## 4 Discussion  
Girdling is a commonly used horticultural procedure in grape production to improve plant flowering and fruit size, advance maturity and reduce the number of harvests. Nonetheless, girdling also presents several potential hazards to the vines. Girdling can weaken the ability of root absorption and interception of nutrients and water, and even severely damage plants by restricting root growth and promoting excess flower bud differentiation [47]. Therefore, foliar fertilization with K is often used after girdling to reduce the tissue damage, which is caused by girdling. However, little is known about the influence of foliar fertilization with K on grape aroma composition and other qualities, in combination with girdling or otherwise. The quality of table grape mainly depends on cluster shape and size, berry size, sugar/ acidity ratio, color and aroma [48]. Previous reports have suggested that girdling after full bloom (30-35 days) and fertilization with K can accelerate the accumulation of sugars and anthocyanins [49; 50; 51]. In our study, the results showed that the skin color of G, F and GF treatments were much deeper than the control group (Figure 1). Additionally, the weight of 20 berries was affected significantly by G, F and GF in each period, indicating that girdling and foliar fertilization with K can facilitate fruit development and enlargement. Among the four treatments, the combination of girdling and foliar fertilization with K had the most notable effects on berry weight, grape skin TSS and TA contents (Figure 2). Proanthocyanations are a group of biologically active polyphenols, which are the most potent antioxidants and free radical scavengers identified to date [52]. In our study, GF significantly increased the accumulation of proanthocyanidins in berry skin (Figure 3). [PERSON] et al. [53] found that total grape proanthocyanidin contents at both 7 and 9 weeks after girdling was almost 1.8-fold higher than ungirdled 'Sable' vines. Our results are in agreement with that study, but also indicated that adding foliar fertilization with K following girdling can further increase grape proanthocyanidin content. In our study, the volatile aroma composition in four treatments throughout fruit development were determined by GC-MS analysis. Our results showed that girdling and foliar fertilization with K led to different effects on volatile aroma composition (Figure 4 and Table 1). A previous study showed that the total level of terpen was reduced by 1.6-fold after girdling in 'Sable' vines [53]. In agreement, our study also indicated a significant decrease in the accumulation of terpen and other volatile compounds after girdling, except for aldehydes. In the four treatment groups, the effect of combined girdling and foliar K fertilization was most striking, where the accumulation of the majority  
Figure 6: Effects of girdling and foliar fertilization with K on the sensory properties of ‘Hanxiangmi’ table grapes. of volatile compounds was significantly enhanced, including 1-heptanol, (E)-2-hexenal, hexanal, nerol and geraniol, all of which have a low odor threshold. Previous studies have demonstrated that the concentrations of volatile free aroma compounds, especially monoterenes, increased with positive correlation with soluble solids [54; 55]. We suggest that the higher aroma accumulation in the GF group might be the consequence of achieving higher TSS. There are a large number of terpene compounds produced in plants with extensive variation in their structure and functionalities. All terpene compounds in plants are synthesized from their isoprenoid precursors, which are derived from the common precursor isopopentenyl diphosphate (IPP) formed in the plastitial MEP and the cytoplasmic mexulonate (MVA) pathways [56]. IPP and dimethylallyl pyrophosphate (DMAPP) are further catalyzed to form geranyl diphosphate (GPP), famesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP).