea gardens conforming to high-quality fertility standards. The remaining gardens were distributed as follows: BKN, GFZ, and DBS at grade II, and BDao and BD at grade III. Soil organic matter (SOM) content ranged from 18.4 to 94.9 g/kg, with 84.62% of the tea gardens meeting high-quality fertility standards. The MN and MA tea gardens exhibited SOM levels at grade II, accounting for 15.38% of the total sample.  
Cluster analysis of soil nutrient profiles revealed distinct groupings among the sampling sites. Specifically, SH, BD, DBS, DG, BS, and BDao were classified into the T1 group, while XN, BKN, MA, MN, PS, GFZ, and WLS formed the T2 group (Figure 6A). Statistical analysis demonstrated significantly higher soil AP content in the T1 group (3.94-6.75 mg/kg) compared to the T2 group (0.69-3.00 mg/kg). OPLS-DA was subsequently conducted to identify key differentiating factors between the two groups. The model demonstrated satisfactory goodness of fit, with parameter values of R2X:0.621, R2X:0.878, and Q2:0.827. According to established validation criteria in multivariate analysis, both R\({}^{2}\) (coefficient of determination) and Q2 (cross-validated predictive ability) values exceeding the threshold of 0.5 indicate acceptable model performance in both explanatory and predictive capacities. This analysis identified five mineral elements meeting the follow  
Figure 5: Map of soil nutrient differences.  
ing criteria: FC > 1.5 or <0.8, VIP > 1, \(p\) < 0.05. These elements were determined to be the principal mineral components contributing to the intergroup differentiation (Figure 6B,C). Comparative analysis revealed significant upregulation of multiple soil parameters in the T1 group relative to the T2 group, including TP, AP, TN, SOM, and TK. These findings suggest that these soil characteristics may serve as key indicators for the observed grouping patterns and potentially influence the regional differentiation in tea quality parameters.  
Figure 6: Soil nutrient clustering heat map (**A**), volcano map (**B**), and VIP value map of OPLS-DA (**C**).