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Article

Correlations among Soil Properties, Growth Characteristics, and Ginsenoside Contents in Wild-Simulated Ginseng with Different Ages

by
Yeong-Bae Yun
,
Jeong-Hoon Huh
and
Yurry Um
*
Forest Medicinal Resources Research Center, National Institute of Forest Science, Yeongju 36040, Gyeongbuk, Republic of Korea
*
Author to whom correspondence should be addressed.
Forests 2022, 13(12), 2065; https://doi.org/10.3390/f13122065
Submission received: 22 November 2022 / Revised: 24 November 2022 / Accepted: 30 November 2022 / Published: 4 December 2022
(This article belongs to the Section Forest Soil)
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Abstract

:
Wild-simulated ginseng (WSG) is naturally cultivated in forest environment without any artificial facilities or chemicals. Soil property is one of the major factors affecting the growth and active compound synthesis of vegetation. Therefore, growth characteristics and ginsenoside contents of WSG can be affected by soil properties of the cultivation field. Therefore, the aim of this study was to investigate correlations among soil properties, growth characteristics, and ginsenoside contents of WSG with different ages using Spearman’s coefficient analysis method. It was found that most of growth characteristics of WSG except for rhizome length were significantly increased in 7-year-old WSG for both the above-ground part and root part. Soil pH, and exchangeable cations (Ca, Mg) of 13-year-old WSG cultivation site were significantly higher than those of 4-year-old WSG. However, available phosphate of 4-year-old WSG soil was higher than that of 13-year old WSG soil. Contents of ginsenosides of 4-year-old WSG were higher than those of 13-year-old WSG in the above-ground part. Otherwise, in the root part, contents of ginsenosides of 13-year-old WSG were higher than those of 4-year-old WSG. In correlation analysis, growth characteristics of 4-year-old WSG were correlated with more ginsenoside types. Correlations between soil properties and ginsenoside contents in leaves and roots of WSG with the same age also differed. These results suggest that soil properties play essential role in growth and ginsenoside synthesis of WSG. Based on results of this study, growth characteristics, soil properties, and ginsenoside contents of WSG in different WSG cultivation sites need to be further investigated to identify the most suitable cultivation site for WSG.

1. Introduction

Wild-simulated ginseng (Panax ginseng C.A. Meyer, WSG) belongs to the genus Panax of the family Araliaceae. WSG has been one of the important traditional medicines or foods [1]. It is native to Republic of Korea, Japan, North Korea, Russia, and China [2]. WSG can be cultivated through sowing its seeds or transplanting of seedlings in a mountainous area [3]. In Korea, WSG is defined as a kind of ginseng produced without any artificial facilities or chemical compounds. Recently, due to infectious diseases such as SARS, MERS, and COVID-19 that can rapid spread globally, interest in enhancing the immunity and demand for WSG are increasing [4]. The Korea Forest Service is promoting industrial revitalization through scientific research studies, such as the development of standard cultivation methods for WSG, transparency of distribution and processing, and verification of pharmacological components and efficacy [5].
The number of farmhouses and cultivation area of WSG has steadily increased. Furthermore, the production amount of WSG has increased from 26 tons in 2013 to 158 tons in 2020. The cost of production was increased from $27.3 million in 2012 to $38.8 million in 2020 [6]. However, since information on quality standards of WSG is insufficient, it is difficult to set the selling price of WSG by year. Therefore, it is necessary to strengthen the transparency of the WSG distribution market by presenting scientific evidence to distinguish differences in growth characteristics and ginsenoside contents of WSG with different ages and soil properties.
WSG grows and reproduces well with specific conditions: acidic or weak acidic soil (pH 4–6), 10–30° slope, sufficient organic matter (OM), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) [4]. According to soil conditions, growth characteristics and ginsenoside contents of WSG show large differences. In experimental fields with higher contents of soil OM, total nitrogen (TN), cation exchangeable capacity (CEC), and higher temperatures, WSG shows better growth characteristics [7]. Furthermore, contents of ginsenosides (Rb1, Rb2, Rc, Rd, Re, Rf, Rg1, Rg2) showed significantly positive correlation with various growth characteristics of WSG [7]. Ginsenosides are named according to their retention factor (Rf) in thin layer chromatography (TLC).
Active compounds of cultivated ginseng and WSG include ginsenosides, phytosterol, flavonoids, and polyacetylene [8,9,10]. Ginsenosides can be divided into two groups, protopanaxadiol and protopanaxatriol, according to their molecular structures [11]. They show various pharmacologically beneficial effects, including anti-inflammatory activity, antioxidation, vasorelaxation, antidiabetic, antiallergic, and anticancer effects [2,12]. Compositions and contents of ginsenosides are different depending on the part of the plant [above-ground part (leaf, stem) and root part], cultivation period, and cultivation area of WSG [13]. Contents of ginsenoside Rb1 and Re were significantly higher in 9-year-old WSG than in 3-, 5-, and 7-year-old WSG [14]. However, studies on growth characteristics, ginsenoside contents, and soil chemical properties of WSG by year are insufficient. Therefore, the aim of this study was to investigate correlation among soil properties, growth characteristics, and ginsenoside contents of WSG with different ages. Since the growth characteristics and ginsenoside content of WSG largely can be affected by soil properties, we investigate the correlation among these factors (soil properties, growth characteristics, ginsenoside content) of WSG with different ages. The results of this study may help for selection of the most optimal conditions for cultivation of WSG.

