_Applied_  
_sciences_  
_Article_  
**The Effect of Elevated CO2 on Berry Development**  
**and Bunch Structure of _Vitis vinifera_ L. cvs. Riesling and Cabernet Sauvignon**  
**[PERSON] 1,*, [PERSON] 1, [PERSON] 2\({}^{\text{(c)}}\), [PERSON] 3, [PERSON] 4 and [PERSON] 1**  
1 Department of General and Organic Viticulture, Hochschule Geisenheim University, Von-Lade-Strasse 1, 65366 Geisenheim, Germany; [EMAIL_ADDRESS] (S.T. ); [EMAIL_ADDRESS] (M.S.) 2 Department of Modeling and Systems Analysis, Hochschule Geisenheim University, Von-Lade-Strasse 1, 65366 Geisenheim, Germany; [EMAIL_ADDRESS]  
3 Department of Microbiology and Biochemistry, Hochschule Geisenheim University, Von-Lade-Strasse 1, 65366 Geisenheim, Germany; [EMAIL_ADDRESS]  
4 Department of Agronomy and Plant Breeding I, Justus Liebig University, Schubertstrasse 81, 35392 Giessen, Germany; [EMAIL_ADDRESS]  
* Correspondence: [EMAIL_ADDRESS]; Tel. : +49-6722-502-144  
in greenhouses were also conducted [11; 12; 13]. Even though the effect of eCO\({}_{2}\) on grapevines was studied over the last few decades, the effect on fruit structure and grape quality is not sufficiently investigated. In a recent VineyardFACE study, eCO\({}_{2}\) did not alter bunch number per vine but increased yield, bunch weight, and berry number for cvs. Riesling and Cabernet Sauvignon, and it resulted in higher bunch compactness for Cabernet Sauvignon [9]. [PERSON] [3] also affirmed increased cluster weights in one of three experimental years for cv. Touriga Franca under eCO\({}_{2}\), whereas [PERSON] et al. [6] reported an increased berry fresh weight for cv. Sangiovese. However, berry size was discussed to be related to berry and wine quality [14; 15; 16; 17; 18; 19; 20; 21]. Hence, the quality of grapes grown under eCO\({}_{2}\) might be affected. In other perennial fruit crops like pears and sour oranges, enhanced fruit weight, volume, and diameter were detected under eCO\({}_{2}\)[22; 23; 24]. Soluble solids content of pears was also increased under eCO\({}_{2}\), but the effect depended on growth stages of the fruit [22; 23]. Studies on annual crops under eCO\({}_{2}\) concentrations showed increased fruit yield and berry size of strawberries and raspberries [25; 26; 27], while, in strawberries, sugar content and aroma compounds were increased, and the organic acid content was decreased [26]. This shows that eCO\({}_{2}\) could positively affect fruit structure and fruit quality of several special crops. Whether increasing CO\({}_{2}\) concentration may not have negative effects on grape composition was discussed, but little [2; 7; 28]. Only the anthocyanin concentration of red grape varieties grown under arid climatic conditions was described to possibly increase with increasing CO\({}_{2}\) concentration [7; 28; 29]. By comparing compositional variation in the context of abiotic parameters of 10 successive vintages in multiple Australian regions, a relationship between the annual CO\({}_{2}\) increase and total anthocyanin concentration was reported [28]. In cv. Shiraz, [PERSON] et al. [5] showed that eCO\({}_{2}\) treatment was advanced in phenological development and, therefore, in total soluble solids accumulation with an increasing effect over seasons. Acid and sugar concentrations of cv. Sangiovese were affected by eCO\({}_{2}\), even though results did not show a consistent response over the ripening period [7]. [PERSON] et al. [2] detected higher pH and fructose concentration in berries of cv. Touriga Franca at the beginning of grape maturation in the first season and higher total acidity in grape juice in the second season under eCO\({}_{2}\). So far, no continuous response in the composition of berries or must of different grape varieties grown under eCO\({}_{2}\) concentration over a longer period is described. Therefore, the main objective of this study was to examine the effect of eCO\({}_{2}\) within the VineyardFACE experiment on berry development and bunch structure of two grapevine cultivars (_Vitis vinifera_ L. cvs.