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Effects of seawater irrigation on fruit quality of grapevine, soil properties and microbial diversity
Scientia Horticulturae 253 (2019) 80–86
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Effects of seawater irrigation on fruit quality of grapevine, soil properties and microbial diversity
T
C. Liua,1, L.P. Huanga,1, M.L. Liua, S.Q. Haob, Heng Zhaia, X.J. Shaoa, , Y.P. Dua, ⁎
a b
⁎
College of Horticulture Science and Engineering, Shandong Agricultural University/State Key Laboratory of Crop Biology, Tai’an, Shandong, China Shandong Agricultural Administrator Institute, Jinan, Shandong, China
ARTICLE INFO
ABSTRACT
Keywords: Seawater Cabernet Sauvignon Fruit quality Soil properties and microbial diversity
Extensive researches have been conducted over the decades to investigate the effects of seawater on many crop plants, either by irrigation or foliar spray, in an attempt to enhance yield and quality, but there are few studies on the effects of seawater irrigation on soil properties. The purpose of this study was to determine the effects of seawater irrigation on the fruit quality of Cabernet Sauvignon grapevines, soil pH, soil salinization, soil bulk density properties and soil microbial diversity. Field experiments were conducted using seawater (10% concentrations) during the fruit expansion period, the early veraison period, the veraison period and the late veraison period in Penglai (pH 6.5–6.7). Seawater irrigation led to increased levels of fruit soluble solids, phenolic content, anthocyaninand sugar/acid ratio, resulting in slowly-increased pH values of soils. After 4 years of continuous seawater irrigation, the pH value of the 0–20 cm soil layer increased 0.24 units at the vineyard of the Guobin Winery and increased 0.17 and 0.18 units after one and two years of seawater irrigation, respectively, at the vineyard of the COFCO Winery. Moreover, seawater irrigation did not affect soil properties, since soil bulk density, specific gravity and porosity did not differ significantly from the control soil. Furthermore, seawater irrigation had less effect on the types of soil microbial communities. The results suggest that combined with rainfall, seawater irrigation could be useful for improving fruit quality and soil pH without inducing secondary soil salinization problems, and seawater irrigation could be used in acidic vineyard soils.
1. Introduction Extensive research has been conducted over the decades to investigate the effects of seawater and supporting measures on many crop plants either by irrigation or foliar spray in an attempt to enhance yield and quality (Chaudhary et al., 2016; Sgherri et al., 2008). The fruits picked from tomato plants irrigated with diluted seawater produced berries characterized by a higher nutritional value, berries showed higher amounts of vitamin C, vitamin E, dihydrolipoic acid, and chlorogenic acid (Sgherri et al., 2008). Research on apples also has shown that spraying seawater can improve apple fruit quality (Zheng et al., 2013). Moderate seawater treatment resulted in the marked accumulation of soluble sugar, protein, polyphenol, carotene and fatty acid in leafy vegetable crops (Long et al., 2008; Ventura et al., 2011). However, seawater has a salinity of nearly 3.5%, and the major components of the dissolved salts are sodium, magnesium, calcium and potassium, induced salinity stress to plants and field. The study of
Chaudhary et al. (2016) showed that irrigation with more than 20% concentrations of seawater had significant impact on soil chemical and microbial properties which was attributed due to the salinity stress, but irrigation with 10% concentrations of seawater increased Salvadora plants dry matter and had less impact on soil chemical and microbial properties. The study of Li et al. (2001) suggested that salinity levels lower than 5 g/L was safe to irrigate wheat, corn, and cotton in their mid-season stages. Pang et al. (2004) demonstrated that the yield of wheat irrigated with saline water (3–5 g/L) increased by 5.1% compared with freshwater irrigation, while during the experimental stages the total soluble salts in a 1 m soil profile did not accumulate. So the appropriate concentration of seawater irrigation won’t induce secondary soil salinization problem. Besides, the accumulated salt due to seawater irrigation can be leached by rainfall. Although seawater irrigation were widely studied on crop plants, there was no investigation of seawater irrigation ongrapevine, especially considering about the rainfall pattern. So in this experiment, 10% concentrations of seawater
Corresponding authors. E-mail addresses: [email protected] (X.J. Shao), [email protected] (Y.P. Du). 1 Equal contribution to this work. ⁎
https://doi.org/10.1016/j.scienta.2019.04.022 Received 20 November 2018; Received in revised form 24 March 2019; Accepted 11 April 2019 Available online 18 April 2019 0304-4238/ © 2019 Elsevier B.V. All rights reserved.
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irrigation was carried out according to the rainfall pattern during the rainy season. The aim was to determine the effects of seawater irrigation on fruit quality, soil physical and chemical properties and soil microbial diversity and to provide a theoretical basis for the feasibility of seawater irrigation in the Jiaodong coastal areas of China.
Table 2 Seawater irrigation in COFCO vineyard.
2. Materials and methods
Note: 2y: The vines received seawater for 2 consecutive years (from 2015 to 2016). 1 y: The vines received seawater in 2016.
2.1. Field condition and plant material The own-rooted ‘Cabernet Sauvignon’ (Vitis. vinifera L.) vines were used in this study. This study was carried out in two commercial vineyards (Guobin vineyards and COFCOvineyard) in Penglai city, Shandong Province (37.48 °N, 120.45 °E), which is in a temperate continental monsoon climate zone with annual sunshine of 2511.4 h, an average annual temperature of 12.8 °C, and annual rainfall of 683.9 mm. The rainy season is usually from July to September, and there is an average annual frost-free period of 206 d. Vines were spaced at 2.5 m × 1 m and in north–south row orientation. Vines were trained to a bilateral cordon at 0.6 m above ground, shoots were trained upwards and each vine carried approximately 20 grape clusters. The vertical shoot-positioned canopies were uniformly managed. The sandy soil properties of Guobin vineyards were tested as 1.3% organic matter, 41.4 mg/kg available phosphorus, 106.8 mg/kg available nitrogen, and 227.7 mg/kg available potassium, respectively. Soil properties of COFCO vineyards were tested as 1.2% organic matter, 59.1 mg/kg available phosphorus, 83.7 mg/kg available nitrogen, and 179.3 mg/kg available potassium, respectively.
Irrigation years
2015 (6.18; 7.30; 8.13; 9.16)
2016 (7.8; 8.2; 8.30; 9.20)
CK 1y 2y
water water 10% seawater
water 10% seawater 10% seawater
Table 3 Physical and Chemical Properties of original concentration seawater. Na+ mg/L
Ca2+ mg/L
Mg2+ mg/L
Cl− mg/L
SO42− mg/L
HCO3− mg/L
Degree of mineralization g/ L
pH
10560
300
1690
18980
2560
142
35
7.79-8.22
2.3. Determination method 2.3.1. Chlorophyll and net photosynthetic rate (Pn) measurement Randomly chose the leaves (4–5 nodes position) of different treatments for the measurement of chlorophyll content and net photosynthetic rate (Pn) in late August. The chlorophyll content was measured by SPAD-502 chlorophyll meter. And net photosynthetic rate (Pn) were measured using the LI-6400 gas exchange system (Li-Cor Biosciences, Lincoln, NE, USA). 2.3.2. Fruit quality related indicators determination Total soluble solids (TSS) measured using a TD-45 digital refractometer (TOP, Zhejiang, China). The berry pH was measured using PB-10 pH meter (Sartorius, Gottingen, Germany). Titratable acid (TA) was determined with sodium hydroxide titration. The total anthocyanin content was determined by the formula OD = A530 −0.25 × A657, and the results were calculated by means of a calibration curve with the standard malvidin-3-monoglucoside (Extrasynthese, Lyon, France) (Li et al., 2013). The total phenol content was determined using the FolinCiocalteu method as previously described (Dewanto et al., 2002). The results were calculated using a calibration curve made with gallic acid. The total tannin content was analysed by spectrophotometric methods. Total tannins (as mg of catechin) as recommended by Ribéreau-Gayon and Stonestreet (1996).
