## 4 Discussion
### Clones Show Different Hydraulic Behavior, Stomatal Regulation, and Vine Water Use
In contrast, high-vigor Monastrell clones (4, 94, 188) showed a nearly-isohydric behavior and maintained a better vine water status (measured by \(\Psi_{\rm s}\) and \(g_{\rm s}\)) during the growing season, which suggests a greater root water uptake/water transport capacity and irrigation efficiency in invigorating clones compared to low-vigor clones (26), despite being grafted on the same drought-tolerant rootstock (110R). In addition, high-vigor vines maintained a higher plant carbon assimilation (higher leaf gas exchange and total leaf area, Tables 3 and 5) during the growing season and had a higher water spending under irrigated and non-irrigated conditions (Figure 4). These genotypes (especially clones 4 and 94) showed an \"elastic\" behavior, as they maintained unchanged \(A\) and \(\rm WUE_{leaf}\) levels (\(A/g_{\rm s}\)) under both well-watered and water-stressed conditions (56). The lower disposition to a rapid stomatal closure and the maintenance of a higher stomatal aperture in high-vigor clones (e.g., clone 4) did not translate into substantial reductions in \(\Psi_{\rm s}\), contrary to what was observed in other varieties (cv. Syrah) (61). Greater \(E\), leaf \(\Delta\Psi\), and leaf area development (e.g., clones 4, Tables 3 and 5) would also suggest an enhanced whole plant hydraulic conductance that is able to offset the water losses by transpiration, maintaining a high \(\Psi_{\rm s}\) (less negative). Nevertheless, the an-(isohydric) classification has been called into question (62), as recent analysis shows that a continuum exists in the range of stomatal sensitivities to water stress in _V. vinifera_, rather than an isohydric-anisohydric dichotomy, that is further enriched by the diversity of scion-rootstock combinations (63) or even depending on the intensity of the water deficit (64). It is also noticed that the same physiological patterns were repetitively encountered when water was substantially restricted in these clones (year 2021). The same groups of high-vigor clones maintained a better water status and a greater stomatal aperture and leaf gas exchange and were systematically more productive and the most efficient (\(\rm WUE_{\rm yield}\)) despite watering with less water, while low-vigor clones (irrigated with more water, Table 2) maintained a lower leaf gas exchange and leaf area and were less efficient (Tables 3 and 5). This suggests that those differences are truly fixed at a genetic level, regardless of ambient/irrigation conditions, as observed in clones from other varieties (11). It is still unclear which of the two, iso/anisohydric, represents cultivars that are better adapted to drought, but a major factor associated with water deficit tolerance in other _Vitis_ genotypes (e.g., cv. _Ramsey_, Cabernet Sauvignon/M4) was associated with the maintenance of a better water status in the vine and a higher stomatal conductance and photosynthesis during soil water deficit, as a consequence of a greater rooting depth and a higher uptake of water from the soil (65,66). Indeed, during the highest evaporative demand period, high-vigor clones 94 and 188's vines showed a different physiological behavior compared to those of the high-vigor clone 4: (1) a more anisohydric behavior (more vine water stress during the growing season), (2) more efficiency at the leaf level in the short term (higher \(A/g_{\rm s}\)) and the long-term (higher \(\delta^{13}\)C), and (3) a stronger stomatal regulation of gas exchange and water use (seasonal and daily). Thus, clones 94 and 188 behaved like more water saver clones compared to clone 4, which was the highest water spender and the least efficient at the leaf (\(A/g_{\rm s}\)) and plant (\(\rm WUE_{\rm yield}\), \(\delta^{13}\)C\({}_{\rm berries}\)) levels.