C. van Leeuwen 1, O. Trégoat 2, X. Choné 3, J.-P. Gaudillère 4, D. Pernet 5

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different environmental conditions, different results Different environmental conditions, different results: the role of controlled environmental stress on grape quality potential and the way to monitor it C. van Leeuwen 1, O. Trégoat 2, X. Choné 3, J.-P. Gaudillère 4, D. Pernet 5 1 ENITA de Bordeaux, I.S.V.V., UMR EGFV, 1 Cours du Général de Gaulle, CS 40201, 33175 Gradignan-Cedex, France. 2 39 Rue A. Miquel, 34500 Béziers, France. 3 28 Rue Pagès, 33000 Bordeaux, France. 4 INRA Centre de Bordeaux, BP81, 33883 Villenave d Ornon cedex, France. 5 SOVIVINS, Centre de ressources Montesquieu, 1 avenue Jean Rostand, 33650 Martillac, France. Corresponding author s e-mail: k-van-leeuwen@enitab.fr Abstract Environmental stress, such as water deficit or limited nitrogen availability, reduces grape yield, but generally promotes grape quality potential for red table wine production. Limited nitrogen uptake limits grape yield but enhances grape quality potential for red table wine production, because it reduces berry size and enhances phenolic compound synthesis. Water deficit stress has one negative effect (reduction of photosynthesis), and many positive effects (shoot growth cessation, reduction of berry size and stimulation of phenolic compound synthesis). Mild water deficit stress increases berry quality potential, despite reduced photosynthesis. This can be explained not only by a reduced competition for sugars between shoot growth and fruit ripening, but also by reduced berry size. For red Bordeaux wine, vintage quality is well correlated to the drought of the vintage. Many tools are available for monitoring vine water status. Among them, two are of particular interest: stem water potential and carbon isotope discrimination measured on grape sugars ( 13 C/ 12 C ratio or δ 13 C). Stem water potential is better related to vine transpiration than leaf water potential. Stem water potential is a more precise indicator of vine water status than pre-dawn leaf water potential in soils with heterogeneous humidity, which is the case in irrigated soils. 13 C/ 12 C ratio in grape sugar (δ 13 C) is related to vine water status during grape ripening and can be measured with mass spectrometry. This indicator can be implemented to assess the severity of vine water deficit stress in dry farmed vineyards without any measurement in the field. For companies buying grapes from deficit irrigated vineyards it can be used to control the irrigation management on a mere sample of grape juice. Grape production can be made economically viable through high yields, high quality allowing high selling prices or low production costs. Strategic winery management implies deciding which of these parameters should be optimised. High yields can be obtained by fertirrigation of vines planted in fertile sites. High quality red table wine allowing high selling prices are produced by vines grown under environmental stress. Moreover, specific terroir expression is related to environmental stress. Production costs can be reduced by mechanisation and low labour input vineyard design. Introduction The vine is a resistant species to environmental stress. Historically, in the Old World, fertile land was preferentially used for grazing and annual crops. Shallow soils, stony soils and steep slopes were used for vineyards or olive tree plantations (van Leeuwen and Seguin 2006). Although yields tend to be moderate to low in these conditions, grape quality potential for wine making is generally high. Traditionally, vine vigour, yield and grape quality potential were controlled through site selection. By trial and error the best locations for quality production were selected. Today, vineyards are planted in a broader range of environmental conditions. The effects of environmental stress on yield and quality parameters are better understood and they can be more easily managed. Soil fertility depends mainly on water and nitrogen availability, generally in relation to soil depth (the deeper the soil, the more fertile it is; Coipel et al. 2006). A limitation in nitrogen uptake reduces vine vigour, berry weight and yield and increases berry sugar, anthocyanin and tannin content (Kliewer 1971, Choné et al. 2001a, Hilbert et al. 2003). Vine nitrogen status can be monitored through petiole, leaf blade or must analysis (Kliewer 1991, van Leeuwen et al. 2000a). Must total nitrogen or must yeast available nitrogen are practical and