Controversies in Midday Water Potential Regulation and Stomatal Behavior Might Result From the Environment, Genotype, and/or Rootstock: Evidence From Carménère and Syrah Grapevine Varieties.

Luis Villalobos-González,Claudio Pastenes,Nicolas Franck,Mariana Muñoz-Araya

doi:10.3389/fpls.2019.01522

Abstract

Controversies exist regarding the iso/anisohydric continuum for classifying plant water-use strategies. Isohydricity has been argued to result from plant–environment interaction rather than it being an intrinsic property of the plant itself. Discrepancies remain regarding the degree of isohydricity (σ) of plants and their threshold for physiological responses and resistance to drought. Thus, the aim of this study was to evaluate the isohydricity of the grapevine varieties Syrah and Carménère under a non-lethal water deficit progression from veraison from two different locations, the Cachapoal Valley (CV) and Maipo Valley (MV), in central Chile and with different rootstock only in Syrah. For this purpose, the midday stem water potential (Ψmds) regulation and stomatal responses to drought, leaf traits related to pressure–volume curves, stomatal sensitivity to ABA, cavitation threshold, and photosynthetic responses were assessed. A higher atmospheric water demand was observed in the CV compared to the MV, with lower Ψmds values in the former for both varieties. Also, the σ values in Carménère were 1.11 ± 0.14 MPa MPa-1 and 0.68 ± 0.18 MPa MPa-1 in the CV and MV, respectively, and in Syrah they were 1.10 ± 0.07 MPa MPa-1 in the CV and 0.60 ± 0.10 MPa MPa-1 in the MV. Even though similar variations in σ between locations in both varieties were evident, Carménère plants showed a conserved stomatal response to Ψmds in both study sites, while those of Syrah resulted in a higher stomatal sensitivity to Ψmds in the site of lower σ. Besides the differences in seasonal weather conditions, it is likely that the different rootstock and clonal variability of each season in Syrah were able to induce coordinated changes in σ, Ψgs12, and osmotic potential at full turgor (π0). On the other hand, irrespective of the σ, and given the similarity between the π0 and Ψgs12 in leaves before drought, it seems that π0 could be a convenient tool for assessing the Ψmds threshold values posing a risk to the plants in order to aid the irrigation decision making in grapevines under controlled water deficit. Finally, water deficits in vineyards might irreversibly compromise the photosynthetic capacity of leaves.

Highlights

The isohydric and anisohydric continuum was introduced initially as the divergent regulation of the midday leaf water potential (Ψmd) in plants (Berger-Landefeldt, 1936; Tardieu and Simonneau, 1998)
It has been argued that plants with a high stomatal sensitivity, i.e. where stomatal conductance has been reduced at a relatively high water potential, could still show anisohydric behavior provided that its hydraulic transport system is more sensitive to declining water availability than stomata (Martínez-Vilalta et al, 2014)
Considering the importance of the plant water potential on growth and metabolism, it is relevant to know how plant species respond to water scarcity, in grapevines; they are a species often cultivated under controlled water deficit conditions with contrasting responses between varieties in their water status under stress (Bota et al, 2016; Lavoie-Lamoureux et al, 2017)

Summary

Introduction

The isohydric and anisohydric continuum was introduced initially as the divergent regulation of the midday leaf water potential (Ψmd) in plants (Berger-Landefeldt, 1936; Tardieu and Simonneau, 1998). Anisohydric plants have been extensively defined as less responsive at the stomatal level upon reductions in the soil water content, progressively reducing their Ψmd, but they are capable of maintaining transpiration and photosynthesis (Tardieu and Simonneau, 1998; Sade et al, 2012). To quantify the plant species position in the isohydric–anisohydric continuum, it has been proposed that the degree of isohydricity (σ) assessing the Ψmd response as the soil water content is reduced (Martínez-Vilalta et al, 2014), among others (for a review see: Hochberg et al, 2018 and Feng et al, 2019). The evidence indicates that stomatal behavior in response to decreasing water potential is highly correlated with the beginning of xylem cavitation (Brodribb et al, 2003; Li et al, 2015; Bourne et al, 2017; Li et al, 2018) and leaf embolism in grapevines (Hochberg et al, 2017)

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