2.2. Seawater irrigation treatment A randomized block design was carried out with three replications for each irrigation treatment. The vines were irrigated with 10% concentration seawater at the fruit expansion period, the early veraison period, the veraison period and the late veraison period. The vines received seawater for 4 consecutive years (from 2013 to 2016) in Guobin vineyard (Table 1). The vines received seawater for 2 consecutive years (from 2015 to 2016) and 1 year (2016) in COFCO vineyard (Table 2). Each replication consisted of one row of 60 vines, the control were irrigated with water. The original physical and chemical properties of the seawater were showed in Table 3. Each irrigation was based on weather forecasts approximately 2 days before the rain. The experiment used the method of furrow irrigation, the furrow was 40 cm wide and 100 cm long for each plant, The average irrigation amount per plant was 20 L. Plants were slightly hoed and covered with soil after irrigation to reduce the evaporation of water. Soil samples at a distance of 40 cm and at depths of 0–20 cm and 20–40 cm were taken in mid-November to test the physical and chemical properties of the soil and soil microbial diversity. When the fruits reached the local winery requirements. Fifteen bunches of grapes were randomly selected for each treatment. Three hundred berries of the upper, middle and lower parts of each bunch were randomly selected for the determination of weight of 100 berries, anthocyanins, total soluble solids, titratable acid, pH, tannin and total phenol contents. These samples were stored at −80 °C for subsequent analysis of their physicochemical composition.
2.3.3. Soil physical and chemical properties and microbial diversity determination The soil bulk density was determined by the ring cutter method, the specific gravity of the soil was measured by the pyknometer method, the total soil porosity (%) = 100 * (1-weight / specific gravity). Soil pH value determined by potentiometry, water to soil ratio of 1: 1 leaching, with the Sartorius PB-10 acidity measured three times. Total salt content of soils was determined by residue drying-mass method. Soil chloride ion was determined by Mohr's method. Soil sulfate ion was measured by EDTA indirect titration. Bulk density was determined by weighing the soil after drying at 105 °C for 72 h. Soil specific gravity was determined using pyknometer method. Total soil porosity was calculated from bulk density. The total salt content of soil was
Table 1 Seawater irrigation in Guobin vineyard. Irrigation years
2013 (7.7; 8.15; 9.25; 10.1)
2014 (7.4; 8.1; 8.31; 9.16)
2015 (6.18; 7.30; 8.13; 9.16)
2016 (7.8; 8.2; 8.30; 9.20)
CK 4y
water 10% seawater
water 10% seawater
water 10% seawater
water 10% seawater
Note: 4 y: The vines received seawater for 4 consecutive years (from 2013 to 2016). 81
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determined by measuring the electrical conductivity using an electrical conductivity meter. The Cl− was determined by AgNO3 titration method. The SO42− was determined by ion chromatography. Microbial diversity was determined by next generation sequencing library preparations and Illumina MiSeq sequencing. DNA samples were quantified using a Qubit 2.0 Fluorometer (Invitrogen, Carlsbad, CA, USA). 30–50 ng DNA was used to generate amplicons using a MetaVx™ Library Preparation kit (GENEWIZ, Inc., South Plainfield, NJ, USA). V3 and V4 hypervariable regions of prokaryotic 16S rDNA were selected for generating amplicons and following taxonomy analysis. GENEWIZ designed a panel of proprietary primers aimed at relatively conserved regions bordering the V3 and V4 hypervariable regions of bacteria and Archaea16S rDNA. The v3 and v4 regions were amplified using forward primers containing the sequence “CCTACGGRRBGCASCAGKVRVGAAT” and reverse primers containing the sequence “GGACTACNVGGGTWTCTAATCC”. 1 st round PCR products were used as templates for 2nd round amplicon enrichment PCR. At the same time, indexed adapters were added to the ends of the 16S rDNA amplicons to generate indexed libraries ready for downstream NGS sequencing on Illumina Miseq. DNA libraries were validated by Agilent 2100 Bioanalyzer (Agilent Technologies, Palo Alto, CA, USA), and quantified by Qubit 2.0 Fluorometer. DNA libraries were multiplexed and loaded on an Illumina MiSeq instrument according to manufacturer’s instructions (Illumina, San Diego, CA, USA). Sequencing was performed using a 2 × 300 paired-end (PE) configuration; image analysis and base calling were conducted by the MiSeq Control Software (MCS) embedded in the MiSeq instrument. The QIIME data analysis package was used for 16S rRNA data analysis. The forward and reverse reads were joined and assigned to samples based on barcode and truncated by cutting off the barcode and primer sequence. Quality filtering on joined sequences was performed and sequence which did not fulfill the following criteria were discarded: sequence length < 200 bp, no ambiguous bases, mean quality score > = 20. Then the sequences were compared with the reference database (RDP Gold database) using UCHIME algorithm to detect chimeric sequence, and then the chimeric sequences were removed. The effective sequences were used in the final analysis. Sequences were grouped into operational taxonomic units (OTUs) using the clustering program VSEARCH(1.9.6) against the Silva 119 database preclustered at 97% sequence identity. The Ribosomal Database Program (RDP) classifier was used to assign taxonomic category to all OTUs at confidence threshold of 0.8. The RDP classifier uses the Silva 123 database which has taxonomic categories predicted to the species level. Sequences were rarefied prior to calculation of alpha and beta diversity statistics. Alpha diversity indexes were calculated in QIIME from rarefied samples using for diversity the Shannon index, for richness the Chao1 index. Beta diversity was calculated using weighted and unweighted UniFrac and principal coordinate analysis (PCoA) performed. Unweighted Pair Group Method with Arithmetic mean (UPGMA) tree from beta diversity distance matrix was builded.
higher than the control. The content of titratable acid decreased significantly after seawater irrigation and decreased with increasing seawater irrigation years, decreasing by 0.21 (4.22%), 0.9 (18.07%) and 0.89 g / L (20.37%) after 1, 2 and 4 years, respectively. The pH value of the grapes showed a significant increasing trend, and the pH value of the grapes after 1 year, 2 years and 4 years of seawater irrigation increased by 0.2, 0.25 and 0.03, respectively. TSS / TA showed an upward trend. TSS / TA increased by 0.27 (7.34%), 0.86 (23.37%) and 1.37 (30.51%) after 1, 2 and 4 years of seawater irrigation, respectively (Table 5). The contents of anthocyanin, tannin and total phenol content in grapes increased after seawater irrigation, and the total phenol content with seawater irrigation significantly increased by 0.26 (3.62%), 0.42 (5.84%) and 3.23 mg / g (44.13%) after 1, 2 and 4 years of seawater treatment, respectively. There was no significant effect of seawater irrigation on fruit tannin content for 1 year and 2 consecutive years of seawater treatment. Fruit tannin content significantly increased by 1.4 mg / g (30.17%) after 4 consecutive years of seawater irrigation. The anthocyanin content increased significantly by 0.56 (39.44%), 0.6 (42.25%) and 0.11 mg / g after 1 year, 2 years and 4 years of seawater irrigation, respectively (Table 5). 3.2. Effect of seawater irrigation on the physical and chemical properties of soil The application of 10% seawater slowly increased soil pH and improved soil acidification. After 4 consecutive years of seawater irrigation in Guobin vineyard, the pH value of the 0–20 cm soil layer increased from 6.71 to 6.95, an increase of 0.24 units, in the 20–40 cm soil layer, irrigation after 4 years increased by 0.02 units compared with the control. In COFCO vineyard, the pH value of one year and two years of seawater irrigation increased 0.17 and 0.18 units, respectively, compared with the control in the 0–20 cm soil layer and increased 0.21 and 0.23 units in the 20–40 cm soil layer (Table 6). In this study, the bulk density of the 0–20 cm soil layer in Guobin vineyard increased by 1.67%, the specific gravity increased by 0.8% compared with the control, and the soil porosity decreased by 7.03%, but there was no significant difference from the control (Table 6). The changes in bulk density, specific gravity and soil porosity after seawater irrigation were minor and showed no significant difference from the control in the 0–20 cm and 20–40 cm soil layers (Table 6). Seawater irrigation has little effect on soil salinity, soil water-soluble salts, soil Cl− content and SO42- content increased 0.0200 g / kg (8.33%), 0.0012 g / kg (8.11%) and 0.0292 g / kg (13.19%) after 4 years of seawater irrigation compared with the control in Guobin vineyard, and there was no significant difference from the control. After 2 years of seawater irrigation, the soil water-soluble salinity, soil water content and SO42- content in COFCO vineyard increased by 0.043 g/kg (36.13%), 0.0015 g/kg (5.88%) and 0.0027 g/kg, respectively (Table 7). The total amount of water-soluble salts increased by 0.039 g/ kg (1.2%). No significant difference was observed with the control.