accurate indicators. Vine nitrogen uptake can be reduced through cover crop (Soyer et al. 1996) and increased through fertilisation. A limitation in water uptake also reduces vine vigour, berry weight and yield and increases berry anthocyanin and tanin content (Hardie and Considine 1976, Matthews and Anderson 1988,1989, van Leeuwen and Seguin 1994, Koundouras et al. 2006). The effect on berry sugar content is yield-dependant; in low yields, vine water deficit enhances berry sugar content and in high yields it depresses berry sugar content (Tregoat et al. 2002). Vine water status can be assessed through (i) soil water monitoring, by means of neutron moisture probes (Seguin 1986) or Time Domaine Reflectometry (Koundouras et al. 1999), (ii) water balance modelling (Lebon et al. 2003), or (iii) the use of physiological indicators (van Leeuwen et al. 2001a, Cifre et al. 2005). Among physiological indicators two are of particular interest: stem water potential (Choné et al. 2001b) and the 13 C/ 12 C ratio measured on grape sugar at ripeness (δ 13 C or carbon isotope discrimination, van Leeuwen et al. 2001b, Gaudillère et al. 2002). Vine water deficit can be increased by withholding irrigation water and increasing leaf area on a per hectare basis. Vine water deficit can be reduced by selecting drought resistant rootstocks (110Richter), by limiting leaf area, by limiting crop, by selecting drought resistant varieties (Grenache, Carignane) and by irrigation. Grape production can be made economically viable through i) high yields ii) high quality allowing high selling prices iii) low production costs. To obtain high yields, vines should be planted in fertile soils and irrigated if rainfall is limited during the growing season. High quality for red table wine production is obtained if vines are grown under environmental stress (van Leeuwen et al. 2004). When environmental stress is moderate, high quality can be combined with reasonably high yields. When environmental stress is severe, a low yield is necessary to obtain high quality. Low production costs can be obtained either by mechanisation or by low labour input vineyard design, such as unirrigated bush vines. In such vineyards, production cost per ton of grapes is low, even in low yields. PROCEEDINGS THIRTEENTH AUSTRALIAN WINE INDUSTRY TECHNICAL CONFERENCE 1

van leeuwen et al. Materials and methods This review paper contains some original results from various experiments. Materials and methods for these results have been presented in previous publications. For the study of the effect of nitrogen supply on vegetative development, yield and must composition on a network of Cabernet-Sauvignon plots in Saint- Julien (Bordeaux), see Choné et al. 2001a. The materials and methods for the study of the effects of water deficit on vine growth, yield and grape composition are presented in Tregoat et al. 2002. Materials and methods for the study of the relationship between leaf water potential, stem water potential and vine transpiration are presented in Choné et al. 2001b. Materials and methods for spatialisation of soil resistivity and δ 13 C are presented in Deschepper et al. 2006. Among other soil minerals, nitrogen has the greatest influence on vine development, yield parameters and must and wine composition The soil provides minerals to the vines. Among these, potassium, nitrogen, magnesium, calcium, phosphorus and iron are the most important, at least from a quantitative point of view. Potassium, magnesium and iron deficiencies provoke leaf symptoms that are likely to alter grape quality. Symptoms of calcium or phosphorus deficiency are rarely reported in field conditions. Excess of potassium can increase must and wine ph (Morris et al. 1983, Soyer and Molot 1993, Cahurel 2007). Except in situations of clear deficiency or obvious excess, no evidence is reported about the possible effects of these minerals on grape quality potential (van Leeuwen et al. 2004). Conversely, many studies report the influence of nitrogen on vine development, yield parameters and must and wine composition (Kliewer 1971, Bell et al. 1979, Spayd et al. 1994, van Leeuwen et al. 2000a, Choné et al. 2001a, 2006). The nitrogen available to the vine is related to the soil type and the soil depth. Nitrogen availability increases with soil organic matter content and soil organic matter turnover. The latter is high when C/N ratio of soil organic matter is low, ph is high, soil temperature is high and soil moisture content is close to field capacity, resulting in high soil