## 3 Results
#### 3.1.1 Vine Water Status and Leaf Gas Exchange
Thesignificant and positive linear relationship between \(\Delta\Psi\) in the leaves and leaf transpiration (similar in control and stress vines) suggests that, in general, vines with a greater \(E\) were associated with a greater leaf \(\Delta\Psi\) (Figure 3B). However, this positive relationshipwas only significant in clones 276 and 372 (Figure 3C). In addition, there were no signifi-cant differences in Kleaf among clones (Figure 3C). Figure 3: (**A**) Differences in midday stem water potential (\(\Psi\)s) between control and stress treatments for each clone during post-veraison periods (average data from two years: 2020 and 2021). (**B**) Significant linear relationship between leaf transpiration rate (E) and \(\Delta\Psi\) (\(\Psi\)i-\(\Psi\)s) measured at midday during post-veraison in 2020. * \(p<0.05\). In (**B**), points represent data from all of the clones. (**C**) Significant relationships between gradient of water potential in the leaves and leaf transpiration measured at midday for each clone, during post-veraison period in 2020 (20 th August 2020). In (**C**), each single point is a single measurement made in the same leaf in a vine. Kleaf was calculated in August 2020 for each clone using the evaporative flux method (see Material and methods). ns, not significant, * \(p<0.1\), ** \(p<0.05\), *** \(p<0.01\). Essentially, the stress treatment significantly decreased leaf gas exchange (\(A\), \(g_{s}\), \(Ci\)) and increased \(A/g_{s}\) in all of the clones during the pre-veraison period in 2020 (Table 3). However, during post-veraison, significant interactive effects in gas exchange parameters (\(A\), \(g_{s}\), \(Ci\), \(E\), \(A/g_{s}\)) indicated different leaf gas exchange regulation under water stress, depending on the clone (Table 3). Therefore, during post-veraison, vines from 276 and 373, under water stress, showed a significant decrease in \(A\), \(g_{s}\), and \(E\) and an increased \(A/g_{s}\) at the early morning compared to their control vines (Figure 4A-D). In the same way, at midday, clone 276 under WS had a strong decrease in \(A\), \(g_{s}\), and \(E\) (38-52%) and an enhanced \(A/g_{s}\) (38%) compared to its control. Other clones, such as 373 and 188, also restricted their leaf gas exchange at midday, but to a lesser extent; between 16% and 9.5% on average, respectively (significantly lower \(g_{s}\) in 188 under WS compared to their Control) (Figure 4E-H). In other clones, there were no significant differences in leaf gas exchange between control and stress vines at the early morning or midday. The significant relationships found between midday stem water potential (\(\mathbf{V_{s}}\)) and leaf gas exchange parameters (Figure 5) revealed that: (1) in general, low-vigor clones had lower  
Figure 4: Significant interactive effects of the clone and irrigation treatment on leaf gas exchange parameters measured at early morning and midday during the post-veraison in 2020. Different letters indicate significant differences according to [PERSON] ’s multiple range test at the 95% confidence level. \(\Psi_{\rm s}\) than high-vigor clones (minimum around \(-1.7\) MPa vs. 1-3 MPa, respectively); the point cloud is always leftmost (Figure 5A); (2) for the same \(\Psi_{\rm s}\), high-vigor clones showed a greater leaf gas exchange (\(A\), \(E\), \(g_{\rm s}\)) and lower (\(A\)/\(g_{\rm s}\)) than low-vigor clones, and this was accentuated by severe water stress (\(g_{\rm s}\) and \(A\)/\(g_{\rm s}\)) (Figure 5A,C,E,G); (3) clone 4 maintained greater \(g_{\rm s}\) for the same \(\Psi_{\rm s}\) value, compared to the rest of the clones (Figure 5B); (4) clone 4 maintained greater \(g_{\rm s}\) when WS developed (lower slope); in contrast, in clones 188 and 373, leaf gas exchange decreased sharply when water stress developed (higher slope) (Figure 5B,D,F); (5), while clone 4 practically did not enhance \(A\)/\(g_{\rm s}\) under WS, clone 373 and mainly clone 360 linearly enhanced it when WS developed (Figure 5H). For values above \(-1.3\) MPa, an abrupt rise in \(A\)/\(g_{\rm s}\) was observed.