Carbon isotope ratio (δ13C) is known to be related to water use efficiency and water status in grapevines. However, there is no consensus on which is the temporal sensitivity of this parameter, i.e. which is the time-span this parameter integrates best. The aim of this work was to evaluate the usefulness of whole berry δ13C to integrate plant water status in grapevine, and to determine its temporal sensitivity. Comparing δ13C of berries sampled 10 days after veraison and at harvest with average stem water potential at different moments of the season; we observed that the moment at which water deficit occurs remarkably conditioned the response observed. The moments for which the sensitivity was greatest were two periods critical for sugar accumulation: veraison and 4–6 weeks before harvest. This gives a particular relevance to δ13C measured in whole berries, as its sensitivity is higher at critical moments of berry ripening, but it also implies that care has to be taken when interpreting δ13C values, considering the variations in sensitivity depending on sampling time.
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Santesteban et al. (2012) studied this question.