2.4. Statistical analysis
3.3. Effects of seawater irrigation on rhizosphere microbes
Mean and standard deviation of values, significance of difference analysis and correlation analysis were analyzed by using software SPSS statistics 20.0 (IBM, Armonk, NY, USA).
3.3.1. Effects of seawater irrigation on the rhizosphere soil microbial community Fig. 1 shows the soil microbial gene Venn diagram. It can be seen from the figure that long-term seawater irrigation had little effect on the types of microbe communities in the soil. There are a large number of the same OTUs and a few unique OTUs. There are 1207 OTUs in common between the control and 4 years of seawater irrigation in Guobin vineyard, 61 unique OTUs for the 4 years of seawater irrigation treatment and 59 unique OTUs for the control in Guobin vineyard. There are 1337 OTUs in common among the treatments in COFCO vineyard, and there were 59 and 54 unique OTUs for 1- and 2 years seawater irrigation treatments, respectively.
3. Results and discussion 3.1. Effect of seawater irrigation on Chlorophyll, Pn and grape quality In this study, seawater irrigation had no significant effect on the Chlorophyll, Pn, bu bunch weight and weight of 100 berries, which suggested that seawater irrigation didn’t affect plant and fruit growth (Table 4). Total soluble solids (TSS) increased after seawater treatment, and fruit TSS after 4 years of seawater irrigation was significantly 82
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Table 4 Effects of seawater irrigation on the plant and fruit growth.
Guobin
CK 4y CK 1y 2y
COFCO
SPAD reading
Pn (μmolm−2s-1
Bunch weight(g)
weight of 100 berries (g)
18.34 18.18 18.23 18.04 18.17
13.06 12.39 12.96 12.67 13.18
235.30 237.81 282.55 284.49 286.61
162.19 163.49 155.79 156.44 157.69
± ± ± ± ±
0.25a 0.41a 0.16a 0.32a 0.38a
± ± ± ± ±
2.04a 1.27a 1.18ab 1.04a 2.01a
± ± ± ± ±
7.37a 6.82a 7.61a 8.48a 7.22a
± ± ± ± ±
4.21a 3.85a 3.57ab 4.14a 4.00a
Note: Data are the mean ± SD; the data within a column followed by different small letters show significant differences at the 5% level. The same is true below. Table 5 Effects of seawater irrigation on the quality of grapes.
Guobin COFCO
CK 4y CK 1y 2y
titratable acid (g/l)
total soluble solids (TSS) (Brix)
pH
4.37 3.49 4.98 4.67 4.08
19.93 20.81 18.21 18.61 18.70
3.57 3.60 3.44 3.64 3.69
± ± ± ± ±
0.18a 0.12b 0.09a 0.05b 0.03c
± ± ± ± ±
2.72b 1.30a 1.35a 1.29a 1.24a
± ± ± ± ±
0.03b 0.07a 0.02b 0.06a 0.06a
TSS / TA
Total phenol contents (mg/g)
Tannin (mg/g)
Anthocyanin(μg/g)
4.49 5.86 3.68 3.95 4.54
7.32 ± 0.02b 10.55 ± 0.03a 7.19 ± 0.07b 7.45 ± 0.03a 7.61 ± 0.08a
4.64 6.04 3.06 3.00 2.94
2.60 2.71 1.42 1.98 2.02
Table 8 showed that Ace and Chao1 richness decreased after 4 years of seawater irrigation, while the Shannon and Simpson indexes were slightly reduced, and goods coverage was slightly increased in Guobin vineyard. Ace and Chao1 richness slightly increased after 1 year and 2 years of seawater irrigation, and the Shannon and Simpson indexes and goods coverage slightly increased in COFCO vineyard. However no significant difference was observed with the control in Guobin and COFCO vineyard (Table 8).
± ± ± ± ±
0.09b 0.11a 0.09c 0.05b 0.10a
± ± ± ± ±
0.01b 0.04a 0.08a 0.06a 0.05a
± ± ± ± ±
0.01b 0.01a 0.02c 0.05ab 0.03a
Table 7 Effects of seawater irrigation on soil salt content.
Guobin COFCO
3.3.2. Effects of seawater irrigation on the abundance of microorganisms in rhizosphere soil In this study, the abundance of Azoarcus, Bacillus, Bradyrhizobium, Burkholderia, Arthrobacter, Candidatus, Koribacter, Candidatus and Solibacter in the soil decreased after 4 consecutive years of seawater irrigation in Guobin vineyard, there were no significant changes between the seawater irrigation and control except for Bradyrhizobium, 84.54% lower than the abundance found in the control. The abundance of Planctomyces, Rhodoplanes, Azoarcus, Candidatus, Koribacter, Candidatus and Solibacter in soil decreased after 1 year and 2 years of seawater irrigation in COFCO vineyard, also there were no significant changes between the seawater irrigation and control except for Burkholderia, significantly decreased by 72.3% after 2 years of seawater irrigation (Table 9).
CK 1y 4y CK 1y 2y
Soil water-soluble salts (g/kg)
Soil Cl− content (g/kg)
SO42− content (g/ kg)
0.2400a 0.22a 0.26a 0.119a 0.151a 0.162a
0.0148b 0.0113a 0.016a 0.0255a 0.0262a 0.0270a
0.2213a 0.1835a 0.25a 0.1293a 0.1227a 0.1320a
the other hand, seawater has a salinity of nearly 3.5%, and moderate salinity stress affects the increase of gluconeogenesis, resulting in an increase in glucose and fructose (Cramer et al., 2007). The results of this study showed that seawater irrigation increased the soluble solids content of grapevine, reduced the titratable acid, and increased the content of phenolic compounds in grapes. Studies on tomatoes and apples showed that using seawater irrigation or spraying can significantly increase the soluble solids content of fruit and reduce apple titratable acid (Sgherri et al., 2008; Zheng et al., 2013), which is consistent with our findings. With the high production benefit of fruit, overdose of fertilizer especially nitrogen fertilizer inthe orchardleads to the soil acidification, soil acidification is an important factor that restricts the yield and quality of fruits. Soil acidification can lead to soil hardening, a decrease in the C/N ratio, and the washing away of many mineral nutrients (Ca, Mg, P, etc.) (Li et al., 2014). Soil acidification can also increase the release of some toxic metals (Cd, Cr, Pb, Mn, Al, etc.). At present, more than 1/5 of the soil in China is acidic. The pH is below 5.5, with many having a pH less than 5.0 and even below 4.5 (Chen et al., 2012).
