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Potassium Accumulation by Grapevines
Uncovering the relationship between potassium and pH in grape juice and wine
Potassium (K) is the major cation in ripe grapes, accounting for about 75% of the total mineral cations. Grape juice pH is strongly correlated with grape juice K and largely determines the pH of the wine after fermentation, with high wine pH negatively impacting wine color, stability and taste.18
Adjustment of pH with tartaric acid during vinification is routinely applied to protect against such impacts.5 The aim is generally to bring pH to below 3.0 for white wines and below 3.5 for red wines.8 Rootstocks can lead to differences in K concentrations in grape berries and grape juice,15 which can carry over into wine. Balanced K accumulation by grapevines is important to avoid deficiency (see Malbec and Chardonnay photos above) or excessive uptake. The interrelationships between K and pH in grape juice and wine are discussed below.
Potassium accumulation by grapevines
Among the ungrafted vines, rootstock 1103 Paulsen had the highest total K uptake, and rootstock 110 Richter had the lowest total K uptake.9 For grafted vines, Shiraz on 110 Richter and 140 Ruggeri had higher total K uptake than Shiraz on Ramsey and 1103 Paulsen, indicating a scion-rootstock interactive effect on total K uptake.10
Potassium translocation efficiency (ratio of K content in shoot to K content in shoot plus roots) of 101-14 was higher than that of 140 Ruggeri for both ungrafted and grafted vines.9,10 Unfortunately, there are no field studies to compare with these greenhouse studies on K translocation efficiency, since destructive harvest and analysis of whole vines from the field is required.
Accumulated K in grapevines can be retranslocated to other plant parts. This was demonstrated by S. Kodur et al. in studies using rubidium (Rb) as an analogue of K that involved an initial loading of Rb into leaves.11 For example, concentrations of Rb in leaves decreased significantly during a 48-hour period after loading and increased significantly in lateral shoots, stem and roots (there were no clusters on these vines). W.J. Conradie provided evidence that leaves, shoots and roots could each potentially contribute to accumulated K in bunches.2
Potassium accumulation is also higher with higher soil K supply. For example, in an experiment involving fruiting Sultana grapevines in a greenhouse receiving either low K supply (0.05 g of K per week as KH2PO4) or high K supply (0.15 g of K per week as 0.05 g of KH2PO4 and 0.10 g of K2SO4), the high K supply vines accumulated significantly higher concentrations of K (56.8 mmol/L) and malate (1.20 g/L) and had higher pH (4.08) in grape juice relative to low K supply vines (46.8 mmol/L K, 0.94 g/L malate and 3.95 pH). Tartaric acid concentrations in grape juice were similar between high and low K supply vines.16
Critical role of potassium in plant stress response
Today there is an emerging appreciation of K’s role in plant resistance to biotic and abiotic stresses. Balanced fertilization and efficient K usage in combination with other nutrients not only contribute to a crop’s growth, yield and quality, they also influence plant health and reduce the impacts from environmental stresses.24
Canopy effects on K accumulation
Fruit from vines subjected to different shading treatments were shown to have the highest K concentrations at harvest in the most heavily shaded treatment and lowest in the totally exposed treatment.14 Results suggested that the effect on fruit K concentration was driven more by leaf shading than cluster shading. Further, high-must K has been shown to be associated with a shaded microclimate.17 It is well known that the degree of shading in the canopy increases as vine vigor increases.13
In an attempt to compare K uptake and growth characteristics between a relatively low-vigor rootstock (110 Richter) and a relatively high-vigor rootstock (Rupestris St. George), B.A. Swanton and W.M. Kliewer used a flowing nutrient solution system to make the comparison.19 Total root surface area and leaf blade K (percent weight basis) were higher in Rupestris St. George than in 110 Richter. They used total quantity of K taken up divided by the total transpiration volume, termed xylem K approximation, as a non-destructive measure of xylem sap K. They found that this was significantly higher in Rupestris St. George than in 110 Richter and a better indicator of the foliage K concentration than K influx (K uptake per cm2 root surface area per hour).
Rootstock vigor, vine performance and berry traits
In a field trial with seven scions (Gamay, Chasselas, Ehrenfelser, Reichensteiner, Egiodola, Perdea and Rousanne) grown on their own roots and on five different rootstocks (SO4, Schwarzmann, 1103 Paulsen, Ramsey and Dogridge), a wide range in vine vigor was observed that was conferred primarily through the rootstock. This enabled correlations to be tested between variables.
Grape juice K concentration was positively correlated with pruning wood weight (r=0.55, P<0.001), and grape juice pH was positively correlated with juice K (r=0.77, P<0.001). Grape juice tartaric acid was negatively correlated with yield (r=0.62, P<0.001) and berry weight (r=0.56, P<0.001), while grape juice malic acid was positively correlated with pruning wood weight (r=0.57, P<0.001) and juice K (r=0.69, P<0.001).
