Use of stomatal conductance and pre-dawn water potential to classify terroir for the grape variety Kékfrankos

Abstract

Background and Aims: A 3-year study was carried out in order to evaluate the ecophysiology, yield and quality characteristics of Vitis vinifera L. cv. Kékfrankos (syn. Limberger) at Eger-Nagyeged hill (steep slope) and at Eger-Kőlyuktető (flat) vineyard sites located in the Eger wine region, Hungary. The aim of this paper was to analyse the effect of ‘vintage’ and ‘terroir’ on the seasonal changes of Kékfrankos ecophysiology and its possible relationship with yield and wine composition. Methods and Results: Grapevine physiological responses (midday- and pre-dawn water potential, pressure–volume analysis and gas-exchange), growing stages, yield and wine composition of each vineyard were studied. Lower grapevine water supply was detected at Eger-Nagyeged hill in each season due to its steep slope and soil characteristics. Pressure-volume curves indicated that there was no osmotic adjustment in the leaves of this variety. Higher osmotic concentration was measured at turgor loss and full turgor in the leaves of the unstressed vineyard (Eger-Kőlyuktető) presumably due to higher photosynthetic activity. Differences in soil water content of the vineyards resulted in a slightly altered cell wall elasticity. Stomatal conductance, transpiration rate and photosynthetic production per unit leaf area were affected by water availability. Lower yield in Eger-Nagyeged hill was partly associated with decreased photosynthetic production of the canopy. Improved wine quality of Eger-Nagyeged hill was due to moderate water stress which induced higher concentration of anthocyanins and phenolics in the berries. The duration of the phenological stages was dependent on vintage temperature characteristics rather than on vineyard site. Conclusion: There was a close relationship between environmental conditions, Kékfrankos gas-exchange, water relations, yield and wine composition. Water deficit plays an important role in creating a terroir effect, resulting in decreased yield, better sun exposure of leaves and clusters and thus higher concentration of phenolics and anthocyanins. Although quality is mainly influenced by vintage differences, vineyard characteristics are able to buffer unfavourable vintage effects even within a small wine region. Significance of the Study: Stomatal conductance, pre-dawn water potential and climatic data may be reliable parameters for terroir classification, although variety–terroir interactions must always be considered.