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Article

Exogenous Application of Applied Microbial Agents to Alleviate Salt Stress on ‘Pinot Noir’ Grapes and Improve Fruit Yield and Quality

by
Zhilong Li
1,
Lei Ma
1,
Guojie Nai
2,
Zhihui Pu
1,
Jingrong Zhang
1,
Sheng Li
1,3,*,
Bing Wu
1 and
Shaoying Ma
4
1
College of Life Science and Technology, Gansu Agricultural University, Lanzhou 730070, China
2
College of Horticulture, Gansu Agricultural University, Lanzhou 730070, China
3
State Key Laboratory of Aridland Crop Science Co-Constructed by the Province and Ministry, Gansu Agricultural University, Lanzhou 730070, China
4
Laboratory and Practice Base Management Center, Gansu Agricultural University, Lanzhou 730070, China
*
Author to whom correspondence should be addressed.
Agriculture 2025, 15(18), 1960; https://doi.org/10.3390/agriculture15181960
Submission received: 18 August 2025 / Revised: 11 September 2025 / Accepted: 16 September 2025 / Published: 17 September 2025
(This article belongs to the Special Issue Abiotic Stress Responses in Horticultural Crops)
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Abstract

Microbial inoculants, as a new type of product that combines economic efficiency with ecological sustainability, play an important role in promoting plant growth and development, increasing crop yields, and enhancing plant resistance to abiotic stress. This study used the wine grape cultivar (Vitis vinifera ‘Pinot Noir’) as experimental material to systematically investigate the effects of microbial inoculants on the soil–leaf–fruit system during the late growth stage of grapes under salt stress conditions (200 mM NaCl). This study analyzed the regulatory effects of microbial inoculants on soil physicochemical properties, leaf physiological and biochemical characteristics, as well as fruit yield and quality. The results showed that salt stress significantly inhibited the growth of Pinot Noir grapes. However, the application of microbial inoculants effectively alleviated the negative effects of salt stress. By enhancing the plant’s antioxidant defense capacity and regulating physiological metabolic pathways such as osmotic balance, the inoculants significantly mitigated the inhibitory effect of salt stress on fruit development. Notably, the S+JH treatment group demonstrated particularly outstanding results, with hundred-berry weight, single-bunch weight, and yield per plant increasing significantly by 15.96%, 12.47%, and 28.93%, respectively, compared to the salt stress group (S). Additionally, this treatment also stabilized free amino acid content and suppressed excessive organic acid synthesis. This study provides new technical insights into the application of microbial inoculants for saline-alkali land improvement and stress-resistant cultivation of horticultural crops such as grapes, holding significant practical value for promoting the sustainable development of the grape industry in saline-alkali regions.

1. Introductory

Grapes are one of the most widely grown and economically valuable berry crops in the world, and about 71% of grapes are used for winemaking. As a result, wine grapes have been widely emphasized and cultivated. Originally from Burgundy, France, and widely planted around the world, Pinot Noir grapes were first introduced and planted in China in 1892 [1,2]. By virtue of the superior natural conditions such as abundant light and large temperature difference between day and night, Northwest China has developed into the largest wine grape growing base in China [3]. As the birthplace of China’s wine industry, the Gansu Wuwei Mogao region is located in the golden belt of grape cultivation at 38° N latitude, and its unique soil structure and climatic conditions provide favorable environmental conditions for the cultivation of high-quality wine grape varieties such as Pinot Noir [4]. Pinot Noir grapes are small, thin-skinned and purple-black in color, with moderate acidity and tannin content, both fresh and fruity and light floral aromas, and unique flavor qualities that make it the preferred choice for producing of high-quality red wines by many renowned wineries, such as Romanee Conti and Drouin. Due to the arid climate and inappropriate irrigation in the Northwest, soil salinization is a growing problem, leading to difficulties in grape growing and a significant decline in yield and quality [5,6].
Salinization is one of the key issues limiting agricultural productivity improvement and ecosystem sustainability [7]. It is estimated that more than 900 million hectares, or about 7% of the total land area, is chronically affected by salinization globally [8]. Over the years, soil salinization has been increasing due to a combination of topographic, climatic, and anthropogenic factors [9]. Data show that about 10% of China’s total land area, i.e., more than 100 million hectares, has been salinized [10]. Based on this, various types of improvement measures have been adopted to increase the agricultural utilization of saline land. These measures include methods such as flooding to wash salt and increasing the application of organic fertilizers. Although these methods can improve soil conditions to a certain extent, they have obvious limitations and may even lead to new problems such as secondary pollution. Therefore, the promotion of eco-friendly soil conditioners is imminent to alleviate salt damage in saline soils, improve soil quality, and increase crop yields against the backdrop of surging demand for food and land constraints in agriculture [9,11]. Among numerous management solutions, microbial agents have emerged as a breakthrough in improving the condition of saline-alkali soil [12].
Microbial agents produced using beneficial microbial fermentation technology are a new type of ecological organic biofertilizer. Microbial inoculants are rich in various beneficial microorganisms, which promote soil nutrient cycling, enhance crop nutrient absorption and utilization efficiency, and effectively increase crop yield and quality [13,14]. Sustainable management of saline soils can also be achieved by reducing the use of measures such as chemical amendments, thereby reducing the risk of environmental pollution [15]. At the same time, the application of microbial inoculants can alter the amino acid, sugar, and volatile substance ratios in Pinot Noir grapes, significantly improving the flavor and texture of the fruit [16]. The results of Yan et al. showed that microbial agent GB03 could alleviate the adverse effects of salt stress on soil physicochemical properties and inter-root microorganisms and improve the yield and quality of fruits under stress conditions [6]. The results of Liang et al. showed that the microbial agent Streptomyces lasalocidi JCM 3373T alleviated soybean salt stress and optimized root architecture by secreting the metabolite indole-3-carboxaldehyde [17]. Yield, soil fast-acting phosphorus, potassium, alkaline-hydrolyzed nitrogen, and soil enzyme activity levels were significantly increased by applying complex microbial fertilizers to sweet sorghum [14].
However, few studies have focused on the use of microbial inoculants to enhance salt tolerance, yield, and fruit quality in grapes. Therefore, this study aimed to evaluate the effects of microbial inoculants on salt tolerance, yield, and quality in wine grapes, and to identify effective inoculation concentrations through membership function analysis, thereby providing a theoretical basis for improving grape production under salt stress.

2. Materials and Methods

2.1. Overview of the Trial Site

The field experiment was conducted in the ecological agriculture demonstration plantation area of Mogao Industrial Development Co., Ltd., Huangyanghe Farm, Huangyang Town, Wuwei City, China (102°52′14.96″, 37°50′12.16″), at an altitude of 1632 m. The average annual temperature of the test area is 6.9 °C, the average annual sunshine hours is 2724.8 h, the annual precipitation is 191 mm, the average annual evapotranspiration is 2130.8 mm, and the frost-free period is 150 d. The soil type is a neutral to weakly alkaline gravelly sandy loam that is deep and well aerated.

