Effect of Media pH on Growth and Leaf Tissue Element Concentration of ‘Vidal blanc’ and ‘Norton’ Grape Cultivars

Abstract

The study involved two grape cultivars (‘Vidal blanc’ and ‘Norton’), grown in pots with media amended to pH 4.5, 5.9, 7.2, or 8.5. The objectives were to determine vegetative growth and mineral element concentration of these cultivars as affected by media pH and to determine the optimum pH range within those tested for cultivar growth. ‘Vidal blanc’ was superior to ‘Norton’ in all growth measurements. Raising media pH from 5.9 to ≥7.2 led to significant reductions in shoot length, specific leaf weight, leaf and shoot dry weight, and an increase in root to shoot ratio for ‘Norton’, but not for ‘Vidal blanc’. For ‘Norton’, a comparatively higher reduction in shoot versus root growth was responsible for increased root to shoot ratio above ≥7.2. Except for low P concentration in ‘Norton’ at media pH 8.5 and high Mg concentration in ‘Vidal blanc’ at media pH 5.9, other macronutrient concentrations did not differ with media pH or cultivars. Despite having a similar or even higher Fe concentration than ‘Vidal blanc’, ‘Norton’ showed noticeable Fe deficiency symptoms at media pH above 5.9. At harvest, plants at media pH 4.5 had 10–20 times more Mn and 3–8 times more Al than plants grown at alternative media pH levels. Media pH range 5.9 to 7.2 and 7.2 to 8.5 appears to encompass the optimum pH for growth of ‘Norton’ and ‘Vidal blanc’, respectively.

Keywords:

• amended media pH
• grape cultivars
• growth
• mineral element content

INTRODUCTION

Effects of physical and chemical soil conditions on crop growth differ with species and cultivar (French and Ewing, 1989; Baligar et al., 2001) and a similar observation has been reported for grapes (Campiglia et al., 2005). In crops like blueberry, optimum pH for growth may fall outside of the generally accepted pH range of 5.5–7.0 found for most crops. In order to obtain high crop yields, soil pH that optimizes nutrient availability should be obtained prior to crop establishment. In grapevines, increasing growth media pH from 4.1 to 5.0 or 6.0 increased grapevines shoot weight by 27 and 87%, and root weights by 11 and 32%, respectively (Conradie, 1983). In ‘Concord’ grapevines, reduction in root dry weight and an even greater reduction in shoot dry weight led to a higher root to shoot ratio at pH below 4.5 (Terence et al., 2002). The effect of media pH effects on the availability of plant mineral nutrients for uptake will result in changes in grapevines leaf nutrient concentration. At low media pH of 4.5, low P, K, and Ca concentration found in ‘Concord’ leaf was attributed to high solution Al concentration (Terence et al., 2002). At a pH range of 5.0–7.0, Al and Fe concentrations in ‘Concord’ leaves decreased while P concentration increased. Reduced root penetration in soil with acidic sub-soil results in poor utilization of subsoil water and nutrients (Marschner, 1991) increases nutrient leaching losses and the risk of water stress in plants (Goldman et al., 1989). At low pH, root length reduction was attributed to toxic levels of Al and Mn (Kirchhof et al., 1991). Economic production of crops in soil with pH levels outside of the range considered ideal for plant growth may be achieved through soil pH amendments. Alternatively, selecting crop cultivars with inherent tolerance to a given soil pH can be an appropriate strategy. Differences in tolerance to strongly acid soils between ‘White Riesling’ and ‘Chardonnay’ have been reported (Himelrick, 1991). Increasing soil pH from 4.8 to 6.7 increased shoot dry weight by 8% in ‘White Riesling’ and by 27% in ‘Chardonnay’.

‘Norton’ and ‘Vidal blanc’ are important wine cultivars in the Midwestern United States. ‘Norton’ is considered to be a natural hybrid of Vitis aestivalis and Vitis labrusca and is native to Eastern and Midwestern United States where soils tend to be more acidic (Winkler et al., 1974). ‘Vidal blanc’ is a complex hybrid of a calcareous soil tolerant species Vitis vinifera and other American Vitis species (Galet, 1979). Knowing the optimum soil pH at which each of these cultivars thrives is important in establishing and managing a vineyard. Amending the soil to the desired pH range prior to planting the vineyard will result in better vine growth. Good vine growth and root establishment results in efficient use of soil mineral elements and applied fertilizer with less runoff or leaching. This study was undertaken to address this lack of information for pH effects on growth and nutrient concentration of these two cultivars. The study objectives were: (1) to determine growth and leaf nutrient concentration of ‘Vidal blanc’ and ‘Norton’ at varying media pH and (2) to determine probable media pH within the range tested for optimum growth of these cultivars.