2. Materials and Methods

2.1. Determination of Soil Properties in WSG Cultivation Site and Growth Characteristics of WSG

WSG samples of different ages (4-, 7-, 10-, 13-year-old) from five cultivation sites (Pyeongchang, Muju, Sancheong, Yeongwol, Yeongju) were collected from July to September 2021 (five replicates for each, Figure 1 and Table S1). These collected samples were washed with sterilized distilled water and dried under natural shade at room temperature (20 °C) until the surface moisture was removed. After observing morphological characteristics of samples, they were stored at −70 °C. Cultivated ginseng was used as a control for ginsenoside content analysis of WSG. All samples were dried in a freeze dryer (FD8518, Ilshin, Republic of Korea) and then pulverized with a grinder (HMF-4070TG, Hanil Electric Co., Ltd., Wonju, Republic of Korea). Powder samples were passed through an 80-mesh standard sieve and stored at 70 °C.
One-hundred gram of rhizosphere soils in each WSG cultivation area was collected at a depth within 20 cm after removing surface soils. Soil samples collected from WSG cultivation sites were dried at room temperature (20 °C) and then passed through a 10-mesh sieve. Analysis of soil properties was performed following the standard analysis manual of the Rural Development Administration (RDA) in Korea [15]. Briefly, after diluting dried soil and distilled water (1:5), pH and electrical conductivity of soil were measured by pH meter and EC meter, respectively. Organic matter was measured using Walkey-Black method and available phosphate was measured using spectrophotometer and 1-amino-2-naphtol-4-sulfanic acid according to the Lancaster extraction method. Total nitrogen was measured by Kjeldhal method after digesting the sample using sulfuric acid and block digester. Cation exchange capacity were measured using 1 N-NH4OAc and Kjeldhal method and exchangeable cations were measured by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). According to the Test Guideline of each crop (ginseng), growth characteristics, including stem length, stem diameter, the number of leaflets per stem, petiole length, leaflet length, leaflet width, root weight, total weight, rhizome length, root length, main root diameter, the number of rootlets, and dry weight, were measured [16].

