Grape sampling.

This study was carried out at the Basic Experiment Teaching Center (West Building) of Gansu Agricultural University in 2021. When the wine grapes were suitable for picking (the time of harvest was based on the minimum Brix° level of the grapes; the minimum Brix° of ‘Pinot Noir’, ‘Merlot’, and ‘Vidal’ is 18.5, 17, and 16, respectively), samples were collected from the main wine manors in the Hexi Corridor: Mogao Wine, Guofeng Wine, and Zixuan Wine vineyard. During sampling, three main varieties of each manor were selected and 15 grape vines with good growth and no diseases and pests were randomly selected. Three grape bunches were harvested from the shady and sunny sides of each grape vine, and 150 berries were randomly selected from the upper, middle, and lower parts of each bunch. The harvested berries were packaged on the same day, quickly transported back to the laboratory (within 6 h), and stored at 4 °C until needed for fruit quality analysis. Three biological replicates were performed for fruit quality index.

Soil sampling.

The “s” type sampling method was used for multipoint sampling in each test area, and five sampling points were determined between rows. Soil samples with a depth of 0 to 60 cm were collected from each sampling point in layers (20 cm is a layer). Before taking the soil samples, a 5-cm layer of floating soil and sundries on the surface was removed. Then, a uniform amount of soil was sampled from each soil layer using a ring knife and an aluminum box. The soil samples collected from each test area were mixed according to the level, and plant residues, stones, and animals were removed from the pooled samples. The cleaned soil samples were transferred into bags, which were then sealed and placed in an incubator with ice bags. At the same time, undisturbed soil samples collected from each sampling point were transferred into aluminum boxes in their original structural state and taken back to the laboratory.

Meteorological survey.

Climate-related data were collected from the meteorological institutions at each of the three different production areas (Table 1).

Table 1.Meteorological data collected from three different grape producing areas in the Hexi Corridor.

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Measurement of grape quality indices.

The 100-grain weight of grape berries was measured using Ae224 electronic analytical balance (Shanghai Shunyu Technology Instrument Co., Ltd., Shanghai, China). The identity and contents of sugar and acid compounds in the grape berries were determined using the FOSS DK-3400 multifunctional wine analyzer [FOSS (Beijing) Science and Trade Co., Ltd, Beijing, China]. The titratable acid content of grape berries was determined using the NaOH neutralization titration method (Balic et al. 2014). Total phenol and tannin contents were measured using the Folin-Ciocalteu (McDonald et al. 2001) method and Folin-Denis method (Schanderl 1970), respectively. The Brix° was determined using a PR-101 α Digital display total sugar instrument (ATAGO company of Japan, Tokyo, Japan). The anthocyanin content of grape berries was determined using the Liang method (Liang et al. 2008), with slight modifications.

Measurement of soil indices.

The total salt, available P, and available K contents of soil were determined according to soil agrochemical analysis (Lewis et al. 1991). To determine the soil K⁺ and Na⁺ contents, the soil samples were air-dried, ground in self-sealing bags, and passed through a 0.5-mm sieve. Then, the soil K⁺ and Na⁺ contents were measured using flame spectrophotometer FP6450 (Shanghai Yidian Scientific Instrument Co., Ltd, Shanghai, China) (Netzer et al. 2014).

Data analysis.

The statistical analysis of data were conducted using Microsoft Excel 2010 (Redmond, WA, USA). PCA and correlation analysis were conducted using the SPSS 23.0 software (IBM, Corp, Armonk, NY, USA).

Analysis of the quality berries produced in different areas of the Hexi Corridor.