4. Discussion Seawater is not only rich in mineral elements and chlorine, sulfate ions, bicarbonate, etc. but also contains a large amount of trace elements (Zhang, 1998). Mineral nutrition plays an extremely important regulatory role in the physiological metabolism and quality formation of grapes and other fruit trees (Wei and Jiang, 2012; Lu et al., 2011). On
Table 6 Effects of seawater irrigation on soil pH, bulk density, specific gravity and total porosity. pH 0-20 cm soil layer
Guobin COFCO
20-40 cm soil layer
Guobin COFCO
CK 4y CK 1y 2y CK 4y CK 1y 2y
6.71 6.95 6.61 6.78 6.79 6.78 6.80 6.53 6.74 6.76
± ± ± ± ± ± ± ± ± ±
0.01b 0.02a 0.01b 0.02a 0.03a 0.01a 0.01a 0.06c 0.01ab 0.02a
83
Bulk density (g/m3)
Specific gravity (mg/m3)
Total porosity (%)
1.8 ± 0.02a 1.83 ± 0.02a 1.57 ± 0.03b 1.81 ± 0.03a 1.83 ± 0.07a 1.72 ± 0.03a 1.73 ± 0.02a 1.71 ± 0.02b 1.76 ± 0.06ab 1.96 ± 0.02a
2.50 ± 0.04a 2.48 ± 0.01a 2.455 ± 0.04a 2.489 ± 0.01a 2.520 ± 0.01a 2.66 ± 0.01a 2.97 ± 0.07a 2.68 ± 0.06ab 2.61 ± 0.08ab 2.55 ± 0.05b
28.29 26.30 30.70 27.68 28.68 41.48 40.62 36.23 30.73 36.24
± ± ± ± ± ± ± ± ± ±
0.1a 0.2a 0.1a 0.3a 0.2a 0.8a 0.9a 0.2a 0.4a 0.6a
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acidification. 2 and 4 consecutive years seawater irrigation induced pH value of the 0–20 cm soil layer increased 0.18 and 0.24 units, respectively. Previous studies have shown that seawater irrigation has a negative impact on the physical and chemical properties of soil. The main problem is the decrease of soil permeability, resulting in increased soil salinity and soil solution conductivity, which reduces soil porosity. Studies showed that irrigation with brackish water with a salinity of 3–5 g/L caused varying degrees of salinization, and excess salinity caused soil compaction, resulting in decreased soil permeability, the effect of irrigation water on soil properties mainly affects exchangeable sodium and conductivity in soils (Feigen et al., 1991). In this study, after 4 years of seawater irrigation, the soil water-soluble salinity, SO42− content and total amount of water-soluble salts had no significant difference with the control. This might be due to rainfall during the growth period, as the salt in the soil gradually moves downward with rainfall. Reasonable amounts of seawater irrigation combined with reasonable rainfall leaching amounts will slow the formation of soil salinization. The depth of salt accumulation is closely related to the brackish water irrigation amount, the rainfall amount, the irrigation method and the soil properties (Hipp, 1977). Tests by Shi (Shi et al., 2005) showed that salinity in the soil surface is in a relatively balanced condition when irrigated with brackish water with a salinity of less than 3 g / L. Soil salinization does not harm plants due to rainfall or freshwater irrigation during brackish water irrigation (Wu and Wang, 2010). To ensure that the soil is not over-salted because of long-term brackish water irrigation, sufficient freshwater irrigation or heavy rainfall is required once a year (Liu et al., 2010; Wei and Jiang, 2012). The rainfall was 689.3 mm, 243.5 mm, 468.7 mm and 261.3 mm in 2013, 2014, 2015 and 2016 during the treatment of seawater irrigation, respectively. And were accounted for 76.55%, 65.72%, 71.60% and 56.67% of total annual rainfall. The rainfall amount was 246.2 mm, 3 mm, 2.1 mm and 0.4 mm in ten days after each seawater irrigation in 2013, and 6.5 mm, 8.1 mm, 12 mm and 66.8 mm in 2014, and 18.9 mm, 90.2 mm, 24.9 mm and 5.1 mm in 2015, and 2.2 mm, 41.2 mm, 44.3 mm and 3.8 mm in 2016. And the frequency of precipitation over 10 mm were thirteen, eight, eleven and seven times in 2013, 2014, 2015 and 2016 during the treatment of seawater irrigation, respectively. The frequency of heavy rainfall (precipitation over 50 mm) were five, two, two and one times in 2013, 2014, 2015 and 2016 during the treatment of seawater irrigation (Fig. 2). With the rainfall of Penglai during the growth period, the leaching effect was obvious. The pH value of the soil significantly increased without causing salt accumulation and soil salinization. Therefore, seasonal heavy rainfall or reasonable and effective irrigation measures can effectively prevent the occurrence of soil salinization. The soil microbial biomass is the principle component of the decomposer subsystem regulating nutrient cycling, energy flow and ultimately plant and ecosystem productivity, is a major indicator of soil development, and biochemical intensities often affect the conversion factors and pools of nutrients required by plants. Moreover, changes in the soil microbial population and community structure are important biological indicators of soil environmental quality assessment, which can reflect soil quality and health condition (Zhang et al., 2008). Bacteria, actinomycetes and fungi are the main biomass components of soil microorganisms (Mackay et al., 2016). They are involved in the synthesis of organic compounds in soil and closely related to the formation of soil fertility (Yao and Huang, 2006). Studies have shown that salt stress will undermine the microbial community structure in the soil to some extent, reducing soil bacteria (Yang and Xu, 2002). Our result showed that 2 and 4 consecutive years of seawater irrigation had little effect on soil microbial biomass. Which suggested that combined with seasonal heavy rainfall, seawater irrigation can effectively prevent the decrease of soil microbial biomass.
Fig. 1. OTU Venn diagram analysis of different irrigation treatments. Gck, control at Guobin vineyard; G4, 4 years seawater irrigation treatment at Guobin vineyard; Zck, control at COFCO vineyard; Z1, 1 year seawater irrigation treatment at COFCO vineyard; 2 years seawater irrigation treatment at COFCO vineyard. Table 8 Analysis of diversity differences between different groups.
Guobin COFCO
Sample
Ace
Chao1
Shannon
Simpson
Goods coverage
Control 4y Control 1y 2y
1504.82a 1501.19a 1637.62a 1688.05a 1672.36a
1529.06a 1525.25a 1656.71a 1724.40a 1689.58a
8.72a 8.71a 8.84a 8.88a 8.98a
0.993a 0.992a 0.993a 0.993a 0.994a
0.9937a 0.9940a 0.9937a 0.9937a 0.9940a
Table 9 Taxa Statistics at the Genus level. Genus
Aquicella Nitrospira Planctomyces Rhodoplanes Azoarcus Bacillus Paenibacillus Sphingomonas Bradyrhizobium Burkholderia Arthrobacter Candidatus_Koribacter Candidatus_Solibacter
Guobin
COFCO
Control
4y
Control
1y
2y
0.1633a 0.1333a 0.200a 0.0867a 0.1000a 0.5733a 0.0333a 0.2733a 0.0102a 0.0967a 0.0100a 0.0867a 0.0367a
0.1967a 0.2033a 0.2767a 0.1733a 0.0800a 0.4800a 0.0567a 0.3633a 0.0003b 0.015a 0.0033a 0.0767a 0.0233a
0.5933a 0.3767a 0.5533a 0.2167a 0.2233a 0.5800a 0.0467a 0.3000a 0.0600b 0.1500a 0.0133a 0.0867a 0.0133a
0.8633a 0.3967a 0.5067a 0.1367a 0.1600a 0.8800a 0.0600a 0.3267a 0.1533a 0.0567a 0.0300a 0.0733a 0.0137a
0.9267a 0.4633a 0.5300a 0.1800a 0.1700a 0.7667a 0.1533a 0.3367a 0.1033a 0.0600b 0.0200a 0.0700a 0.0103a
According to a survey, the average pH value of soil in China has been reduced by 0.6 units on average over the past 30 years, and the area of acidic cultivated land has risen by 7% to the current level of 18%. According to a survey, soil acidification is particularly serious in the orchards of the Jiaodong Peninsula, China, with an average pH value of approximately 5.2 (Ge et al., 2014), which seriously affects fruit tree growth. The pH value of seawater is 8.0–8.5, and to a certain extent, can improve acidified soil. Our result showed that application of 10% seawater for irrigation slowly raised soil pH and improved soil
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Fig. 2. The rainfall in Penglai from 2013 to 2016 during the treatment of seawater irrigation.
5. Conclusion
without inducing secondary soil salinization problems.
