## 1 Introduction  
The Tieguanyin tea tree, also known as _Camelia sinensis_, is a perennial evergreen plant that originated in Anxi County, Fujian Province, China. The tea tree is an acidophilic plant. A soil pH of 4.5-5.5 is suitable for its cultivation, and a soil pH of less than 4.5 is unsuitable [1, 2]. [PERSON] et al. [3] analyzed the pH of soil and its effects on the yield and quality of tea at 145 tea plantations in Nanjing County, Fujian Province, and found that 82.1% of the tea plantations had soil pH levels < 4.5 and that the soil pH was significantly and positively correlated with the yield and quality of the tea. [PERSON] et al. [4] found that 37.67% of tea plantation soils in Anxi County, Fujian Province, China, also experienced soil acidification (pH < 4.5). The yield and quality of tea showed decreasing trends after soil acidification [5]. It was evident that soil acidification reduced the yield and quality of tea and limited the development of the tea industry. Yield and quality guarantee the economic benefits of tea plantations; in particular, the improvement of tea quality has a more important economic value [6, 7]. Tieguanyin tea is a typical representative of oolong tea and is one of the top ten most famous teas in China [8]. According to the current standards for evaluating tea quality in China, the aroma index accounts for 35% of the score in the quality evaluation of oolong tea, which is an important index for oolong tea [9]. The aroma of tea is mainly formed by the volatile compounds contained in the tea leaves [10]. During research, the content of volatile compounds in tea leaves is often used to evaluate the aroma quality of tea leaves [11]. However, there is a wide variety of volatile compounds in tea leaves, and more than 300 volatile compounds have been reported to be involved in the formation of the aroma of oolong tea [12]. The content of volatile compounds is related to the intensity of the aroma and the odor characteristics of tea, but the aroma thresholds of different compounds vary greatly, so the content of a compound is not equivalent to its contribution to the intensity of the aroma and the odor characteristics of a tea [13]. The aroma contribution of a compound depends mainly on its odor activity value (OAV), and only when the OAV value of a compound is greater than 1 may the compound actually contribute to the aroma [14]; a compound making an actual contribution will exhibit a characteristic odor [15]. Therefore, the OAV value is used to analyze changes in the aroma of tea which can reflect the effects of environmental changes on the quality of the tea's aroma more comprehensively. It has been widely reported that soil acidification is highly susceptible to the degradation of tea quality [16; 17; 18]. Secondly, soil acidification also causes changes in the fertility of soil, especially in rhizosphere soil, which affects the uptake of nutrients by plants, leading to a decrease in plant yield or quality [19]. This change may be due to the acidification of soil altering the amount and type of plant root secretions which, in turn, affects the colonization of the rhizosphere soil by microorganisms and the soil enzyme activities, especially those related to nutrient cycling, altering the nutrient contents of a plant's rhizosphere soil and affecting plant yield and quality [20; 21]. However, there are few reports on the effects of soil acidification on the fertility of rhizosphere soil and the quality of tea aroma, especially the effect of the soil fertility index on the aroma of tea evaluated using the OAV value method. In this study, rhizosphere soil of tea trees planted on soil with different pH values was collected; in addition, one bud and three leaves were collected from each tea trees.