The sequence and thresholds of leaf hydraulic traits underlying grapevine varietal differences in drought tolerance

Abstract

<jats:title>Abstract</jats:title> <jats:p>Adapting agriculture to climate change is driving the need for the selection and breeding of drought-tolerant crops. The aim of this study was to identify key drought tolerance traits and determine the sequence of their water potential thresholds across three grapevine cultivars with contrasting water use behaviors, Grenache, Syrah, and Semillon. We quantified differences in water use between cultivars and combined this with the determination of other leaf-level traits (e.g. leaf turgor loss point, π TLP), leaf vulnerability to embolism (P50), and the hydraulic safety margin (HSM P50). Semillon exhibited the highest maximum transpiration (Emax), and lowest sensitivity of canopy stomatal conductance (Gc) to vapor pressure deficit (VPD), followed by Syrah and Grenache. Increasing Emax was correlated with more negative water potential at which stomata close (Pgs90), π TLP, and P50, suggesting that increasing water use is associated with hydraulic traits allowing gas exchange under more negative water potentials. Nevertheless, all the cultivars closed their stomata prior to leaf embolism formation. Modeling simulations demonstrated that despite a narrower HSM, Grenache takes longer to reach thresholds of hydraulic failure due to its conservative water use. This study demonstrates that the relationships between leaf hydraulic traits are complex and interactive, stressing the importance of integrating multiple traits in characterizing drought tolerance.</jats:p>

The physiology of drought stress in grapevine: towards an integrative definition of drought tolerance

“…The same relationships between Ψ TLP and stomatal closure have been found in grapevines ( Fig. 2 ; Hochberg et al , 2017 a ; Dayer et al , 2020 ).The Ψ TLP is a plastic trait and most plant species decrease the osmotic potential under drought conditions by accumulating osmotically active solutes in leaf cells (i.e. osmotic adjustment).…”

“…Recent work suggests that all genotypes regulate vine water use (i.e. stomatal conductance) in order to protect against more severe damage such as petiole or leaf cavitation and leaf shedding ( Hochberg et al , 2017 c ; Dayer et al , 2020 ). However, it is unclear to what extent differences in the regulation of vine water use between varieties result from innate genotypic differences, as was traditionally thought, or environmental factors ( Hochberg et al , 2018 ).…”

“… Gowdy et al , 2018 ) or phenotyping facilities (e.g. Coupel-Ledru et al , 2014 ; Charrier et al , 2018 ; Dayer et al 2020 ). In addition to the effects that directly originate from environmental factors (soil water potential, soil hydraulic conductivity, and vapor pressure deficit), the exposure to different environments will also shape the vine’s hydraulic properties (i.e.…”

Nighttime transpiration represents a negligible part of water loss and does not increase the risk of water stress in grapevine

“…The leaf minimum conductance ( g min ) presented mean values of around 9.5 μmol m −2 s −1 with no differences among cultivars as previously reported (Dayer et al, 2020; Table S1).…”

“…One limitation in understanding the significance of E night and g night for whole plant water balance is that we still do not know if this trait plays a key role in exacerbating water stress and the risk of hydraulic failure. In a recent study in grapevine (Dayer et al, 2020), we observed that the maximum water use given by maximum daytime transpiration ( E max ) was strongly correlated with other drought‐related traits such as the water potential at stomatal closure (P gs 90 ), the leaf turgor loss point (π TLP ) and the leaf water potential inducing 50% of loss of hydraulic conductance (P 50 ), highlighting the importance of integrating multiple traits in characterizing drought tolerance. In the current study, we used the same three cultivars to explore E night and g night in natural conditions (i.e., outdoors, to avoid any artefactual VPD effects brought about by a greenhouse environment) to address the following question: Is nighttime water loss a key trait in exacerbating water stress?…”