## 3 Results and Discussion
### Free Amino Acids (FAAs) Determination  
Principal component analysis (PCA) was conducted on the content of 19 detected amino acids. The first and second principal components (PC1 and PC2) accounted for 81.77% and 9.72% of the total variance, respectively, with all samples clearly clustered according to their geographical origin (Figure 3). Table 1 lists the types, taste attributes, and contents of FAAs detected in _B. roseflavus_ from different regions. The total content of 15 free amino acids was significantly higher in the CN group compared to the DBG group. Regarding taste attributes, the CN group showed significantly higher levels of umami, sweet, bitter, and other amino acids compared to the DBG group. Regarding individual amino acid content, Glu and Gln were the most prominent in both DBG and CN. The content of Gly in the CN group was three times higher than in DBG, and Ser content was 2.6 times higher in the CN group. Table 2 presents the TAVs for the free amino acids. As shown in Table 2, 12 out of 19 free amino acids in the CN group had significantly higher TAVs than those in the DBG group. In the CN group, five free amino acids had TAVs greater than 1, which were identified as characteristic flavor components: Glu, Ala, Gly,Ser, and His. In the DBG group, four free amino acids had TAVs greater than 1, which were identified as characteristic flavor components: Glu, Ala, Arg, and His. This indicates that in CN, Glu is the major contributor to umami, Ala, Gly, and Ser contribute mainly to sweetness, and His is a major contributor to bitterness. In DBG, Glu contributes mainly to umami, Ala to sweetness, and Arg and His to bitterness. Based on these experimental results, we observed that the content of free amino acids in _B. roseflavus_ changed during growth, which influenced the umami, sweetness, and bitterness, leading to a more umami-sweet taste in CN compared to DBG. [PERSON] et al. observed significant differences in amino acid content in ginkgo leaves growing in different locations [26], which is similar to what we observed in _B. roseflavus_ samples. We performed a correlation analysis between the free amino acid content of CN and DBG samples and their environmental conditions (Figure S2A). The results showed that the content of Glu, Asp, Gly, Ser, Arg, Ile, His, Leu, Trp, Lys, and Val was positively correlated with altitude and soil electrical conductivity, and negatively correlated with soil temperature, soil humidity, air temperature, air humidity, and light intensity. In contrast, Ala, Thr, Tyr, and Pro were negatively correlated with altitude and soil electrical conductivity, and positively correlated with soil temperature, soil humidity, air temperature, air humidity, and light intensity. Phe, Met, and Asn showed no significant correlation with environmental factors. Free amino acids (FAAs) are essential flavor compounds in edible fungi [27] and have unique sensory characteristics, primarily responsible for the formation of components related to sweetness, bitterness, and umami (one of the five basic tastes) in edible fungi [28]. As precursors of volatile substances in biological systems, the conversion methods and pathways have been validated in various plants and plant organs [29; 30; 31]. For instance, Methionine (Met) acts as a precursor for a variety of sulfur and non-sulfur volatiles through the non-dependent pathway of the Yang cycle. In melon and strawberry fruits, methanethiol is further metabolized into volatile sulfur esters by acyl transferase-like enzymes. Phenylalanine (Phe) serves as a precursor for the biosynthesis of volatile phenylpropanoids, including eugenol and isoeigenpol [32]. The composition, concentration, and degradation