## 4 Discussion  
### Consequences of Water Deficit on Pinot Noir Physiology and Berry Skin Anthocyanin Content  
Important changes in physiological responses are typically observed in _Vitis vinifera_ under different levels of water stress, such as decrease of leaf stomatal conductance and photosynthetic rate [1; 11; 56], which often affect berry sugar accumulation [57; 58; 59]. A moderate restriction of water supply improves the quality of red wines by achieving optimal sugar levels, due to the competition for carbon assimilates between berry ripening and shoot growth and to a lower sugar concentration in berries because of increased berry size [60]. When the limitation in vine water uptake is severe, the stomatal closure restricts photosynthesis, reducing berry weight, accumulation of sugars, and yield [2; 61; 62]. In our study, as expected, \(P_{n}\), \(g_{s}\), \(\Psi_{\text{pd}}\), \(\Psi_{\text{stem}}\), and RWC were significantly reduced by drought in WS vines with respect to WW ones; moreover, low water availability decreased titratable acidity, pH, berry weight, and, consequently, cluster weight and yield. However, water availability did not significantly affect berry sugar accumulation. This result is in agreement with the results observed by [PERSON] et al. [63] on Pinot noir cv. in pot conditions, whereas the same cultivar showed a decrease in berry sugar content induced by high soil water availability compared to water stresses plants in field conditions [64]. This discrepancy between pot and field trials can be linked to the space limitation for root development impaired by the pot, which does not occur in the open field. This restraint may have restricted carbohydrates reserves stored in grapevine roots, which are known to contribute to berry sugar accumulation, after translocation to berries, by hydrolyzation of the starch into soluble sugars [65; 66]. At biochemical level, an increment in malvidin and in total anthocyanin contents was found in water stressed vines, suggesting that low water availability drove a major flux of carbon in the anthocyanin pathway, particularly towards more stable malvidin-based derivatives [67]. This effect partly compensated the reduction in anthocyanin biosynthesis caused by the reduction in \(P_{n}\) because of stomatal closure [23]. Moreover, in WS berry skins, we observed an increase in the methoxylated to nonmethoxylated anthocyanin ratio, confirming that water stress boosts methoxylation, thus anthocyanin stability, as an adaptive strategy to adverse climatic conditions, like heat stress and high radiation load [68; 23; 69]. Timing of Action of A. nodosum Extract in Improving Plant Physiological Performance and Water Relations  
Our results confirm that _A. nodosum_ treatments during the last stages of berry development allow to improve leaf gas exchanges of _V. vinifera_ and show for the first time that the beneficial effect of these treatments can be observed under water stress conditions. Indeed, in SWE vines subjected to water stress, despite the occurrence of a severe reduction in stomatal conductance (\(g_{s}<50\) mmol H\({}_{2}\)O m\({}^{-2}\) s\({}^{-1}\)) [1; 11], diffusional limitation to photosynthesis were less pronounced compared to CTRL vines, thus resulting in a higher WUE. The effectiveness of _A. nodosum_ treatment on vine physiology could be also discerned at t\({}_{1}\) under water stress conditions, since SWE plants maintained higher water potentials (\(\Psi_{\text{pd}}\), \(\Psi_{\text{stem}}\)) than in CTRL vines. At this sampling point, the high air temperature induced a strong decrease in RWC; however, this decline was much more evident in nontreated plants, supporting the hypothesis of a positive effect of _A. nodosum_ in preventing excessive leaf dehydration [70]. The effect of the treatments on plant water status persisted and was intensified with water stress progression. Indeed, at t\({}_{2}\), SWE vines showed a better Kplant than CTRL vines.