Estimation of plant hydraulics of grapevine in various «terroirs» in the Canton of Vaud (Switzerland)

The study of the physiological behaviour of the grapevine (cv. Chasselas), and of plant hydraulics in particular, was conducted on various « terroirs » in the Canton of Vaud (Switzerland) between 2001 and 2003 by Agroscope Changins-Wädenswil ACW, in collaboration with the firm I. Letessier (SIGALES) in Grenoble and the Federal Polytechnic School of Lausanne (EPFL). An evaluation of the vine plant hydraulics was made by means of physiological indicators (leaf and stem water potentials, transpiration and leaf stomatal conductance, carbon isotope discrimination and a model of transpirable soil water), in relation to estimations of the soil water reservoir and climatic factors. A close relationship came to light between the plant hydraulics, estimated by the pre-dawn leaf water potential, and the reserves of useful soil water (RU), from a network of about 30 study sites over a period of observation covering three climatically different years (2001 very wet year, 2002 intermediate year, and 2003 dry year). The study showed that measurement of the minimum stem water potential, carried out when evaporation was at its highest during the day, was able to account for momentary water stress. Observations from the present study indicate that the carbon isotope discrimination technique (ΔC13) in grape sugars was closely correlated to the plant hydraulics noted in the vine during the ripening stage (phase of sugar accumulation in berries). The use of a transpirable soil water model (Riou and Payan, 2001; Lebon et al., 2003) allowed the levels of water stress from the different sites to be determined according to the three principal components: precocity, duration and intensity. The total of transpirable soil water (TTSW) was estimated by combining the model with values of pre-dawn leaf water potential. The estimations of TTSW and RU observed at the different study sites were in good agreement.