2.2. Experimental Materials

In 2024, 11-year-old own-rooted wine grape vines of Vitis vinifera ‘Pinot Noir’ with consistent growth and vigorous performance were selected from the Mogao Ecological Agricultural Demonstration Planting Park as experimental materials. The plants were spaced at 0.6 m within rows and 2.0 m between rows and were labeled accordingly.
The growth-promoting and disease-preventing microbial inoculant used is composed of Bacillus subtilis and Trichoderma harzianum, with an effective live bacterial count of ≥109 CFU·mL−1. It is mainly sourced from plant residues, compost, and organic waste. The inoculant was developed by the Gansu Academy of Agricultural Sciences and purchased from Gansu Daxing Fertilizer Co., Ltd. (Lanzhou, China).

2.3. Experimental Methods

2.3.1. Field Trial Design

Within the Pinot Noir planting area, a randomized block design was used. Along each row of vines, two trenches were dug on either side of the vine, 20 cm from the trunk. Each trench was 30 cm deep, 20 cm wide, and 60 cm long. Each time the treatment is carried out, 5 L of the corresponding solution is applied to each plant to ensure that the solution reaches the roots of the grapevine. Salt stress treatment was performed using a 200 mmol·L−1 NaCl solution [18], with a total of four treatments. After 10 days of salt treatment, plants were treated with diluted low-concentration microbial inoculant (5 L, inoculant: water = 1:50) and high-concentration microbial inoculant (5 L, inoculant: water = 1:25) [6]. A total of four treatment groups were established: the control group (CK), the salt stress treatment group (S), the salt + low-concentration bacterial agent treatment group (S+JL), and the salt + high-concentration bacterial agent treatment group (S+JH). Each treatment consisted of three replicates, and each replicate consisted of five grapevines, with two grapevines plants as intervals between each treatment. This experiment was conducted four times, with treatment dates on 21 April 2024 (E-L stage 9: 2 to 3 leaves separated; shoots 2–4 cm long), 21 May 2024 (E-L stage 23: 17–20 leaves separated; 50% caps off), 21 June 2024 (E-L stage 32: beginning of bunch closure, berries touching), and 21 July 2024 (E-L stage 35: berries begin to color and enlarge) [19].
Throughout the entire experimental period, all plants remained healthy without any severe disease or pest infestation. To ensure consistency in field management practices, irrigation, fertilization, pruning, and pest control in the demonstration park strictly adhered to the technical standards established in previous years. The grapevines were trained using a single-arm trellis system and were irrigated with a drip irrigation system. During the high-incidence period of diseases and pests, a unified foliar spray application was implemented using 25% tebuconazole emulsion in water (EW) and 10% imidacloprid wettable powder (WP), among other agents, with applications performed every 14 days. Pest and disease control measures were completely consistent across all treatment groups to eliminate potential interference of this factor with the experimental results.

2.3.2. Sample Collection

Soil samples were collected at a depth of 20–40 cm around grapevine roots during E-L stage 32 (21 June 2024), E-L stage 35 (21 July 2024), and E-L stage 38 (21 August 2024) [20]. For each treatment, three replicates were collected, with each replicate consisting of a composite soil sample from five sampling points. These samples were used for determining soil nutrient indicators and soil enzyme activities [21].
Leaf samples were collected at E-L stage 32 (21 June 2024), E-L stage 35 (21 July 2024), and E-L stage 38 (21 August 2024) for indicator measurements. The third and fourth fully expanded leaves were collected from the top of each grapevine in the treatment group. Three leaves were selected from each plant and subsequently averaged.
Grape berry samples were harvested at E-L stage 32 (21 June 2024), E-L stage 35 (21 July 2024), and E-L stage 38 (21 August 2024), respectively. For picking, select the upper-middle part of the plant’s vine, because it is well-developed with consistent light conditions. Each treatment had three replications and three bunches were picked from each replication. Bunches picked at fruit maturity were used for actual yield determination (weighed and recorded). All fruit samples collected were transported back to the laboratory on the same day and stored at 4 °C for determination of actual yield and quality indicators.

2.4. Determination of Parameters

2.4.1. Determination of Soil Nutrients

Total nitrogen content in soil was determined using the Kjeldahl method [22]; ammonium nitrogen and nitrate nitrogen were determined using a fully automatic intermittent chemical analyzer (Smart Chem 450, AMS Alliance, Rome, Italy).

2.4.2. Soil Enzyme Activity

Soil alkaline phosphatase (S-ALP, G0305W48), soil urease (S-UE, G0301W), soil sucrase (S-SC, G0302W), and soil catalase (S-CAT, G0303W) were measured using kits from Suzhou Greentech Biotechnology Co., Ltd. (Suzhou, China).

2.4.3. Leaf Physical and Chemical Indicators

Photosynthetic parameters were measured using a CI-340 portable photosynthesis system (CID Bio-Science, Camas, WA, USA); chlorophyll fluorescence parameters were measured using a FluorPen FP110/D handheld chlorophyll fluorometer (Beijing Yiketa Ecological Technology Co., Ltd., Beijing, China); and leaf SPAD values (relative chlorophyll content) were measured using a TYS-B handheld chlorophyll meter (Zhejiang Dingyun Agricultural Technology Co., Ltd., Hangzhou, China). All the aforementioned physiological measurements were conducted on clear days during the morning (10:00–11:30) and afternoon (15:30–17:30) to avoid the midday period of environmental stress.

2.4.4. Determination of Antioxidant Substances in Leaves

Superoxide dismutase (SOD, G0101W48), peroxidase (POD, G0107W48), catalase (CAT, G0105W48), and ascorbate peroxidase (APX, G0203W) activity, as well as malondialdehyde (MDA, G0109W), hydrogen peroxide (H2O2, G0112W48), proline (Pro, G0111W48), and reduced ascorbic acid (AsA, G0201W48) were measured using specialized biochemical assay kits (Suzhou Greetech Biotechnology Co., Ltd., Suzhou, China). All parameters were analyzed in triplicate.

2.4.5. Fruit Yield and Quality

The yield per plant was measured using an electronic balance (Huaying Weighing Apparatus Co., Ltd., Yongkang, China) with a precision of 0.01 g. On the fruit ripening date (21 August 2024), the grape clusters from each vine were weighed to determine the fruit yield under different treatment groups. The hundred-berry weight and single-bunch weight were measured using an Ae224 electronic analytical balance (Shunyu Technology Instrument Co., Ltd., Shanghai, China) with a precision of 0.0001 g.
The levels of sucrose, fructose, glucose, reducing sugars, tartaric acid, malic acid, gluconic acid, and total acid in the fruit were determined using a WINESCAN S20 FLEX multifunctional wine analyzer (FOSS (Beijing) Science and Trade Co., Ltd., Beijing, China) [23].
Amino acid analysis was conducted using an Agilent 6470 liquid chromatography–mass spectrometry system (Agilent Technologies, Santa Clara, CA, USA; Agilent Technologies Co., Ltd., Shanghai, China). The detection method was based on Agilent’s official publication, “Methods for Analyzing Underivatized Amino Acids Using Liquid Chromatography-Mass Spectrometry Systems.” The chromatographic conditions were set as follows: Column: Agilent Infinity Lab Poroshell 120 HILIC-Z (100 mm × 2.1 mm, 1.8 µm); Column temperature: 30 °C; Flow rate: 0.80 mL·min−1; Mobile phase A: water–acetonitrile (90:10, v/v) containing 200 mM ammonium formate (pH 3.0); Mobile phase B: acetonitrile–water (90:10, v/v) containing 200 mM ammonium formate (pH 3.0); Gradient elution program: 0.00–10.00 min: 100% → 70% B; 10.00–11.00 min: 70% B (hold); 11.00 min: 70% → 100% B; 11.00–16.00 min: 100% B (hold); Injection volume: 0.25 µL; Mass spectrometry parameters: Ionization mode: ESI positive ion mode; Drying gas temperature: 300 °C; Drying gas flow rate: 7.0 L·min−1; Nebulizer pressure: 45 psi; Sheath gas temperature: 400 °C; Sheath gas flow rate: 11 L·min−1; Capillary voltage: 3500 V; Nozzle voltage: 0 V.