2.2. Sample Extraction and Reagents

To assess ginsenoside contents in collected WSG, 10 mL of 80% methanol was added to 0.2 g of each pulverized sample. Extraction was performed for 1 h with a sonicator (JAC-5020, KODO, Wonju, Republic of Korea). Stirring extraction was then performed using a stirrer (HG-15D, Daihan, Wonju, Republic of Korea) for 1 h. Extracts were centrifuged at 3000 rpm for 10 min using a centrifuge instrument (Labogene, BMS, Republic of Korea). Supernatants were filtered with 0.2 µm membrane filters (Whatman, Maidstone, United Kingdom) [7]. Ginsenoside standards used for analysis were purchased from ChromaDex (Los Angeles, CA, USA). All reagents used for ginsenoside extraction and HPLC analysis, including methanol, acetonitrile, and distilled water, were purchased from J.T. Baker (Easton, PA, USA).

2.3. Analysis of Ginsenoside Contents of WSG

Analysis of ginsenoside contents was performed using an Ultimate 3000 HPLC (Thermo Dionex, Waltham, MA, USA). The column used for the analysis was an Inno C-18 column (4.6 × 250 mm, 5 µm, Youngjin Biochrom, Seongnam-si, Republic of Korea). The oven temperature was set to be 50 °C and maintained. For mobile phase, solvent A and solvent B were set to be water and acetonitrile, respectively. Solvent conditions over time were analyzed by gradient elution as follows: 0–1 min, 5% B; 1–45 min, 70% B; 45–55 min, 95% B; and 55–60 min, 5% B. The analysis time for each sample was set to be 60 min. Flow rate was 1.0 mL min−1 and injection volume was 10 µL. Absorbance of each sample was measured at 210 nm using a photodiode array (PDA) detector. Ginsenoside standards at concentration of 10, 25, 50, and 100 µg mL−1 were used to prepare a calibration curve. Components of each sample were then quantitatively analyzed [7].

2.4. Data Analysis

Data are expressed as mean ± standard error (S.E.). Statistical analysis was performed using Statistical Analysis System (SAS) software (version 9.4, SAS Institute, Cary, NC, USA) for one-way analysis of variance (ANOVA) and Tukey’s test, with statistical significance was set at p < 0.05 [17]. Correlation analyses among soil properties in WSG cultivation sites, growth and ginsenoside contents of WSG were conducted using Spearman’s coefficient analysis (IBM SPSS Statistics, version 25, IBM Corp., Armonk, NY, USA).

3. Results and Discussion

3.1. Soil Properties of Cultivation Sites Collecting WSG with Different Ages

Regarding soil chemical properties of WSG cultivation sites, the soil with 13-year-old WSG cultivated had significantly higher pH (p < 0.0003), Ex. Ca (p < 0.02), and Ex. Mg (p < 0.0109) than soil with 4-year-old WSG cultivated (Figure 2, Table S2). However, available phosphate (p < 0.0468) in 4-year-old WSG cultivation soil was higher than that of 13-year-old WSG cultivation soil. Soil pH and contents of exchangeable cations (Ca, Mg) were significantly increased with increasing cultivation period, while contents of available phosphate were significantly decreased. It was thought that WSG may take up phosphate for its growth. Kim et al. [18] investigated various soil chemical properties and the contents of available phosphate showed ranging from 41.9 ppm to 752.7 ppm in different cultivation areas. Therefore, we observed that the results of this study were the same as those of previous studies.
Phosphate in soil can exist as inorganic form and phosphate bound to organic matter. Inorganic forms are very stable and converted to available phosphate form via weathering and bacterial degradation. The solubilization of phosphate by phosphate-solubilizing microbes (PSMs) is associated with the production of organic acids and proton (H+) release resulting in acidification of soils [19]. PSMs have been shown to release a variety of organic acids, including acetic acid, oxaloacetic acid, citric acid, gluconic acid [20], various bacterial (Pseudomonas, Bacillus, Burkholderia, Rhizobium) and fungal (Aspergillus, Penicillium) genera have been shown to possess phosphate-solubilizing abilities [21]. Huh et al. [22] isolated nitrogen fixing bacteria from wild-simulated ginseng cultivation areas. Among isolated nitrogen fixing bacteria, since there were Burkholderia and Bacillus genera, it can be thought that solubilization of phosphate in soil may have progressed. In the study of solubilization of phosphate using biofertilizer Pantoea agglomerans (Enterobacter agglomerans), 698 ppm and 912 ppm of CaHPO4 and hydroxyapatite were solubilized, respectively [23]. It showed better efficiency of phosphate solubilization than Penicillium radicum (176 ppm of CaHPO4) and Rahnella aquatilis (230 ppm of hydroxyapatite) [23,24]. Since the type of insoluble phosphate in the soil of WSG cultivation area and the type of inhabiting bacteria are different, it is thought that the level of available phosphate may be different. In the future, if a study on the soil microbial community in various WSG cultivation areas is conducted, it is thought that the cause of the change in the available phosphate content can be identified. Eo et al. [25] reported that fused calcium magnesium phosphate (17% phosphorus) can enhance the growth of WSG. They explained that phosphorus could greatly affect the growth of WSG. As strategies to improve WSG growth and phosphate nutrition, phosphobacteria, including phosphate solubilizing bacteria and phosphate mineralizing bacteria, were collected and identified as described previously [26]. For enhancing the growth of high-age WSG, rhizospheric microorganisms play an essential role in facilitating phosphate nutrition. Furthermore, since the cultivation of WSG does not allow the use of any chemicals, microorganisms have been recognized for their potential use as an environmentally friendly alternative to chemical phosphate fertilization. The photosynthetic rate of WSG leaves was significantly lower in an environment where phosphorus was insufficient [27]. Furthermore, the size of WSG was smaller than that of cultivated ginseng since its growth rate was lower [28].

