## 3 Results and Discussion
### Midday Stem Water Potential  
Midday stem water potential, \(\Psi\)stem, accurately reflected the tree water status in both young and mature sweet cherry trees (Figure 2). \(\Psi\)stem has been reported as a sensitive water stress indicator in mature sweet cherry trees [6; 8]; however, there is scarce information about the use of this indicator in young sweet cherry trees, for which pre-dawn stem water potential and midday leaf water potential have been reported as robust water status indicators [37; 38]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Location**} & \multirow{2}{*}{**Parameter**} & **May.** & **Jun.** & **Jul.** & **Aug.** & **Sep.** & **Oct.** & **Nov.** \\  & & **(121–151)** & **1** & **(152–181)** & **(182–212)** & **(213–243)** & **(244–273)** & **(274–304)** & **(305–334)** \\ \hline \multirow{4}{*}{Plot 1} & VPD (kPa) & 0.88 & 1.16 & 1.10 & 1.42 & 0.99 & 0.71 & 0.51 \\  & ET\({}_{0}\) (mm d\({}^{-1}\)) & 4.99 & 5.78 & 6.11 & 5.34 & 3.81 & 2.54 & 1.60 \\  & P (mm) & 3.60 & 14.00 & 0.00 & 0.00 & 70.20 & 42.60 & 106.60 \\  & T (\({}^{\circ}\)C) & 18.69 & 22.79 & 25.62 & 26.89 & 24.42 & 18.91 & 14.62 \\ \hline \multirow{4}{*}{Plot 2} & VPD (kPa) & 0.76 & 1.27 & 2.07 & 1.44 & 0.83 & 0.61 & 0.34 \\  & ET\({}_{0}\) (mm d\({}^{-1}\)) & 4.25 & 5.21 & 6.07 & 4.81 & 3.09 & 2.09 & 1.25 \\  & P (mm) & 22.95 & 35.27 & 0.00 & 21.17 & 35.21 & 22.06 & 27.95 \\  & T (\({}^{\circ}\)C) & 15.44 & 20.44 & 24.97 & 23.99 & 20.61 & 14.19 & 9.65 \\ \hline \multicolumn{2}{c}{VPD: vapour pressure deficit; ET\({}_{0}\): crop reference evapotranspiration; P: accumulated rainfall; T: mean air temperature. \({}^{1}\): Day of year.} & \multicolumn{1}{c}{} & & & & \\ \end{tabular}
\end{table} 
Table 1: Environmental conditions of Plot 1 (La Palma) and Plot 2 (Jumilla) during the experimental period. Figure 2: Seasonal evolution of the midday stem water potential (\(\Psi\)stem) in young (**a**) and mature (**b**) sweet cherry trees during the study period. Each point corresponds to the mean \(\pm\) standard error of the mean for six measurements per treatment. Asterisks indicate statistically significant differences between treatments by ANOVA (\(p<0.05\)). CTL and S correspond to control and deficit irrigation treatment for young (\(\Upsilon\)) and mature (M) sweet cherry trees, respectively. 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 crop water requirements (ETc) applied to mature sweet cherry trees (Plot 2). The mean \(\
abla\)stem measured in young and mature CTL trees was between \(-0.5\) and \(-0.7\) MPa, values typical of well-watered trees. These differences in water potential of control trees were due to changes in the climatic demand. Regarding the water stress treatments, the lowest \(\
abla\)stem values were measured in young trees which were submitted to two drought and recovery cycles, with minimum values that fell below \(-1.7\) and \(-2.1\) MPa for the first and second cycle, respectively. After irrigation was resumed, recovery of \(\
abla\)stem in young sweet cherry trees was rapid in both cycles. The \(\
abla\)stem values measured in the young trees showed that they were submitted to severe water stress. During the first drought period, \(\
abla\)stem in young sweet cherry trees continuously declined from values similar to those of CTL trees down to \(-1.7\) MPa in 16 days, and needed eight days of full irrigation to exhibit similar values to CTL trees. During the second drought cycle, a steeper drop of \(\
abla\)stem was observed, and the minimum value reached \(-2.1\) MPa (Figure 2a). \(\
abla\)stem values measured were lower than those reported by [PERSON] et al. [39] for unirrigated young sweet cherry trees. In the mature trees (Figure 2b), deficit irrigation trees resulted in \(\
abla\)stem values that remained above \(-1.5\) MPa, which could be considered a mild-severe water stress that would not compromise the tree's yield the following year [5; 40].