2.5. Statistical Analysis

Data analysis was performed using Microsoft Excel 2021 software. Single-factor analysis of variance (ANOVA, significance level p < 0.05), correlation analysis, and membership function analysis were conducted using SPSS 27.0. Graphs and charts were created using GraphPad Prism 2024 and Origin 2024 (64-bit).

3. Results

3.1. Effect of Different Concentrations of Microbial Inoculants on Soil Nitrogen Nutrients and Soil Enzyme Activity During the Late Growth Stage of Grapes Under Salt Stress

As shown in Figure 1a,b, compared with CK, the S treatment group showed a significant reduction in both ammonium nitrogen and nitrate nitrogen content. Relative to S, the S+JL treatment at E-L stage 38 exhibited no significant difference in ammonium nitrogen, while nitrate nitrogen increased significantly by 20.59%. The S+JH treatment led to a 29.77% increase in ammonium nitrogen and a 27.22% rise in nitrate nitrogen at the same stage. As illustrated in Figure 1c, the soil total nitrogen content in the S treatment group displayed a decreasing trend from E-L stage 32 to E-L stage 38. Compared with CK, the total nitrogen under S treatment decreased significantly. In comparison with S, the S+JL treatment at E-L stage 38 showed no significant difference, while the S+JH treatment increased total nitrogen by 24.75%.
As shown in Figure 1d–g, compared with CK, the S treatment significantly inhibited soil enzyme activities, with alkaline phosphatase (S-ALP), urease (S-UE), sucrase (S-SC), and catalase (S-CAT) showing progressive decreases throughout the growth period. In comparison with S, the S+JL treatment at E-L stage 38 showed no significant effect, whereas the S+JH treatment significantly increased the activities of S-ALP, S-UE, S-SC, and S-CAT. The results indicated that the S+JH treatment effectively alleviated salt stress by enhancing soil nitrogen cycling and improving soil enzyme activities through increased contents of ammonium nitrogen, nitrate nitrogen, and total nitrogen.

3.2. Effect of Different Concentrations of Microbial Inoculants on Sodium and Potassium Ion Content and Sodium–Potassium Ion Ratio in Grape Leaves During the Late Growth Stage Under Salt Stress

As shown in Figure 2a–c, compared with CK, the S treatment group exhibited a significant increase in Na+ content and Na+/K+ ratio, while the K+ content decreased markedly. Relative to S, the microbial inoculant treatments resulted in significantly lower Na+ content and Na+/K+ ratio from E-L stage 32 to E-L stage 38. Specifically, K+ content was significantly lower than that in the S group at E-L stage 32, but significantly higher from E-L stage 35 to E-L stage 38. Compared with S, the S+JL treatment at E-L stage 38 showed a significant reduction in Na+ content and Na+/K+ ratio. The S+JH treatment led to a notable decrease in Na+ content, a significant increase in K+ content, and a markedly lower Na+/K+ ratio. The results demonstrated that the S+JH treatment effectively regulated ion homeostasis by reducing Na+, elevating K+, and lowering the Na+/K+ ratio, thereby significantly mitigating the sodium and potassium ion imbalance caused by salt stress.

3.3. Effects of Different Concentrations of Microbial Inoculants on Photosynthetic Characteristics of Grape Leaves During the Late Growth Stage Under Salt Stress

As shown in Figure 3a–d, compared with CK, the S treatment significantly reduced Pn, Tr, and Gs from E-L stage 32 to E-L stage 38, while Ci significantly increased from E-L stage 32 to stage 35 but decreased markedly at E-L stage 38. In contrast, microbial inoculant treatments significantly enhanced Pn, Tr, and Gs and reduced Ci during the same period relative to S. Compared with S, the S+JL treatment did not cause significant changes in Pn, Tr, or Gs from E-L stage 32 to E-L stage 38, although Ci was significantly decreased. In the S+JH treatment group, Pn, Tr, and Gs were significantly increased, while Ci was notably reduced.
As shown in Figure 3e–h, compared with CK, the S treatment significantly increased Fo and decreased Fm, Fv/Fm, and SPAD from E-L stage 32 to E-L stage 38. In contrast, microbial inoculant treatments significantly reduced Fo and enhanced Fm, Fv/Fm, and SPAD during the same period relative to S. Furthermore, the S+JH treatment demonstrated a more pronounced effect than S+JL in improving photosynthetic capacity. The results showed that the S+JH treatment group significantly increased Fm, Fv/Fm, and SPAD by enhancing Pn, Tr, and Gs, while reducing Ci. This enhanced the light adaptation ability and the function of photosystem II of the grape plants, thereby effectively alleviating salt stress.

3.4. Effects of Different Concentrations of Microbial Inoculants on Antioxidant Substances, Osmotic Regulatory Substances, and Oxidative Damage-Related Substances in Grape Leaves During the Late Growth Stage Under Salt Stress

As shown in Figure 4a–d, compared with CK, the activities of SOD, POD, CAT, and APX in the S treatment group increased significantly from E-L stage 32 to E-L stage 38, while the AsA content decreased markedly. In comparison with S, the microbial inoculation treatments significantly increased AsA content and reduced the activities of SOD, POD, CAT, and APX during the same period. Specifically, the S+JL treatment led to a notable increase in AsA content and a decrease in SOD, POD, CAT, and APX activities relative to S. Moreover, the S+JH treatment demonstrated more pronounced effects than S+JL in alleviating salt stress.
As shown in Figure 4e–h, compared with CK, the contents of Pro, H2O2, and MDA in grapes from the S treatment group increased significantly from E-L stage 32 to E-L stage 38. In comparison with S, the microbial agent treatments significantly reduced Pro, H2O2, and MDA levels from E-L stage 32 to E-L stage 38. Specifically, the S+JL treatment led to a notable decrease in MDA content relative to the S group, while the S+JH treatment significantly reduced Pro, H2O2, and MDA. The results showed that the S+JH treatment group effectively restored the activity of antioxidant enzymes, increased the content of AsA, reduced the contents of H2O2 and MDA, and achieved a multi-cooperative effect of redox balance, osmotic homeostasis, and membrane system protection, thereby effectively alleviating salt stress.