3.2. Growth Characteristics and Ginsenoside Contents of WSG with Different Ages

Growth characteristics of 4-year-old WSG were significantly lower than those of WSG with other ages. Especially, stem length (p < 0.0001), stem diameter (p < 0.0001), number of leaflets per stem (p < 0.0001), petiole length (p < 0.0001), leaflet length (p < 0.0001), leaflet width (p < 0.0001), root weight (p < 0.0001), and main root diameter (p < 0.0001) of 4-year-old WSG were significantly different from those of WSG with other ages. Total weight (p < 0.0001), root length (p < 0.0006), and dry weight (p < 0.0052) of 7-year-old WSG were significantly higher than those of 4-year-old WSG. It was found that most of growth characteristics of WSG except for rhizome length were significantly increased in 7-year-old WSG for both the above-ground part and root part (Figure 3, Table S3). In a previous study, when growth characteristics of 3-, 5-, 7-, and 9-year-old WSG were compared, rhizome length and total weight were increased with increasing cultivation period. However, root length and main root diameter were significantly lower in 9-year-old WSG than in WSG with younger ages [14]. These different results can be affected by the location environment of different WSG cultivation areas. Kim et al. [4] have reported that a cultivated region composed of mixed forests with a high proportion of conifers is suitable for WSG cultivation. Factors that can increase growth characteristics of WSG have been reported to be high average height of tree, high ratio of coniferous trees in cultivation area, high above sea level, and low slope. As a result of topography in this study, the slope directions of wild-simulated ginseng cultivation were southwest, southeast, northeast and northwest, the slope was 8–25°, the above sea level was 391–931 m, and the soil texture was silty clay loam, loamy sand, and sandy loam. In forest physiognomy of cultivation areas, Pyeongchang was mixed forest condition dominated with Ulmus davidiana (69.2%) and Pinus densiflora (15.4%) and it consists of Betula dahurica and Quercus mongolica. Larix kaempferi (55.6%) and Morus alba (44.4%) were dominated in Muju. In Sancheong, P. densiflora (63.6%) and Q. mongolica (36.4%) were domiated. B. platyplhylla (50.0%), Plathcarya strobilacea (18.6%), and Quercus variabilis (12.5%) were dominated in Yeongwol and it also consists of Prumus sargentii, Pinus densiflora, and Morus bombycis. In Yeongju, Q. mongolica (70.0%) and Robinia pseudoacacia (26.7%) were dominated. Furthermore, the average values of diameter at breast height and tree height in WSG cultivation sites were 19.9 cm and 13.5 m, respectively (Table S1). The Standard Manual for Wild-simulated Ginseng Cultivation has suggested that optimal cultivation condition for WSG is a mixed forest with more than 15 cm of diameter at breast height and more than 10 m of tree height [29].
Results of ginsenoside contents analysis of different year-old WSG showed significant differences between above ground part and root part (Figure 4, Table S4). In the above ground part, contents of Rb2, Rb3, Rc, Rd-p, and Rg3 in 4-year-old WSG were significantly higher than those in 13-year-old WSG. However, F2-AS was higher in 13-year-old than in 4-year-old WSG. In the root part, contents of F2-AS and Rd-p in 4-year-old WSG were higher than those in 13-year-old WSG. However, Rb1, Rf-p, Rg1, and Ro were significantly higher in 13-year-old WSG than in 4-year-old WSG. Especially, the content of ginsenoside Rd-p in both above ground part and root part was higher in 4-year-old WSG than older WSG. Kim et al. [7] reported that the content of Rd-p was higher in 13-year-old WSG than 7-year-old WSG. The difference in the content of ginsenoside might be affected by collection period and the location environments. Furthermore, the content of Rd-p in above ground part (15,664.18 mg/kg) was about 10-fold higher than that in root part (1582.31 mg/kg). The beneficial effects of Rd-p were antitumor [30], cardiac hypertrophy [31] and neuroprotective effect [32,33]. When manufacturing pharmacological products or health functional foods using WSG, it is thought that the products using the above-ground parts together may show higher efficiency in terms of economy and efficacy.