In summary, combined with rainfall amount of over 240 mm and more than once heavy raifall from fruit expansion to late veraison period, the use of 10% seawater irrigation in the grape growing season over four years can improve fruit quality and increase the soil pH, which effectively alleviates the harm caused by soil acidification
Acknowledgements This research was supported by the China agricultural research system(CARS-29-zp-02), Program for Changjiang Scholars and Innovative Research Team in University(IRT15R42). 85
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Effects of seawater irrigation on fruit quality of grapevine, soil properties and microbial diversity
T
C. Liua,1, L.P. Huanga,1, M.L. Liua, S.Q. Haob, Heng Zhaia, X.J. Shaoa, , Y.P. Dua, ⁎
a b
⁎
College of Horticulture Science and Engineering, Shandong Agricultural University/State Key Laboratory of Crop Biology, Tai’an, Shandong, China Shandong Agricultural Administrator Institute, Jinan, Shandong, China
ARTICLE INFO
ABSTRACT
Keywords: Seawater Cabernet Sauvignon Fruit quality Soil properties and microbial diversity
Extensive researches have been conducted over the decades to investigate the effects of seawater on many crop plants, either by irrigation or foliar spray, in an attempt to enhance yield and quality, but there are few studies on the effects of seawater irrigation on soil properties. The purpose of this study was to determine the effects of seawater irrigation on the fruit quality of Cabernet Sauvignon grapevines, soil pH, soil salinization, soil bulk density properties and soil microbial diversity. Field experiments were conducted using seawater (10% concentrations) during the fruit expansion period, the early veraison period, the veraison period and the late veraison period in Penglai (pH 6.5–6.7). Seawater irrigation led to increased levels of fruit soluble solids, phenolic content, anthocyaninand sugar/acid ratio, resulting in slowly-increased pH values of soils. After 4 years of continuous seawater irrigation, the pH value of the 0–20 cm soil layer increased 0.24 units at the vineyard of the Guobin Winery and increased 0.17 and 0.18 units after one and two years of seawater irrigation, respectively, at the vineyard of the COFCO Winery. Moreover, seawater irrigation did not affect soil properties, since soil bulk density, specific gravity and porosity did not differ significantly from the control soil. Furthermore, seawater irrigation had less effect on the types of soil microbial communities. The results suggest that combined with rainfall, seawater irrigation could be useful for improving fruit quality and soil pH without inducing secondary soil salinization problems, and seawater irrigation could be used in acidic vineyard soils.
1. Introduction Extensive research has been conducted over the decades to investigate the effects of seawater and supporting measures on many crop plants either by irrigation or foliar spray in an attempt to enhance yield and quality (Chaudhary et al., 2016; Sgherri et al., 2008). The fruits picked from tomato plants irrigated with diluted seawater produced berries characterized by a higher nutritional value, berries showed higher amounts of vitamin C, vitamin E, dihydrolipoic acid, and chlorogenic acid (Sgherri et al., 2008). Research on apples also has shown that spraying seawater can improve apple fruit quality (Zheng et al., 2013). Moderate seawater treatment resulted in the marked accumulation of soluble sugar, protein, polyphenol, carotene and fatty acid in leafy vegetable crops (Long et al., 2008; Ventura et al., 2011). However, seawater has a salinity of nearly 3.5%, and the major components of the dissolved salts are sodium, magnesium, calcium and potassium, induced salinity stress to plants and field. The study of
Chaudhary et al. (2016) showed that irrigation with more than 20% concentrations of seawater had significant impact on soil chemical and microbial properties which was attributed due to the salinity stress, but irrigation with 10% concentrations of seawater increased Salvadora plants dry matter and had less impact on soil chemical and microbial properties. The study of Li et al. (2001) suggested that salinity levels lower than 5 g/L was safe to irrigate wheat, corn, and cotton in their mid-season stages. Pang et al. (2004) demonstrated that the yield of wheat irrigated with saline water (3–5 g/L) increased by 5.1% compared with freshwater irrigation, while during the experimental stages the total soluble salts in a 1 m soil profile did not accumulate. So the appropriate concentration of seawater irrigation won’t induce secondary soil salinization problem. Besides, the accumulated salt due to seawater irrigation can be leached by rainfall. Although seawater irrigation were widely studied on crop plants, there was no investigation of seawater irrigation ongrapevine, especially considering about the rainfall pattern. So in this experiment, 10% concentrations of seawater
Corresponding authors. E-mail addresses: [email protected] (X.J. Shao), [email protected] (Y.P. Du). 1 Equal contribution to this work. ⁎
https://doi.org/10.1016/j.scienta.2019.04.022 Received 20 November 2018; Received in revised form 24 March 2019; Accepted 11 April 2019 Available online 18 April 2019 0304-4238/ © 2019 Elsevier B.V. All rights reserved.
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irrigation was carried out according to the rainfall pattern during the rainy season. The aim was to determine the effects of seawater irrigation on fruit quality, soil physical and chemical properties and soil microbial diversity and to provide a theoretical basis for the feasibility of seawater irrigation in the Jiaodong coastal areas of China.
Table 2 Seawater irrigation in COFCO vineyard.
2. Materials and methods
Note: 2y: The vines received seawater for 2 consecutive years (from 2015 to 2016). 1 y: The vines received seawater in 2016.
2.1. Field condition and plant material The own-rooted ‘Cabernet Sauvignon’ (Vitis. vinifera L.) vines were used in this study. This study was carried out in two commercial vineyards (Guobin vineyards and COFCOvineyard) in Penglai city, Shandong Province (37.48 °N, 120.45 °E), which is in a temperate continental monsoon climate zone with annual sunshine of 2511.4 h, an average annual temperature of 12.8 °C, and annual rainfall of 683.9 mm. The rainy season is usually from July to September, and there is an average annual frost-free period of 206 d. Vines were spaced at 2.5 m × 1 m and in north–south row orientation. Vines were trained to a bilateral cordon at 0.6 m above ground, shoots were trained upwards and each vine carried approximately 20 grape clusters. The vertical shoot-positioned canopies were uniformly managed. The sandy soil properties of Guobin vineyards were tested as 1.3% organic matter, 41.4 mg/kg available phosphorus, 106.8 mg/kg available nitrogen, and 227.7 mg/kg available potassium, respectively. Soil properties of COFCO vineyards were tested as 1.2% organic matter, 59.1 mg/kg available phosphorus, 83.7 mg/kg available nitrogen, and 179.3 mg/kg available potassium, respectively.
Irrigation years
2015 (6.18; 7.30; 8.13; 9.16)
2016 (7.8; 8.2; 8.30; 9.20)
CK 1y 2y
water water 10% seawater
water 10% seawater 10% seawater
Table 3 Physical and Chemical Properties of original concentration seawater. Na+ mg/L
Ca2+ mg/L
Mg2+ mg/L
Cl− mg/L
SO42− mg/L
HCO3− mg/L
Degree of mineralization g/ L
pH
10560
300
1690
18980
2560
142
35
7.79-8.22
2.3. Determination method 2.3.1. Chlorophyll and net photosynthetic rate (Pn) measurement Randomly chose the leaves (4–5 nodes position) of different treatments for the measurement of chlorophyll content and net photosynthetic rate (Pn) in late August. The chlorophyll content was measured by SPAD-502 chlorophyll meter. And net photosynthetic rate (Pn) were measured using the LI-6400 gas exchange system (Li-Cor Biosciences, Lincoln, NE, USA). 2.3.2. Fruit quality related indicators determination Total soluble solids (TSS) measured using a TD-45 digital refractometer (TOP, Zhejiang, China). The berry pH was measured using PB-10 pH meter (Sartorius, Gottingen, Germany). Titratable acid (TA) was determined with sodium hydroxide titration. The total anthocyanin content was determined by the formula OD = A530 −0.25 × A657, and the results were calculated by means of a calibration curve with the standard malvidin-3-monoglucoside (Extrasynthese, Lyon, France) (Li et al., 2013). The total phenol content was determined using the FolinCiocalteu method as previously described (Dewanto et al., 2002). The results were calculated using a calibration curve made with gallic acid. The total tannin content was analysed by spectrophotometric methods. Total tannins (as mg of catechin) as recommended by Ribéreau-Gayon and Stonestreet (1996).
