A pragmatic modeling approach to assessing vine water status

Abstract

Context and purpose of the study – Climate change scenarios suggest an increase in temperatures and an intensification of summer drought. Measuring seasonal plant water status is an essential step in choosing appropriate adaptations to ensure yields and quality of agricultural produce. The water status of grapevines is known to be a key factor for yield, maturity of grapes and wine quality. Several techniques exist to measure the water status of soil and plants, but stem water potential proved to be a simple and precise tool for different plant species. The interpretation however of this value remains difficult because it is influenced by both soil water content and climatic conditions at the time of measurement. Where soil water content usually follows a decreasing curve during the summer season and climatic conditions follow a more erratic evolution. With predawn leaf water potentials (PLWP) serving as a proxy for soil water content and midday stem water potentials (SWP) reflecting water supply and climatic conditions, it becomes possible to separate the effect of soil water content and climatic conditions on vine water status. Direct use of PLWP measurements on soils with heterogeneous water content is not an option because it is less accurate than SWP measurements and a late-night measurement is not practical. The objectives of this study are (i) to provide a model that separates the effect of soil water content from the effect of climatic conditions on the SWP value and (ii) to standardize the SWP value to a value under predefined reference climatic conditions to better reflect soil water availability, and to compare SWP values under different climatic conditions.

Material and methods – Vine water status was assessed on three soil types in the AOC Saint-Émilion in 2015 and on 5 soil types in the AOC Margaux in 2018. Over the growing season, SWP and PLWP were measured on mature leaves using a pressure chamber.

Results – New models with easily accessible variables can separate the effect of soil water content from the effect of climatic conditions on the SWP values. The measurement of the PLWP is no longer necessary. More research is needed however to understand the changing relationship between SWP and daily maximum temperature over time. SWP values can be brought back to a theoretical value representative of standard climatic conditions. This standardization can be particularly interesting in a context of climate change, where a greater variability of climatic conditions between years is observed. A more precise interpretation allows the winegrower and consultant to more adequately decide on adaptations to implement in both the short- and long term to ensure yields and grape quality.