3.3. Correlations between Growth Characteristics and Ginsenoside Contents of WSG with Different Ages

In the above-ground part of 4-year-old WSG, stem length showed significant negative correlations with F1, Rb1, and Rd-p, while it had significant positive correlations with F2-AS and Re-p (Table S5A). Leaflet width in 4-year-old WSG showed significantly negative correlation with F1 and Rg6. Leaflet length showed significantly positive correlation with F2-AS in 4- and 7-year-old WSG. In 7-year-old WSG, leaflet width showed significantly positive correlation with F2-AS and it had significantly negative correlations with Rb1, Rb2, Rb3, Rc, Rd-p, and Ro. In 10-year-old WSG, petiole length showed significantly positive correlation with 10 out of 16 ginsenosides. In the root part of WSG, total weight showed significantly negative correlation with F2-AS in 4-year-old WSG (Table S5B). However, most of the ginsenoside contents in WSG cultivated for more than 7 years showed positive correlation with root weight and root diameter of WSG. The number of rootlets of WSG showed significantly positive correlation with various ginsenoside [Ro (4-year), compound K, Rb1, Rb3, Re-p, Rg1, Rg6 (7-year), Rd-p, Rg3 (10-year), and Rh1 (13-year)].
In older than 4-year-old WSG, both growth characteristics and ginsenoside contents in above-ground part and root part showed significant positive correlations. Kim et al. [34] have reported that ginsenoside contents show significant positive correlations with rhizome length, total weight, and volume. This result might be due to the influence of rhizosphere microorganisms or endophytes inhabiting the cultivated area [35]. Efficient bacterial and fungal strains are a rich source of natural products that can improve crop yield in various biological ways, including plant nutrient availability (nitrogen fixation, siderophores), phytohormone (auxin, ethylene, cytokinin, and gibberellins) modulation, and mobilization of insoluble nutrients (phosphate solubilization). Additionally, these microorganisms have potential for biocontrol of phytopathogens and pest insects, stress tolerance, and bioremediation [36]. Plant growth-promoting rhizobacteria and endophytes have diverse beneficial effects on host plants through different mechanisms. These microorganisms are generally referred to as plant growth-promoting microbes (PGPMs). Roots of the plant can release exudates containing nutrients and compounds that can be used by PGPM for their development. The inoculation of PGPM into plants is considered an environmentally friendly alternative to chemical fertilization [37]. To improve the growth of younger WSG, additional studies are needed to investigate the ability of rhizobacteria and endophytes to enhance soil quality for cultivating WSG. It was revealed that the growth characteristics of above-ground part in 4-year and 7-year-old WSG showed significantly negative correlation with most of ginsenoside contents. However, the growth characteristics of root part in cultivated more than 7-year-old WSG showed significantly positive correlation with ginsenoside contents. Fang et al. [38] reported that growth years might affect the expression of genes for ginsenoside biosynthesis by influencing the expression of the transcription factors, such as myeloblastosis, APETALA2/ethylene-responsive factor (AP2/ERF) and basic helix-loop-helix (bHLH). According to the results of this study, it is suggested that some of the genes involved in the ginsenoside biosynthesis pathway may be suppressed by growth-related genes in younger aged WSG. Furthermore, at a cultivation age higher than 7 years, ginsenoside biosynthesis genes can be expressed together with genes related in WSG growth due to the influence of the cultivation environment, and it is thought to show a significant positive correlation.

