A 3-year application of different mycorrhiza-based plant biostimulants distinctively modulates photosynthetic performance, leaf metabolism, and fruit quality in grapes (Vitis vinifera L.)

The use of microbial biostimulants in agriculture is recognized as a sustainable approach to promoting crop productivity and quality due to improved nutrient uptake, enhanced stress tolerance, and improved ability to cope with non-optimal environments. The present paper aimed to comparatively investigate the effect of seven different commercial mycorrhizal-based treatments in terms of yield, phytochemical components, and technological traits of Malvasia di Candia Aromatica grape (Vitis vinifera L.) plants. Metabolomic analysis and photosynthetic performance were first investigated in leaves to point out biochemical differences related to plant growth. Higher photosynthetic efficiency and better PSII functioning were found in biostimulant-treated vines, reflecting an overall decrease in photoinhibition compared to untreated plants. Untargeted metabolomics followed by multivariate statistics highlighted a robust reprogramming of primary (lipids) and secondary (alkaloids and terpenoids) metabolites in treated plants. The analysis of berry yield and chemical components exhibited significant differences depending on the biostimulant product. Generally, berries obtained from treated plants displayed improved contents of polyphenols and sugars, while yield remained unchanged. These results elucidated the significant role of microbial biostimulants in determining the quality of grape berries and eliciting biochemical changes in vines.

A Review on the Observed Climate Change in Europe and Its Impacts on Viticulture

The European climate is changing displaying profound on agriculture, thus strongly reaching the scientific community’s attention. In this review, the compilation of selected scientific research on the agroclimatic conditions’ changes and their impact on the productivity parameters (phenology timing, product quality and quantity) of grapevines and on the spatiotemporal characteristics of the viticultural areas are attempted for the first time. For this purpose, a thorough investigation through multiple search queries was conducted for the period (2005–2021). Overall, increasing (decreasing) trends in critical temperature (precipitation) parameters are the reality of the recent past with visible impacts on viticulture. The observed climate warming already enforces emerging phenomena related to the modification of the developmental rate (earlier phenological events, shortening of phenological intervals, lengthening of the growing season, earlier harvest), the alteration of product quality, the heterogeneous effects on grapevine yield and the emergence of new cool-climate viticulture areas highlighting the cultivation’s rebirth in the northern and central parts of the continent. The vulnerability of the wine-growing ecosystem urges the integration of innovative and sustainable solutions for confronting the impacts of climate change and safeguarding the production (quantity and quality) capacity of viticultural systems in Europe under a continuously changing environment.

Future Climate Change Impacts on European Viticulture: A Review on Recent Scientific Advances

Climate change is a continuous spatiotemporal reality, possibly endangering the viability of the grapevine (Vitis vinifera L.) in the future. Europe emerges as an especially responsive area where the grapevine is largely recognised as one of the most important crops, playing a key environmental and socio-economic role. The mounting evidence on significant impacts of climate change on viticulture urges the scientific community in investigating the potential evolution of these impacts in the upcoming decades. In this review work, a first attempt for the compilation of selected scientific research on this subject, during a relatively recent time frame (2010–2020), is implemented. For this purpose, a thorough investigation through multiple search queries was conducted and further screened by focusing exclusively on the predicted productivity parameters (phenology timing, product quality and yield) and cultivation area alteration. Main findings on the potential impacts of future climate change are described as changes in grapevine phenological timing, alterations in grape and wine composition, heterogeneous effects on grapevine yield, the expansion into areas that were previously unsuitable for grapevine cultivation and significant geographical displacements in traditional growing areas. These compiled findings may facilitate and delineate the implementation of effective adaptation and mitigation strategies, ultimately potentiating the future sustainability of European viticulture.

Water stress assessment on grapevines by using classification and regression trees

Multiple factors, such as the vineyard environment and winemaking practices, are known to affect the development of vines as well as the final composition of grapes. Water stress promotes the synthesis of phenols and is associated with grape quality as long as it does not inhibit production. To identify the key parameters for managing water stress and grape quality, multivariate statistical analysis is essential. Classification and regression trees are methods for constructing prediction models from data, especially when data are complex and when constructing a single global model is difficult and models are challenging to interpret. The models were obtained by recursively partitioning the data space and fitting a simple prediction model within each partition. The partitioning can be represented graphically as a decision tree. This approach permitted the most decisive variables for predicting the most vulnerable vineyards and wine quality parameters associated with water stress. In Priorat AOC, Carignan grapevines had the highest water potential and abscisic acid concentration in the early growth plant stages and permitted vineyards to be classified by mesoclimate. This information is useful for identifying which measurements could most easily differentiate between early and late-ripening vineyards. LWP and Ts during an early physiological stage (pea size) permitted warm and cold areas to be differentiated.