microbiological activity. Soil aeration also stimulates organic matter turnover. Vine nitrogen status can be monitored by soil analysis or analysis on vine organs. Soil analyses are difficult to interpret, because of high spatial variability of soil composition. Moreover, they provide values for total soil nitrogen and not mineral nitrogen. Leaf blade, petiole, must total nitrogen and must yeast available nitrogen are accurate and practical indicators of vine nitrogen status (van Leeuwen et al. 2000a). The effect of the availability of soil nitrogen on vine behaviour can best be observed when vine water status is not limited. In 1997, which was a rainy vintage in Bordeaux, a clear effect of soil nitrogen supply on vegetative development, yield and must composition was observed on a network of plots planted with Cabernet Sauvignon and located on various soils of a Grand Cru Classé of Saint-Julien (Bordeaux). Vigour depended on vine nitrogen status: exposed leaf area and pruning weight were positively correlated to must total nitrogen content (Figures 1 and 2). Grape sugar was negatively correlated to must total nitrogen content (Figure 3). The wines produced from these plots were tasted and the best wine, with the highest phenolic content, was produced from the plot where vine nitrogen status was lowest and close to deficiency (data not shown). The positive effect of low nitrogen status on grape quality for red wine production is mainly the result of reduced vigour, limited berry size and stimulated phenolic compound synthesis in berries. For white grapes (and particularly varieties containing volatile thiols, like Sauvignon Blanc) low vine nitrogen status is not desirable, because it limits aroma precursor synthesis (Peyrot de Gachons et al. 2005, Choné et al. 2006). The nitrogen supply to the vines should be carefully managed. Excessive nitrogen in vines enhances bunch rot and reduces phenolic compounds in red grapes. Limited nitrogen supply reduces yield and reduces volatile thiols in white grapes. The nitrogen supply to the vines can be increased by mineral or organic fertilisation. It can be reduced by the use of cover crop, which competes for soil nitrogen with the vines. The effects of water deficit on vine growth, yield and grape composition Water deficit is undoubtedly the most frequent form of environmental stress to which vines are subjected. Water deficit reduces photosynthesis through stomatal closure (Hsiao 1973) and affects growth parameters (Lebon et al. 2006). To assess the effect of water deficit stress on vine development, yield parameters and grape quality potential, we monitorred vine water status on a network of 10 dry-farmed plots planted with Merlot throughout the Bordeaux region in 2000, which was a dry vintage. Vine water status was highly variable and depended on soil water holding capacity. The precociousness of shoot growth cessation was positively correlated with the intensity of water deficit stress: high water deficit stress (low stem water potential readings) resulted in early shoot growth cessation (Figure 4). Berry weight (Figure 5) and yield (Figure 6) were also correlated to the intensity of water deficit stress. Berry size was reduced by 37% in water stress conditions. When vines faced water deficit, must malic acid was reduced (Figure 7) and berry anthocyanin content was increased, even when water deficit was severe (Figure 8). Sugar content was highest Exposed leaf area (m 2 /vine) Figure 1. Correlation between must total nitrogen content at harvest and exposed leaf area Pruning weight (kg/vine) Must sugar content (g/l) 220 210 200 190 180 170 160 1.6 1.2 0.8 0.4 0 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 R 2 = 0.7522 p < 0.05 R 2 = 0.8044 p < 0.05 0 100 200 300 400 0 100 200 300 400 Figure 2. Correlation between must total nitrogen at harvest and pruning weight R 2 = 0.8672 Must total nitrogen (mg/l) Must total nitrogen (mg/l) 0 100 200 300 400 Must total nitrogen (mg/l) Figure 3. Correlation between must total nitrogen and must sugar content at harvest 2 PROCEEDINGS THIRTEENTH AUSTRALIAN WINE INDUSTRY TECHNICAL CONFERENCE