2.2. Seawater irrigation treatment A randomized block design was carried out with three replications for each irrigation treatment. The vines were irrigated with 10% concentration seawater at the fruit expansion period, the early veraison period, the veraison period and the late veraison period. The vines received seawater for 4 consecutive years (from 2013 to 2016) in Guobin vineyard (Table 1). The vines received seawater for 2 consecutive years (from 2015 to 2016) and 1 year (2016) in COFCO vineyard (Table 2). Each replication consisted of one row of 60 vines, the control were irrigated with water. The original physical and chemical properties of the seawater were showed in Table 3. Each irrigation was based on weather forecasts approximately 2 days before the rain. The experiment used the method of furrow irrigation, the furrow was 40 cm wide and 100 cm long for each plant, The average irrigation amount per plant was 20 L. Plants were slightly hoed and covered with soil after irrigation to reduce the evaporation of water. Soil samples at a distance of 40 cm and at depths of 0–20 cm and 20–40 cm were taken in mid-November to test the physical and chemical properties of the soil and soil microbial diversity. When the fruits reached the local winery requirements. Fifteen bunches of grapes were randomly selected for each treatment. Three hundred berries of the upper, middle and lower parts of each bunch were randomly selected for the determination of weight of 100 berries, anthocyanins, total soluble solids, titratable acid, pH, tannin and total phenol contents. These samples were stored at −80 °C for subsequent analysis of their physicochemical composition.
2.3.3. Soil physical and chemical properties and microbial diversity determination The soil bulk density was determined by the ring cutter method, the specific gravity of the soil was measured by the pyknometer method, the total soil porosity (%) = 100 * (1-weight / specific gravity). Soil pH value determined by potentiometry, water to soil ratio of 1: 1 leaching, with the Sartorius PB-10 acidity measured three times. Total salt content of soils was determined by residue drying-mass method. Soil chloride ion was determined by Mohr's method. Soil sulfate ion was measured by EDTA indirect titration. Bulk density was determined by weighing the soil after drying at 105 °C for 72 h. Soil specific gravity was determined using pyknometer method. Total soil porosity was calculated from bulk density. The total salt content of soil was
Table 1 Seawater irrigation in Guobin vineyard. Irrigation years
2013 (7.7; 8.15; 9.25; 10.1)
2014 (7.4; 8.1; 8.31; 9.16)
2015 (6.18; 7.30; 8.13; 9.16)
2016 (7.8; 8.2; 8.30; 9.20)
CK 4y
water 10% seawater
water 10% seawater
water 10% seawater
water 10% seawater
Note: 4 y: The vines received seawater for 4 consecutive years (from 2013 to 2016). 81
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determined by measuring the electrical conductivity using an electrical conductivity meter. The Cl− was determined by AgNO3 titration method. The SO42− was determined by ion chromatography. Microbial diversity was determined by next generation sequencing library preparations and Illumina MiSeq sequencing. DNA samples were quantified using a Qubit 2.0 Fluorometer (Invitrogen, Carlsbad, CA, USA). 30–50 ng DNA was used to generate amplicons using a MetaVx™ Library Preparation kit (GENEWIZ, Inc., South Plainfield, NJ, USA). V3 and V4 hypervariable regions of prokaryotic 16S rDNA were selected for generating amplicons and following taxonomy analysis. GENEWIZ designed a panel of proprietary primers aimed at relatively conserved regions bordering the V3 and V4 hypervariable regions of bacteria and Archaea16S rDNA. The v3 and v4 regions were amplified using forward primers containing the sequence “CCTACGGRRBGCASCAGKVRVGAAT” and reverse primers containing the sequence “GGACTACNVGGGTWTCTAATCC”. 1 st round PCR products were used as templates for 2nd round amplicon enrichment PCR. At the same time, indexed adapters were added to the ends of the 16S rDNA amplicons to generate indexed libraries ready for downstream NGS sequencing on Illumina Miseq. DNA libraries were validated by Agilent 2100 Bioanalyzer (Agilent Technologies, Palo Alto, CA, USA), and quantified by Qubit 2.0 Fluorometer. DNA libraries were multiplexed and loaded on an Illumina MiSeq instrument according to manufacturer’s instructions (Illumina, San Diego, CA, USA). Sequencing was performed using a 2 × 300 paired-end (PE) configuration; image analysis and base calling were conducted by the MiSeq Control Software (MCS) embedded in the MiSeq instrument. The QIIME data analysis package was used for 16S rRNA data analysis. The forward and reverse reads were joined and assigned to samples based on barcode and truncated by cutting off the barcode and primer sequence. Quality filtering on joined sequences was performed and sequence which did not fulfill the following criteria were discarded: sequence length < 200 bp, no ambiguous bases, mean quality score > = 20. Then the sequences were compared with the reference database (RDP Gold database) using UCHIME algorithm to detect chimeric sequence, and then the chimeric sequences were removed. The effective sequences were used in the final analysis. Sequences were grouped into operational taxonomic units (OTUs) using the clustering program VSEARCH(1.9.6) against the Silva 119 database preclustered at 97% sequence identity. The Ribosomal Database Program (RDP) classifier was used to assign taxonomic category to all OTUs at confidence threshold of 0.8. The RDP classifier uses the Silva 123 database which has taxonomic categories predicted to the species level. Sequences were rarefied prior to calculation of alpha and beta diversity statistics. Alpha diversity indexes were calculated in QIIME from rarefied samples using for diversity the Shannon index, for richness the Chao1 index. Beta diversity was calculated using weighted and unweighted UniFrac and principal coordinate analysis (PCoA) performed. Unweighted Pair Group Method with Arithmetic mean (UPGMA) tree from beta diversity distance matrix was builded.
higher than the control. The content of titratable acid decreased significantly after seawater irrigation and decreased with increasing seawater irrigation years, decreasing by 0.21 (4.22%), 0.9 (18.07%) and 0.89 g / L (20.37%) after 1, 2 and 4 years, respectively. The pH value of the grapes showed a significant increasing trend, and the pH value of the grapes after 1 year, 2 years and 4 years of seawater irrigation increased by 0.2, 0.25 and 0.03, respectively. TSS / TA showed an upward trend. TSS / TA increased by 0.27 (7.34%), 0.86 (23.37%) and 1.37 (30.51%) after 1, 2 and 4 years of seawater irrigation, respectively (Table 5). The contents of anthocyanin, tannin and total phenol content in grapes increased after seawater irrigation, and the total phenol content with seawater irrigation significantly increased by 0.26 (3.62%), 0.42 (5.84%) and 3.23 mg / g (44.13%) after 1, 2 and 4 years of seawater treatment, respectively. There was no significant effect of seawater irrigation on fruit tannin content for 1 year and 2 consecutive years of seawater treatment. Fruit tannin content significantly increased by 1.4 mg / g (30.17%) after 4 consecutive years of seawater irrigation. The anthocyanin content increased significantly by 0.56 (39.44%), 0.6 (42.25%) and 0.11 mg / g after 1 year, 2 years and 4 years of seawater irrigation, respectively (Table 5). 3.2. Effect of seawater irrigation on the physical and chemical properties of soil The application of 10% seawater slowly increased soil pH and improved soil acidification. After 4 consecutive years of seawater irrigation in Guobin vineyard, the pH value of the 0–20 cm soil layer increased from 6.71 to 6.95, an increase of 0.24 units, in the 20–40 cm soil layer, irrigation after 4 years increased by 0.02 units compared with the control. In COFCO vineyard, the pH value of one year and two years of seawater irrigation increased 0.17 and 0.18 units, respectively, compared with the control in the 0–20 cm soil layer and increased 0.21 and 0.23 units in the 20–40 cm soil layer (Table 6). In this study, the bulk density of the 0–20 cm soil layer in Guobin vineyard increased by 1.67%, the specific gravity increased by 0.8% compared with the control, and the soil porosity decreased by 7.03%, but there was no significant difference from the control (Table 6). The changes in bulk density, specific gravity and soil porosity after seawater irrigation were minor and showed no significant difference from the control in the 0–20 cm and 20–40 cm soil layers (Table 6). Seawater irrigation has little effect on soil salinity, soil water-soluble salts, soil Cl− content and SO42- content increased 0.0200 g / kg (8.33%), 0.0012 g / kg (8.11%) and 0.0292 g / kg (13.19%) after 4 years of seawater irrigation compared with the control in Guobin vineyard, and there was no significant difference from the control. After 2 years of seawater irrigation, the soil water-soluble salinity, soil water content and SO42- content in COFCO vineyard increased by 0.043 g/kg (36.13%), 0.0015 g/kg (5.88%) and 0.0027 g/kg, respectively (Table 7). The total amount of water-soluble salts increased by 0.039 g/ kg (1.2%). No significant difference was observed with the control.