Spatial Variability of Soil and Plant Water Status and Their Cascading Effects on Grapevine Physiology Are Linked to Berry and Wine Chemistry

The relationships between differences in plant water status, induced by spatial variability in soil texture, and the changes in berry and wine composition were investigated in an irrigated Cabernet Sauvignon (Vitis vinefera L.) vineyard for 2 years. A stratified and an equidistant grid were overlaid on the vineyard to characterize the soil texture by proximal sensing, soil sampling, and grapevine physiological and berry chemical development. Based on the mid-day stem water potential (Ψ _stem ) integrals, the vineyard was divided into two functional homogenous zones: Zone 1 with higher water stress and Zone 2 with lower water. Zone 1 consistently had lower Ψ _stem , net carbon assimilation, and stomatal conductance in both years. Berry weight and titratable acidity were lower in Zone 1 at harvest. Zone 2 reached 26 and 24°Bx total soluble solids (TSS) at harvest in Years 1 and 2, respectively, with higher TSS values of 30 and 27°Bx in Zone 1. Ravaz index did not vary spatially. Fruits were harvested differentially in both years and vinified separately from the two zones. In Year 1, all berry skin anthocyanin derivatives, tri-, di- hydroxylated, and total anthocyanins concentrations were higher in Zone 2. However, in Year 2, only malvidin, tri-hydroxylated, and total anthocyanins were higher in Zone 1. There were no differences in wine flavonoids in Year 2 when harvest commenced earlier. In both years, Ψ _stem , berry weight, and TSS were directly related to soil bulk electrical conductivity (EC). Our results indicated vineyard variability stemmed from soil texture that affected long-term plant water status which does not affect spatial variability of Ravaz Index. In conclusion, our work provides fundamental knowledge about the applicability of soil bulk EC sensing in the vineyards, and its potential directional utilization by connecting proximal soil sensing to spatial distribution of whole-plant physiological performance together with berry and wine chemistry.

Proximal Sensing of Soil Electrical Conductivity Provides a Link to Soil-Plant Water Relationships and Supports the Identification of Plant Water Status Zones in Vineyards

The majority of the wine grapes are grown in Mediterranean climates, where water is the determining factor for grapevine physiology and berry chemistry. At the vineyard scale, plant water status is variable due to the variability in many environmental factors. In this study, we investigated the ecophysiological variability of an irrigated Cabernet Sauvignon (Vitis vinifera L.) vineyard. We used equidistant grid sampling to assess the spatial variations of the plants and soil, including plant water status by stem water potential (Ψ stem ), leaf gas exchange, and on-site soil analysis. We also measured soil electrical conductivity (EC) by proximal sensing at two depths [0.75 - 1.5 m (sub soil); 0 - 0.75 m (top soil)]. Ψ stem integrals were calculated to represent the season-long plant water status. On the base of realized Ψ stem integrals, the vineyard was delineated into two functional homogeneous zones (fHZs) with one severely water stressed zone and one moderately water stressed zone. Sub soil EC was directly related to Ψ stem (r 2 = 0.56) and g s (r 2 = 0.39) when the soil was proximally sensed at harvest in 2018. Although the same trend was evident in 2019 we could not deduce a direct relationship. The fruits from the two fHZs were harvested differentially. Comparing the two fHZs, there was no significant difference in juice total soluble solids or pH. The severely water stressed zone showed significantly higher malvidin and total anthocyanins on a dry skin weight basis, but lower peonidin, malvidin on a per berry basis in 2018. In 2019, there were more quercetin and total flavonols per berry in the severely water stressed zone. Overall, this study provided fundamental knowledge of the viability of managing spatial variability by delineating vineyard into distinct zones based on plant water status, and the potentiality of proximally sensed soil EC in the spatial assessment of plant water status and the supporting of vineyard management.

Swift metabolite changes and leaf shedding are milestones in the acclimation process of grapevine under prolonged water stress

BACKGROUND

Grape leaves provide the biochemical substrates for berry development. Thus, understanding the regulation of grapevine leaf metabolism can aid in discerning processes fundamental to fruit development and berry quality. Here, the temporal alterations in leaf metabolism in Merlot grapevine grown under sufficient irrigation and water deficit were monitored from veraison until harvest.

RESULTS

The vines mediated water stress gradually and involving multiple strategies: osmotic adjustment, transcript-metabolite alteration and leaf shedding. Initially stomatal conductance and leaf water potential showed a steep decrease together with the induction of stress related metabolism, e.g. up-regulation of proline and GABA metabolism and stress related sugars, and the down-regulation of developmental processes. Later, progressive soil drying was associated with an incremental contribution of Ca²⁺ and sucrose to the osmotic adjustment concomitant with the initiation of leaf shedding. Last, towards harvest under progressive stress conditions following leaf shedding, incremental changes in leaf water potential were measured, while the magnitude of perturbation in leaf metabolism lessened.

CONCLUSIONS

The data present evidence that over time grapevine acclimation to water stress diversifies in temporal responses encompassing the alteration of central metabolism and gene expression, osmotic adjustments and reduction in leaf area. Together these processes mitigate leaf water stress and aid in maintaining the berry-ripening program.

