• Energy Research

Reproductive development of grapevine and berry composition are both strongly influenced by temperature. To date, the molecular mechanisms involved in grapevine berries response to high temperatures are poorly understood. Unlike recent data that addressed the effects on berry development of elevated temperatures applied at the whole plant level, the present work particularly focuses on the fruit responses triggered by direct exposure to heat treatment (HT). In the context of climate change, this work focusing on temperature effect at the microclimate level is of particular interest as it can help to better understand the consequences of leaf removal (a common viticultural practice) on berry development. HT (+ 8°C) was locally applied to clusters from Cabernet Sauvignon fruiting cuttings at three different developmental stages (middle green, veraison and middle ripening). Samples were collected 1, 7, and 14 days after treatment and used for metabolic and transcriptomic analyses. The results showed dramatic and specific biochemical and transcriptomic changes in heat exposed berries, depending on the developmental stage and the stress duration. When applied at the herbaceous stage, HT delayed the onset of veraison. Heating also strongly altered the berry concentration of amino acids and organic acids (e.g., phenylalanine, γ-aminobutyric acid and malate) and decreased the anthocyanin content at maturity. These physiological alterations could be partly explained by the deep remodeling of transcriptome in heated berries. More than 7000 genes were deregulated in at least one of the nine experimental conditions. The most affected processes belong to the categories "stress responses," "protein metabolism" and "secondary metabolism," highlighting the intrinsic capacity of grape berries to perceive HT and to build adaptive responses. Additionally, important changes in processes related to "transport," "hormone" and "cell wall" might contribute to the postponing of veraison. Finally, opposite effects depending on heating duration were observed for genes encoding enzymes of the general phenylpropanoid pathway, suggesting that the HT-induced decrease in anthocyanin content may result from a combination of transcript abundance and product degradation.

Hannah et al. (1) recently published a comprehensive study showing substantial impacts of climate change on viticultural suitability, leading to potential ecological issues. We agree that expansion of viticulture into new areas can lead to a decrease in biodiversity and that an increase in water use for irrigation might lead to major freshwater conservation impacts. However, we disagree with the alarming statement that suitability for winegrowing of main wine-producing areas worldwide will dramatically decrease over the next 40 y. We point out major methodological flaws in ref. 1, mostly linked to (i) the misuse of bibliographical data to compute suitability index, (ii) underestimation of adaptations of viticulture to warmer conditions, and (iii) the inadequacy of the monthly time step in the …

Context and purpose of the study: Like in other wine producing regions around the world, Bordeaux vineyards already experience the effects of climate change. Recent trends as well as model outputs for the future strongly support an increase of average and extreme temperatures. For the maturation period, this increase will by far exceed mean atmospheric temperature increase, as the ripening period will occur earlier in hotter climatic conditions. Therefore, a detrimental secondary metabolism response is expected in grape berries, and of particular concern are the impacts on phenolics and aromas and aroma precursors. The effects of high temperatures on secondary metabolism control have been partly characterized for phenolics, however mostly in artificial growing conditions, while little is known with respect to aromas. A better understanding of how high temperatures influence grape berry secondary metabolites could help vineyard growers to adapt to climate change and maintain wine quality.Material and methods: A two-year field study was carried out in 2015 and 2016 in a vineyard in Bordeaux, France. Two treatments, heated (H) and control (C), were applied to two varieties, Cabernet-Sauvignon and Sauvignon blanc, from fruit-set to maturity. Field heating was achieved by a very local greenhouse effect applied to the bottom of the rows, by enclosing most of the underlying soil surface by polycarbonate shields. As the training system was vertically trellised, the heated volume surrounded most of the bunches but did not disturb most of the leaves in the canopy. This simple and robust setup allowed an increase of berry temperature by about +1.5°C in mean value, up to +5°C at times during clear sky days. This moderate increase of temperature was indicative of the predicted future climatic conditions for the mid-21st century. Berry samples were collected at 4 time points from bunch closure to maturity for each cultivar and treatment. Primary and secondary metabolites were measured in whole berries or skins.Results and conclusions: With this moderate temperature increase, primary metabolite content in berries did not change significantly. In H samples, anthocyanins were reduced and tannins increased before veraison, and both decreased thereafter. H samples also exhibited lower concentrations of some amino acids, especially alanine, serine and phenylalanine. IBMP (2-methoxy-3-isobutylpyrazine) concentrations were also reduced in H samples of Cabernet-Sauvignon, in both seasons, especially at bunch closure stage, but the differences diminished at full maturity. For thiol 3-sulfanyl hexanol precursors, H samples again exhibited much lower concentrations for both varieties, with weak differences at early stages that increased at later stages (up to -70% decline at maturity in 2015 for Sauvignon blanc). These results demonstrate the potential negative impact of elevated temperature on polyphenols and aroma quality of grape berries.Significance and impact of the study: For viticulture to adapt to new climatic conditions, the negative impacts of high temperature on secondary metabolites and aromas, and therefore on wine quality, need to be contemplated. Thus, already established or new vineyard plantings must prepare and consider practices able to mitigate these impacts, for instance practices that increase bunch shading.