MATERIALS AND METHODS

Potted plants established from stem cuttings were used. Growing media was a mixture of two parts coarse sand and one part silty clay loam with a textural composition of 74% sand, 14% silt, and 12% clay. The media with pH 7.2 had an organic matter content of 2.2%; a cation exchange capacity of 3.9 meq/100 g; and base saturation of 3.6% K, 71.0% Ca, and 25.0% Mg. The experiment was a 2 × 4 factorial in a randomized complete block design with six replications. Two grape cultivars, ‘Vidal blanc’ and ‘Norton’ were grown in media of pH 4.5, 5.9, 7.2, or 8.5. Media pH was adjusted using sulfuric acid (H₂SO₄) or calcium hydroxide (Ca (OH)₂). Pots were spaced 1 m apart within and between rows. Plants were grown under full sunlight and two shoots per plant were vertically trained and tied to bamboo stakes. Peter's soluble fertilizer (20% N-10% P-20% K) was applied at 300 ppm N once a week. Irrigation water tested at a pH of 7.3 and a total alkalinity of 224 mg CaCO₃/L. was acidified to pH 5.8 using citric acid.

Shoot length was determined by taking a measurement from their origin on the two-year old stem to the growing tips. Total leaf area per plant at harvest was determined by use of a LI-3000 portable leaf area meter and a LI-3050A transparent belt conveyer accessory (LI-COR Inc., Lincoln, NE, USA). The harvested above ground materials were oven dried at 70°C to a constant weight, and then weighed. After 40 days of growth, when plants grown at media pH 4.5 were harvested, leaf width (widest portion of leaf base) and length (between petiole-leaf interface and leaf tip) of all intact leaves on plants grown at higher media pH was determined. At the termination of the experiment (94 days after establishment), leaves of varying sizes were obtained, length and width were determined, and leaf area was calculated. Actual leaf area of each of these leaves was determined with a leaf area meter. A regression between leaf area as determined by multiplication of length × width (assuming that the leaf is triangular) and actual area as determined with leaf area meter had a R ²-value of 0.98. The actual area of leaves of plants grown at media pH 5.9, 7.2, and 8.5 at 40 days of growth was calculated using length and width measurements previously obtained and the regression equation developed. Leaves at the third to sixth position from the proximal end were selected for nutrient analysis. Selected leaves were washed with distilled water to remove surface contaminants and oven dried at 70°C to a constant weight. Dried leaf samples were ground and levels of P, K Ca, Mg, Fe, Mn, and Al determined by inductively coupled plasma spectroscopy (ICP-AES). The shoots were harvested and the plant root system was carefully washed from the growing media and sieved off. Roots were sorted from dead organic material and with shoots were oven dried at 70°C to a constant weight. Analysis of variance (ANOVA) was done using the Minitab statistical package (Minitab Inc., College Road, PA, USA) and Tukey's pair wise test used to determine means that differed.

RESULTS

Plant Growth

Plants grown at media pH 4.5 were terminated after 40 days due to poor growth and appearance of necrotic symptoms (Fig. 1A and 1B). Plants at pH 5.9, 7.2, and 8.5 were allowed to grow for 94 days before the experiment was terminated. ‘Norton’ plants growing at media pH ≥7.2 showed chlorotic symptoms during this period of their growth as shown for plants at media pH 7.2 after 70 days of growth (Fig. 1D). Compared to plants grown at higher media pH, plants grown at media of pH 4.5 were smaller in size after 40 days of growth as indicated by their leaf surface area (Fig. 2). At harvest, 94 days after establishment, ‘Vidal blanc’ had greater shoot lengths than ‘Norton’ (Table 1). There were no visual nutrient deficiency symptoms for either cultivar at media pH 5.9, but for ‘Norton’, plants at this media pH were taller than those growing in other media pH treatments (Table 1). Between 40 days of growth and termination of the experiment, growth height in ‘Vidal blanc’ increased four-fold in all media pH. However, it is only at media pH 5.9 that there was a four-fold increase in shoot length.

FIGURE 1 Appearance of ‘Vidal blanc’ and ‘Norton’ after 40 days of growth at media pH 4.5 (A and B) and after 70 days of growth at media pH 7.2 (C and D) (color figure available online).

FIGURE 2 Leaf area of ‘Vidal blanc’ and ‘Norton’ grown at varying media pH levels after 40 days (continuous line) and 94 days (dotted line) of growth. Values are means ± SE (n = 6).