2.4. Statistical analysis
3.3. Effects of seawater irrigation on rhizosphere microbes
Mean and standard deviation of values, significance of difference analysis and correlation analysis were analyzed by using software SPSS statistics 20.0 (IBM, Armonk, NY, USA).
3.3.1. Effects of seawater irrigation on the rhizosphere soil microbial community Fig. 1 shows the soil microbial gene Venn diagram. It can be seen from the figure that long-term seawater irrigation had little effect on the types of microbe communities in the soil. There are a large number of the same OTUs and a few unique OTUs. There are 1207 OTUs in common between the control and 4 years of seawater irrigation in Guobin vineyard, 61 unique OTUs for the 4 years of seawater irrigation treatment and 59 unique OTUs for the control in Guobin vineyard. There are 1337 OTUs in common among the treatments in COFCO vineyard, and there were 59 and 54 unique OTUs for 1- and 2 years seawater irrigation treatments, respectively.
3. Results and discussion 3.1. Effect of seawater irrigation on Chlorophyll, Pn and grape quality In this study, seawater irrigation had no significant effect on the Chlorophyll, Pn, bu bunch weight and weight of 100 berries, which suggested that seawater irrigation didn’t affect plant and fruit growth (Table 4). Total soluble solids (TSS) increased after seawater treatment, and fruit TSS after 4 years of seawater irrigation was significantly 82
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Table 4 Effects of seawater irrigation on the plant and fruit growth.
Guobin
CK 4y CK 1y 2y
COFCO
SPAD reading
Pn (μmolm−2s-1
Bunch weight(g)
weight of 100 berries (g)
18.34 18.18 18.23 18.04 18.17
13.06 12.39 12.96 12.67 13.18
235.30 237.81 282.55 284.49 286.61
162.19 163.49 155.79 156.44 157.69
± ± ± ± ±
0.25a 0.41a 0.16a 0.32a 0.38a
± ± ± ± ±
2.04a 1.27a 1.18ab 1.04a 2.01a
± ± ± ± ±
7.37a 6.82a 7.61a 8.48a 7.22a
± ± ± ± ±
4.21a 3.85a 3.57ab 4.14a 4.00a
Note: Data are the mean ± SD; the data within a column followed by different small letters show significant differences at the 5% level. The same is true below. Table 5 Effects of seawater irrigation on the quality of grapes.
Guobin COFCO
CK 4y CK 1y 2y
titratable acid (g/l)
total soluble solids (TSS) (Brix)
pH
4.37 3.49 4.98 4.67 4.08
19.93 20.81 18.21 18.61 18.70
3.57 3.60 3.44 3.64 3.69
± ± ± ± ±
0.18a 0.12b 0.09a 0.05b 0.03c
± ± ± ± ±
2.72b 1.30a 1.35a 1.29a 1.24a
± ± ± ± ±
0.03b 0.07a 0.02b 0.06a 0.06a
TSS / TA
Total phenol contents (mg/g)
Tannin (mg/g)
Anthocyanin(μg/g)
4.49 5.86 3.68 3.95 4.54
7.32 ± 0.02b 10.55 ± 0.03a 7.19 ± 0.07b 7.45 ± 0.03a 7.61 ± 0.08a
4.64 6.04 3.06 3.00 2.94
2.60 2.71 1.42 1.98 2.02
Table 8 showed that Ace and Chao1 richness decreased after 4 years of seawater irrigation, while the Shannon and Simpson indexes were slightly reduced, and goods coverage was slightly increased in Guobin vineyard. Ace and Chao1 richness slightly increased after 1 year and 2 years of seawater irrigation, and the Shannon and Simpson indexes and goods coverage slightly increased in COFCO vineyard. However no significant difference was observed with the control in Guobin and COFCO vineyard (Table 8).
± ± ± ± ±
0.09b 0.11a 0.09c 0.05b 0.10a
± ± ± ± ±
0.01b 0.04a 0.08a 0.06a 0.05a
± ± ± ± ±
0.01b 0.01a 0.02c 0.05ab 0.03a
Table 7 Effects of seawater irrigation on soil salt content.
Guobin COFCO
3.3.2. Effects of seawater irrigation on the abundance of microorganisms in rhizosphere soil In this study, the abundance of Azoarcus, Bacillus, Bradyrhizobium, Burkholderia, Arthrobacter, Candidatus, Koribacter, Candidatus and Solibacter in the soil decreased after 4 consecutive years of seawater irrigation in Guobin vineyard, there were no significant changes between the seawater irrigation and control except for Bradyrhizobium, 84.54% lower than the abundance found in the control. The abundance of Planctomyces, Rhodoplanes, Azoarcus, Candidatus, Koribacter, Candidatus and Solibacter in soil decreased after 1 year and 2 years of seawater irrigation in COFCO vineyard, also there were no significant changes between the seawater irrigation and control except for Burkholderia, significantly decreased by 72.3% after 2 years of seawater irrigation (Table 9).
CK 1y 4y CK 1y 2y
Soil water-soluble salts (g/kg)
Soil Cl− content (g/kg)
SO42− content (g/ kg)
0.2400a 0.22a 0.26a 0.119a 0.151a 0.162a
0.0148b 0.0113a 0.016a 0.0255a 0.0262a 0.0270a
0.2213a 0.1835a 0.25a 0.1293a 0.1227a 0.1320a
the other hand, seawater has a salinity of nearly 3.5%, and moderate salinity stress affects the increase of gluconeogenesis, resulting in an increase in glucose and fructose (Cramer et al., 2007). The results of this study showed that seawater irrigation increased the soluble solids content of grapevine, reduced the titratable acid, and increased the content of phenolic compounds in grapes. Studies on tomatoes and apples showed that using seawater irrigation or spraying can significantly increase the soluble solids content of fruit and reduce apple titratable acid (Sgherri et al., 2008; Zheng et al., 2013), which is consistent with our findings. With the high production benefit of fruit, overdose of fertilizer especially nitrogen fertilizer inthe orchardleads to the soil acidification, soil acidification is an important factor that restricts the yield and quality of fruits. Soil acidification can lead to soil hardening, a decrease in the C/N ratio, and the washing away of many mineral nutrients (Ca, Mg, P, etc.) (Li et al., 2014). Soil acidification can also increase the release of some toxic metals (Cd, Cr, Pb, Mn, Al, etc.). At present, more than 1/5 of the soil in China is acidic. The pH is below 5.5, with many having a pH less than 5.0 and even below 4.5 (Chen et al., 2012).
