Carbon isotope discrimination in berry juice sugars: changes in response to soil water deficits across a range of vitis vinifera cultivars

Abstract

Context and purpose of the study – In wine producing regions around the world, climate change has the potential to decrease the frequency and amount of precipitation and increase average and extreme temperatures. This will lower soil water availability and increase evaporative demand, thereby increasing the frequency and intensity of water deficit experienced in vineyards. Among other things, grapevines manage water deficit by regulating stomatal closure. The dynamics of this regulation, however, have not been well characterized across the range of Vitis vinifera cultivars. Providing a method to understand how different cultivars regulate their stomata, and hence water use in response to changes in soil water deficits will help growers manage vineyards and select plant material to better meet quality and yield objectives in a changing climate.

Material and methods – Berry samples were collected at maturity from 41 different Vitis vinifera cultivars at replicate locations within the VitAdapt common-garden vineyard at the Institut des Sciences de la Vigne et du Vin (ISVV) in Bordeaux, France. Carbon isotope ratios were measured in berry juice sugars from these samples to determine the level of carbon isotope discrimination (δ13C) existing when the sugars were accumulated. The level of δ13C in berry juice sugar is considered an effective indicator of the level of stomatal closure during the sugar accumulation period. Then, using local meteorology and observed phenology, a water balance model was used to estimate the average soil water content during the berry ripening period for each cultivar in each year. Replicate measurements of δ13C in each cultivar for 2012 through 2016 were then compared against modeled average soil water content for the associated berry ripening period, with results characterized and classified by cultivar.

Results – As soil water content during the berry ripening period decreased, the corresponding δ13C measurements in berry juice sugars for all cultivars became less negative, indicating greater stomatal closure during this period. Using data from years 2012 through 2016 this trend was well demonstrated with a power function regression curve that gave similar shapes for all cultivars, although statistically significant differences in overall levels of δ13C were observed between many cultivars. Also, the difference in δ13C measurements between dry versus wet conditions for a given cultivar provides an indication of that cultivar’s stomatal closure sensitivity in response to increasing soil water deficits. These results support the use of δ13C measurements in berry juice sugars as a simple and effective way of assessing differences in stomatal behavior among cultivars in the field, perhaps across different rootstock, soil, and/or climate conditions. Next steps for continuing and improving the analysis are also presented