Relationships between sensitivity to high temperature, stomatal conductance and vegetative architecture in a set of grapevine varieties

Introduction

High temperatures influence plant development and induce a large set of physiological responses at the leaf scale. Stomatal closure is one of the most observed responses to high temperatures. This response is commonly considered as an adaptive strategy to reduce water loss and embolism in the vascular system caused by the high evaporative demand (Jones and Sutherland., 1991). Nevertheless, this response negatively impacts plant functioning, as it decreases photosynthesis and raises the leaf temperature (Tuzet et al., 2003). This increase in temperature is due to a decrease in energy loss by evaporative cooling. In extreme cases, this increase can induce leaf burning symptoms and lead to leaf or entire plant mortality (Webb et al., 2010).

In the context of global warming, the occurrence of extreme heatwaves events is expected to increase in almost all the vineyard areas. These events can cause major risks for the perennity of this cropping system. In this context there is a need to develop new varieties more adapted to high temperatures. For instance in the south of France in June 2019 a major heatwave was observed with air temperature higher than 45°C. Previous analyses made during this period, showed high genotypic variability in the sensitivity to this leaf burn symptoms in a core collection of varieties that was grown in Montpellier (South of France).

To apprehend the physiological determinants explaining these genotypic differences, it is necessary to understand the factors that affect leaf temperature. Leaf temperature results from the leaf energy balance. This energy balance depends on the amount of solar radiation intercepted by the canopy and on the ability of the leaf to transfer this energy through evapotranspiration. In that context, there exist two leverages that limit this increase in leaf temperature. First, reducing the amount of light intercepted and secondly maintaining stomatal aperture even under high temperature. Previous studies in grapevine showed high genotypic variability in stomatal behavior under water deficit in grapevine (Coupel-Ledru et al., 2014). Conversely, the studies on the response to temperature are more scarce. Regarding the amount of light intercepted, plant architecture plays a major role in light capture (Louarn et al., 2008). From the multitude of architectural traits: leaf shape and size, petiole length, and leaf 3D orientation significantly influence the efficiency of radiation interception (Falster and Westoby, 2003; Valladares and Brites, 2004).

A large genotypic variability in architectural traits was also observed in many plants (Segura et al., 2007 in apple). However, no study investigated the genotypic variation in architectural traits in grapevines and their potential impact on leaf functioning. In grapevine, a previous study showed intra-plant variability in leaf angles with respect to the training systems (Mabrouk et Carbonneau, 1997). However, this study did not consider any genotypic variability. Consequently, the definition of new architectural and functional ideotypes to face hatewaves in vineyards is a particularly relevant research topic.