Carbon isotope compositions of whole wine, wine solid residue, and wine ethanol, determined by EA/IRMS and GC/C/IRMS, can record the vine water status-a comparative reappraisal.

Recently, we reported that the carbon isotope composition of the solid residues obtained by freeze-drying white and red wines (δC) could be used for tracing the water status of the vines whose grapes were used to produce them. Here, we compare different methods using δC values of other wine components, particularly those of whole wine (δC) obtained by elemental analysis and isotope ratio mass spectrometry (EA/IRMS) and of wine ethanol (δC) obtained by gas chromatography/combustion/IRMS (GC/C/IRMS), for their suitability to assess the vine water status. The studied wines were obtained from field-grown cultivars (Vitis vinifera L. cv. Chasselas, Petite Arvine, and Pinot noir) under different water treatments during the 2009-2014 seasons and were the same wines in which the δC was measured previously. The EA/IRMS method for whole wine used two successive EA analytical cycles in each acquisition period to reduce the residence time of the sample capsules in the autosampler. The sample aliquots for the EA/IRMS and GC/C/IRMS analyses were optimized for peak-size differences less than 10% between the sample and reference gas. For all wine varieties, the δC and δC values were linearly correlated with the predawn leaf water potential (Ψ) and therefore serve as reliable indicators of vine water status, as do the δC values for must sugars and wine solid residues. The strongest negative correlations with Ψ were for δC (r = -0.94, n = 54) and δC (r = -0.91) and were lower but still highly significant (p < 0.00001) for δC (r = -0.71) and δC (r = -0.70). An evaluation of the advantages and drawbacks of the different methods is presented, showing that the δC analysis of wine ethanol by GC/C/IRMS is the most appropriate.