4. Discussion Seawater is not only rich in mineral elements and chlorine, sulfate ions, bicarbonate, etc. but also contains a large amount of trace elements (Zhang, 1998). Mineral nutrition plays an extremely important regulatory role in the physiological metabolism and quality formation of grapes and other fruit trees (Wei and Jiang, 2012; Lu et al., 2011). On
Table 6 Effects of seawater irrigation on soil pH, bulk density, specific gravity and total porosity. pH 0-20 cm soil layer
Guobin COFCO
20-40 cm soil layer
Guobin COFCO
CK 4y CK 1y 2y CK 4y CK 1y 2y
6.71 6.95 6.61 6.78 6.79 6.78 6.80 6.53 6.74 6.76
± ± ± ± ± ± ± ± ± ±
0.01b 0.02a 0.01b 0.02a 0.03a 0.01a 0.01a 0.06c 0.01ab 0.02a
83
Bulk density (g/m3)
Specific gravity (mg/m3)
Total porosity (%)
1.8 ± 0.02a 1.83 ± 0.02a 1.57 ± 0.03b 1.81 ± 0.03a 1.83 ± 0.07a 1.72 ± 0.03a 1.73 ± 0.02a 1.71 ± 0.02b 1.76 ± 0.06ab 1.96 ± 0.02a
2.50 ± 0.04a 2.48 ± 0.01a 2.455 ± 0.04a 2.489 ± 0.01a 2.520 ± 0.01a 2.66 ± 0.01a 2.97 ± 0.07a 2.68 ± 0.06ab 2.61 ± 0.08ab 2.55 ± 0.05b
28.29 26.30 30.70 27.68 28.68 41.48 40.62 36.23 30.73 36.24
± ± ± ± ± ± ± ± ± ±
0.1a 0.2a 0.1a 0.3a 0.2a 0.8a 0.9a 0.2a 0.4a 0.6a
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acidification. 2 and 4 consecutive years seawater irrigation induced pH value of the 0–20 cm soil layer increased 0.18 and 0.24 units, respectively. Previous studies have shown that seawater irrigation has a negative impact on the physical and chemical properties of soil. The main problem is the decrease of soil permeability, resulting in increased soil salinity and soil solution conductivity, which reduces soil porosity. Studies showed that irrigation with brackish water with a salinity of 3–5 g/L caused varying degrees of salinization, and excess salinity caused soil compaction, resulting in decreased soil permeability, the effect of irrigation water on soil properties mainly affects exchangeable sodium and conductivity in soils (Feigen et al., 1991). In this study, after 4 years of seawater irrigation, the soil water-soluble salinity, SO42− content and total amount of water-soluble salts had no significant difference with the control. This might be due to rainfall during the growth period, as the salt in the soil gradually moves downward with rainfall. Reasonable amounts of seawater irrigation combined with reasonable rainfall leaching amounts will slow the formation of soil salinization. The depth of salt accumulation is closely related to the brackish water irrigation amount, the rainfall amount, the irrigation method and the soil properties (Hipp, 1977). Tests by Shi (Shi et al., 2005) showed that salinity in the soil surface is in a relatively balanced condition when irrigated with brackish water with a salinity of less than 3 g / L. Soil salinization does not harm plants due to rainfall or freshwater irrigation during brackish water irrigation (Wu and Wang, 2010). To ensure that the soil is not over-salted because of long-term brackish water irrigation, sufficient freshwater irrigation or heavy rainfall is required once a year (Liu et al., 2010; Wei and Jiang, 2012). The rainfall was 689.3 mm, 243.5 mm, 468.7 mm and 261.3 mm in 2013, 2014, 2015 and 2016 during the treatment of seawater irrigation, respectively. And were accounted for 76.55%, 65.72%, 71.60% and 56.67% of total annual rainfall. The rainfall amount was 246.2 mm, 3 mm, 2.1 mm and 0.4 mm in ten days after each seawater irrigation in 2013, and 6.5 mm, 8.1 mm, 12 mm and 66.8 mm in 2014, and 18.9 mm, 90.2 mm, 24.9 mm and 5.1 mm in 2015, and 2.2 mm, 41.2 mm, 44.3 mm and 3.8 mm in 2016. And the frequency of precipitation over 10 mm were thirteen, eight, eleven and seven times in 2013, 2014, 2015 and 2016 during the treatment of seawater irrigation, respectively. The frequency of heavy rainfall (precipitation over 50 mm) were five, two, two and one times in 2013, 2014, 2015 and 2016 during the treatment of seawater irrigation (Fig. 2). With the rainfall of Penglai during the growth period, the leaching effect was obvious. The pH value of the soil significantly increased without causing salt accumulation and soil salinization. Therefore, seasonal heavy rainfall or reasonable and effective irrigation measures can effectively prevent the occurrence of soil salinization. The soil microbial biomass is the principle component of the decomposer subsystem regulating nutrient cycling, energy flow and ultimately plant and ecosystem productivity, is a major indicator of soil development, and biochemical intensities often affect the conversion factors and pools of nutrients required by plants. Moreover, changes in the soil microbial population and community structure are important biological indicators of soil environmental quality assessment, which can reflect soil quality and health condition (Zhang et al., 2008). Bacteria, actinomycetes and fungi are the main biomass components of soil microorganisms (Mackay et al., 2016). They are involved in the synthesis of organic compounds in soil and closely related to the formation of soil fertility (Yao and Huang, 2006). Studies have shown that salt stress will undermine the microbial community structure in the soil to some extent, reducing soil bacteria (Yang and Xu, 2002). Our result showed that 2 and 4 consecutive years of seawater irrigation had little effect on soil microbial biomass. Which suggested that combined with seasonal heavy rainfall, seawater irrigation can effectively prevent the decrease of soil microbial biomass.
Fig. 1. OTU Venn diagram analysis of different irrigation treatments. Gck, control at Guobin vineyard; G4, 4 years seawater irrigation treatment at Guobin vineyard; Zck, control at COFCO vineyard; Z1, 1 year seawater irrigation treatment at COFCO vineyard; 2 years seawater irrigation treatment at COFCO vineyard. Table 8 Analysis of diversity differences between different groups.
Guobin COFCO
Sample
Ace
Chao1
Shannon
Simpson
Goods coverage
Control 4y Control 1y 2y
1504.82a 1501.19a 1637.62a 1688.05a 1672.36a
1529.06a 1525.25a 1656.71a 1724.40a 1689.58a
8.72a 8.71a 8.84a 8.88a 8.98a
0.993a 0.992a 0.993a 0.993a 0.994a
0.9937a 0.9940a 0.9937a 0.9937a 0.9940a
Table 9 Taxa Statistics at the Genus level. Genus
Aquicella Nitrospira Planctomyces Rhodoplanes Azoarcus Bacillus Paenibacillus Sphingomonas Bradyrhizobium Burkholderia Arthrobacter Candidatus_Koribacter Candidatus_Solibacter
Guobin
COFCO
Control
4y
Control
1y
2y
0.1633a 0.1333a 0.200a 0.0867a 0.1000a 0.5733a 0.0333a 0.2733a 0.0102a 0.0967a 0.0100a 0.0867a 0.0367a
0.1967a 0.2033a 0.2767a 0.1733a 0.0800a 0.4800a 0.0567a 0.3633a 0.0003b 0.015a 0.0033a 0.0767a 0.0233a
0.5933a 0.3767a 0.5533a 0.2167a 0.2233a 0.5800a 0.0467a 0.3000a 0.0600b 0.1500a 0.0133a 0.0867a 0.0133a
0.8633a 0.3967a 0.5067a 0.1367a 0.1600a 0.8800a 0.0600a 0.3267a 0.1533a 0.0567a 0.0300a 0.0733a 0.0137a
0.9267a 0.4633a 0.5300a 0.1800a 0.1700a 0.7667a 0.1533a 0.3367a 0.1033a 0.0600b 0.0200a 0.0700a 0.0103a
According to a survey, the average pH value of soil in China has been reduced by 0.6 units on average over the past 30 years, and the area of acidic cultivated land has risen by 7% to the current level of 18%. According to a survey, soil acidification is particularly serious in the orchards of the Jiaodong Peninsula, China, with an average pH value of approximately 5.2 (Ge et al., 2014), which seriously affects fruit tree growth. The pH value of seawater is 8.0–8.5, and to a certain extent, can improve acidified soil. Our result showed that application of 10% seawater for irrigation slowly raised soil pH and improved soil
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Fig. 2. The rainfall in Penglai from 2013 to 2016 during the treatment of seawater irrigation.
5. Conclusion
without inducing secondary soil salinization problems.
In summary, combined with rainfall amount of over 240 mm and more than once heavy raifall from fruit expansion to late veraison period, the use of 10% seawater irrigation in the grape growing season over four years can improve fruit quality and increase the soil pH, which effectively alleviates the harm caused by soil acidification
Acknowledgements This research was supported by the China agricultural research system(CARS-29-zp-02), Program for Changjiang Scholars and Innovative Research Team in University(IRT15R42). 85
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