different environmental conditions, different results when water deficit was moderate: sugar content was depressed both by unlimited water uptake conditions as by severe water deficit stress (Figure 9). When water deficit stress was severe, grape sugar content was depressed because of limited photosynthesis. However, grape phenolics (Figure 8) and wine quality (data not shown) were high. High grape quality potential can be obtained under severely limited water regimes when the yield is low, which was the case on the most severely stressed plots in this study (between 6 and 7 T/ ha). When the yield is high, severe water deficit stress can lead to incomplete ripening and berry shrivelling, with disastrous effects on grape quality potential and possibly damage on the vines. In the case of unlimited water uptake conditions, grape sugar content was depressed (Figure 9) because of competition for carbohydrates between continued shoot growth and grape ripening and increased berry size (dilution of sugar in a greater berry volume). Wine quality was poor (data not shown). If water deficit stress generally promotes grape quality in red wine production, this is not necessarily the case in white wine production. In Sauvignon Blanc grapes, aroma precursors of volatile thiols are restricted when water deficit is severe (Peyrot des Gachons et al. 2005). The effects of water deficit on vintage quality in Bordeaux The vineyards of Bordeaux are dry-farmed. Hence, water deficit is variable from one vintage to another, depending on rainfall and evaporative demand. The dryness of the vintages from 1972 through 2005 was estimated by means of a water balance model (Pieri and Gaudillère 2005). The output of this model estimates the level of stomatal regulation during grape ripening and ranges from 0 (very dry conditions, 100% stomatal regulation) to 1 (very wet conditions, no stomatal regulation) for a standard soil with a water holding capacity of 200 mm. Vintage quality was rated on a scale of 0 20 by wine brokers Tastet and Lawton (33000 Bordeaux, France). All the dry vintages (water deficit index between 0 and 0.6) were great vintages with ratings > 16 (Figure 10). In not one vintage in Bordeaux over the last 35 years, was overall wine quality negatively affected by excessive water deficit stress. All the poor vintages, with ratings < 14, were wet vintages (water deficit index between 0.8 and 1). However, vintage quality in Bordeaux cannot be explained by vine water status alone: some very good vintages, such as 1982, were vintage without significant water deficit stress. R 2 = 0.70 200 Figure 4. Correlation between the intensity of vine water stress (assessed by measurement of stem water potential at harvest) and the precociousness of shoot growth cessation (Vitis vinfera L. cv. Merlot, 2000, Bordeaux) R 2 = 0.65 R 2 = 0.76 1.0 0.0 Figure 6. Correlation between the intensity of vine water stress (assessed by measurement of stem water potential at harvest) and yield (Vitis vinfera L. cv. Merlot, 2000, Bordeaux) 2.0 1.8 1.6 1.4 1.2 Figure 5. Correlation between the intensity of vine water stress (assessed by measurement of stem water potential at harvest) and berry weight at harvest (Vitis vinfera L. cv. Merlot, 2000, Bordeaux) 300 280 260 240 220 3.0 2.5 2.0 1.5 1.0 0.5 Shoot growth cessation (DOY) Berry weight (g) Yield (kg/vine) R 2 = 0.53 p < 0.05 1.0 Figure 7. Correlation between the intensity of vine water stress (assessed by measurement of stem water potential at harvest) and malic acid content at harvest (Vitis vinfera L. cv. Merlot, 2000, Bordeaux) R 2 = 0.78 1200 Figure 8. Correlation between the intensity of vine water stress (assessed by measurement of stem water potential at harvest) and berry anthocyanin content (Vitis vinfera L. cv. Merlot, 2000, Bordeaux) R 2 = 0.71 p < 0.05 210 Figure 9. Correlation between the intensity of vine water stress (assessed by measurement of stem water potential at harvest) and berry sugar content (Vitis vinfera L. cv. Merlot, 2000, Bordeaux) 3.0 2.5 2.0 1.5 2800 2600 2400 2200 2000 1800 1600 1400 270 260 250 240 230 220 Malic acid (g/l) Anthocyanin (mg/l) Berry sugar content (g/l) PROCEEDINGS THIRTEENTH AUSTRALIAN WINE INDUSTRY TECHNICAL CONFERENCE 3

van leeuwen et al. The assessment of vine water status Vine water status can be monitored by (i) measurements of soil water, (ii) water balance modelling or (iii) physiological indicators. Soil volumetric water content can be measured by means of a neutron moisture probe (Seguin 1986) or Time Domaine Reflectometry (TDR, Koundouras et al. 1999). These devices measure soil volumetric water content in a small sphere around an access tube. If soil texture or rooting depth is variable inside a plot, which is often the case, many access tubes have to be installed to obtain a reliable picture of soil water uptake on a plot scale. The presence of the access tubes modifies root distribution in the soil. To assess total water consumption by the