3.5. Effect of Different Concentrations of Microbial Inoculants on the Yield per Vine of Mature Grapes Under Salt Stress

As shown in Figure 5, significant differences were observed in the yield per plant of ‘Pinot Noir’ grapes under the four treatments. The S treatment group exhibited a significant reduction in yield per plant. In contrast, the S+JH treatment resulted in a significant increase of 28.93% in yield compared to the S treatment. The order is CK (3.21 kg·plant−1) > S+JH (2.54 kg·plant−1) S+JL (2.09 kg·plant−1) > S (1.97 kg·plant−1). The results showed that the S+JH treatment group significantly alleviated salt stress and increased the yield per grape plant.

3.6. Effect of Different Concentrations of Microbial Inoculants on Fruit Yield Components in the Late Growth Stage of Grapes Under Salt Stress

As shown in Figure 6a,b, compared to CK, the S treatment group exhibited a significant reduction in both hundred-berry weight and single-bunch weight from E-L stage 32 to 38. Relative to the S treatment, both the S+JL and S+JH groups showed a significant increase in hundred-berry weight and single-bunch weight at E-L stage 38, with the S+JH treatment demonstrating a more pronounced effect, increasing these values by 15.96% and 12.47%, respectively. The results showed that salt stress significantly reduced the hundred-berry weight and single- bunch weight of grapes in the late reproductive stage compared to the CK group. The S+JH treatment significantly improved the fruit yield components under salt stress.

3.7. Effect of Different Concentrations of Microbial Agents on Sugar and Acid Content in Grape Fruits Under Salt Stress

As shown in Figure 7a–d, compared to CK, the S treatment group showed significant increases in the contents of sucrose, fructose, glucose, and reducing sugars from E-L stage 32 to 35, while the levels of sucrose, fructose, and reducing sugars decreased significantly at E-L stage 38. Compared to the S treatment, the S+JL group exhibited significantly lower Brix, fructose, and reducing sugar levels at E-L stage 38. In contrast, the S+JH treatment significantly increased Brix and glucose content at the same stage, by 14.26% and 15.32%, respectively.
As shown in Figure 7e–h, compared to CK, the S treatment group exhibited significant increases in tartaric acid, malic acid, gluconic acid, and total acid content from E-L stage 32 to 35, while the levels of these acids decreased markedly at E-L stage 38. Relative to the S treatment, the S+JL group showed significantly reduced gluconic acid content throughout E-L stage 32 to 38. In contrast, the S+JH treatment significantly decreased tartaric acid, malic acid, and total acid over the same period but increased gluconic acid content. The results showed that the S+JH treatment group alleviated salt stress and improved fruit quality by increasing the sucrose, glucose, and gluconic acid content, reducing the malic acid and tartaric acid content, and optimizing the sugar–acid composition ratio.

3.8. Effect of Different Concentrations of Microbial Inoculants on Free Amino Acids in Grape Fruits Under Salt Stress

Based on their taste characteristics, amino acids are classified into sweet amino acids (SAA), including Thr, Ala, Ser, His, etc.; bitter amino acids (BAA), including Leu, Arg, etc.; umami amino acids (DAA), including Asp, Glu, Lys, etc.; and aromatic amino acids (AAA), including Tyr, Phe, etc. [24].
As shown in Figure 8a–d, the contents of sweet amino acids exhibited significant variations across treatments and developmental stages: Compared to CK, the S treatment group showed significantly lower levels of Thr, His, and Ser, but a marked increase in Ala from E-L stage 32 to E-L stage 38. Relative to the S treatment, the S+JL group demonstrated significantly elevated Thr and reduced His during the same period, while the S+JH group showed significant increases in both Thr and His, along with a decrease in Ala.
As shown in Figure 8e,f, the contents of bitter amino acids responded differently across treatments and developmental stages: Compared with CK, the S treatment group exhibited significantly increased Arg levels from E-L stage 32 to 38 and elevated Leu from E-L stage 32 to 35, followed by a significant decrease in Leu at E-L stage 38. Relative to the S treatment, the S+JL group showed no significant differences in Arg or Leu throughout E-L stage 32 to 38, whereas the S+JH treatment significantly enhanced Arg content over the same period.
As shown in Figure 8g–i, the contents of umami amino acids varied significantly across developmental stages and treatments: Compared with CK, the S treatment group exhibited significantly decreased Asp and Lys from E-L stage 32 to 38. Glu levels increased significantly from E-L stage 32 to 35 but decreased markedly at E-L stage 38. Relative to the S treatment, the S+JL group showed a significant reduction in Glu throughout E-L stage 32 to 38, whereas the S+JH treatment significantly enhanced Asp across the same stages and increased both Lys and Glu at E-L stage 38.
As shown in Figure 8j,k, the contents of aromatic amino acids responded distinctively to treatments across developmental stages: Compared with CK, the S treatment group showed a significant decrease in Tyr from E-L stage 32 to 38. Phe content increased significantly from E-L stage 32 to 35 but decreased markedly at E-L stage 38. Relative to the S treatment, the S+JL group exhibited significantly elevated Tyr throughout E-L stage 32 to 38. The S+JH treatment also significantly increased Tyr over the same period, while reducing Phe from E-L stage 32 to 35 and elevating it significantly at maturity (E-L stage 38). The results showed that the S+JH treatment group could increase the content of SAA, DAA, and AAA, adjust the BAA ratio, alleviate the negative impact of salt stress on the amino acid metabolism of grape fruit flavor, and improve fruit flavor quality.

3.9. Correlation Analysis of Soil Nutrient Indicators and Fruit Quality in ‘Pinot Noir’ at Maturity Stage Under Salt Stress Treated with Different Microbial Inoculant Concentrations

The results of the correlation analysis among fruit yield, quality, and soil physicochemical indicators are presented in Figure 9. NH4+-N and NO3−-N exhibited highly significant or significant positive correlations with yield per plant (YPP), soluble solids (Bx), and amino acids including Glu, His, Arg, among others. Similarly, soil enzymes S-ALP, S-UE, S-SC, and S-CAT showed highly significant or significant positive correlations with YPP and amino acids such as Asp, Glu, and Tyr, while demonstrating highly significant or significant negative correlations with Ala. These results indicate that NH4+-N, NO3−-N, S-UE, and S-CAT significantly alleviated salt stress and improved fruit yield and quality through synergistic regulation of carbon and nitrogen metabolism and antioxidant capacity. In particular, the activities of S-ALP, S-SC, and S-CAT were closely associated with yield and flavor-related amino acids.

3.10. Correlation Analysis of Leaf Physicochemical Indicators and Fruit Quality in ‘Pinot Noir’ at Maturity Stage Under Salt Stress Treated with Different Microbial Inoculant Concentrations

The results of the correlation analysis among fruit yield, quality, and leaf physicochemical indicators are presented in Figure 10. Leaf K+ content showed a significant positive correlation with yield per plant (YPP) and amino acids such as Asp, Glu, and Arg, while exhibiting a highly significant negative correlation with Ala. Leaf Na+/K+ ratio was significantly positively correlated with Ala. Photosynthetic parameters (Pn, Tr, Gs, and Ci) showed highly significant or significant positive correlations with YPP and amino acids including Asp, Glu, and Phe, and highly significant or significant negative correlations with Ala. Fo was significantly positively correlated with Ala and significantly negatively correlated with Tyr. Fm and Fv/Fm demonstrated highly significant or significant positive correlations with hundred-grain weight (HGW), single-spike weight (SSW), and amino acids such as Asp, Glu, and Leu, along with a significant negative correlation with Ala. APX activity was highly significantly positively correlated with Ala and significantly negatively correlated with YPP, Phe, and Tyr. AsA showed highly significant or significant positive correlations with HGW, YPP, soluble solids (Bx), Asp, Ser, and other amino acids, and a significant negative correlation with Ala. Pro was highly significantly positively correlated with Ala and significantly negatively correlated with YPP, Asp, Phe, and Tyr. H2O2 exhibited highly significant or significant negative correlations with YPP, Bx, Asp, Glu, and other amino acids, and a significant positive correlation with Ala. These results suggest that under salt stress, leaf K+ promotes fruit yield and the synthesis of flavor-related amino acids by maintaining photosynthetic efficiency, while acting synergistically with AsA to inhibit Ala accumulation. The increase in antioxidant enzyme activity reflects the degree of plant damage and represents a non-protective response mechanism.

