## 4 Discussion  
The girdling of shoots or the trunk to prevent the basipetal movement of assimilates and plant growth regulators is an old technique that has been applied with variable success in many fruit tree species [12; 31]. In kiwifruit, girdling of canes or the trunk during the early fruit developmental stages aims mainly at improving fruit size, while girdling applied during the later stages of fruit development (stages of slower fruit development) focuses mainly on increasing fruit dry matter [32; 33; 34; 35]. In the present experiment, the girdling was applied at the end of summer and early autumn, when fruit growth is slower, aiming at improving fruit quality characteristics and storability. The most immediate effect of girdling seen in kiwifruit vines was a decrease in the carbon assimilation rate, which occurred within one month after girdling. Both in September as well as at harvest, the leaves in shoots sprouting from girdled cares presented lower photosynthetic rates without any significant changes in intercellular CO\({}_{2}\) or stomatal conductance. Similar results concerning the reduction of photosynthetic rates have been reported by many other researchers, both in kiwifruit [36] as well as in other fruit species [24; 37; 38; 39; 40; 41; 42], while non-significant impacts have also been observed [31; 43]. The reduction of the photosynthetic capacity of the leaf has been attributed to a feedback inhibition mechanism (or feedback sink regulation) [41; 42] due to the accumulation of excessive amounts of carbohydrates in the leaves above the girdle zone [24; 44; 42]. Others attribute this reduction to the reduced stomatal conductance (possibly due to the elevated concentration of ABA in the leaves above the girdle zone) [24], which greatly influences the diffusion of CO\({}_{2}\) into the sub-stomatal area and reduces at the same time transpiration rates [24]. In the present experiment, though, such reductions in stomatal conductance and transpiration rates were recorded only in September's measurement (under the GA treatment) but not at harvest, indicating that the reduction of photosynthesis should not be solely attributed to stomatal limitations. The reduced efficiency of the PS II reaction center has also been proposed as the main factor limiting photosynthesis after girdling [41; 45]. In  
Figure 4: Major nutraceuticalul and health-promoting compounds per fruit under the various girdling treatments. Abbreviations: TS, total sugars (g); TPh, total phenols (mg); FRAP (umol equiv. Trolox); DPPH (umol equiv. Trolox); ASA, ascorbic acid (mg); GA, August girdling; GS, September girdling; GAS, double girdling in August and again in September. The asterisks denote significant differences from the control treatment based on [PERSON]’s test. the present experiment, the slight increase in the intercellular CO\({}_{2}\), although not significant, could mean that non-stomatal limitations may also exist, as has been reported in peach [46], orange tree [45], mango [14], and pistachio [47]. The reduction of the photosynthetic rate due to girdling has also been attributed to the reduction of leaf nitrogen concentration [42]. Although nitrogen concentration was not measured in the present experiment, it would be safe to assume that its reduction would lead to leaf yellowing, as indicated here by the reduced SPAD index at harvest, especially under GAS treatment. Furthermore, it has been reported that girdling accelerates leaf senescence, leading to decreased chlorophyll content [48; 49; 50] and thus photosynthetic rates due to reduced cytokin levels together with increased ABA ones [50]. This reduction of chlorophyll levels was supported in the present experiment by the low SPAD index under the double girdling treatment, which may have accelerated leaf senescence compared to other treatments. All girdling treatments had a significant effect on increasing fruit dry matter at harvest, with this effect remaining even post-storage.