## 3 Results and Discussion
### Canopy Temperature  
The pattern of Tc was in accordance with the evolution of \(\
abla\)stem in young sweet cherry trees (Figure 3); however, in mature trees it was not possible to differentiate between the control and water-stressed trees at the end of the season (September, DOY 270 onwards) using the temperature of the canopy, when the air temperature significantly decreased from 24 to 13 \({}^{\circ}\)C (Figure 3a,b). Figure 3: Seasonal evolution of the canopy temperature (Tc) and the difference between canopy and air temperature (\(\Delta\)T) in young (**a**,**c**) and mature (**b**,**d**) sweet cherry trees during the study period. Each point corresponds to the mean \(\pm\) standard error of the mean for six images per treatment. CTL and S correspond to control and deficit irrigation treatment for young (\(\gamma\)) and mature (M) sweet cherry trees, respectively. Asterisks indicate statistically significant differences between treatments by ANOVA (\(p<0.05\)). FI is full irrigation period, D is drought period and R is recovery period in young sweet cherry trees (Plot 1), and 100% and 55% are the percentages of ET applied in mature sweet cherry trees (Plot 2). As expected, young and mature control trees had lower values of canopy temperature minus air temperature than water-stressed trees during the period of water restriction (Figure 3c,d). Regarding the control trees, it was observed that mature control trees had a canopy temperature on average 2.5 \({}^{\circ}\)C below the temperature of the air, while in the same period the young trees had a temperature of the canopy only 1 \({}^{\circ}\)C below the air temperature. This difference in \(\Delta\)T of control trees depended on their age, according to [PERSON] et al. [15], who related the influence of leaf area on the temperature of the plants. Thus, mature trees with greater canopy volume exhibited lower canopy temperatures than young trees with lower canopy volume. The maximum \(\Delta\)T was measured on DOY 239 in stressed young trees (3.5 \({}^{\circ}\)C), which was the day with the lowest \(\Psi\)stem (\(-\)2.1 MPa, Figure 2a). The difference in canopy temperature between stressed and control young trees was higher than 4 \({}^{\circ}\)C on that day. These results indicated a smaller difference than that reported by [PERSON] et al. [41] and [PERSON] and [PERSON] [42] in non-irrigated citrus (\(\Delta\)T = 5.0 \({}^{\circ}\)C) and peach trees (\(\Delta\)T = 6.5 \({}^{\circ}\)C) under similar values of \(\Psi\)stem (\(<\)\(-\)2.0 MPa). Similarly, the maximum difference of \(\Delta\)T observed between water-stressed and control mature trees was 4.4 \({}^{\circ}\)C (DOY 204, Figure 3d). The difference of 4.4 \({}^{\circ}\)C between treatments was mainly due to the contribution of the control trees (\(\Delta\)T\({}_{\rm{MCTL}}\) = \(-\)3.1 \({}^{\circ}\)C) rather than the high value of the temperature of the canopy of water-stressed trees above the air temperature (\(\Delta\)T\({}_{\rm{MS}}\) = 1.3 \({}^{\circ}\)C). These values of canopy temperatures that were lower than the air temperature in control sweet cherry trees are similar to those reported in almond [43] and peach trees [42], but are contrary to those recorded for orange trees [44]. This difference with citrus trees might be due to the stomatal closure of citrus trees at midday, which increases the leaf temperature even though the tree has no soil water restrictions, while in well-watered _Prunus_ trees this does not occur [45; 46]. Data from control and water-stressed trees were pooled to determine the upper (non-transpiration) and lower (non-water-stress) baselines for the mature and young sweet trees (Figure 4). All the obtained equations for the non-water-stress baselines showed a strong linear relationship between VPD and canopy temperature of sunny leaves (Table 2). Regardless of the different location and age of trees, the non-water-stress baseline did not differ among them, and fitted in the linear regression: \(\Delta\)T = 3.87 \(-\) 2.62\(\cdot\)VPD (R\({}^{2}\) = 0.91).