vines, access tubes have to be installed at great depth to cover the entire root zone, which is rarely the case. Hence, soil water monitoring by neutron moisture or TDR probes is an expensive and not very reliable indicator of vine water uptake conditions in production units (van Leeuwen et al. 2001a). In water balance models (Lebon et al. 2003), soil water content is simulated from day to day during the season, taking into account the water stock at the beginning of the season (total transpirable soil water at field capacity), water losses through transpiration and direct evaporation from the soil surface and the refill of soil water through rainfall or irrigation: ASW = TTSW + R + I CT SE Where: ASW = Available Soil Water (mm) TTSW = Total Transpirable Soil Water at Field Capacity R = Rainfall I = Irrigation CT = Crop Transpiration SE = Soil Evaporation Most of the terms of the water balance model can be correctly measured or estimated except for TTSW at field capacity. TTSW depends on soil texture, soil bulk density, the percentage of coarse elements and rooting depth. Precise data on rooting depth is rarely available; consequently, water balance models lack accuracy for simulating water deficit at the plot scale. Vine water status can also be monitored by physiological indicators (Cifre et al. 2005). These are based on the principle that vine physiology is modified by water deficit. Many physiological indicators have been developed over the last decades: transpiration, water potentials (Begg and Turner 1970), micro variations in stem or berry diameter (Garnier and Berger 1986, Greenspan et al. 1994, van Leeuwen et al. 2000b), differences between leaf and air temperature ( Jones 1999), carbon isotope discrimination measured on grape sugars (Farquhar et al. 1989, van Leeuwen et al. 2001b, Gaudillère et al. 2002), sap flow measurement (Escalona et al. 2002) and growth parameters (Pellegrino et al. 2005). Among these physiological indicators two are of particular interest: stem water potential and carbon isotope discrimination measured on grape sugars. (I) Among various water potentials, stem water potential is the most reliable indicator of vine water status Water potentials in vascular plants can be measured by means of a pressure chamber (Scholander et al. 1965). They are generally measured on leaves. Applications of the pressure chamber technique are: (i) leaf water potential, (ii) pre-dawn leaf water potential and (iii) stem water potential. The range of midday leaf water potential values, midday stem water potential values and pre-dawn leaf water potential values with regard to vine water deficit are presented in Table 1. However, these values are average thresholds which may vary from plot to plot, depending on root distribution and vine vigour. They also depend on climatic parameters (temperature, VPD, wind speed). Leaf water potential can be measured during the course of the day. The more negative the water potential in the leaf, the greater the water deficit in the vine. Leaf water potential reaches a minimum in the early afternoon. This moment is generally chosen for comparing measurements. Although it has been shown that leaf water potential varies with vine water status, it is also highly variable depending on the microclimatic environment of each particular leaf (Tables 2a and 2b). Moreover, vines have an isohydric behaviour (Schultz 2003) and they limit variations in water potential of their leaves by stomatal regulation. For these two reasons, midday leaf water potential is not a very accurate indicator of vine water status. When water potential is measured on leaves at the end of the night (socalled pre-dawn leaf water potential), microclimatic conditions are homogeneous among leaves and vines are not transpiring. In those conditions, each single leaf of a vine has a similar water potential. This water potential is in equilibrium with the most humid soil layer explored by the root system. Although it better represents vine water status in relation with soil water availability than midday leaf water potential, it underestimates water deficits when soil water is heterogeneous. For a given level of pre-dawn leaf water potential, vines will be more subject to water deficit stress during the day when soil water content is heterogeneous. A small humid soil layer might be able to rehydrate a vine overnight (pre-dawn leaf water potential values close to zero), but might not be able to provide enough water to the vine during the day to meet evaporative demand, particularly when