Effects of Different Planting Densities of Solanum nigrum L. on the Growth and Cadmium Uptake of Young Grapevines
by
, ,
Yuanxiang Yang
1, 
Qinfeng Zheng
1,
Jin Wang
2,
Xiulan Lv
2,
Dong Liang
2,
Renyan Liao
3,* and
Lijin Lin
2,* 1
College of Environmental Sciences, Sichuan Agricultural University, Chengdu 611130, China
2
College of Horticulture, Sichuan Agricultural University, Chengdu 611130, China
3
College of Traditional Chinese Medicine and Rehabilitation, Yaan Polytechnic College, Yaan 625000, China
*
Authors to whom correspondence should be addressed.
Agronomy 2024, 14(12), 3056; https://doi.org/10.3390/agronomy14123056
Submission received: 13 November 2024
/
Revised: 17 December 2024
/
Accepted: 20 December 2024
/
Published: 21 December 2024
(This article belongs to the Section Innovative Cropping Systems)
Abstract
:We determine the best planting density of Solanum nigrum L. when intercropping with young grapevines to decrease cadmium (Cd) uptake by young grapevines. The effects of different planting densities (plant spacing × row spacing, in centimeters, and designated as 40 × 80, 40 × 40, 20 × 40 and 20 × 20, respectively) of S. nigrum on the growth and Cd uptake of young grapevines were studied. The 40 × 80 and 40 × 40 treatments increased the biomass, photosynthetic pigment content and photosynthesis of young grapevines, while the 20 × 40 and 20 × 20 treatments decreased these traits compared with the monoculture. With increasing intercropping density, the antioxidant enzyme activity of both plant species increased. Intercropping with S. nigrum decreased the Cd content in young grapevines, and the 40 × 80, 40 × 40, 20 × 40 and 20 × 20 treatments decreased the shoot Cd content in young grapevines by 20.89%, 26.11%, 38.12% and 45.95%, respectively, compared with the monoculture. Additionally, increasing the intercropping density increased the Cd content and extraction of S. nigrum. Thus, intercropping young grapevine with S. nigrum can decrease Cd uptake in young grapevines while remediating soil Cd-contamination, and the most optimal treatment is 20 × 20 in this experiment.
1. Introduction
With industrial and agricultural development, the input of the heavy metal cadmium (Cd) into the soil environment has increased [1], resulting in a rise in soil Cd levels and a threat to human health [2,3]. As a non-essential element in plants, long-term exposure to the Cd-contaminated environments inhibits plant photosynthesis, triggers oxidative stress and thus inhibits plant growth [4,5]. Studies have shown that several types of agricultural land (including orchards) have been impacted by Cd contamination, which seriously affects crop growth and food safety [6,7]. Therefore, appropriate measures must be taken to reduce Cd uptake by crops.
Currently, researchers use a variety of measures to remediate soil Cd contamination and decrease Cd accumulation in crops [8,9]. However, these measures may result in high implementation costs and secondary pollution or require time to implement [10]. Therefore, new strategies to produce safe crops must be developed. Intercropping is a traditional farming practice that can promote ecological sustainability [11]. In the Cd-contaminated conditions, intercropping can affect Cd accumulation in crops [12,13]. When Cd-hyperaccumulators were intercropped with food crops, the Cd content in the crop tissues decreased, and the crop yields increased [14]. Intercropping with the Cd-hyperaccumulator Sedum alfredii Hance decreased the Cd accumulation in medicinal plant Pinellia ternate (Thunb.) Makino and increased the plant’s biomass [15]. Additionally, intercropping with Solanum nigrum L. (a Cd-hyperaccumulator) increased the aboveground dry weight and reduced the Cd content in seeds of upland rice [16]. However, S. alfredii intercropped with oilseed rape not only decreased S. alfredii dry weight but also increased oilseed rape Cd content [14]. Intercropping with S. nigrum decreased wheat biomass while increasing its Cd content [17]. Additionally, intercropping with the Cd-accumulator Sonchus asper (L.) Hill decreased the Cd content and biomass of Vicia faba L. [18], and intercropping with Hylotelephium spectabile (Boreau) H. Ohba promoted peach growth and decreased its Cd content [19]. Therefore, intercropping with the Cd-hyperaccumulators has varying effects on the growth and Cd accumulation of different crop species because of the differences in genetic background.