TABLE 1 Shoot Length of ‘Vidal blanc’ and ‘Norton’ Grapevines Grown at Varying Media pH Levels after 40 and 94 Days of Growth

		Days after transplanting
Cultivar	Media pH	40	94
Vidal blanc	4.5	—	—
	5.9	22a ^z	86a
	7.2	24a	100a
	8.5	23a	87a
Norton	4.5	—	—
	5.9	15b	67b
	7.2	14b	48c
	8.5	18b	48c
^zValues in same column followed by different letters are statistically different at p = 0.05.

‘Vidal blanc’ grown at media pH 7.2 or 8.5 had higher total leaf area (Fig. 2) and shoot dry weight (Fig. 3A) than ‘Norton’ grown in the same media pH. While ‘Norton’ plants grown at media of pH 5.9 increased its surface area from 718 cm² to 5,251 cm² (7-fold increase) during the last 54 days of growth, surface area of plants grown at media pH ≥7.2 increased from a mean value of 600 cm² to about 3,340 cm² (Fig. 2). Unlike in ‘Norton’, leaf surface area of ‘Vidal blanc’ were similar (∼1,200 cm²) after 40 days in all media pH and increased 5-fold to 6,500 cm² at 94 days of growth (Fig. 2). While no differences in leaf area for ‘Vidal blanc’ at different media pH were observed at project termination, media pH above 5.9 caused a significant (P = 0.05) reduction in leaf area in ‘Norton’. Trends similar to that of surface area was observed for shoot dry weight (Fig. 3A). ‘Vidal blanc’ had higher root dry weights than ‘Norton’ at all media pH (Fig. 3B). While no significant differences in root dry weights between media pH treatments was observed in ‘Vidal blanc’, ‘Norton’ at media of pH 8.5 had significantly (P = 0.05) lower root dry weight compared to that grown at pH 5.9 or 7.2. Root to shoot ratios were similar at all media pH for ‘Vidal blanc’, but in ‘Norton’, plants grown at media pH 5.9 had a significantly lower ratio compared to those at pH ≥7.2 (Table 2). Specific leaf weight and specific shoot weight decreased with increasing pH above 5.9 in ‘Norton’ but remained similar in ‘Vidal blanc’ for plants at all media pH (Table 2). At media pH above 5.9, ‘Vidal blanc’ had higher specific leaf weight and specific shoot weight than ‘Norton’ and lower root:shoot ratio.

FIGURE 3 Shoot (A) and root (B) dry weight of ‘Vidal blanc’ and ‘Norton’ grown at varying media pH levels. Values are means ± SE (n = 6).

TABLE 2 Root:Shoot Ratio, Specific Leaf Weight, and Specific Shoot Weight of ‘Vidal blanc’ and ‘Norton’ Grapevines Grown at Varying Media pH

Cultivar	Media pH	Root:shoot ratio	Specific leaf weight (mg cm^−2)	Specific shoot weight (mg cm^−2)
Vidal blanc	5.9	0.57ab ^z	5.95ab	8.93a
	7.2	0.55b	6.06a	9.62a
	8.9	0.55b	5.46ab	8.47a
Norton	5.9	0.59b	4.88b	6.94a
	7.2	0.78a	3.77c	5.75b
	8.9	0.78a	3.65c	5.52b
^zValues in same column followed by different letters are statistically different at p = 0.05.

Leaf Macro- and Micronutrient Concentrations

The two cultivars had similar P and K foliar concentrations at the same media pH (Table 3). There was a general tendency for lower P with increasing media pH. In fact ‘Norton’ had significantly higher P at media pH 5.9 compared to 8.5. In both cultivars, there was a tendency for higher Ca and lower Mg with increasing media pH (Table 3). ‘Vidal blanc’ had similar Mg concentration as ‘Norton’ at media pH ≥7.2, and which were lower than concentration at media pH 5.9. ‘Norton’ had significantly higher Fe concentration than ‘Vidal blanc’ at pH media 7.2 and 8.5 but lower at pH 5.9 (Table 3). While increasing pH led to a significant reduction in leaf Fe and Mn in ‘Vidal blanc’, it increased Fe and caused no effect on Mn in ‘Norton’. Within a cultivar, Al concentrations were not different between plants at different media pH. For plants grown at media pH 4.5, Fe concentration were 2- to 3-fold higher than in plants grown at other media pH treatment. In both cultivars, high Mn and Al were observed in plants grown at media pH 4.5 with Mn reaching millimolar concentrations. At this media pH, ‘Vidal blanc’ had twice as much Al as ‘Norton’ but only half as much Al. Compared to other media pH, media pH 4.5 had an Mn concentration of ∼25-fold and 10-fold and an Al concentration of 4-fold and 6-fold higher in ‘Vidal blanc’ and ‘Norton’, respectively.