3.11. Comprehensive Evaluation of the Yield and Quality of Mature ‘Pinot Noir’ Grapes Under Salt Stress Treated with Different Concentrations of Bacterial Agents

As shown in Table 1, the comprehensive evaluation scores derived from membership function analysis of fruit yield and quality at E-L stage 38 under salt stress with different microbial inoculant concentrations indicated that the order of superiority among the four treatments was CK > S+JH > S > S+JL. Among these, CK has the highest comprehensive score of 2.63, indicating the best fruit yield and quality. followed by the S+JH treatment group with a comprehensive score of 1.49, the S+JL treatment group with a comprehensive score of 1.31, and the S treatment group with the lowest comprehensive score of 1.24, indicating that it had the poorest fruit yield and quality under salt stress.

4. Discussion

4.1. Effects of Microbial Inoculants on Soil Properties Under Salt Stress

Salt stress adversely affects soil nutrient availability and enzyme activity, inevitably limiting agricultural productivity [25]. Our results demonstrate that salt stress (200 mM NaCl) significantly inhibits soil nitrogen conversion and enzyme activity, which aligns with findings reported by Lu Hailing, Meng Yali et al. [26], and Pan et al. [27]. The application of microbial inoculants effectively alleviates this inhibition caused by salt stress and significantly enhances crop yield. Both soil nitrogen conversion and crop yield increase with higher application rates of the inoculants. Under high concentrations of microbial inoculants, soil condition is optimally improved, leading to the highest grape yield—a result consistent with observations in sweet sorghum by Wu et al. [14]. This effect may be partly attributed to the organic nutrients supplied by the microbial inoculants themselves. Our data show that high-concentration microbial inoculant treatment significantly increased the contents of NH4+-N, NO3−-N, and total nitrogen (TN) in the soil. Another important mechanism may involve the enhancement of rhizosphere nutrient levels through microbial inoculant application, which directly promotes microbial diversity [28] and subsequently improves the soil environment [19]. Thus, the use of microbial inoculants can establish a positive feedback loop between the microbial community structure and soil environmental factors, collectively contributing to the optimization of soil conditions. It is worth noting that Yan et al. [6] found in their study that under saline-alkali stress, the application of Bacillus subtilis significantly increased the diversity of soil microbial communities. However, the response of microbial communities to fertilization depends on the environment and is usually closely related to the content of certain soil nutrients such as S-SC and S-UE (soil sucrose enzyme and soil urease) and is significantly influenced by local environmental factors [29]. Therefore, this response may vary greatly in different research locations.

4.2. Regulation of Ion Homeostasis and Photosynthesis

Maintaining Na+/K+ homeostasis in the cytoplasm is crucial for plants to detoxify excessive Na+ ion damage and restore the normal function of multiple metabolic pathways under salt stress [30]. Our results demonstrate that salt stress significantly increased Na+ content and decreased K+ content, consistent with previous reports [31]. Following the application of microbial inoculants, both parameters were markedly improved—Na+ content decreased and K+ content increased—likely due to the activation of the SOS signaling pathway and K+ transporters. These changes enhance Na+ efflux and Na+/H+ exchange efficiency across the cell membrane, while reducing Na+ uptake and promoting K+ accumulation, thereby effectively maintaining ion homeostasis [32] and improving plant salt tolerance [31,33].
Salt stress also significantly inhibits photosynthesis [34]. Our data show that it led to reduced photosynthetic efficiency, impaired photosystem function, and accumulation of oxidative stress-related compounds in grape plants, which aligns with findings by Li et al. [18] and Mittova et al. [35]. Microbial inoculant application counteracted these effects, significantly improving photosynthetic efficiency and reducing oxidative stress. This may be attributed to direct increases in chlorophyll content and photosynthetic performance, a mechanism consistent with that reported for Bacillus GB03 in Arabidopsis [36], as well as enhanced capacity for reactive oxygen species (ROS) scavenging, alleviating oxidative damage under stress conditions [37].
Additionally, microbial inoculants may enhance salt tolerance indirectly by modulating plant hormone pathways. For example, certain Bacillus strains produce volatile compounds such as 3-hydroxy-2-butanone and 2,3-butanediol [14], which help regulate the synthesis and balance of endogenous hormones—including gibberellic acid and abscisic acid—thereby promoting plant growth and improving stress adaptation [38].

4.3. Modulation of Fruit Metabolism and Quality

This study revealed that ongoing salt stress treatment throughout a single growing season induced stage-specific metabolic changes during grape berry development: from E-L stage 32 to E-L stage 35, the contents of sugars such as sucrose, fructose, glucose, reducing sugars, and gluconic acid accumulated significantly; however, by E-L stage 38, their levels decreased markedly. Meanwhile, the contents of organic acids such as tartaric acid and malic acid, as well as amino acids including arginine, aspartic acid, lysine, and tyrosine, decreased significantly at E-L stage 38, while the levels of glutamic acid and phenylalanine increased markedly. This observation aligns with phenomena reported in crops such as strawberries [39] and tomatoes [40], where salt stress suppresses overall growth yet enhances sugar content in early-stage fruits. A possible explanation is that salt stress stimulates sugar accumulation during initial fruit development, but these levels decline toward ripening due to intensified catabolic metabolism. The application of high-concentration microbial inoculants significantly mitigates the adverse effects of salt stress on grape fruit quality. This improvement may be attributed to the ability of microbial inoculants to enhance photosynthetic capacity and optimize organic acid metabolism, effectively increasing the contents of sugar and gluconic acid while reducing the accumulation of tartaric and malic acids. Consequently, the overall acid composition ratio is improved, which is consistent with the findings of Shi et al. [41]. Furthermore, other studies suggest that microbial inoculants may promote the accumulation of umami-related amino acids (Glu, Asp, Lys) and the sweet amino acid Thr, thereby improving osmotic regulation and enhancing plant salt tolerance, as also reported by Xiao et al. [42].
In summary, microbial inoculants optimize sugar–acid metabolism and improve amino acid profiles, synergistically enhancing both fruit quality and overall plant stress resistance under saline conditions. Thus, we speculate that microbial inoculants alleviate salt stress by facilitating sodium ion efflux, regulating internal ion balance, and protecting photosynthetic systems. These insights offer valuable technical references for grape cultivation in saline-alkali soils.

