## 4 Discussion  
The two seasons of the study were different from a weather point of view. In fact, 2012 was generally warmer and drier than 2013 (Table 1). The conditions of 2013 enhanced vine vigor avoided summer water stress and delayed the timing of all phenological phases. Nevertheless, dry and warm condition from mid-September to mid-October prolonged vine metabolic activity, and allowed it to reach an optimal level of berry ripening. The thermal and radiative microclimate indices allowed separating south facing vineyards from the west facing ones, but neither the sampling dates, nor the vigor levels (Figure 1). In general, the southern vineyards were the hottest even if, as evidenced by the significant interaction year\"treatment for SD \(\geq\) 35 and NH15 - 25, the differences between the south and west vineyards were amplified in the cooler and wetter season (2013) whereas they were mitigated in the warmer season (2012). ST:SPAR was smaller in the southern than in the western vineyards in both years. This index is an expression of two synergistic effects. Firstly, in hilly conditions such as those of the study, the southern aspect intercepted higher amount of solar radiation (higher values of SPAR). Secondly, the west side of the hill registered the maximum daily temperature (thus, the high value of ST) when, in the afternoon, the Sun's rays were perpendicular to the slope. This index showed a good potential in characterizing the microclimates and it contributed to their separation when inserted into the dataset analyzed by PCA. The PCA analysis conducted on both microclimatic indices and carotenoid compounds, effectively separated the west facing vineyards from the south facing ones and, in the latter case, also the two levels of vigor (Figure 5). The vineyards separation along Prin1 was determined by the sum of the carotenoids and by both the microclimatic indices NH15 - 25 and ST:SPAR, whose values were greater in the west facing plots. All these variables were positively correlated with Prin1 (Table 5), thus, the overall amount of the carotenoids was favored by cooler conditions. The differences between the vintages and between the levels of vigor were evident in the warmer vineyards where the intercepted radiation was greater (South) but not in the fresher ones (West) whose conditions were evidently less favorable for the degradation of carotenoids (Figure 5). This observation led to think that the negative effect of higher temperatures prevails over the positive effect of a higher interception of radiation on grape carotenoid concentration at harvest. In the first part of this study [31], higher amount of C13 norisoprenoids was found in the sunniest year and in the more sunlit vineyards. The decrease in the concentration of those compounds in the warmer SouthV\(-\) plot in the last ripening stage was likely attributable to the effect of high temperatures. This decrease was more evident for some compounds and less for others, \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Prin1** & **Prin2** & **Prin3** \\ \hline Explained variance (\%) & 39 & 27 & 20 \\ Eigenvalues & 2.7 & 1.9 & 1.4 \\ Loadings of the variables & & & \\ Neoxanthin (\%) & 0.15 & **0.67** & 0.02 \\ Sum of carotenoids (\(\mu\)g berry\({}^{-1}\)) & **0.46** & 0.09 & \(-\)0.12 \\ Lutein: \(\beta\)-carotene & 0.18 & **0.65** & 0.04 \\ NH15-25 & **0.53** & \(-\)0.20 & 0.23 \\ NH25 -35 & \(-\)0.13 & \(-\)0.02 & **-0.79** \\ NH35 & \(-\)0.41 & 0.05 & **0.54** \\ ST:SPAR & **0.51** & \(-\)0.26 & 0.09 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Principal Component Analysis (PCA): Percentage of variance explained by the three principal components (Prin1, Prin2, and Prin3), eigenvalues and loadings indicating the correlation between the variables and the three principal components. thus microclimate had an effect on both concentration and profile of C13-norisoprenoids in Nebbiolo grapes [31] confirming, at least in part, results already issued [14].