## 3 Results and Discussion
### Factors Affecting SDT Quality Differences Across Regions  
The biosynthesis of aroma and flavor compounds in SDT is significantly influenced by regional altitudinal variations and soil nutrient composition. Empirical evidence from previous studies, corroborated by the current investigation, has demonstrated substantial heterogeneity in soil nutrient profiles across different regions of Yunnan Province [13; 38]. Furthermore, the enhancement of tea quality has been established as a critical factor in improving the economic value of tea products [39]. To systematically investigate the environmental determinants underlying regional quality variations in SDT, this study employed Pearson correlation analysis and interactive Mantel tests to examine the relationships between soil nutrient content, altitudinal factors, and tea quality components across 13 distinct regions. The analytical results demonstrated significant positive correlations between soil pH and several biochemical components in SDT, including total polyphenols (TP), myricetin, quercetin, protein content, kaempfer, and GA. Soil parameters, particularly SOM, TN, and AN, exhibited positive correlations with FAA, SS, rutin, EC, and CA in SDT, while showing negative correlations with total polyphenols (TP). Furthermore, SOM, total phosphorus (TP), and AP were positively correlated with rutin, EC, CA, and ECG, but negatively correlated with EGCG (Figure 7A). These findings partially diverge from previous research by [PERSON] [38], which reported positive correlations between SOM, TN, AN and FAA, positive correlations with total polyphenols (TP), and negative correlations with pH and total phosphorus (TP) in Pu'er tea gardens. Altitude demonstrated significant positive correlations with rutin, myricetin, kaempfer, CA, and EC in SDT, while exhibiting a negative correlation with bitter-tasting EGCG. Analysis of non-volatile compounds revealed distinct taste profiles between sample groups: L1 group samples (TP/FAA < 10) were characterized by a sweet and mellow taste, whereas L2 group samples (TP/FAA > 10) exhibited a heavier and thicker taste profile. Notably, with the exception of GFZ and BDao, L1 group samples were predominantly from higher altitudes compared to L2 group samples, suggesting altitude as a critical environmental factor influencing SDT taste characteristics. Specifically, high-altitude samples tended to demonstrate sweeter and mellower profiles, while low-altitude samples exhibited heavier and thicker taste characteristics. These variations are potentially attributable to the synergistic effects of light intensity and temperature on tea plant metabolism at different altitudes [12]. The photodegradation of theanine into ethylamine and glutamic acid, which serve as precursors for catechin synthesis [40], combined with reduced light intensity and duration in high-altitude regions due to increased cloud cover and precipitation, may contribute to lower TP/FAA ratios in tea leaves. Given the established role of TP/FAA ratio in determining the balance between heavy/thick and sweet/aftertaste characteristics of tea infusion [41; 42], the observed lower TP content and higher theanine levels in L1 group samples likely account for their sweeter and mellower taste profile compared to L2 group samples. The mineral element phosphorus (P) and altitude emerged as the most significant factors influencing the differentiation in aroma-active substances in SDT. Statistical analysis revealed significant positive correlations between phosphorus content/altitude and floral compounds, specifically geraniol and linalool, while demonstrating negative correlations with isophorone (woody), 2-pentyl furan (caramel), 1-octanol (fatty), D-limonene (fruity), and benzaldehyde (fruity) (Figure 7B). Comparative analysis between groups showed significant upregulation of geraniol and jasmone in C1 relative to C2, whereas isophorone, 2-pentyl-furan, 1-octanol, D-limonene, and benzaldehyde were significantly downregulated.