## 3 Results and Discussion
### Screening of Characteristic Volatile Compounds of Ta Tee Leaves Under Magnesium Regulation
It was evident that the key to the effect of magnesium regulation on volatile compounds in tea tree leaves was also focused on terpenoids, esters, and heterocyclic compounds, and changes in the content of these three groups of volatile compounds may affect the formation of odor characteristics of tea. Contribution Weighting Analysis of Characteristic Volatile Compounds in Differentiating Between Different Magnesium Concentrations  
On the basis of the previous analysis, this study further used TOPSIS weighting analysis to determine the contribution weights of the characteristic volatile compounds in distinguishing between different magnesium concentrations, and the results showed (Figure 4A) that for the 35 characteristic volatile compounds, only 15 of them had contribution weights greater  
Figure 3: Screening and content analysis of characteristic volatile compounds of tea tree leaves under magnesium regulation. Note: ML: Mg\({}^{2+}\) concentration 0 mmol/L; MM: Mg\({}^{2+}\) concentration 0.4 mmol/L; MH: Mg\({}^{2+}\) concentration 0.8 mmol/L; (**A**) Screening of characteristic volatile compounds under magnesium regulation by bubble feature map; (**B**) Classification of characteristic volatile compounds and their content analysis. Figure 2: Screening and content analysis of key differential volatile compounds in tea tree leaves under magnesium regulation. Note: ML: Mg\({}^{2+}\) concentration 0 mmol/L; MM: Mg\({}^{2+}\) concentration 0.4 mmol/L; MH: Mg\({}^{2+}\) concentration 0.8 mmol/L; (**A**) Volcano plot screening and K-Means clustering analysis of differential volatile compounds under magnesium regulation; (**B**) OPLS-DA model of ML, MM, and MH for screening of key differential volatile compounds; (**C**) Classification and content analysis of key differential volatile compounds. than 10%, which were heptyl formate (83.20%), t-geraniol (66.50%), metaldehyde (46.78%), 2-octen-4-one (45.78%), t-geranyl alcohol (43.93%), t-iso-geraniol (43.93%), 2,4-dimethyl-2-oxazoline-4-methanol (37.31%), 1,7-diazabicyclo [2.2.1]heptane (36.30%), cycloheptanol (35.23%), 2,2,6-trimethylcyclohexanone (18.97%), D-pantolactone (13.13%), (E)-carvone oxide (11.34%), t-(-)-limonene (10.46%), t-D-limonene (10.46%), and t-limonene (10.46%). Moreover, the content of all the above 15 characteristic volatile compounds showed an increasing trend with the increase in magnesium concentration (Figure 4B). It was evident that after magnesium regulation, these 15 characteristic volatile compounds played a key role in distinguishing between different magnesium treatments, especially heptyl formate and t-geraniol, both of which were higher in contribution and content. Figure 4: Contribution weights of characteristic volatile compounds and their content analysis under magnesium regulation. Note: ML: Mg\({}^{2+}\) concentration 0 mmol/L; MM: Mg\({}^{2+}\) concentration 0.4 mmol/L; MH: Mg\({}^{2+}\) concentration 0.8 mmol/L; **(A)** TOPSIS analysis of the weights of characteristic volatile compounds in distinguishing between different magnesium concentrations; **(B)** Content analysis of characteristic volatile compounds with more than 10% of the contribution weight; different lower case letters indicate that the differences between different samples reached the \(p<\) 0.05 level. Further transformation analysis of the 15 characteristic compounds with high contribution rates revealed (Figure 5) that cycloheptanol could be converted to heptyl formate by oxidation, while heptyl formate could be converted to 2-octen-4-one by oxidation and synthesis. Secondly, acetic acid could synthesize three characteristic volatile compounds, such as 2-octen-4-one, metaldehyde, and 2,4-dimethyl-2-oxazoline-4-methanol, under suitable conditions, and 2,4-dimethyl-2-oxazoline-4-methanol was converted to 1,7-diazabicyclo [2.2.1]heptane by synthesis.