Although a considerable number of studies have been carried out to assess the physiological and spectral responses of grapevine WS, specific knowledge of these responses under combined stresses and HS with different evaporative cooling systems is lacking. There are a wide range of spectral vegetation indices (VIs) used to describe WS, and some preliminary studies have been conducted on HS. Environmental RH during HS correlated positively with the red edge region and growing degree days correlated negatively with the short wave near-infrared (SWIR, 1610 nm) region. The NIR spectral band can provide a reliable assessment of the water status of leaves and canopy. For example, the green (550 and 570 nm), red (670 nm), red edge (>700 nm), and near-infrared (NIR, 800 nm) spectral bands can provide a reliable prediction of Carménère water status. Non-destructive techniques to quantify the effects of extreme weather events on crops are emerging using reflectance or spectral techniques. Īn accurate estimation of the physiological behavior of grapevine under stress conditions entails the use of complex and, in some cases, destructive equipment. For example, combined HS and WS leads to increased leaf temperature due to stomatal closure, whereas during individual HS, heat is dissipated through stomata. Some studies have underlined that the consequences of combined stresses may be substantially different from those of individuals stresses. To date, less attention has been paid to the combined effects of HS and WS on grapevines. Moreover, WS may cause oxidative damage via the production of reactive oxygen species, which damage the cells and their components. Although moderate WS increases the quality of red varieties, e.g., promoting the accumulation of quality-related metabolites, it substantially reduces berry size and yield. WS affects the morphological traits (e.g., reduction in leaf size and vegetative growth) and physiological traits (e.g., reduction in P n, stomatal conductance- g s, and leaf transpiration rate- E) of vegetation. Given the environmental conditions of high temperature and low relative humidity (RH) that occur during a heatwave, if soil water is limited, HS is associated with water stress (WS), due to the increased evaporative demand. A three-step band selection process allowed the identification of the spectral traits’ responsive to HS and combined stress, i.e., 1336–1340 nm, 1967–1971 nm, and 600–604 nm. However, their physiological recovery was not achieved within this time, as shown by the Simple Ratio Index (SRI), Transformed Chlorophyll Absorption Ratio Index (TCARI), and TCARI/Optimized Soil-Adjusted Vegetation Index (TCARI/OSAVI). The vines undergoing combined stress (SDI) showed greenness amelioration 10 days after stress, as revealed by the greenness vegetation indices (VIs), i.e., Green Index (GI), Normalized Difference Greenness Vegetation Index (NDGI), and Visible Atmospherically Resistant Index (VARI). Consistent with the physiological analysis, the proximal spectral responses of leaves identified SPRI and SI+ as putative cooling strategies to minimize vine HS. We also identified the spectral response of grapevine to HS and combined HS and WS (resulting from SDI). All the physiological indicators measured were significantly lower after the end of HS in the SDI treatment. Compared to the other treatments, in the early stages after the occurrence of HS, the vine water status of SPRI and SI+ improved, with high stomatal conductance ( g s) (SPRI) and stem water potential ( Ψ stem SPRI and SI+). The treatments were: standard drip irrigation (SI), extra drip irrigation (SI+), extra sprinklers irrigation (SPRI), and sustained deficit irrigation (SDI 50% of SI). Sauvignon blanc to individual (HS) and combined (HS + WS) stress under four different cooling and irrigation strategies. In this study, we evaluated the physiological and spectral responses of Vitis vinifera L. Heat stress (HS) and water stress (WS) pose severe threats to viticulture, and effective management solutions to counter their effects on grapevine performance must be examined.
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