The quality indices of different varieties of grapes in the three production areas are summarized in Table 2. The berries of Merlot grape cultivar grown in Zhangye showed the highest contents of malic acid (4.9 mg·g⁻¹), tartaric acid (3.26 mg·g⁻¹), and total tannins (12.03 mg·g⁻¹), and the pH of these grapes (4.57) was significantly higher than those of ‘Merlot’ grapes grown in Wuwei and Jiayuguan (P < 0.05). In addition, the reducing sugar content and Brix value of ‘Merlot’ grapes grown in Zhangye were 212.88 mg·g⁻¹ and 26.88%, respectively. The ‘Merlot’ grapes grown in Wuwei showed the highest 100-grain weight (167.03 g). No significant differences were observed in the citric acid, titratable acid, total anthocyanin, fructose, and glucose contents of ‘Merlot’ grapes among the three regions. The ‘Pinot Noir’ grape grown in Wuwei showed the highest malic acid (2.35 mg·g⁻¹), titratable acid (0.69%), reducing sugar (224.53 mg·g⁻¹), total tannin (11.99 mg·g⁻¹), and total phenol (48.93 mg·g⁻¹) contents and 100-grain weight (166.27 g). The ‘Pinot Noir’ grape grown in Jiayuguan showed the highest citric acid (0.62 mg·g⁻¹) and tartaric acid (3.36 mg·g⁻¹) contents and Brix° (23.7%). The ‘Pinot Noir’ grape showed no significant difference in glucose content and pH among the three regions. The Brix value and tartaric acid, reducing sugar, fructose, total tannin, and total phenol contents of ‘Vidal’ grape were the highest in Jiayuguan (23.9%, 3.79 mg·g⁻¹, 201.03 mg·g⁻¹, 87.98 mg·g⁻¹, 10.36 mg·g⁻¹, and 61.25 mg·g⁻¹, respectively). There was no significant difference in the malic acid, citric acid, titratable acid, and glucose contents and grape pH of ‘Vidal’ among the three production areas.

Table 2.Quality of grape berries of three varieties grown in three areas in the Hexi Corridor.

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Physical and chemical properties of soil in the three different areas of the Hexi Corridor.

The physical and chemical properties of soil in the three production areas were quite different (Table 3). Zhangye showed the highest average soil pH (8.09), followed by Wuwei (8.03) and Jiayuguan (7.89), and the average value of soil pH showed no significant difference between Wuwei and Zhangye regions. The content of K⁺ in Wuwei (3.65 mg·g⁻¹) was significantly higher than that in Zhangye and Jiayuguan, and its value was the lowest in Jiayuguan (2.77 mg·g⁻¹). The Na⁺ (2.77 mg·g⁻¹), total salt (2.54 mg·g⁻¹), and available P (21.87 mg·g⁻¹) contents of soil in Jiayuguan were significantly higher than those in Wuwei and Zhangye; the latter area showed the lowest contents of Na⁺ (2.62 mg·g⁻¹), total salt (0.4 mg·g⁻¹), and available P (14.6 mg·g⁻¹). The contents of available P (186.88 mg·g⁻¹) and total N (0.59 g·kg⁻¹) in the Wuwei area were significantly higher than those in Jiayuguan and Zhangye; the latter area showed the lowest contents of available K (151.03 mg·g⁻¹) and total N (0.26 g·kg⁻¹). The contents of soil nutrients were the highest in Wuwei, and those of various ions were the highest in Jiayuguan.

Table 3.Physical and chemical properties of soil in the three grape production areas in the Hexi Corridor.

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Analysis of climate in the three main grape production areas of the Hexi Corridor.

Climate has a significant impact on grape planting and wine production. As shown in Table 4, the three main grape production areas in the Hexi Corridor showed considerable differences in climate. During the growing season (April–October), maturation period (August–September), and the whole year, the annual average temperature, annual average maximum temperature, annual average minimum temperature, and GDD were the highest in Zhangye. Among the three regions, Wuwei was the coldest, and Jiayuguan showed the lowest annual average maximum temperature. The annual sunlight duration was the highest in Jiayuguan, and rainfall was the highest in Wuwei and lowest in Zhangye.

Table 4.Climate data during the grape growing season (April–October) and ripening period (August–September) in the studied regions.

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Correlation analysis of grape quality, soil physical and chemical properties, and climatic conditions in different grape production areas.

