Water status response of Vitis vinifera L. cv Cabernet-Sauvignon during the first years within the long-term VineyardFACE (Free Air Carbon dioxide Enrichment) study

Abstract

Understanding the water-use responses of grapevines to increasing atmospheric carbon dioxide concentrations is mandatory when assessing the impact of climate change on viticulture as it is a critical part of the adaptation process. Therefore, besides established field measurements on vine water status modelling efforts are required to understand to what extent adaption will be possible under longer term CO2 emission and water supply scenarios. Previously, at the VineyardFACE (Free Air Carbon dioxide Enrichment) experiment in Geisenheim, Germany, plant physiology measurements, e.g. leaf gas exchange and pre-dawn leaf water potential (Ψpd), were made as Vitis vinifera cv. Cabernet Sauvignon established from planting under ambient CO2 (aCO2) and elevated CO2 (eCO2, aCO2 + 20%) concentrations. In contrast to the majority of previous observations on mature grapevines and other perennial plant species under CO2 enrichment, the young vines of the VineyardFACE experiment showed an increased intrinsic water use efficiency (WUEi) under eCO2, which was mainly associated with an increase in net assimilation (A) rather than a decrease in stomatal conductance (gs).

To determine the impact of this stomatal conduction response to eCO2 on whole vine water use of Cabernet Sauvignon, heat balance sap flow gauges were installed for subsequent seasons (2016/2017) when trunks reached a sufficient diameter. Complementary measurements of leaf gas exchange, pre-dawn leaf water potential (Ψpd), soil water content and recording of weather data were performed. In addition, a vineyard water balance model was used to test the implications of the eCO2 response, and possible explanations. Net assimilation and intrinsic water use efficiency values were higher for Cabernet Sauvignon under eCO2 conditions, as were transpiration rates (E) and stomatal conductance. The results were supported by whole vine transpiration measurements, indicating higher water use of young vines under eCO2. The difference in daily vine water use between the two CO2 treatments was higher on days of high evaporative demand. Furthermore, pre-dawn leaf water potentials were slightly lower under aCO2, suggesting a potentially lower risk of drought stress for young vines under eCO2.