In a second field study with Shiraz grafted to five rootstocks (Freedom, Ramsey, 1103 Paulsen, 140 Ruggeri and Dogridge) and to 55 hybrid rootstocks from the Commonwealth Scientific and Industrial Research Organization (CSIRO) rootstock-breeding program, a similar wide range in vine vigor was obtained that was conferred primarily by rootstock genotype. In this case, based on three season means for the respective variables, positive correlations were obtained between grape berry K concentration and pruning wood weight (r=0.81, P<0.001).
Grape juice pH was positively correlated with berry K concentration (r=0.93, P<0.001), pruning wood weight (r=0.70, P<0.001) and berry weight (r=0.55, P<0.001). Grape juice titratable acidity was positively correlated with pruning wood weight (r=0.85), yield (r=0.66) and berry weight (r=0.66) (all P<0.001).
The CSIRO rootstock breeding program has aimed to select rootstock types with lower K accumulation in order to achieve lower grape juice pH and therefore reduced need for pH adjustment during winemaking. Three low- to medium-vigor selections demonstrating lower grape juice K accumulation in Sunraysia (Victoria) trials have progressed to release in Australia with Plant Breeders Rights protection.1,22
Grape juice and wine K and pH relationships for Chardonnay and Shiraz
Four trial sites were established in different wine regions of Australia (Merbein and Koorlong in Victoria; Barossa Valley and Padthaway in South Australia) in the early 1990s. Each involved Chardonnay and Shiraz on their own roots and grafted to eight different rootstocks (Ramsey, 1103 Paulsen, 140 Ruggeri, K 51-40, Schwarzmann, 101-14, Rupestris St. George and 1202C). All were drip irrigated, but irrigation water electrical conductivity was different between the sites, ranging from 0.4 decisiemens per meter at one site to 3.3 decisiemens per meter at another site. Soil K concentrations also varied from site to site.23
Data for grape juice and wine K and pH for Chardonnay and Shiraz across own-rooted vines and the range of rootstocks confirmed the strong positive correlation between K and pH in both grape juice and wine.23 It was clear from the data that as grape juice and wine K increase, [H+] decreases and pH increases. The relationship was linear for Chardonnay and exponential for Shiraz for both grape juice and wine.23
It was also clear from this work that certain rootstocks can result in higher K in wine produced from different sites. For example, rootstock K 51-40 resulted in the highest wine K concentrations at the Merbein Chardonnay and Shiraz sites and also at the Nuriootpa Chardonnay and Rowland Flat Shiraz sites in the Barossa Valley.23 However, at another site in Padthaway, South Australia, K concentration in grape juice of Chardonnay and Shiraz from K 51-40 rootstock was comparable with other rootstocks, indicating rootstock-site interactive effects on grape juice K.
Grape juice K is correlated with juice total soluble solids
When grape juice K and total soluble solids were measured at regular intervals between post-fruit set and berry maturation at two sites (Merbein and Koorlong, Victoria) for Shiraz grapes on own roots, or grafted to Ramsey, 1103 Paulsen, 140 Ruggeri and 101-14 rootstocks, positive linear relationships (R2=0.9) were obtained between grape juice K concentration and grape juice total soluble solids.21 Furthermore, the slope of the relationships was the same at both sites, despite large differences in electrical conductivity of the irrigation water, specifically 0.4 decisiemens per meter at one site (Koorlong) and 2.1 decisiemens per meter at the other site (Merbein).
Using data for grape juice K and total soluble solids obtained at harvest for each Chardonnay and Shiraz trial at four sites involving vines on own roots or grafted to eight different rootstocks, strong positive correlations (R2=0.7) were obtained between the variables.23 Both sucrose and K are transported in the phloem to developing berries.12 This close association between the variables is further evidence of a potential relationship during phloem loading and unloading.
Wine color hue is positively correlated with wine pH
The strong correlation between K and pH in grape juice and wine has been noted. As previously reported by T.C. Somers, high wine pH has a negative impact on wine color.18 Using Shiraz wine data from the trials at four sites, where wine was made using fruit from own-rooted vines and from Shiraz grafted to five different rootstocks, wine color hue was positively correlated with wine pH.23 Low color hue means a brighter wine, conversely, a higher color hue with higher wine pH means less bright wines. Similar observations were made by H. Gong et al.6
Distribution of K in grape berries
When examined in terms of total berry K content, the percentage of total berry K in skins has been found to be similar to the percentage of total berry K in pulp, with only a small percentage of total berry K in seeds.