Aims: Climate change imposes increasingly warm and dry conditions in most winegrowing regions. Mediterranean vineyards are particularly vulnerable and have registered, in most situations, declining yields over the past years. Although a majority of Mediterranean vineyards are still dry-farmed, yields can be increased by the implementation of irrigation. However, irrigation has an impact on increasingly affected water resources. An alternative solution to irrigation can be the adaptation of training systems. As can be shown by water balance modeling, low density non-irrigated vineyards are much less vulnerable to climatic drought compared to medium or high density vineyards. And while yields tend to be lower in low density vineyards, so are production costs. The aim of this study is to investigate to what extent low density vineyards can be a sustainable and cost effective adaptation for grape growing in dry climates.Methods and results: A water balance model was applied to conceptual vineyards with different soil water holding capacities and different planting densities over recent past (1981-2010) and near future (2041-2070) climatic conditions for two winegrowing scenarios (Cabernet-Sauvignon in Bordeaux and Grenache in Avignon, Côtes du Rhône). Row spacings of 2.0, 3.0 and 4.0 m were investigated for vineyards with 100, 200 and 300 mm total transpirable soil water (TTSW), while inter-vine spacing, vine architecture, and canopy height were kept similar. Projected yields were estimated to vary according to vine density and water deficit based on a meta-analysis of data published in the literature. Production costs were calculated according to an operation-based costing methodology and compared among the different scenarios on a cost per hectare basis. Gross profit per hectare, defined as grape sales revenue minus production costs, was then computed for two grape sale revenue scenarios (1 €/kg and 3 €/kg). The modeled average fraction of transpirable soil water (FTSW) varied across the different winegrowing scenarios, climate periods (recent past or near future), and TTSW and row spacing assumptions. In soils with 200 or 300 mm TTSW, the 30-day average FTSW prior to modeled grape harvest roughly doubled when 4.0 m versus 2.0 m spacing was assumed in both the recent past and near future climate scenarios. In soils with 100 mm TTSW, water deficit was more severe overall and the effect of row spacing on average FTSW was less pronounced. Changes in projected yields were estimated as a function of vine density and FTSW based on relationships published in the literature. Yields decreased with decreasing vine density and increasing water deficits, while production costs decreased with decreasing vine density. When the assumed revenue from grape sales was lower (1 €/kg), the effect of reduced production cost savings outweighed the loss in revenue caused by reduced yields, leading to increased gross profit per hectare. On the other hand, when higher grape revenue was assumed (3 €/kg), the effect of reduced yield on revenue outweighed the associated reduction in production costs, leading to reduced gross profit per hectare.Conclusions: Lower density, dry-farmed vineyards will experience less water deficit under warmer and drier climate conditions, although this difference is less pronounced in soils with less water holding capacity. When considering differences in yields, revenues, and production costs, lower density vineyards producing lower value grapes (1 €/kg) may also experience an associated increase in gross profit, while such vineyards producing higher value grapes (3 €/kg) might experience a decrease in gross profit.Significance and impact of the study: The implementation of dry-farmed, low density vineyards provides a sustainable solution for grape growing by reducing the need for irrigation water. It allows maintaining vineyards in very dry areas where water is not readily available for irrigation and where other crops (except possibly olive trees) cannot be grown. Modeling of yield, revenue, and production costs shows that this solution is also economically viable, particularly for vineyards producing lower value (€/kg) grapes. Unlike goblet trained bush vine, low density trellised vineyards are perfectly adapted for mechanization.

<p style="text-align: justify;"><strong>Aim</strong>: Polyphenol composition, an important component of grape quality, is strongly influenced by fruit microclimate. However, information relies exclusively on whole berry data and the underlying response functions to microenvironment variables remain essentially unknown. The aim of this study was therefore to analyze the biochemical composition of grapes at both bunch and berry scales, in relation with microclimate.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Whole berries and berry halves were sampled in mature defoliated bunches from two neighboring Bordeaux vineyards with contrasting row orientations (<em>Vitis vinifera</em> cv. Merlot). Flavonoid and amino-acid contents were analyzed by HPLC methods. The main sources of variation were bunch azimuth, berry exposure and, only in South-exposed bunches, berry side. Models were used to estimate radiation at the berry surface and temperature. Intense effects of bunch side and berry side on total flavonol and anthocyanin concentrations were observed. These results were all consistent at both bunch and berry scales. However, the most intense effects were observed at berry scale and mitigated by scaling up from berry to bunch.</p><p style="text-align: justify;"><strong>Conclusion</strong>: Total flavonol concentrations in the berry skin exhibited a clear positive linear relationship with solar radiation. The large heterogeneity of composition at berry scale is consistent with the better known heterogeneity at bunch scale.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: Models and original response functions to microclimate could help optimize vineyard management and grape ripening.</p>