the canopy is large. This is typically the case in irrigated vines and pre-dawn leaf water potential is not an accurate indicator of vine water status for irrigation management (Ameglio et al. 1999). Stem water potential is measured during the day on a leaf that is bagged with an opaque plastic bag one hour prior to measurement. The opaque bag prevents the leaf from transpiring. During the hour between bagging and the water potential measurement, the water potential in the leaf equilibrates with the water potential in the stem xylem. Although the measurement is carried out on a leaf, the obtained value represents whole vine water potential (Tables Vintage quality rating 20 19 18 17 16 2005 1998 2000 2001 1995 2003 1990 1982 1996 1983 1976 15 14 R 2 = 0.45 13 1992 12 1974 1984 11 1977 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Water deficit stress index veraison harvest Figure 10. Relationship between vintage quality rating and water deficit stress index (WDSI) for the period veraison ripeness. WDSI = 1 means no water deficit stress; WDSI = 0 means maximum water deficit stress 1986 Table 1. Water potential and 13 C/ 12 C ratio values with respect to vine water deficit thresholds Midday Stem Water Potential (MPa) Midday Leaf Water Potential (MPa) Pre-dawn Leaf Water Potential (MPa) 13 C/ 12 C ratio No water deficit > -0.6 > -0.9 > -0.2 < -26 Weak water deficit -0.6 to -0.9-0.9 to -1.1-0.2 to -0.3-24.5 to -26 Moderate to weak water deficit Moderate to severe water deficit -0.9 to -1.1-1.1 to -1.3-0.3 to -0.5-23 to -24.5-1.1 to -1.4-1.3 to -1.4-0.5 to -0.8-21.5 to -23 Severe water deficit < -1.4 < -1.4 < -0.8 > -21.5 4 PROCEEDINGS THIRTEENTH AUSTRALIAN WINE INDUSTRY TECHNICAL CONFERENCE

different environmental conditions, different results Table 2a. Stem water potential, Leaf water potential and Pre-dawn leaf water potential measured on 6 vines with 6 replicates per vine (Merlot, 10 August 2006, Saint-Emilion, Bordeaux, France) Midday stem water potential Vine 161 Vine 162 Vine 301 Vine 302 Vine 281 Vine 282 Mean 6 vines -0.81-1.43-1.45-1.27-0.56-0.68-0.88-1.32-1.33-1.29-0.74-0.86-0.89-1.38-1.48-1.36-0.72-0.91-0.85-1.41-1.46-1.39-0.71-0.78-0.92-1.47-1.30-1.34-0.74-0.75-0.97-1.49-1.40-1.50-0.79-0.83 Mean -0.89-1.42-1.40-1.36-0.71-0.80-1.10 Standard Deviation 0.06 0.06 0.07 0.08 0.08 0.08 0.07 Variation Coefficient % -6.2% -4.4% -5.3% -6.1% -11.1% -10.3% -7.2% Midday leaf water potential Vine 161 Vine 162 Vine 301 Vine 302 Vine 281 Vine 282 Mean 6 vines -1.43-1.43-1.45-1.40-1.37-1.05-1.31-1.41-1.49-1.46-1.11-1.02-1.18-1.43-1.46-1.35-1.48-1.19-1.25-1.46-1.34-1.35-0.94-0.87-1.20-1.38-1.33-1.30-0.97-1.26-1.00-1.44-1.47-1.30-0.81-0.98 Mean -1.23-1.43-1.42-1.36-1.11-1.06-1.27 Standard Deviation 0.14 0.03 0.07 0.06 0.26 0.14 0.12 Variation Coefficient % -11.7% -1.9% -4.9% -4.5% -23.5% -13.4% -10.0% Pre-dawn leaf water potential Vine 161 Vine 162 Vine 301 Vine 302 Vine 281 Vine 282 Mean 6 vines -0.31-0.46-0.49-0.59-0.23-0.24-0.20-0.48-0.56-0.52-0.18-0.31-0.28-0.41-0.57-0.45-0.26-0.19-0.38-0.41-0.55-0.52-0.31-0.29-0.27-0.45-0.64-0.56-0.32-0.26-0.24-0.52-0.51-0.50-0.26 Mean -0.28-0.46-0.55-0.52-0.26-0.26-0.39 Standard Deviation 0.06 0.04 0.05 0.05 0.06 0.04 0.05 Variation Coefficient % -22.0% -9.3% -9.5% -9.3% -22.3% -16.1% -14.7% Table 2b. Stem water potential, Leaf water potential and Pre-dawn leaf water potential measured on 6 vines with 6 replicates per vine (Cabernet Sauvignon, 5 September 2006, Margaux, Bordeaux, France) Midday stem water potential (MPa) Vine 1 Vine 2 Vine 3 Vine 4 Vine 5 Vine 6 Mean 6 vines -1.08-1.22-1.10-0.90-0.93-1.11-1.10-1.24-1.13-0.92-0.97-1.12-1.11-1.28-1.16-0.99-0.98-1.13-0.96-1.18-0.98-0.90-0.94-0.88-1.01-1.19-1.06-0.95-0.98-0.89-1.08-1.21-1.09-0.96-0.98-1.00 Mean -1.06-1.22-1.09-0.94-0.96-1.02-1.05 Standard Deviation 0.06 0.04 0.06 0.04 0.02 0.12 0.06 Variation Coefficient % -5.5% -3.0% -5.9% -3.9% -2.1% -11.4% -5.3% Midday leaf water potential (MPa) Vine 1 Vine 2 Vine 3 Vine 4 Vine 5 Vine 6 Mean 6 vines -1.32-1.40-1.37-1.23-1.17-1.37-1.33-1.41-1.40-1.26-1.23-1.38-1.35-1.43-1.43-1.28-1.24-1.39-1.13-1.33-1.26-1.03-0.94-1.02-1.16-1.33-1.28-1.04-0.96-1.03-1.20-1.34-1.29-1.04-0.96-1.03 Mean -1.25-1.37-1.34-1.14-1.08-1.20-1.23 Standard Deviation 0.10 0.04 0.07 0.12 0.14 0.19 0.11 Variation Coefficient % -7.9% -3.2% -5.1% -10.6% -13.2% -15.9% -9.3% Pre-dawn leaf water potential (MPa) Vine 1 Vine 2 Vine 3 Vine 4 Vine 5 Vine 6 Mean 6 vines -0.23-0.32-0.25-0.15-0.13-0.10-0.23-0.32-0.26-0.16-0.13-0.12-0.24-0.33-0.27-0.17-0.13-0.12-0.26-0.34-0.27-0.17-0.14-0.13-0.32-0.34-0.28-0.18-0.14-0.13-0.33-0.36-0.34-0.18-0.15-0.14 Mean -0.27-0.33-0.28-0.17-0.14-0.12-0.22 Standard Deviation 0.04 0.01 0.03 0.01 0.01 0.01 0.02 Variation Coefficient % -16.4% -4.0% -10.5% -7.3% -5.8% -8.9% -8.8% PROCEEDINGS THIRTEENTH AUSTRALIAN WINE INDUSTRY TECHNICAL CONFERENCE 5

