## 3 Results and Discussion
### PCA and OPLS-DA Statistical Analyses of the Volatile Compounds
Figure 6: The orthogonal projections to latent structures–discriminant analysis (OPLS-DA) score plot for SH-S vs. SH-A. SH-S: Sanhua1951, spring; SH-A: Sanhua1951, autumn. Figure 7: Cross-validation model for SH-S vs. SH-A. SH-S: Sanhua1951, spring; SH-A: Sanhua1951, autumn. As shown in Table S5, there were a total of 65 compounds with VIP > 1, which were the best discriminators between FD-S and FD-A, including the characteristic compounds of different tea cultivars. As shown in Figure 12, for 'Fudinghamdai', based on the principle of \(p<0.05\), VIP > 1 and fold change \(\geq\) 2 (up-regulated) or \(\leq\)0.5 (down-regulated), 57 differential volatile components in FD-S vs. FD-A (36 upregulated and 21 downregulated) (Table S6). As shown in Figure 2B, there were 24 volatile compounds detected only in FD-S, and 21 volatile compounds detected only in FD-A. In addition to the compounds mentioned above, a comparative analysis of other significantly differential volatile compounds was conducted (Figure 13), including 2-methyl-2-butenal, 1-pentanol, (\(Z\))-linal oxide, (\(E\))-linalool oxide, styrene, phenylethyl alcohol, cis-citral, 2-methylnaphthalene, \(\alpha\)-cubebeene, 2-butyl-2-octal, (\(Z\))-jasmone, \(\alpha\)-ionone, (\(E\))-geranylacetone, \(\beta\)-ionone, \(\delta\)-cadinene, and (\(E\))-nerolidol. Moreover, these were the main sources of these aforementioned compound compounds, and the corresponding \(\alpha\)-cubebeene, \(\alpha\)-cubebeene, \(  
changes. Volatile terpenoids contributed to floral fragrance, primarily originating from the methylerythritol phosphate pathway, and their content in tea varies significantly across different producing regions [39]; examples include linalool oxide, \(\alpha\)-cubebene, \(\delta\)-cadinene, and (\(E\))-nerolidol. The carotenoids in fresh tea leaves undergo nonenzymatic degradation (for instance, pyrolysis, isomerization, aromatization, cyclazation, and polymerization) and enzymatic oxidation to produce abundant aromatic compounds under different growth environments and harvest seasons, such as (\(E\))-geranylacetone and carotenoid-derived aroma substances. Phenylethyl alcohol is an important volatile compound in white tea [40], primarily released through the hydrolysis of glycosides or the shikimic acid synthesis pathway. The contents of phenylethyl alcohol were lower in autumn teas than spring teas (Figure 13). (\(Z\))-jasmone, a compound with floral notes, is the product of \(\alpha\)-linolenic acid. Through distinct metabolic pathways involving enzymes such as alcohol dehydrogenase, allene oxide synthase, and lipoxygenase, these biochemical processes collectively lead to the formation of key volatile aroma compounds [41]. The contents of (\(Z\))-jasmone were lower in autumn teas than spring teas (Figure 13). Based on the relative abundance of these aroma-related compounds, their odor characteristics, and prior studies [7; 8; 9], the change in the levels of the above-mentioned compounds play a pivotal role in shaping the aroma profile of white teas harvested in spring versus autumn. These compounds are likely responsible for the distinct 'floral/herbal/fruity/fresh' aromatic characteristics observed in these teas. Figure 11: Cross-validation model of FD-S vs. FD-A. FD-S: Fudingdabai, spring; FD-A: Fudingdabai, autumn. Figure 10: The orthogonal projections to latent structures–discriminant analysis (OPLS-DA) score plot for FD-S vs. FD-A. FD-S: Fudingdabai, spring; FD-A: Fudingdabai, autumn.