For example, for the grape varieties Muscat Gordo Blanco, Shiraz, Riesling, Cabernet Sauvignon and Chardonnay, all grown on their own roots at Loxton, South Australia, the mean percentage of total berry K content in skin, pulp and seed was 43%, 50% and 7%, respectively.20
For each variety grafted on Ramsey at the Loxton site, the mean percentage of total berry K content in skin, pulp and seed was 41.5%, 53% and 6%, respectively.20 On a concentration basis, because skins are only a small percentage of total berry weight, K concentrations can be much higher in berry skins than in pulp.
For example, in fruit from Padthaway, South Australia, and Merbein, Victoria, skin K concentrations were 4.0 to 4.5 times higher than in the pulp for Chardonnay and 4.0 to 5.5 times higher than in pulp for Shiraz.6
Potassium concentration in fermenting musts
In a study involving four varieties during fermentation on skins, there was a 50% to 120% increase in must K concentration during the first two or three days of fermentation, after which concentrations plateaued over the next 10 days. During juice fermentation (no skin contact), the increase over the same period was smaller (0% to 38%), followed by a plateau or decline.20 This suggests that significant K is released from skins into the must during early stages of fermentation. The subsequent plateau in must K concentrations may be explained by pressing off the skins after three days.
The R.R. Walker et al. study20 also showed that K concentration in ferments was higher from Ramsey-grafted vines than from own-rooted vines, most likely reflecting higher K concentrations in the pulp and skin of berries from Ramsey-grafted vines than from own-rooted vines, as demonstrated in the stu dy by H. Gong et al.6
Juice K/wine K relationship in red and white wine
Using data obtained from the study of Chardonnay and Shiraz grown on own roots and grafted to eight different rootstocks at four different sites in Australia, and where wine was made from grapes harvested at the various sites, it was observed that K concentrations in wines (measured on average 10 months after completion of vinification) showed a decrease of more than 50% for white wines and around 20% for red wines relative to concentrations in grape juice. This agrees with observations by T.C. Somers,18 although recently for Shiraz, we observed a wide range, from increases of around 20% to decreases of around 40% in K concentrations between grape juice and wine.
The main influencing factors are likely to involve formation and precipitation of potassium bitartrate during vinification,3,4 extraction of K from skins and time on skins during the making of red wines,20 and possible adsorption of K on pomace.7
Summary
Potassium is essential for vegetative growth and berry development. There is an interaction between rootstock, scion, management and environment in determining tissue concentrations. Grape juice pH is positively correlated with grape juice K, and high grape juice pH requires more pH adjustment in winemaking with higher cost to bring to required levels. Potassium accumulates in berry pulp and skins, and leakage of potassium from skins to must during fermentation on skins contributes to higher wine potassium and pH. Higher pH correlates with higher color hue, which is associated with less bright wines.
Canopy management to reduce excessive shade—and monitoring of soil and plant potassium to ensure optimum but not excessive supply—is essential for sustaining plant health and production. Rootstocks selected for potassium uptake at the lower end of the adequate range may assist to achieve low grape and wine potassium concentrations.
Rob Walker, chief research scientist at CSIRO Agriculture, Waite Campus in Urrbrae, South Australia, specializes in plant response to abiotic stress, plant salt tolerance and salt exclusion, grapevine potassium partitioning and function. Peter Clingeleffer, chief research scientist at CSIRO Agriculture, specializes in grapevine scion and rootstock breeding, grapevine management and the interaction between genotype, environment and management.
This text was edited from the original publication in the March 2016 issue of Australian & New Zealand Grapegrower & Winemaker, with permission of Winetitles. The authors acknowledge support from CSIRO and the Grape and Wine Research and Development Corp. (now Wine Australia).
References
1. Clingeleffer, P., B. Smith, E. Edwards, E., M. Collins, N. Morales, H. Davis, S. Sykes and R. Walker. 2011 “Industry puts low-medium vigour rootstocks to the test.” Wine & Viticulture Journal, May/June 2011, 72-76.
2. Conradie, W.J. 1981 “Seasonal uptake of nutrients by Chenin Blanc in sand culture: II. Phosphorus, potassium, calcium and magnesium.” South African J. Enology & Viticulture 2, 7-13.
3. Dunsford, P.R. and R. Boulton. 1981a “The kinetics of potassium bitartrate crystallization from table wines. I. Effect of particle size, particle surface area and agitation.” Am. J. of Enol & Vit. 32, 100-105.
4. Dunsford, P. and R. Boulton. 1981b “The kinetics of potassium bitartrate crystallization from table wines. II. Effect of temperature and cultivar.” Am. J. of Enol & Vit. 32, 106-110.