van leeuwen et al. 2a and 2b). Hence, when measurements are carried out on several leaves of the same vine, the coefficient of variation (%) of stem water potential is consistently lower compared to pre-dawn leaf water potentials or leaf water potentials. Stem water potential values reach a minimum in the early afternoon. This moment is generally chosen for comparing measurements among sites. Stem water potential values reflect soil water availability, but they also depend on climatic parameters. To compare measurements in relation to soil water availability, they should be carried out in similar climatic conditions, for instance on sunny days without extreme temperatures. Stem water potential is consistently well correlated to vine transpiration (Figure 11a), which is not always the case for midday leaf water potential (Figure 11b). Because stem water potential represents whole vine water status during the day, it is a particularly useful tool for irrigation management. It accurately represents vine water status, even if soil water content is heterogeneous, for example in irrigated vineyards. It can also be used in dry farmed vineyards for measuring residual water deficits after rainfall. However, the threshold of stem water potential that gives way to irreversible damage on canopy and grapes varies with the vigour of the vines. Water deficit damage is caused by vascular embolism (Schultz and Matthews 1988). On vigorous vines with large xylem vessels, that are brutally exposed to water deficit, embolism might occur at stem water potential readings of 1.2MPa. Low vigour vines, that are progressively exposed to water deficits, might resist to stem water potential levels of -1.6 MPa. In dry-farmed, Bordeaux vineyards it is a current observation that vines resist remarkably well to drought conditions when water deficits develop progressively during the season. R 2 = 0.73 10 8 6 4 2 Transpiration flow (µg/cm -2 /s -1 ) Carbon isotope discrimination measured on grape sugars at ripeness (δ 13 C) Ambient CO 2 contains 98.9% of 12 C isotope and 1.1% of 13 C isotope. 12 C is more easily used by the enzymes of photosynthesis in their production of hexoses. Therefore, the sugar produced by photosynthesis contains a higher rate of the 12 C isotope than ambient CO 2. This process is called isotope discrimination. When plants face water deficit conditions, isotope discrimination is reduced because of stomatal closure (Farquhar et al. 1989). Therefore, 12 C/ 13 C ratio in products of photosynthesis form a signature of plant water uptake conditions over the period in which they were synthesised. When measured on grape sugar at ripeness, 12 C/ 13 C ratio (so-called δ 13 C) is an integrative indicator of vine water status during grape ripening (van Leeuwen et al. 2001b, Gaudillère et al. 2002). δ 13 C can easily be measured by mass spectrometry in specialised laboratories. The results vary from 20 (severe water deficit stress) to 27 (no water deficit stress, Table 1). δ 13 C is well correlated to stem water potential (Figure 12). No field measurements have to be carried R 2 = 0.86 δ 13 C (p. 1000) -25-24 -23-22 -21 0.0 Figure 12. Correlation between stem water potential measured at harvest and carbon isotope discrimination (δ 13 C) measured on grape sugar at ripeness (Vitis vinifera L. cv. Merlot, Bordeaux, 2000) -0.2-0.4-0.6-0.8-1.0-1.2-1.4-1.6-1.8 Stem water potential at harvest (MPa) 0-1.2-1 -0.8-0.6-0.4 Stem (MPa) Figure 11a. Correlation between stem water potential and transpiration flow Figure 13a. Spatial representation of vine water status, assessed by δ 13 C measurements on grape sugar, in a Bordeaux estate R 2 = 0.039 n.s. 10 8 6 4 2 Transpiration flow (µg/cm -2 /s -1 ) 0-1.4-1.2-1 -0.8 Leaf (MPa) Figure 11b. Correlation between leaf water potential and transpiration flow Figure 13b. Soil resistivity mapping. Cold colors represent low resistivity and warm colors represent high resistivity 6 PROCEEDINGS THIRTEENTH AUSTRALIAN WINE INDUSTRY TECHNICAL CONFERENCE