3.4. Correlation between Soil Properties of Cultivation sites and Ginsenoside Contents of WSG with Different Ages

In the soil of 7-year-old WSG cultivation site, pH showed positive correlation with F2-AS and Rf-p in 13-year-old WSG (Table S6A). Exchangeable magnesium (Ex. Mg) in the soil of 13-year-old WSG cultivation site showed significantly positive correlation with F1, F2-AS, Rc, Rd-p, and Re-p. Organic matter and total nitrogen in the soil of 13-year-old WSG cultivation site showed significantly positive correlation with Rb3, Rf-p, Rg1, Rg2-s, and Rh1. Furthermore, cation exchange capacity in 13-year-old WSG cultivation soil showed significantly positive correlation with Rf-p, Rg1, and Rh1. Interestingly, in the root part, electrical conductivity, organic matter, total nitrogen, exchangeable magnesium, and cation exchange capacity in the soils of 4- and 7-year-old WSG cultivation sites showed significantly negative correlation with the contents of Rb1 and Rb3. However, in 13-year-old WSG cultivation soil, exchangeable magnesium showed significantly positive correlation with Rb3 and Rh1 (Table S6B). Generally, organic matter, total nitrogen, and cation exchange capacity have a high correlation in the natural vegetation [39]. The correlation between soil properties and bacterial community in WSG cultivation sites showed that the soil bacterial community is significantly correlated with soil pH, organic matter, total nitrogen, and cation exchange capacity [17]. There may be differences in the distribution of the microbial community in different year-old WSG cultivation areas. Therefore, if a study on the soil microbial community in various WSG cultivation areas is conducted, it is thought that the effect of microbial community for change in the soil properties and ginsenoside contents also can be identified.
Since ginseng might require more calcium to grow [40], the biosynthesis of ginsenoside can also be affected by calcium in WSG cultivation soil. Furthermore, since ginseng plants take up calcium more readily in soils, calcium deficiencies can be seen in stunted ginseng that lack general vigor with smaller and more fragile growth buds [41,42]. In Brassica rupestris Raf., there are no significant correlations between soil physical parameters and phytochemicals in Brassica leaves. However, soil chemical and biochemical properties can influence total antioxidant capacity and the synthesis of carotenoids and glucosinolates [43]. The most important soil factors influencing amounts of phytochemicals in B. rupestris are soil organic matter, dehydrogenase activity, fluorescein diacetate hydrolysis, microbial biomass carbon, and humic acid/fulvic acid ratio. The decrease in the synthesis of chlorophylls, carotenoids, and anthocyanins in B. rupestris grown on soil with scarce fertility shows that soil fertility can directly influence pigment production in plants [44]. It has been previously confirmed that soil fertility can affect secondary metabolite production in Stevia rebaudiana [44]. Zhang et al. [45] have reported that photosynthetically active radiation (PAR) and soil water potential have a greater impact on ginsenoside accumulation in root tissues, while temperature and relative humidity have a greater impact on ginsenoside accumulation in leaf tissues.
The biosynthesis of ginsenosides as secondary metabolites and active compounds of WSG is regulated by various environmental factors and the expression of enzyme genes [46]. These factors include external environmental factors (light, temperature, water, salinity, etc.) and internal developmental genetic circuits (regulated gene, enzyme) [11,45,47]. When ginsenoside contents of WSG were measured, not all parts of WSG contained both Rg5 and Rk1 (Table S4). Contents of F1 and F2-AS in the above-ground part were 100 times higher than those in the root part. The content of Rd-p in the above-ground part was 10 times higher than that in the root part. Contents of Re-p, Rg1, and Rg3 in the above-ground part were 3–8 times higher than those in the root part. In contrast, content of Rb1 in the root part was 10 times higher than that in the above-ground part. Contents of Rf-p and Ro in the root part were 4–7 times and 2–5 times higher than those in above-ground part, respectively (Table S4). Ginsenosides can be divided into two types: protopanaxadiol type and protopanaxatriol type [48]. The content of