4.4. Comprehensive Evaluation and Future Perspectives

Plant salt tolerance is governed by the synergistic effects of multiple physiological factors, and mitigating salt stress relies on the integrated regulation of these processes. The membership function method standardizes data and eliminates dimensional discrepancies through normalization (0–1), allowing multi-indicator comparisons on a unified scale and enhancing the validity of inter-treatment evaluations. In this study, the membership function method was employed to assess the improvement of grape fruit quality resulting from microbial agent applications. A comprehensive evaluation score was used to quantify salt stress resistance, with higher values indicating superior physiological, biochemical, and fruit quality indicators. Based on the comprehensive evaluation using the membership function, the conclusion drawn is that the S+JH treatment group shows the most significant improvement in fruit yield and quality. However, the efficacy of microbial agents in alleviating salt stress varies across crop types and varieties. Further in-depth research is necessary to elucidate the mechanisms through which microbial agents mitigate salt stress at hormonal, metabolic, and molecular levels.
This study is based on data collected from a single growing season at one experimental site, providing a preliminary analysis. Given that soil–plant system properties and fruit yield and quality are highly susceptible to interannual climate and rainfall variations, we plan to conduct continuous multi-year and multi-regional trials. Such extended observations will generate more robust datasets and contribute to the establishment of a reliable database, thereby strengthening the scientific foundation for the application of microbial agents in improving saline-alkali soils and enhancing crop productivity and quality.

5. Conclusions

This study systematically evaluated the effects of microbial inoculants at varying concentration gradients on soil properties, leaf physiological and biochemical characteristics, and fruit yield and quality of Vitis vinifera ‘Pinot Noir’ under salt stress. The results demonstrated that microbial inoculation significantly enhanced soil enzyme activities and nutrient availability, improved leaf photosynthetic efficiency and ion homeostasis, and promoted the accumulation of sugars and amino acids in berries. In particular, the S+JH treatment group showed the most significant improvement in the overall performance of the grapes under salt stress.
While these findings support the potential use of microbial inoculants in alleviating salt stress in viticulture, this study has certain limitations that should be addressed in future work. First, as the experiment was conducted at a single site over one growing season, interannual climate variations and soil heterogeneity may affect the generalizability of the results. Although the proposed mechanisms (e.g., SOS pathway modulation) provide a novel explanatory framework for our observations, direct molecular evidence remains a focus for future research.
To advance the application of microbial inoculants in saline vineyard management, further studies should conduct multi-year and multi-location trials to validate the efficacy and stability of inoculants under diverse edaphic and climatic conditions; employ omics technologies (transcriptomics, metabolomics, and metagenomics) to elucidate the mechanistic details of plant–microbe interactions under stress; evaluate the effectiveness of combined microbial consortia (e.g., PGPR with AM fungi) compared to single-strain applications; and investigate the economic feasibility and practical integration of microbial treatments within existing viticultural practices.
In conclusion, microbial inoculants show promising potential for enhancing salt tolerance and fruit quality in grapevines. However, more robust and extensive field studies are necessary to translate these experimental results into scalable and reliable strategies for sustainable viticulture in saline-alkaline regions.

Author Contributions

Designing experiments, analyzing data, and writing manuscripts: Z.L. and S.L.; conducting experiments: Z.P., J.Z. and G.N.; providing experimental equipment and venues: S.M.; revising manuscripts: S.L., B.W., G.N. and L.M. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Project funded by the Central Government—Guided Local Scientific and Technological Development Funds (25ZYJA033) and Gansu Provincial Key Talent Project (2023RCXM23).

Data Availability Statement

All data used during the study are proprietary or confidential and only limited data can be provided.

