## 3 Results
#### 3.1.1 Vine Water Status and Leaf Gas Exchange
Figure 5: Significant relationships between midday stem water potential (\(\Psi_{\rm s}\)) and leaf gas exchange parameters measured at midday (12:15–13:45 p.m.) for high (4, 94, and 188) and low/moderate-vigor clones (276, 360, 372, and 373) (**A,C,E,G**) and for each clone (**B,D,F,H**) during the post-veraison period (August) in 2020. Each point represents a single measurement of \(\Psi_{\rm s}\) and leaf gas exchange made in the same vine. ns, not significant; \(*\)\(p<0.05\). The analysis of regulation of daily leaf gas exchange from the early morning to midday also showed that \(A\) and \(g_{s}\) decreased more in clone 276 (16% and 18%, respectively) and in clone 94 (12% and 19%, respectively) compared to the rest of the clones (Figure 6). In addition, in these clones, \(E\) increased less from the early morning to midday (22-23%) compared to the rest of the clones (between 35-55%). These clones also showed a slightly greater increase in \(A/g_{s}\) at midday compared to the rest of the clones, where \(A/g_{s}\) decreased at midday (Figure 6). The analysis of the behavior of \(E\) (from the early morning to midday) for each clone under control and WS conditions also revealed different daily regulation of water use at a leaf level, with clones 4 and 188 showing significant increases at midday in \(E\) under control and water stress (Figure S1, supporting information), compared to the rest of the clones (with no significant differences). In addition, clones also had different seasonal regulation (from pre-veraison to post-veraison) of leaf gas exchange, with vines from clones 4 and 188 showing a lower seasonal stomatal regulation (significantly lower decrease in \(A\) and enhanced \(g_{s}\) and \(E\)) compared to the rest of the clones (especially 276 and 360), where \(A\), \(g_{s}\), and \(E\) decreased substantially as the summer progressed (Tables S1 and S2, supporting information). This is also supported by the positive linear relationship between \(E\) and the daily atmospheric vapour pressure deficit (VPD) during the season (Figure 7); this relationship was similar in all of the clones, except in clone 276, where \(E\) increased linearly as atmospheric VPD intensified during the summer in control irrigated vines, but it increased less in water stressed vines (less steep slope) (Figure 7A). Figure 6: Differences between mean values of leaf gas exchange rates measured at early morning and midday for each clone during the post-veraison in 2020. Vertical bars represent the standard errors. ns, not significant; \({}^{*}p<0.1\), \({}^{**}p<0.05\), \({}^{***}p<0.01\), \({}^{***}p<0.001\). Separation was made by [PERSON]’s multiple range test at the 95% confidence level. There were significant relationships between \(g_{s}\) and \(A\) (positive, Figure 8A) and \(g_{s}\) and \(A/g_{s}\) (negative, Figure 8C) at the early morning and at midday. Moreover, a detailed analysis of these relationships indicated that for the same value of \(g_{s}\) (between 0.10 and 0.30 mol m\({}^{-2}\) s\({}^{-1}\)), clone 4 had a lower \(A\) than clones 276, 188, or 372, over all at higher \(g_{s}\) (\(>\)0.15 mol m\({}^{-2}\) s\({}^{-1}\)) (Figure 8B). In addition, for the same \(g_{s}\) value, clone 4 also showed a lower \(A/g_{s}\) compared to other clones; this effect was more accentuated with a low \(g_{s}\) (Figure 8D). In addition, there were significant relationships between stomatal conductance (\(g_{s}\)) and intercellular CO\({}_{2}\) concentration (Ci) for each clone, except for clone 4, which showed an unchanged Ci for a wide range of \(g_{s}\) (from 0.35 to 0.15 mol m\({}^{-2}\) s\({}^{-1}\)) at the early morning, compared to the rest of the clones, where Ci decreased linearly as stomatal closure occurred (Figure 8E). This effect was more accentuated at midday, with clone 4 showing a lower slope (significant relationship), while in clones 276 and 372, Ci decreased most quickly as stomatal closure occurred (higher slope) (Figure 8F).