## 3 Results  
### Berry Development  
In Figure 1, single berry weight during berry development is shown for both cultivars under aCO\({}_{2}\) and eCO\({}_{2}\) over three consecutive seasons. In contrast to 2014, differences occurred for both cultivars in the following years between the two CO\({}_{2}\) treatments during berry development (Figure 1). In 2015, Riesling showed higher single berry weights under eCO\({}_{2}\) on the last four out of five sampling dates (Figure 1b) and, in 2016, the date closest to harvest (Figure 1c). This last sampling date in 2016 also showed the highest overall single berry weights for Riesling with 1.7 and 2.0 g per berry for aCO\({}_{2}\) and eCO\({}_{2}\), respectively. Single berry weights of Cabernet Sauvignon increased for all dates during ripening in 2015 (Figure 1e) and 2016 (Figure 1f). Cabernet Sauvignon highest single berry weights were also detected at the end of 2016 season with 1.4 and 1.7 g for aCO\({}_{2}\) and eCO\({}_{2}\), respectively. The berry weight of Cabernet Sauvignon in general was lower compared to Riesling berries over all three years. For both cultivars, higher single berry weights under eCO\({}_{2}\) usually occurred on sampling dates close to harvest where differences between treatments were higher than at the beginning of veraison. The Bayesian generalized linear mixed model analyses of the berry quality parameter single berry weight (SBW) was attested to be affected by elevated CO\({}_{2}\) conditions when comparing posterior predictions of the differences between eCO\({}_{2}\) and aCO\({}_{2}\) for both cultivars (Figures 8 and 9). No significant differences, i.e., 90% of the one-sided posterior predicted differences being larger (lower) than zero, were found for the year 2014 and both cultivars. SBWs on measurement dates in 2015 and 2016 were most affected with probabilities of 78%-95% and 91%-99% for Riesling (Figure 8) and Cabernet Sauvignon (Figure 9), respectively. The single berry weight of Cabernet Sauvignon was consistently and significantly higher throughout both years for eCO\({}_{2}\) compared to aCO\({}_{2}\) (Figure 9). Riesling was affected less consistently throughout the years. As shown in Figure 8, for both years, the estimated SBW close to harvest date was significantly higher for eCO\({}_{2}\) compared to aCO\({}_{2}\) by probabilities of a difference greater than zero of 95% (2015) and 93% (2016). For both cultivars, median differences close to harvest were estimated to be approximately 0.2 g. In 2015 and 2016, the median difference appeared to increase with time and, therefore, with maturity of the berries. In accordance with the Bayesian generalized linear mixed model analyses for single berry weight, Figure 2 shows the effect of eCO\({}_{2}\) on single berry weight of Riesling and Cabernet Sauvignon overall years and for single years (Figure S1, Supplementary Materials). Over all three years, eCO\({}_{2}\) stimulated single berry weight of Riesling by 7% (Figure 2a), due to a low response in 2014 with \(y=0.9742x+0.0921\), \(R^{2}=0.83352\) (Figure S1a, Supplementary Materials). In contrast, the response in 2015 was 20% (\(y=1.2042x-0.0748\), \(R^{2}=0.91801\)) and that in 2016 was 13% (\(y=1.1250x-0.0274\), \(R^{2}=0.94525\)) due to eCO\({}_{2}\) (Figure S1a, Supplementary Materials). Figure 1: Single berry weights of Riesling (**a**–**c**) and Cabernet Sauvignon (**d**–**f**) for the two treatments aCO\({}_{2}\) and eCO\({}_{2}\) and the three seasons 2014, 2015, and 2016 during berry development. Letters indicate development stages veraison (V) and harvest (H). Mean values per treatment \(\pm\) SD of the three FACE rings. Figure 2: Relation between aCO\({}_{2}\) and eCO\({}_{2}\) values of single berry weight [g] between pre-veraison and harvest for Riesling (**a**) and Cabernet Sauvignon (**b**) of three independent sets of data collected in three different seasons 2014, 2015, and 2016.