The results of correlation analysis are shown in Fig. 1. The titratable acid content of grape berries was significantly negatively correlated with average temperature from August to September, average minimum temperature from August to September, average minimum temperature from April to October, annual mean minimum temperature, GDD from August to September, and total N content. The average rainfall from April to October, annual mean rainfall, and available K were significantly positively correlated with the titratable acid content of grape berries, indicating that the average temperature from August to September, average minimum temperatures from August to September and from April to October, annual mean minimum temperature, GDD from August to September, and increase in total N are not conducive to the accumulation of titratable acid in grape berries. The increase of average rainfall from April to October, annual mean rain, and available K content were conducive to the accumulation of titratable acid in grape berries.

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Grape pH was significantly negatively correlated with annual mean rainfall and available K (correlation coefficients: −0.673 and −0.674, respectively), indicating that the pH of grape berry juice decreases with the increase in rainfall during ripening. However, the grape pH was significantly positively correlated with average temperature and average minimum temperature from August to September, average minimum temperature from April to October, GDD from August to September, and total N content, indicating that the pH of grape berry juice increases gradually with the increase in temperature during ripening. Brix° showed a significant negative correlation with average rainfall from August to September and soil Na⁺ content (correlation coefficients: −0.680 and −0.694, respectively), indicating that the increase in rainfall during fruit ripening and the excess amount of Na⁺ in soil are not conducive to the accumulation of sugars in grape berries. Thus, we conclude that the titratable acid content, pH, and Brix° of grape berries are greatly affected by each climate and soil parameter tested in this study. No significant correlation was detected between the other quality indices and each climate and soil parameter.

PCA of grape quality in different areas.

To evaluate the effects of climate and soil parameters on the quality of ‘Merlot’, ‘Pinot Noir’, and ‘Vidal’ grapes in three production areas, we performed PCA (Table 5). Two principal components (PCs; PC1 and PC2) were extracted from the three varieties through PCA, and the cumulative contribution rate reached 100%, indicating that the two PCs extracted from the three varieties could explain all the information of the original quality indicators. The variance contribution rates of PC1 and PC2 in ‘Merlot’ grape were 58.92% and 41.08%, respectively; the corresponding values were 58.83% and 41.17%, respectively, in ‘Pinot Noir’ grape, and 68.24% and 31.76%, respectively, in ‘Vidal’ grape. The indices with the greatest contribution to PC1 were total tannin content, grape pH, and glucose content in ‘Merlot’; citric acid and Brix° in ‘Vidal’; and titratable acid content, total tannin content, and grape pH in ‘Pinot Noir’. The indices contributing the most to PC2 were citric acid, fructose, and total anthocyanin contents in ‘Merlot’; total phenol, total anthocyanin, and malic acid contents and Brix° in ‘Vidal’; and tartaric acid and glucose contents in ‘Pinot Noir’.

Table 5.PCA of the effects of climate and soil parameters on the berry quality of three grape cultivars in different production areas.

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The PCA results of ‘Merlot’, ‘Pinot Noir’, and ‘Vidal’ grapes in the three regions are shown in Table 6. The quality of the same variety planted in different regions varied greatly, and the dominant varieties suitable for planting in different regions also varied. ‘Merlot’ showed the highest quality score in Zhangye among the three production areas, which indicated that the quality of ‘Merlot’ berries in Zhangye was better than that in Jiayuguan and Wuwei. The ‘Pinot Noir’ berries showed the highest quality score in Wuwei among the three production areas, which indicated that the quality of ‘Pinot Noir’ berries in Wuwei was better than that in Jiayuguan and Zhangye. The ‘Vidal’ berries showed the highest quality score in Jiayuguan among the three production areas, which indicated that the quality of ‘Vidal’ berries in Jiayuguan was better than that in Wuwei and Zhangye. Together, our results suggest that ‘Merlot’, ‘Pinot Noir’, and ‘Vidal’ are suitable for large-scale planting in Zhangye, Wuwei, and Jiayuguan, respectively.

Table 6.Principal-component analysis of the same grape variety from different grape production areas.

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