## 5 Conclusions  
The present study provides evidence that eCO\({}_{2}\) did alter some bunch and berry parameters without causing any negative effects on fruit quality during berry development and structure of bunches.  
During berry development, eCO\({}_{2}\) resulted in higher single berry weight and malic acid for both cultivars in two seasons and lower tartaric acid for Riesling in one season. Effects were evident from the second season of investigations after CO\({}_{2}\) enrichment was applied. So far, no substantial differences were detected for total soluble solids or for citric, shikimic, and amino acid concentration.  
As vnification from smaller berries supposedly results in higher quality wines due to a higher concentration of compounds located in the grape skin such as flavonols or anthocyanins [14], it is advisable to investigate if the higher single berry weights derived from eCO\({}_{2}\) treatment might have a negative effect on the amount of grape skin compounds in both cultivars. Additionally, the variation in berry size among Rieseling clones is reported not to be responsible for different levels of C\({}_{13}\)-norisoprenoid aroma compounds like 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) [21], well known to produce petrol-like off-flavors in Riesling wine [62]. Therefore, it could be of interest to study the impact of different CO\({}_{2}\) environments on TDN concentration in Riesling.  
Based on the results of this study starting from the initial adaption of perennial plants to CO\({}_{2}\) enrichment, seasonal measurements of the berry compounds should be continued to investigate the long-term response of the two different cultivars to elevated CO\({}_{2}\) concentration.  
The following are available online at [[http://www.mdpi.com/2076-3417/10/7/2486/s1](http://www.mdpi.com/2076-3417/10/7/2486/s1)]([http://www.mdpi.com/2076-3417/10/7/2486/s1](http://www.mdpi.com/2076-3417/10/7/2486/s1)): Figure S1: Regression between aCO\({}_{2}\) and eCO\({}_{2}\) values of single berry weight [g] for Riesling (a) and Cabernet Sauvignon (b) of the three single datasets of the three different seasons (2014, 2015, and 2016); Table S1: Posterior predicted probabilities for differences in berry size categories between eCO\({}_{2}\) and aCO\({}_{2}\) being different from zero (P (difference \(<\) 0) and P (difference \(>\) 0)) for each year and both cultivars, Cabernet Sauvignon (CS) and Riesling (R), from Bayesian mixed-effects adjacent category models.  
Conceptualization, Y.W. and M.S.; methodology, Y.W., S.T., D.S., D.R., and M.S.; formal analysis, Y.W. and D.S.; investigation, Y.W. and S.T.; resources, D.S., D.R., and M.S.; data curation, Y.W., S.T., and D.S.; writing--original draft preparation, Y.W., S.T., M.S., D.S., D.R., and B.H.; writing--review and editing, Y.W., S.T., D.S., D.R., and B.H.; visualization, Y.W. and D.S.; supervision, M.S. and B.H.; project administration, Y.W., S.T., and M.S. All authors read and agreed to the published version of the manuscript.  
The LOEWE excellence cluster FACE2 FACE of the Hessian State Ministry of Higher Education, Research and the Arts (HMWK) funded this research.  
We acknowledge the technical staff of the Department of General and Organic Viticulture for operating vineyard management of the VineyardFACE. Thanks are due to the laboratory team of the Department for helping with sampling, preparation, and analyzation of juices. We thank [PERSON] and [PERSON] for conducting HPLC analyses and preparation of samples. Furthermore, the authors would like to thank the Bachelor and Master students [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] for their help in the field and laboratory.  
The authors declare no conflicts of interest.