Using δ13C and hydroscapes for discriminating cultivar specific drought responses

Measurement of carbon isotope discrimination in berry juice at maturity (delta C-13) provides an integrated assessment of vine water status and water use efficiency (WUE) during the period of berry ripening, and when collected over multiple seasons, can provide an indication of drought stress responses. Berry juice delta C-13 measurements were carried out on 48 different varieties planted in a common garden experiment in Bordeaux, France from 2014 through 2020 and found important differences across this large panel of varieties. Cluster analysis showed that delta C-13 values are likely affected by the differing phenology of each variety, resulting in berry ripening of different varieties taking place under different conditions of soil water availability within the same year. Accounting for these phenological differences, the cluster analysis created a classification of varieties that corresponds well to our current empirical understanding of their relative drought tolerance. In addition, using measurements of predawn and midday leaf water potential measurements collected over four seasons on a subset of six varieties, a hydroscape approach was used to develop a list of metrics indicative of the sensitivity of stomatal regulation to water stress (i.e. an/isohydric behaviour). Key hydroscape metrics were also found to be well correlated with some delta(1)3C metrics. A variety's water potential regulation as characterized by a minimum critical leaf water potential as determined from hydroscapes was strongly correlated to delta C-13 values under well-watered conditions, suggesting that the latter may be a useful indicator of drought stress response.