## 2 Materials and Methods
### Determination of Main Biochemical Components  
Chlorophyll: 10 tea tree leaves were selected and cut into pieces (near the main vein), and 0.2 g of pieces were put in a triangular flask with 25 mL of 96% ethanol, sealing and protecting from light for 24 h. After the pieces turned white, 2 mL of the supernatant and 4 mL of 96% ethanol were mixed, then 96% ethanol was taken as the blank, and the absorbance at wavelengths of 665 nm and 649 nm was measured. Chlorophyll a, chlorophyll b and total chlorophyll were calculated according to [PERSON] [21]. Soluble sugar: 0.2 g of tea leaves sample in each replicate were ground and diluted to 10 mL. After extracting in boiling water for 30 min, filtering the extract into a 25 mL volumetric flask, repeated this step twice, then diluted to the mark with distilled water. A total of 0.2 mL of the extraction, 1.8 mL of distilled water, 0.5 mL of anthrone ethyl acetate, and 5 mL of 98% H\({}_{2}\)SO\({}_{4}\) were added and fully mixed using a shaker. Then measured the OD value at a wavelength of 630 nm by a Beckman DU 800 UV-visible spectrophotometer (Beckman Coulter, Inc., Brea, CA, USA, the same hereafter). The soluble sugar content was calculated according to the method described by [PERSON] et al. [22]. Soluble protein: 0.2 g of tea leaves were weighed in each sample, then grinding it and diluting to 5 mL. Extraction was obtained after centrifuging at 8000 r/min for 15 min at 4 \({}^{\circ}\)C (Allegra X-22R, F1010 Rotor, Beckman Coulter, Inc., Brea, CA, USA). A total of 1 mL of extraction was taken, and 5 mL of Coomassieie brilliant blue G-250 was added, mixing them thoroughly, the soluble protein content was measured in a spectrophotometer at a wavelength of 560 nm, which was according to [PERSON] [23]. Tea polyphenols: 0.2 g dried and crushed tea leave samples were dissolved in 5 mL of 70% methanol. After boiling and centrifuging at 3600 r/min for 10 min twice, the supernatant was gained. A total of 1 mL of gallic acid working solution, 2 mL of distilled water, and 1 mL of test solution were added into the pipette, and then 5 mL of the prepared Folin's phenol (10 mL of distilled water) were added to the pipette, after reacting 3-8 min, then 4 mL Na\({}_{2}\)CO\({}_{3}\) were diluted to 100 mL. Tea polyphenols were estimated with a spectrophotometer at 765 nm. The content of tea polyphenols was calculated according to [PERSON] [21]. POD, SOD, and MDA: 0.2 g tea leaves were ground with 5 mL of phosphate buffer (pH = 7.8) to obtain a homogenate. POD activity was determined by guaiacol method [24]: 0.1 mL of the supernatant and 2.9 mL of the reaction solution (containing 28 \(\upmu\)L of guaiacol and 19 \(\upmu\)L of hydrogen peroxide) were mixed and estimated with spectrophotometer at 470 nm. SOD activity was determined by nitro-tetrazolium-blue-chloride (NBT) photochemical reduction method [25], firstly, transferring the homogenate to a centrifuge tube and centrifuging it at 10,000 rpm for 20 min and then configuring the reaction system, which was made up by 1.5 mL of 50 mmol/L phosphate buffer, 0.3 mL of 130 mmol/L methionine, 0.3 mL of 750 \(\upmu\)mol/L nitro blue tetrazolium, 0.3 mL of 100 \(\upmu\)mol/L ethylene diamine tetraacetic acid, 0.3 mL of 20 \(\upmu\)mol/L riboflavin, and 50 \(\upmu\)L of phosphate buffer or supernatant. Finally, we estimated SOD activity using a spectrophotometer at 560 nm. MDA content was determined by barbituric acid colorimetry [26]. Firstly, we centrifuged the homogenate at 3000 rpm for 20 min, then added 2 mL of supernatant and 2 mL of 0.6% thiobarbituric acid to the tube and put it into boiling water for 20 min. Finally, the absorbance of the supernatant was measured at 450 nm, 532 nm, and 600 nm. Determination of Aroma Components in Fresh Tea Leaves Using Headspace Solid-Phase Microextraction Coupled with Gas Chromatography-Mass Spectrometry (HS-SPME/GC-MS)  
Extraction of aroma components: 2 g of fresh tea leaves in each sample was chopped into pieces and put in 20 mL headspace vials.