5. Godden, P.W. and M. Gishen. 2005 “Trends in the composition of Australian wine 1984 - 2004.” In: Advances in Wine Science, Eds: R.J. Blair, M.E. Francis and I.S. Pretorius. The Australian Wine Research Institute, Glen Osmond Australia. pp 115-139.
6. Gong, H., D.H. Blackmore and R.R. Walker. 2010 “Organic and inorganic anions in Shiraz and Chardonnay grape berries and wine as affected by rootstock under saline conditions.” Australian J. of Grape & Wine Research 16, 227-236.
7. Harbertson, J.F. and E.D. Harwood. 2009 “Partitioning of potassium during commercial -scale red wine fermentations and model wine extractions.” Am. J. of Enol & Vit. 60, 43-49.
8. Iland, P.A., J. Ewart, J. Sitters, A. Markides and N. Bruer. 2000 Techniques for chemical analysis and quality monitoring during winemaking. Patrick Ireland Wine promotions, South Australia. ISBN: 0646 38435 x.
9. Kodur, S., J.M. Tisdall, C. Tang and R.R. Walker. 2010a “Accumulation of potassium in grapevine rootstocks (Vitis) as affected by dry matter partitioning, root traits and transpiration.” Australian J. of Grape & Wine Research 16, 273-282.
10. Kodur, S., J.M. Tisdall, C. Tang and R.R. Walker. 2010b “Accumulation of potassium in grapevine rootstocks (Vitis) grafted to ‘Shiraz’ as affected by growth, root traits and transpiration.” Vitis 49, 7-13.
11. Kodur, S., J.M. Tisdall, C. Tang and R.R. Walker. 2011 “Uptake, transport, accumulation and retranslocation of potassium in grapevine rootstocks.” Vitis 50, 145-149.
12. Lang, A. and M.R. Thorpe. 1989 “Xylem, phloem and transpiration flows in a grape: application of a technique for measuring the volume of attached fruits to high resolution using Archimedes principle.” J. of Experimental Botany 40, 1069-1078.
13. Mpelasoka, B., D.P. Schachtman, M.T. Treeby and M.R. Thomas. 2003 “A review of potassium nutrition in grapevines with special emphasis on berry accumulation.” Australian J. of Grape & Wine Research 9, 154-168.
14. Rojas-Lara, B.A. and J.C. Morrison. 1989 “Differential effects of shading fruit or foliage on the development and composition of grape berries.” Vitis 28, 199-208.
15. Rühl, E.H., P.R. Clingeleffer, P.R. Nicholas, R.M. Cirami, M.G. McCarthy, and J.R. Whiting. 1988 “Effect of rootstocks on berry weight and pH, mineral content and organic acid concentrations of grape juice of some wine varieties.” Australian J. of Experimental Agriculture
28, 119-125.
16. Rühl, E.H. 1989 “Effect of potassium and nitrogen supply on the distribution of minerals and organic acids and the composition of grape juice of Sultana vines.” Australian J. of Experimental Agriculture 29, 133-137.
17. Smart, R.E., J.R. Robinson, G.R. Due and C.J. Brien. 1985 “Canopy microclimate modification for the cultivar Shiraz. II. Effects on must and wine composition.” Vitis 24,119-128.
18. Somers, T.C. 1977 “A connection between potassium levels in the harvest and relative quality in Australian red wines.” Australian Wine Brewing & Spirit Review, May 1977 pp 32-34.
19. Swanton, B.A. and W.M. Kliewer. 1989 “Characterizing potassium uptake and accumulation by grape rootstocks: the xylem potassium approximation.” J. of Plant Nutrition 12, 145-158.
20. Walker, R.R., P.R. Clingeleffer, G.H. Kerridge, E.H. Rühl, P.R. Nicholas and D.H. Blackmore. 1998 “Effects of the rootstock Ramsey (Vitis champini) on ion and organic acid composition of grapes and wine, and on wine spectral characteristics.” Australian J. of Grape & Wine Research 4, 100-110.
21. Walker, R.R., P.E. Read and D.H. Blackmore. 2000 “Rootstock and salinity effects on rates of berry maturation, ion accumulation and color development in Shiraz grapes.” Australian J. of Grape & Wine Research 6, 227-239.
22. Walker, R. and P. Clingeleffer. 2009 “Rootstock attributes and selection for Australian conditions.” Australian Viticulture 13 (4), 70-76.
23. Walker, R.R. and D.H. Blackmore. 2012 “Potassium and pH inter-relationships in grape juice and wine of Chardonnay and Shiraz from a range of rootstocks in different environments.” Australian J. of Grape & Wine Research 18, 183-193.
24. Wang, M., Q. Zheng, Q. Shen and S. Guo. 2013 “The critical role of potassium in plant stress response.” International J. Molecular Science 14 (4), 7370-7390.
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