Managing precision irrigation in vineyards: hydraulic and molecular signaling in eight grapevine varieties

Abstract

Context and purpose of the study – Understanding the physiological and molecular bases of grapevine responses to mild to moderate water deficits is fundamental to optimize vineyard irrigation management and identify the most suitable varieties. In Mediterranean regions, the higher frequency of heat waves and droughts highlights the importance of precision irrigation to meet vine water demands and demonstrates the necessity for a deeper understanding of the different physiological responses among varieties under water stress. In this context, previous reports show an interplay between stomatal regulation of transpiration and changes in leaf hydraulic conductivity, also with the involvement of aquaporins (AQPs), particularly under water stress. However, how those signaling mechanisms are regulated in different grapevine varieties along phenological phases is unclear. We aimed to assess the impact of vine water status and phenology on stomatal and hydraulic adjustments, along with aquaporins expression, of leaves of 8 grapevine varieties (Petit Verdot (PV), Alicante Bouschet (AB), Syrah (S), Vinhão (V), Touriga Nacional (TN), Castelão (Cs), Trincadeira (TR) and Tinta Caiada (TC)) selected according to their contrasting carbon isotopic signatures.

Material and methods – Ten-year-old vines grafted on 1103P, grown in the Alentejo region (Portugal) as part of the ampelographic collection of Esporão commercial vineyard, were subjected to three different irrigation treatments since 2018: full irrigation (FI); deficit irrigation (DI, 50% of FI); no-irrigation (NI). Plant monitoring was done during 2021 at four phenological stages: pea-size (PS), veraison (VER), full-maturation (FM) and post-harvest (Post-H). Measurements included stomatal conductance (g_s), predawn leaf water potential (ψ_pd), hydraulic conductivity (K_leaf) and the expression of 10 genes coding AQPs, previously reported to transport water in vitro.

Results – Results show that K_leaf is a function of grapevine phenology and variety. In all varieties and treatments, K_leaf peaked at veraison and declined thereafter (circa 80%). Water stress either increased or decreased K_leaf, likely depending on the ani- (e.g. TN) or isohydric (e.g. V, S) behavior. Interestingly, post-harvest irrigation increased K_leaf, surpassing values observed at FM, except in TN, suggesting that varieties benefit differently from late season irrigation. Stomatal conductance was highest at VER, in all irrigation treatments, except for TN, which peaked at PS. PV maintained constant g_s throughout the season in all treatments. Non-irrigated AB, S, V, and TR maintained low and constant g_s along the season. A significant correlation between g_s and ψ_pd was observed, except in Cs and PV, indicating that in those varieties additional factors contribute to control stomatal aperture. Studied AQPs were all expressed at PS and VER in all varieties and water treatments, except in TC, TR and AB where some PIPs and NIPs were not expressed under water stress. VviPIP1;2 appears to be constitutive since it is expressed at all phenological stages, irrigation treatments and varieties. Overall, DI and NI induced an up-regulation of AQP expression in anisohydric varieties at PS and VER. In contrast, AQPs were down-regulated by stress at PS in the isohydric varieties. These results indicate that AQPs expression trend is variety and phenology dependent.