Variety-specific response of bulk stomatal conductance of grapevine canopies to changes in net radiation, atmospheric demand, and drought stress

In wine growing regions around the world, climate change has the potential to affect vine transpiration and overall vineyard water use due to related changes in daily atmospheric conditions and soil water deficits. Grapevines control their transpiration in response to such changes by regulating conductance of water through the soil-plant-atmosphere continuum. The response of bulk stomatal conductance, the vine canopy equivalent of stomatal conductance, to such changes were studied on Cabernet-Sauvignon, Merlot, Tempranillo, Ugni blanc, and Semillon vines in a non-irrigated vineyard in Bordeaux France. Whole-vine sap flow, temperature and humidity in the vine canopy, and net radiation absorbed by the vine canopy were measured on 15-minute intervals from early July through mid-September 2020, together with periodic measurements of leaf area, canopy porosity, and predawn leaf water potential. From these data, bulk stomatal conductance was calculated on 15-minute intervals, and multiple linear regression analysis was performed to identify key variables and their relative effect on conductance. For the regression analysis, attention was focused on addressing non-linearity and collinearity in the explanatory variables and developing a model that was readily interpretable.Variability of vapour pressure deficit in the vine canopy over the day and predawn water potential over the season explained much of the variability in bulk stomatal conductance overall, with relative differences between varieties appearing to be driven in large part by differences in conductance response to predawn water potential between the varieties. Transpiration simulations based on the regression equations found similar differences between varieties in terms of daily and seasonal transpiration. These simulations also compared well with those from an accepted vineyard water balance model, although there appeared to be differences between the two approaches in the rate at which conductance, and hence transpiration is reduced as a function of decreasing soil water content (i.e., increasing water deficit stress). By better characterizing the response of bulk stomatal conductance, the dynamics of vine transpiration can be better parameterized in vineyard water use modeling of current and future climate scenarios.COntinental To coastal Ecosystems: evolution, adaptability and governanc

Phenological model intercomparison for estimating grapevine budbreak date (Vitis vinifera L.) in Europe

Budbreak date in grapevine is strictly dependent on temperature, and the correct simulation of its occurrence is of great interest since it may have major consequences on the final yield and quality. In this study, we evaluated the reliability for budbreak simulation of two modeling approaches, the chilling-forcing (CF), which describes the entire dormancy period (endo-and eco-dormancy) and the forcing approach (F), which only describes the eco-dormancy. For this, we selected six phenological models that apply CF and F in dierent ways, which were tested on budbreak simulation of eight grapevine varieties cultivated at dierent latitudes in Europe. Although none of the compared models showed a clear supremacy over the others, models based on CF showed a generally higher estimation accuracy than F where fixed starting dates were adopted. In the latter models, the accurate simulation of budbreak was dependent on the selection of the starting date for forcing accumulation that changes according to the latitude, whereas CF models were independent. Indeed, distinct thermal requirements were found for the grapevine varieties cultivated in Northern and Southern Europe. This implies the need to improve modeling of the dormancy period to avoid under-or over-estimations of budbreak date under dierent environmental conditions. © 2020 by the authors

Varietal responses to soil water deficit: first results from a common-garden vineyard near Bordeaux France

In wine producing regions around the world, climate change has the potential to decrease the frequency and amount of precipitation and increase average and extreme temperatures. This will both lower soil water availability and increase evaporative demand in vineyards, thereby increasing soil water deficits and associated vine stress. Grapevines control their water status by regulating stomatal closure and other changes to internal plant hydraulics. These responses are complex and have not been clearly characterized across a wide range of different Vitis vinifera varieties. Understanding how vine water status responds to changes in soil water deficits and other variables will help growers modify vineyard design and management practices to meet their quality and yield objectives. Carbon isotope discrimination measurements of certain plant tissues have been shown to provide effective characterization of stomatal closure, while water potential measurements provide a well-proven measure of overall vine water status. Using replicated data collected from an experimental common-garden vineyard at the Institut des Sciences de la Vigne et du Vin (ISVV) near Bordeaux, France, this project will analyze the effects on carbon isotope discrimination across 39 varieties and water potential across eight varieties against estimates of soil water deficits made using a water balance model running on local meteorology and considering the phenology of each variety. Similar to the literature, preliminary analysis finds as soil water deficit increases, carbon isotope data suggests greater stomatal closure and water potential measurements indicate greater vine stress. For both parameters, analysis will be performed to distinguish any difference in these responses between varieties

Carbon isotope discrimination (so-called δ¹³C) measured on grape juice is an accessible tool to monitor vine water status in production conditions

Assessment of vine water status is needed to understand the effect of environmental factors and management practices on dry-farmed and irrigated vineyards. Among plant-based indicators, carbon isotope discrimination (δ13C) is easily accessible, reliable, and inexpensive. As it provides a post-hoc assessment of vine water status during the berry ripening period, it can be useful for assessing the results of vineyard management practices during the season, and to map water status in the vineyard to aid in future precision management. Possible applications and limitations of this technique for practical vineyard management are discussed in this article