Effects of the atmospheric vapour pressure deficit and soil water availability on the diurnal pattern of grapevine stem water potential

Abstract

The dependency of ѱ_s on soil water availability and air vapour pressure deficit (VPD) the diurnal pattern of the ѱ_s was assessed during the 2009 growing season in an irrigation experiment set up at the Dão Wine Research Station (CEVDão), Nelas, Portugal. Diurnal ѱ_s patterns were carried out every two hours on vines non-irrigated (NI) and those subjected to deficit irrigation (DI – 50% ETc) in two environmental contrasting days. In the first day of measurements (doy 202) the diurnal pattern of ѱ_s showed, in both treatments, a slight decline in the early morning, achieving at midday values between -0.6 and -0.8 MPa, and a recovery in the late afternoon for both treatments that showed no differences. In the second day of measurements (doy 240) the ѱ_s declined rapidly from morning to early afternoon, achieving the lowest values at 4:00 PM (-1.3 MPa in NI and -1.2 MPa in DI), and also a recovery in the late afternoon. As opposed to day 202, on doy 240, NI vines had a ѱ_s lower than DI for all measurements. In both treatments the ѱ_s had a negative correlation with the VPD measured at the time of the measurements. Results indicated that the rate of decrease of ѱ_s with the increase of VPD was independent of the FASW. Data also showed that when the soil had a higher FASW in deep layers, in days with low VPD the ѱ_s was not different between irrigation treatments.