ginsenoside Rb1 of the protopanaxadiol type showed 10–15 times higher in the root part than in the above-ground part. Contents of other ginsenosides except for Rb1 were 2–100 times higher in the above-ground part than in the root part. Kim et al. [7] have reported that contents of both protopanaxadiol type ginsenosides (Rb1, Rb2, Rc, and Rd) and protopanaxatriol type ginsenosides (Re, Rf, Rg1, and Rg2) show significantly positive correlations with root weight, cross-section area, surface area, and volume of WSG. When ginsenoside contents are analyzed according to harvest period and cultivation conditions, Rg1, Rb1, Rc, and Re are mainly detected [49,50]. In the same 7-year-old WSG, contents of ginsenosides were 4.5-6.5 time higher in WSG harvested in spring than in those harvested in autumn [51]. Moon [52] has also reported that ginsenoside compositions are different depending on cultivation region of WSG. Kang and Kim [53] have reported that the content of Rd in the above-ground part is 20 times higher than that in the root part and that the content of Rb1 in the root part is 10 times higher than that in above-ground part, similar to results of the present study. Since WSG is naturally cultivated without any artificial facilities or chemicals, ingestion of the whole plant is possible.
In conclusion, this study provides an overview of the soil chemical properties of WSG cultivation sites, growth characteristics and ginsenoside contents of WSG with different ages using Spearman’s coefficient analysis method. Comparing growth characteristics and ginsenoside contents of WSG, 4-year-old WSG showed significantly lower growth characteristics and ginsenoside contents than WSG with other ages. Growth characteristics of WSG cultivated for more than 7 years showed significant differences compared to those cultivated for 4 years. These results showed that the growth and ginsenoside contents of WSG increased with the longer duration of cultivation period with soil properties of high soil pH, calcium, and magnesium. Based on the results of this study, we observed that the contents of ginsenosides can be significantly affected by WSG cultivation soil properties (pH, electrical conductivity, organic matter content, total nitrogen content, exchangeable cations content, available phosphate content, cation exchangeable capacity) and growth characteristics (stem length, petiole length, leaflet length, leaflet width, total weight, dry weight, root weight, root diameter, root length, number of rootlets). Therefore, the geographical requirements are the most important to improve the growth and ginsenoside content of WSG. Prior to cultivation of WSG, it is considered essential to find the optimal environment for growing WSG through analysis of forest physiognomy and soil characteristics of WSG cultivation candidates. In addition, soil bacterial community of the planned WSG cultivation sites also should be analyzed to investigate the pathogenic bacterial strains and beneficial endophytes inhabiting in the soil of WSG cultivation sites. Ginsenoside contents of WSG were significantly increased with increasing cultivation periods. In WSG with high ages, contents of various ginsenosides showed significantly positive correlations with growth characteristics, with contents in the above-ground part showing significantly more correlations with growth characteristics than those in the root part. These results suggest that consuming the whole part of WSG is more beneficial than consuming only the root part of cultivated ginseng. In addition, to identify the most suitable cultivation conditions for WSG, the study of growth and ginsenoside content of WSG with different regions will be investigated.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/f13122065/s1. Table S1 shows location environments of wild-simulated ginseng cultivation sites; Table S2 shows soil chemical properties of the rhizosphere planted wild-simulated ginseng with different ages; Table S3 shows growth characteristics of wild-simulated ginseng with different ages; Table S4 shows ginsenoside contents of wild-simulated ginseng with different ages; Table S5 shows comparison of correlation between growth characteristics and ginsenoside contents of WSG with different ages; Table S6 shows comparison of correlation between soil properties and ginsenoside contents of wild-simulated ginseng with different ages.

