## 2 Results and Discussion
### Effects of Rootstocks on Berry Physiological Parameters  
Compared to the own-rooted vines, berry weight was not altered by rootstocks in this study (Table 2), which was in agreement with previous studies [1; 2; 4; 9]. Contrarily, significant differences in berry weight among different grafted vines were also reported [10; 22]. The influence of rootstocks on berry weight may be dependent on rootstock genotypes and seasons [3]. The increases in berry weight of 'Summer Black' induced by SO4 and 5 BB were attributed to the enhanced relative water content. In the present study, slight increases in berry weight were only observed in CS/5 BB rather than CS/SO4 (Table 2).  
In this study, berries in 2015 accumulated more total soluble solids than berries in 2016. Higher rainfall and lower sunshine duration in July in 2016 compared to 2015 may have delayed berry ripening. Rootstocks did not significantly affect total soluble solids (Table 2), which is in agreement with previous studies [2; 5; 10; 11; 15]. However, the significant influence of rootstocks on total soluble solids was also documented [3; 4; 10; 25]. [PERSON] et al. [18] revealed that rootstocks may modify the berry ripening rate through regulating the expression of genes controlling auxin action (ARF and Aux/IAA). In this study, 101-14, 5 BB, and SO4 slightly reduced total soluble solids compared to own-rooted vines, which is similar to the results reported by [PERSON] et al. [19]. Besides, the total soluble solids value in CS was higher relative to that in grafted vines, except for CS/Ganzin 1 and CS/Harmony (Table 2). It was reported that 110R with _Vitis berlandieri_ genetic makeup tended to retard berry maturation and produce lower total soluble solids when compared with 101-14 (_Vitis riparia \(\times\) Vitis rupestris_) [1; 17]. However, in this study, CS/110R accumulated a similar amount of total soluble solids to CS/101-14. In addition, CS/Harmony produced significantly higher total soluble solids in comparison with CS/SO4 (Table 2).  
Juice tittatable acidity and pH were not affected by either rootstock or season in this study (Table 2). There have been no agreed conclusions about the influence of rootstocks on tittatable acidity and pH in previous studies [2; 5; 10; 16; 17; 19; 20; 22; 26; 27]. Since potassium can precipitate tartrates in juice, leading to the reduction of tartaric acid, potassium in juice determines the tittatable acidity and pH to a great extent. The alterations of tittatable acidity and pH induced by rootstocks were generally observed concomitantly with the modified potassium concentrations led by rootstocks. Potassium uptake capability of grapevine depended on scion cultivars, rootstock genotypes, and soil conditions. Same rootstock may have varied effects on potassium concentrations in berries on different scion cultivars [28]. Besides, variations in the potassium absorption ability of different rootstocks can be attributed to the rootstock genetic origins. It was reported that rootstocks with a _Vitis berlandieri_ and/or _Vitis rupestris_ genetic background were generally observed for having a good nutrient uptake ability [2; 7; 29]. The greater availability of potassium from the granite soil may mask the variations in the potassium uptake capability of rootstocks [13]. Overall, in this study, the lack of significant differences in juice tittatable acidity and pH among different grafted vines may be attributed to the high potassium availability of the vineyard soil. In addition, CS/101-14, CS/5 BB, and CS/SO4 produced a little higher tittatable acidity compared to CS (Table 2), which is in agreement with a previous study [19]. Combining the lower concentrations of total soluble solids in CS/101-14, CS/5 BB, and CS/SO4 relative to CS, 101-14, 5 BB, and SO4 showed tendencies to retard berry maturation in this study.