Hydraulics and gas exchange recover more rapidly from severe drought stress in small pot-grown grapevines than in field-grown plants

Modifications of plant hydraulics and shoot resistances (R_shoot) induced by water withholding followed by rewatering, and their relationships with plant water status, leaf gas exchange and water use efficiency at the leaf level, were investigated in pot-grown and field-grown, own-rooted Syrah grapevines in an arid climate. Water stress induced anisohydric behavior, gradually reducing stomatal conductance (g_s) and leaf photosynthesis (A) in response to decreasing midday stem water potential (Ψ_s). Water stress also rapidly increased intrinsic water-use efficiency (A/g_s); this effect persisted for many days after rewatering. Whole-plant (K_plant), canopy (K_canopy), shoot (K_shoot) and leaf (K_leaf) hydraulic conductances decreased during water stress, in tune with the gradual decrease in Ψ_s, leaf gas exchange and whole plant water use. Water-stressed vines also had a lower Ψ gradient between stem and leaf (ΔΨ_l), which was correlated with lower leaf transpiration rate (E). E and ΔΨ_l increased with increasing vapour pressure deficit (VPD) in non-stressed control vines but not in stressed vines. Perfusion of xylem-mobile dye showed that water flow to petioles and leaves was substantially reduced or even stopped under moderate and severe drought stress. Leaf blade hydraulic resistance accounted for most of the total shoot resistance. However, hydraulic conductance of the whole root system (K_root) was not significantly reduced until water stress became very severe in pot-grown vines. Significant correlations between K_plant, K_canopy and Ψ_s, K_canopy and leaf gas exchange, K_leaf and Ψ_s, and K_leaf and A support a link between water supply, leaf water status and gas exchange. Upon re-watering, Ψ_s recovered faster than gas exchange and leaf-shoot hydraulics. A gradual recovery of hydraulic functionality of plant organs was also observed, the leaves being the last to recover after rewatering. In pot-grown vines, K_canopy recovered rather quickly following restoration of Ψ_s, although gas exchange recovery did not directly depend on recovery of K_canopy. In field-grown vines, recovery of water status, gas exchange and hydraulic functionality was slower than in pot-grown plants, and low g_s after rewatering was related to sustained decreased K_plant, K_canopy and K_shoot and lower water transport to leaves. These results suggest that caution should be exercised when scaling up conclusions from experiments with small pot-grown plants to field conditions.

Cultivar specific metabolic changes in grapevines berry skins in relation to deficit irrigation and hydraulic behavior

Deficit irrigation techniques are widely used in commercial vineyards. Nevertheless, varieties respond differently to water availability, prompting the need to elucidate the physiological and molecular mechanisms involved in the interactions between genotypes and their environment. In the present study, the variability in berry metabolism under deficit irrigation was investigated in the field on Shiraz and Cabernet Sauvignon (CS), known for their hydraulic variability. Berry skin metabolite profiling of the two cultivars was performed by parallel GC-MS and LC-MS at four development stages. Under similar irrigation, the cultivars differed in stomata regulation. In response to water deficit, CS exhibited lessened loss in berry weight and milder metabolic alteration of berry-skin primary metabolites, as compared with Shiraz. The metabolic stress responses were shown to depend on berry phenology. Characteristic metabolic changes included a decrease in amino acids and TCA cycle intermediates from veraison onward. In contrast, water deficit induced the accumulation of stress-related metabolites such as: proline, beta-alanine, raffinose, nicotinate and ascorbate, to a greater extent in Shiraz. Polyphenol metabolism in response to water stress also underwent significant changes, unique to each cultivar. Results suggest a link between the vine hydraulics and water-deficit driven changes in the berry skin metabolism, with significant consequences on the metabolic composition of the fruit.

Morpho-structural and physiological response of container-grown Sangiovese and Montepulciano cvv. (Vitis vinifera) to re-watering after a pre-veraison limiting water deficit

A better physiological and productive performance of cv. Montepulciano versus cv. Sangiovese under well-watered conditions has been recently assessed. The objective of this study was to verify that this behaviour is maintained when a pre-veraison deficit irrigation (vines held at 40% pot capacity from fruit-set to veraison) followed by re-watering (pot capacity reported at 90%). Single leaf assimilation rate and stomatal conductance, diurnal and seasonal whole-canopy net CO2 exchange (NCER) and water use efficiency were always higher in Sangiovese under deficit irrigation. Due to water shortage Montepulciano displayed a more compact growing habit due to decreased shoot and internode length. Sangiovese showed excellent recovery upon re-watering as NCER resulted to be higher than the pre-stress period; however, this might also relate to early and severe basal leaf yellowing and shedding. Early deficit irrigation affected xylem characteristics of Montepulciano more than in Sangiovese; vessel density increased (37 vs 29%, respectively, compared with well-watered vines) and the hydraulic conductance decreased more (-13 vs -3% respectively) compared with well-watered vines. Yield components and technological maturity were similar in the two cultivars, whereas Montepulciano grapes had lower anthocyanins and phenolics. Higher physiological and productive efficiency under non-limiting water conditions showed by Montepulciano compared with Sangiovese was basically reversed when both cultivars were subjected to an early deficit irrigation.