Author Contributions

Y.-B.Y. and Y.U. designed and performed experiments and performed data analysis and discussion; J.-H.H. assisted in soil sampling and experiments; Y.U. assisted in data analysis and discussion; Y.-B.Y. wrote the manuscript; Y.-B.Y. and Y.U. performed critical reviewing and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Institute of Forest Science (NIFoS) (grant number FP0802-2022-03 and 2021377A00-2123-BD02).

Data Availability Statement

The data and analyses from the current study are available from the corresponding author upon reasonable request.

Acknowledgments

This work was supported by the research of National Institute of Forest Science (NIFoS).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Sampling locations of wild-simulated ginseng. PC: Pyeongchang, YW: Yeongwol, YJ: Yeongju, MJ: Muju, SC: Sancheong.
Figure 1. Sampling locations of wild-simulated ginseng. PC: Pyeongchang, YW: Yeongwol, YJ: Yeongju, MJ: Muju, SC: Sancheong.
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Figure 2. Soil properties of the rhizosphere planted wild-simulate ginseng with different ages. Value in each column with different letters are statistically differences (p < 0.05) among the treatments according to Tukey’s test (n = 25).
Figure 2. Soil properties of the rhizosphere planted wild-simulate ginseng with different ages. Value in each column with different letters are statistically differences (p < 0.05) among the treatments according to Tukey’s test (n = 25).
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Figure 3. Growth characteristics of wild-simulated ginseng with different ages. (A) Above-ground part, (B) Root part, (C) Weight. Value in each column with different letters are statistically differences (p < 0.05) among the treatments according to Tukey’s test (n = 25).
Figure 3. Growth characteristics of wild-simulated ginseng with different ages. (A) Above-ground part, (B) Root part, (C) Weight. Value in each column with different letters are statistically differences (p < 0.05) among the treatments according to Tukey’s test (n = 25).
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Figure 4. Ginsenoside contents of wild-simulated ginseng with different cultivation periods. (A) Above-ground part, (B) Root part. Value in each column with different letters are statistically differences (p < 0.05) among the treatments according to Tukey’s test (n = 25).
Figure 4. Ginsenoside contents of wild-simulated ginseng with different cultivation periods. (A) Above-ground part, (B) Root part. Value in each column with different letters are statistically differences (p < 0.05) among the treatments according to Tukey’s test (n = 25).
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Yun, Y.-B.; Huh, J.-H.; Um, Y. Correlations among Soil Properties, Growth Characteristics, and Ginsenoside Contents in Wild-Simulated Ginseng with Different Ages. Forests 2022, 13, 2065. https://doi.org/10.3390/f13122065

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Yun Y-B, Huh J-H, Um Y. Correlations among Soil Properties, Growth Characteristics, and Ginsenoside Contents in Wild-Simulated Ginseng with Different Ages. Forests. 2022; 13(12):2065. https://doi.org/10.3390/f13122065

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Yun, Yeong-Bae, Jeong-Hoon Huh, and Yurry Um. 2022. "Correlations among Soil Properties, Growth Characteristics, and Ginsenoside Contents in Wild-Simulated Ginseng with Different Ages" Forests 13, no. 12: 2065. https://doi.org/10.3390/f13122065

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