Acknowledgments

We sincerely thank the editor and reviewers for their time and effort in reviewing our work.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. Changes in soil nitrogen nutrients and soil enzyme activities at different periods after application of microbial agents under salt stress. Note: (a) NH4+-N, ammonium nitrogen; (b) NO3+-N, nitrate nitrogen; (c) TN, total nitrogen; (d) S-ALP, alkaline phosphatase; (e) S-UE, urease; (f) S-SC, sucrase; (g) S-CAT, catalase. Three biological replicates (mean ± s.d.) were performed for each treatment for the above values, and different lowercase letters indicate significant differences (p < 0.05). Control group, no treatment; S, salt treatment; S+JL, salt + low concentration microbial agent treatment; S+JH, salt + high concentration microbial agent treatment.
Figure 1. Changes in soil nitrogen nutrients and soil enzyme activities at different periods after application of microbial agents under salt stress. Note: (a) NH4+-N, ammonium nitrogen; (b) NO3+-N, nitrate nitrogen; (c) TN, total nitrogen; (d) S-ALP, alkaline phosphatase; (e) S-UE, urease; (f) S-SC, sucrase; (g) S-CAT, catalase. Three biological replicates (mean ± s.d.) were performed for each treatment for the above values, and different lowercase letters indicate significant differences (p < 0.05). Control group, no treatment; S, salt treatment; S+JL, salt + low concentration microbial agent treatment; S+JH, salt + high concentration microbial agent treatment.
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Figure 2. Changes in sodium and potassium ions and the sodium–potassium ion ratio in grape leaves at different stages after the application of microbial inoculants under salt stress. Note: (a) Na+, sodium ion; (b) K+, potassium ion; (c) Na+/K+, sodium–potassium ion ratio. Each treatment was subjected to three biological replicates (mean ± s.d.) for the above values. Different lowercase letters indicate significant differences (p < 0.05). Control group, no treatment; S, salt treatment; S+JL, salt + low-concentration microbial inoculant treatment; S+JH, salt + high-concentration microbial inoculant treatment.
Figure 2. Changes in sodium and potassium ions and the sodium–potassium ion ratio in grape leaves at different stages after the application of microbial inoculants under salt stress. Note: (a) Na+, sodium ion; (b) K+, potassium ion; (c) Na+/K+, sodium–potassium ion ratio. Each treatment was subjected to three biological replicates (mean ± s.d.) for the above values. Different lowercase letters indicate significant differences (p < 0.05). Control group, no treatment; S, salt treatment; S+JL, salt + low-concentration microbial inoculant treatment; S+JH, salt + high-concentration microbial inoculant treatment.
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Figure 3. Changes in photosynthetic characteristics of grape leaves at different stages after application of microbial inoculants under salt stress. Note: (a) Pn, photosynthetic rate; (b) Tr, transpiration rate; (c) Ci, intercellular CO2 concentration; (d) Gs, stomatal conductance; (e) Fo, initial fluorescence; (f) Fm, maximum fluorescence; (g) Fv/Fm, maximum photochemical quantum yield of PSII; (h) SPAD, relative chlorophyll content. Each treatment was subjected to three biological replicates (mean ± SD) for the above values. Different lowercase letters indicate significant differences (p < 0.05). Control group: no treatment; S: salt treatment; S+JL: salt + low-concentration microbial inoculant treatment; S+JH: salt + high-concentration microbial inoculant treatment.
Figure 3. Changes in photosynthetic characteristics of grape leaves at different stages after application of microbial inoculants under salt stress. Note: (a) Pn, photosynthetic rate; (b) Tr, transpiration rate; (c) Ci, intercellular CO2 concentration; (d) Gs, stomatal conductance; (e) Fo, initial fluorescence; (f) Fm, maximum fluorescence; (g) Fv/Fm, maximum photochemical quantum yield of PSII; (h) SPAD, relative chlorophyll content. Each treatment was subjected to three biological replicates (mean ± SD) for the above values. Different lowercase letters indicate significant differences (p < 0.05). Control group: no treatment; S: salt treatment; S+JL: salt + low-concentration microbial inoculant treatment; S+JH: salt + high-concentration microbial inoculant treatment.
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Figure 4. Changes in antioxidant enzymes in grape leaves at different stages after the application of microbial inoculants under salt stress. Note: (a) SOD, superoxide dismutase; (b) POD, peroxidase; (c) APX, ascorbate peroxidase; (d) CAT, catalase; (e) Pro, proline; (f) AsA, reduced ascorbic acid; (g) MDA, malondialdehyde; (h) H2O2, hydrogen peroxide. Each treatment was subjected to three biological replicates (mean ± SD) for the above values. Different lowercase letters indicate significant differences (p < 0.05). Control group, no treatment; S, salt treatment; S+JL, salt + low-concentration microbial inoculant treatment; S+JH, salt + high-concentration microbial inoculant treatment.
Figure 4. Changes in antioxidant enzymes in grape leaves at different stages after the application of microbial inoculants under salt stress. Note: (a) SOD, superoxide dismutase; (b) POD, peroxidase; (c) APX, ascorbate peroxidase; (d) CAT, catalase; (e) Pro, proline; (f) AsA, reduced ascorbic acid; (g) MDA, malondialdehyde; (h) H2O2, hydrogen peroxide. Each treatment was subjected to three biological replicates (mean ± SD) for the above values. Different lowercase letters indicate significant differences (p < 0.05). Control group, no treatment; S, salt treatment; S+JL, salt + low-concentration microbial inoculant treatment; S+JH, salt + high-concentration microbial inoculant treatment.
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Figure 5. (a) Changes in grape yield per plant after application of microbial inoculant under salt stress; (b) comparison of grape fruit phenotypes between salt treatment and microbial inoculant treatment, with line segments indicating a length of 1 cm. Note: Each treatment was performed in triplicate (mean ± s.d.). Different lowercase letters indicate significant differences (p < 0.05). Control group: no treatment; S: salt treatment; S+JL: salt + low-concentration microbial agent treatment; S+JH: salt + high-concentration microbial agent treatment.
Figure 5. (a) Changes in grape yield per plant after application of microbial inoculant under salt stress; (b) comparison of grape fruit phenotypes between salt treatment and microbial inoculant treatment, with line segments indicating a length of 1 cm. Note: Each treatment was performed in triplicate (mean ± s.d.). Different lowercase letters indicate significant differences (p < 0.05). Control group: no treatment; S: salt treatment; S+JL: salt + low-concentration microbial agent treatment; S+JH: salt + high-concentration microbial agent treatment.
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Figure 6. Changes in grape yield factors at different stages after the application of microbial inoculants under salt stress. Note: (a) HGW, hundred-berry weight; (b) SSW, single-bunch weight. Each treatment was subjected to three biological replicates (mean ± s.d.) for the above values. Different lowercase letters indicate significant differences (p < 0.05). Control group, no treatment; S, salt treatment; S+JL, salt + low-concentration microbial inoculant treatment; S+JH, salt + high-concentration microbial inoculant treatment.
Figure 6. Changes in grape yield factors at different stages after the application of microbial inoculants under salt stress. Note: (a) HGW, hundred-berry weight; (b) SSW, single-bunch weight. Each treatment was subjected to three biological replicates (mean ± s.d.) for the above values. Different lowercase letters indicate significant differences (p < 0.05). Control group, no treatment; S, salt treatment; S+JL, salt + low-concentration microbial inoculant treatment; S+JH, salt + high-concentration microbial inoculant treatment.
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Figure 7. Changes in sugar and acid content in grape fruits at different stages after the application of microbial inoculants under salt stress. Note: (a) Bx, Brix; (b) Fru, fructose; (c) Glu, glucose; (d) RS, reducing sugar; (e) GA, gluconic acid; (f) TTA, tartaric acid; (g) MA, malic acid; (h) TA, total acidity. Each treatment was subjected to three biological replicates (mean ± SD) for the above values. Different lowercase letters indicate significant differences (p < 0.05). Control group: no treatment; S: salt treatment; S+JL: salt + low-concentration microbial inoculant treatment; S+JH: salt + high-concentration microbial inoculant treatment.
Figure 7. Changes in sugar and acid content in grape fruits at different stages after the application of microbial inoculants under salt stress. Note: (a) Bx, Brix; (b) Fru, fructose; (c) Glu, glucose; (d) RS, reducing sugar; (e) GA, gluconic acid; (f) TTA, tartaric acid; (g) MA, malic acid; (h) TA, total acidity. Each treatment was subjected to three biological replicates (mean ± SD) for the above values. Different lowercase letters indicate significant differences (p < 0.05). Control group: no treatment; S: salt treatment; S+JL: salt + low-concentration microbial inoculant treatment; S+JH: salt + high-concentration microbial inoculant treatment.
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Figure 8. Changes in sweet amino acids in grape fruits at different stages after the application of microbial inoculants under salt stress. Note: (a) Thr, threonine; (b) Ala, alanine; (c) His, histidine; (d) Ser, serine; (e) Asp, aspartic acid; (f) Lys, lysine; (g) Glu, glutamic acid; (h) Arg, arginine; (i) Leu, leucine; (j) Tyr, tyrosine; (k) Phe, phenylalanine. Each treatment was subjected to three biological replicates (mean ± SD) for the above values. Different lowercase letters indicate significant differences (p < 0.05). Control group, no treatment; S, salt treatment; S+JL, salt + low-concentration microbial inoculant treatment; S+JH, salt + high-concentration microbial inoculant treatment.
Figure 8. Changes in sweet amino acids in grape fruits at different stages after the application of microbial inoculants under salt stress. Note: (a) Thr, threonine; (b) Ala, alanine; (c) His, histidine; (d) Ser, serine; (e) Asp, aspartic acid; (f) Lys, lysine; (g) Glu, glutamic acid; (h) Arg, arginine; (i) Leu, leucine; (j) Tyr, tyrosine; (k) Phe, phenylalanine. Each treatment was subjected to three biological replicates (mean ± SD) for the above values. Different lowercase letters indicate significant differences (p < 0.05). Control group, no treatment; S, salt treatment; S+JL, salt + low-concentration microbial inoculant treatment; S+JH, salt + high-concentration microbial inoculant treatment.
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Figure 9. Correlation analysis between soil physical and chemical indicators and fruit quality during the ripening period under salt stress. Note: HGW: hundred-berry weight; SSW: single-bunch weight; YPP: yield per plant; Bx: Brix sugar content; Glu: glucose content; Fru: fructose content; RS: reducing sugar content; TTA: tartaric acid content; MA: malic acid content; GA: gluconic acid content; TA: total acidity; Asp: aspartic acid; Thr: threonine; Ser: serine; Glu: glutamic acid; Leu: leucine; Lys: lysine; His: histidine; Arg: arginine; Phe: phenylalanine; Ala: alanine; Tyr: Tyrosine; NH4+-N: ammonium nitrogen content; NO3+-N: nitrate nitrogen content; TN: total nitrogen content; S-ALP: alkaline phosphatase content; S-UE: urease content; S-SC: sucrase content; S-CAT: catalase content. Positive correlations are indicated in red, negative correlations in blue, and smaller ellipses indicate higher correlation strength. The numbers in the figure represent correlation coefficients, with positive values indicating positive correlations and negative values indicating negative correlations. * indicates significant correlation at the 0.05 level, and ** indicates significant correlation at the 0.01 level.
Figure 9. Correlation analysis between soil physical and chemical indicators and fruit quality during the ripening period under salt stress. Note: HGW: hundred-berry weight; SSW: single-bunch weight; YPP: yield per plant; Bx: Brix sugar content; Glu: glucose content; Fru: fructose content; RS: reducing sugar content; TTA: tartaric acid content; MA: malic acid content; GA: gluconic acid content; TA: total acidity; Asp: aspartic acid; Thr: threonine; Ser: serine; Glu: glutamic acid; Leu: leucine; Lys: lysine; His: histidine; Arg: arginine; Phe: phenylalanine; Ala: alanine; Tyr: Tyrosine; NH4+-N: ammonium nitrogen content; NO3+-N: nitrate nitrogen content; TN: total nitrogen content; S-ALP: alkaline phosphatase content; S-UE: urease content; S-SC: sucrase content; S-CAT: catalase content. Positive correlations are indicated in red, negative correlations in blue, and smaller ellipses indicate higher correlation strength. The numbers in the figure represent correlation coefficients, with positive values indicating positive correlations and negative values indicating negative correlations. * indicates significant correlation at the 0.05 level, and ** indicates significant correlation at the 0.01 level.
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Agriculture 15 01960 g010
Figure 10. Correlation analysis between physicochemical indicators of mature leaves and fruit quality under salt stress. Note: HGW: hundred-berry weight; SSW: single-bunch weight; YPP: yield per plant; Bx: Brix sugar content; Glu: glucose content; Fru: fructose content; RS: reducing sugar content; TTA: tartaric acid content; MA: malic acid content; GA: gluconic acid content; TA: total acidity; Asp: aspartic acid; Thr: threonine; Ser: serine; Glu: glutamic acid; Leu: leucine; Lys: lysine; His: histidine; Arg: arginine; Phe: phenylalanine; Ala: alanine; Tyr: tyrosine; Pn: photosynthetic rate; Tr: transpiration rate; Gs: stomatal conductance; Ci: intercellular CO2 concentration; Na+: sodium ion concentration; K+: potassium ion concentration; Na+/K+: sodium-to-potassium ion ratio; Fo: initial fluorescence; Fm: maximum fluorescence yield; Fv/Fm: maximum photochemical quantum yield of PSII; SPAD: relative chlorophyll content; SOD: superoxide dismutase activity; POD: peroxidase activity; CAT: catalase activity; APX: ascorbate peroxidase activity; MDA: malondialdehyde; AsA: reduced ascorbic acid content; Pro: proline content; H2O2: hydrogen peroxide content. Positive correlations are indicated in purple, negative correlations in green, and smaller ellipses indicate higher correlation strength. The numbers in the figure represent correlation coefficients, with positive values indicating positive correlations and negative values indicating negative correlations. * indicates significant correlation at the 0.05 level, and ** indicates significant correlation at the 0.01 level.
Figure 10. Correlation analysis between physicochemical indicators of mature leaves and fruit quality under salt stress. Note: HGW: hundred-berry weight; SSW: single-bunch weight; YPP: yield per plant; Bx: Brix sugar content; Glu: glucose content; Fru: fructose content; RS: reducing sugar content; TTA: tartaric acid content; MA: malic acid content; GA: gluconic acid content; TA: total acidity; Asp: aspartic acid; Thr: threonine; Ser: serine; Glu: glutamic acid; Leu: leucine; Lys: lysine; His: histidine; Arg: arginine; Phe: phenylalanine; Ala: alanine; Tyr: tyrosine; Pn: photosynthetic rate; Tr: transpiration rate; Gs: stomatal conductance; Ci: intercellular CO2 concentration; Na+: sodium ion concentration; K+: potassium ion concentration; Na+/K+: sodium-to-potassium ion ratio; Fo: initial fluorescence; Fm: maximum fluorescence yield; Fv/Fm: maximum photochemical quantum yield of PSII; SPAD: relative chlorophyll content; SOD: superoxide dismutase activity; POD: peroxidase activity; CAT: catalase activity; APX: ascorbate peroxidase activity; MDA: malondialdehyde; AsA: reduced ascorbic acid content; Pro: proline content; H2O2: hydrogen peroxide content. Positive correlations are indicated in purple, negative correlations in green, and smaller ellipses indicate higher correlation strength. The numbers in the figure represent correlation coefficients, with positive values indicating positive correlations and negative values indicating negative correlations. * indicates significant correlation at the 0.05 level, and ** indicates significant correlation at the 0.01 level.
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Table 1. Comprehensive evaluation results of membership functions for fruit yield and quality at maturity under salt stress using different concentrations of microbial inoculants.
Table 1. Comprehensive evaluation results of membership functions for fruit yield and quality at maturity under salt stress using different concentrations of microbial inoculants.
Treatment GroupPrincipal Component ScoresComprehensive Evaluation
U1U2DSort
CK2.413.812.631
S0.913.031.243
S+JL0.814.081.314
S+JH1.511.391.492
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MDPI and ACS Style