different environmental conditions, different results out, because δ 13 C is measured on a sample of grape juice at ripeness. Hence, many measurements can be carried out. In dry farmed vineyards, δ 13 C is a valuable tool to discriminate water deficits at plot scale. On the Bordeaux estate presented in Figure 13a, dry plots (high δ 13 C values) correspond to gravely soils with low water holding capacity. On these plots, soil resistivity is high (Figure 13b). Plots with higher water holding capacity, because of a higher soil clay content, show more negative δ 13 C values (Figure 13a). On these plots soil resistivity is low (Figure 13b). In many countries, the wine industry buys grapes from independent growers. For red grapes, the buyers generally ask growers to deficit irrigate their vines in order to enhance grape quality potential (reduced berry size, increased anthocyanin and total phenolic content). Growers might be reluctant to reduce irrigation, because deficit irrigation reduces yields. It is too labour intensive for grape buyers to control irrigation in the field. However, δ 13 C measurement provides a tool to grape buyers to control the level of irrigation directly on the purchased grapes, at a reasonable cost. Economic aspects Grape production can be made economically viable through i) high yields ii) high quality allowing high selling prices iii) low production costs. High yields can be obtained by selecting fertile sites and by providing unlimited water and nitrogen uptake condition to the vines by supplementary irrigation and/or fertilisation if necessary. In warm climates, high yields can be combined with good fruit quality though optimised canopy management and particularly light interception (Smart and Robinson 1991). However, to produce high quality red table wines with distinctive characters linked to their environment (soil, climate), two conditions have to be met. Grapevine varieties have to be matched to local climatic conditions, so that the grapes ripen at the end of the season, in September or October in the Northern hemisphere or in March or April in the Southern hemisphere (van Leeuwen and Seguin 2006). This condition is more easily met in cool climates, but can also be achieved in warmer climates with late ripening varieties. Vines have to be grown under environmental stress. This environmental stress is most frequently water deficit, but might as well be limited nitrogen uptake. Environmental stress reduces yield, but grapegrowing can still be highly profitable as long as wine quality and wine typicity linked to specific environmental conditions generate higher selling prices. Wines produced in these conditions are called terroir wines. Wine production can also be made economically viable through reduction of production costs. These can be cut by mechanisation or by low labour input vineyard design. Dry-farmed bush vine vineyards, planted in dry regions, are a good example of low labour input vineyard design. Labour input is limited to pruning, weed control, pest control and harvesting. Although these vineyards are low yielding, production price per ton of fruit is low and fruit quality generally high. Dry-farmed bush vine vineyards are a form of environmentally friendly, sustainable viticulture. They are adapted to arid regions where water restrictions make irrigation not possible. However, at least 300 mm of rainfall per year are necessary to grow vines in these conditions. Conclusion High quality red table wines are generally produced from grapes grown under environmental stress. This environmental stress is most frequently water deficit stress, but can also be limited nitrogen availability. Traditionally, in European vineyards, environmental stress is imposed on the vines through site selection. High quality vineyards are often located on shallow or stony soils. Today, vineyards are planted in a broader variety of environmental conditions. Environmental stress can be managed through deficit irrigation, limitation of fertiliser input or cover crop. Accurate indicators of vine nitrogen and water status are needed to control environmental stress. Vine nitrogen status can be assessed through leaf blade, petiole, or must total nitrogen analysis. Yeast assimilable nitrogen is also a practical and accurate indicator of vine nitrogen status. Vine water status can be monitored by means of physiological indicators. Stem water potential is a powerful indicator for irrigation management and δ 13 C for site selection or post harvest irrigation control. Environmental stress reduces yield and can thus only be accepted if reduced yield is compensated by higher selling prices. References Ameglio, T.; Archer, P.; Cohen, M.; Valancogne, C.; Daudet, F.-A.; Dayau, S; Cruiziat, P. 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