TABLE 3 Leaf Mineral Element Concentrations in ‘Vidal blanc’ and ‘Norton’ Grapevines Grown at Varying Media pH

	Macronutrient (%)				Micronutrient (ppm)
Media pH	P	K	Ca	Mg	Fe	Mn	Al
Vidal blanc
4.5	0.2	1.59	1	1.05	184	2639	101.3
5.9	0.23ab ^z	1.83a	1.39b	0.48a	79.7ab	105.7a	30.4abc
7.2	0.21b	1.81a	1.06d	0.40b	69.5bc	66.7c	24.5c
8.5	0.20b	1.83a	1.21bcd	0.39b	62.9c	73.4bc	26.9bc
Norton
4.5	0.37	1.27	0.77	0.84	199.5	1175	264
5.9	0.26a	1.76a	1.27bc	0.40b	62.5c	92.9ab	34.5abc
7.2	0.25ab	1.82a	1.41abc	0.38b	87.9a	89.9abc	42.6a
8.5	0.23b	1.81a	1.57ab	0.35b	80.7ab	83.8abc	38.3ab
^zValues in same column with different letters are different at P = 0.05.

DISCUSSION

Lack of shoot length differences after 40 days of growth may be attributed to use of stored rather than synthesized food by the plant at initial stages of growth. Significantly low shoot growth in both cultivars at media pH 4.5 after 40 days of growth may be due to direct toxic effects of protons, Al, and Mn on roots. Aluminum and Mn, which are reported to be toxic to plant roots (Crowder and Coltman, 1993; Conradie, 1983) occurred at high concentration in the tissue of plants grown at pH 4.5. The relatively good growth of ‘Vidal blanc’ at pH >5.9 could be due to a higher pH tolerance than ‘Norton’. The relatively lower P and significantly low Mg at media pH ≥7.2 may be responsible for reduced area and shoot dry weight with its impact being greater for ‘Norton’ than ‘Vidal blanc’. Phosphorous deficiency is reportedly responsible for low carboxylation efficiencies and ribulose-1,5-bisphosphate carboxylase (Rubisco) concentrations that result in low photosynthetic rates (Jacob and Lawlor, 1992). Low P has been reported to dramatically reduce leaf surface area in ‘Cabernet sauvignon’ and ‘Chenin blanc’ (Grant and Mathews, 1996). Low levels of Mg at high media pH may have caused poor chloroplast formation, chloroplast destruction, and caused a reduction in photosynthetic activity and leaf dry weight. Similar effects of Mg deficiency on chloroplast functioning have previously been reported (Terry and Ulrich, 1974; Fischer and Bremner, 1993).

‘Norton’ root to shoot ratio showed a tendency to increase at a pH above 5.9, a trend similar to those found for 2-year-old pot-grown ‘Concord’ cultivar (Terence et al., 2002). This may be due to a higher reduction in shoot than root growth for ‘Norton’ compared to ‘Vidal blanc’. Higher specific leaf 180 weight found in ‘Vidal blanc’ compared to ‘Norton’ may indicate cultivar differences in photosynthetic activity and dry matter accumulation. Higher specific leaf weight is reportedly associated with increased photosynthetic activity of the leaf (Sharratt, 1991; Raab, 1994). The lack of significant effect of increased media pH above 5.9 on specific leaf weight in ‘Vidal blanc’, but a reduction in ‘Norton’, may point to cultivar differences in the maintenance of leaf function for dry matter accumulation. Though not determined, ‘Norton’ plants at media pH >5.9 may have had lower photosynthetic rates than ‘Vidal blanc’, which could have resulted in lower carbon fixation and reduced dry weight. Since no differences in Fe concentrations were observed, it is possible that inefficient utilization rather than insufficient Fe in ‘Norton’ may be responsible for chlorosis at higher media pH. In young Riperia (Vitis riperia Michaux) grown on calcareous soils, inactivation of Fe was reported to be responsible for chlorosis (Bernd and Kosegarten, 2002). In Vitis vinifera cv. Pinot noir, Fe deficiency resulted in damaged light harvest proteins, photosynthetic apparatus, and a reduction in photosynthesis (Massimo et al., 2002). In this study, high media pH may have led to comparatively higher photosynthetic apparatus damage in ‘Norton’ than ‘Vidal blanc’ and caused the low dry weights observed. Alternatively, the drastic reduction in biomass production at media pH above 5.9 in ‘Norton’ may have increased Fe concentration. Also, the threshold concentration for visible Fe deficiency symptoms may differ among these two cultivars. A significant decrease in plant growth when pH increases above 5.9 may indicate that media pH ≥7.2 could be outside the medium pH range for optimum ‘Norton’ growth. While in ‘Vidal blanc’, the response may be an indication of its tolerance to high pH and a wider growth pH range.

ACKNOWLEDGMENT

The authors wish to acknowledge Missouri State University for funding this research.