## 3 Results and Discussion
### Variability of Chemical Constituents
#### 3.2.2 Sweet Potato  
The quality traits varied between the sweet potato organs, under influence of water scarcity, either in the reference values of the first trial, or in the predicted values by NIRS of the second trial (Table S3). Taking into consideration the major constituents, M, St and Pt, in both trials, the water scarcity conditions triggered opposite responses. Pearson correlation shown a weaker relationship between these constituents in the second trial compared to the first trial (Table S6 and Table S4, respectively). Still, both trials registered an accumulation of M-tuber and St-shoot, and a decrease in M-shoot and St-tuber, the variation of which was only significant (\(p\leq 0.01\)) in the shoots. Pt also decreased in both trials and organs, with the exception of the Pt-tuber, which increased in the 2 nd trial (Table S3). The average M-tuber increase and M-shoot significant (\(p\leq 0.01\)) decrease in both trials may have been due to the limitation of macro and micronutrient uptake from water-scarce soil. In such conditions, the mineral allocation into the shoots could be reduced, with lower M-shoot allocation registered in the first trial [43; 58]. The scarcity significantly decreased the N-shoot and Pt-shoot in both trials. However, the N-tuber and Pt-tuber also decreased during the first trial but registered an average significant (\(p\leq 0.05\)) increase in the second trial. N is one of the essential primary macronutrients, the uptake of which, as a result of primary assimilation, is strongly compromised during drought stress, with \(\delta^{15}\)N indicating the N fractionation during the N cycle processes [57; 58; 59]. The average content of the shoots \(\delta^{15}\)N and \(\Delta^{13}\)C had the same pattern, by significantly (\(p\leq 0.05\)) decreasing its content in both trials. The reduction in \(\delta^{15}\)N-shoot is a signal of less N retention in aboveground tissue due to drought [59]. The lower \(\Delta^{13}\)C-shoot indicates a low \({}^{13}\)C depletion, through partial stomatal closure, leading to a slight variation in the TC as \({}^{13}\)C fixation due to stress [59]. Both trials showed that stress increased St-shoot and consequently decreased St-tuber. Starch is deposited in the leaf chloroplasts during daylight carbon dioxide fixation in photosynthesis to be broken down to sucrose during the night, which is then mobilized and converted into storage starch in the tubers [60]. The slight downregulation of photosynthesis, possibly due to the partial stomatal closure, still allowed an accumulation of starch at the shoot level, with the second trial registering significantly (\(p\leq 0.01\)) greater St-shoot accumulation. It still allowed good photosynthesis activity and avoided the starch degradation into sugars, reducing its mobilization into tubers. However, in such conditions, the carbohydrate metabolism and photosynthesis oxidative processes can produce oxal acid, forming insoluble salts when combined with free calcium, as CaOx insoluble druse crystals [61]. We observed that the whole-plant CaOx average content decreased in the first trial, with an increase in the second trial. The CaOx increase in the second trial could be due to the plant needing to isolate the excess of calcium accumulated in its tissues [62]. The oscillation in the CaOx formation in stress was probably due to the plant ion balance, leading to the fluctuation of druse crystal formation, according to the availability of free calcium [8; 63]. Acc. 3124 from Guinea-Bissau had one of the best physiological responses to water scarcity during the first trial, namely the highest total plant biomass content and the best water use efficiency [52]. The fact that it showed the combination of high St-tuber, M-shoot, and Pt-shoot content indicates that it had one of the best nutrient allocations into the shoot and tuber starch storage under stress.