Li, Z.; Ma, L.; Nai, G.; Pu, Z.; Zhang, J.; Li, S.; Wu, B.; Ma, S. Exogenous Application of Applied Microbial Agents to Alleviate Salt Stress on ‘Pinot Noir’ Grapes and Improve Fruit Yield and Quality. Agriculture 2025, 15, 1960. https://doi.org/10.3390/agriculture15181960

AMA Style

Li Z, Ma L, Nai G, Pu Z, Zhang J, Li S, Wu B, Ma S. Exogenous Application of Applied Microbial Agents to Alleviate Salt Stress on ‘Pinot Noir’ Grapes and Improve Fruit Yield and Quality. Agriculture. 2025; 15(18):1960. https://doi.org/10.3390/agriculture15181960

Chicago/Turabian Style

Li, Zhilong, Lei Ma, Guojie Nai, Zhihui Pu, Jingrong Zhang, Sheng Li, Bing Wu, and Shaoying Ma. 2025. "Exogenous Application of Applied Microbial Agents to Alleviate Salt Stress on ‘Pinot Noir’ Grapes and Improve Fruit Yield and Quality" Agriculture 15, no. 18: 1960. https://doi.org/10.3390/agriculture15181960

APA Style

Li, Z., Ma, L., Nai, G., Pu, Z., Zhang, J., Li, S., Wu, B., & Ma, S. (2025). Exogenous Application of Applied Microbial Agents to Alleviate Salt Stress on ‘Pinot Noir’ Grapes and Improve Fruit Yield and Quality. Agriculture, 15(18), 1960. https://doi.org/10.3390/agriculture15181960

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