Predawn leaf water potential of grapevines is not necessarily a good proxy for soil moisture

Abstract

Abstract Background In plant water relations research, predawn leaf water potential (Ψpd) is often used as a proxy for soil water potential (Ψsoil), without testing the underlying assumptions that nighttime transpiration is negligible and that enough time has passed for a hydrostatic equilibrium to be established. The goal of this research was to test the assumption that Ψpd = Ψsoil for field-grown grapevines.Results A field trial was conducted with 30 different varieties of wine grapes grown in a single vineyard in arid southeastern Washington, USA, for two years. The Ψpd and the volumetric soil water content (θv) under each sampled plant were measured multiple times during several dry-down cycles. The results show that in wet soil (θv > 0.146 m3 m− 3), Ψpd was significantly lower than Ψsoil for all 30 varieties. Under drought conditions (θv < 0.105 m3 m− 3) Ψpd lined up better with Ψsoil. There were differences between varieties, but these were not consistent over the years.Conclusion These results suggest that for wet soils Ψpd of grapevines cannot be used as a proxy for Ψsoil, while the Ψpd = Ψsoil assumption holds for dry soils.