Predawn leaf water potential of grapevines is not necessarily a good proxy for soil moisture
Thomas Groenveld, Charles Obiero, Yingxue Yu, Markus Flury, Markus Keller
Abstract
Abstract Background In plant water relations research, predawn leaf water potential (Ψ pd ) is often used as a proxy for soil water potential (Ψ soil ), 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 Ψ pd = Ψ soil for field-grown grapevines. Results A field trial was conducted with 30 different cultivars of wine grapes grown in a single vineyard in arid southeastern Washington, USA, for two years. The Ψ pd and the volumetric soil water content (θ v ) under each sampled plant were measured multiple times during several dry-down cycles. The results show that in wet soil (Ψ soil > − 0.14 MPa or relative extractable water content, θ e > 0.36), Ψ pd was significantly lower than Ψ soil for all 30 cultivars. Under dry soil conditions (Ψ soil < − 0.14 MPa or θ e < 0.36) Ψ pd lined up better with Ψ soil . There were differences between cultivars, but these were not consistent over the years. Conclusion These results suggest that for wet soils Ψ pd of grapevines cannot be used as a proxy for Ψ soil , while the Ψ pd = Ψ soil assumption may hold for dry soils.