In addition to the effect that different hyperaccumulator species have on the food crops’ growth and Cd uptake, planting density also affects these parameters [20,21]. Increasing the planting density promoted S. nigrum growth and aboveground Cd accumulation and enhanced its efficiency in remediating the Cd-contaminated soils [22]. In a previous study, we observed that intercropping with S. nigrum decreased the Cd accumulation in young grapevines [23], but we did not study the impact of intercropping planting density of S. nigrum on young grapevine growth and Cd uptake. Therefore, the aim of this study was to determine the planting density of S. nigrum that minimizes the Cd uptake in young grapevines and improves the efficiency of remediating the Cd-contaminated vineyard soils, providing a reference for safe grape production.
2. Materials and Methods
2.1. Materials
A fluvo-aquic soil (Table 1) was collected from a farm of Sichuan Agricultural University (30°33′46″ N, 103°39′36″ E), Chengdu, China, in December 2023.
The grape variety used was ‘Summer Black’ grafted onto ‘Beta’ rootstock. One-year-old grafted grapevines were collected from the nursery of the farm. The grafted grapevines were planted in the plastic pots.
The seeds of S. nigrum were also collected from the farm in October 2023. In March 2024, the seeds were sown in the plastic pots.
Before the above plants were transplanted, the whole pots were filled with water to completely soak the soils, which makes it easy to take out plant seedlings as a whole without damaging the roots.
2.2. Experimental Design
The experiment was conducted in a rain shelter at Chengdu Campus of Sichuan Agricultural University, Chengdu, China. In March 2024, 35 kg of the air-dried soil was added into the pot (length × width × height = 80 cm × 40 cm × 30 cm). Then, CdCl2·2.5H2O was added to adjust the final soil Cd content to 5 mg/kg [23]. After mixing, the soil was kept moist for one month, during which it was turned over and homogenized from time to time. The experiment was divided into five treatments (Figure 1): (1) a monoculture of grapevine (referred to as monoculture) and grapevine intercropping setups with a density of (2) 40 cm (plant spacing) × 80 cm (row spacing) of S. nigrum (referred to as 40 × 80), (3) 40 cm × 40 cm (referred to as 40 × 40), (4) 20 cm × 40 cm (referred to as 20 × 40) and (5) 20 cm × 20 cm (referred to as 20 × 20). Each treatment was conducted in triplicate (three pots). Two grapevine plants were planted in each pot. The monoculture, 40 × 80, 40 × 40, 20 ×40 and 20 × 20 pots contained 0, 4, 6, 9 and 13 S. nigrum seedlings. The experiment used a completely randomized design. A layer of dry bamboo leaves was spread on the soil surface to reduce water evaporation. The pots were watered in a timely manner to keep the soil moist until the plants were harvested.
2.3. Measurements
After 50 days, the middle mature leaves were used to determine the gas exchange parameters [net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci) and transpiration rate (Tr)] using a Li-6400 photosynthetic system (LI-COR, Lincoln, NE, USA). Following this, these leaves were also analyzed for the photosynthetic pigment (chlorophyll a, chlorophyll b and carotenoid) content and antioxidant enzyme [catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD)] activity using established methods [24]. The plants were then harvested, washed and dried in an oven at 75 °C to record the biomass. The Cd content in the samples was determined using an atomic absorption spectrophotometer (PinAAcle 900H, PerkinElmer, Shelton, CT, USA) [25]. The translocation factor of Cd was calculated as the Cd content in shoots/Cd content in roots [26]. Soil samples from the pots were used to determine pH using a pH meter [25] and chemical composition (acid-extractable Cd, reducible Cd, oxidizable Cd and residue Cd) using the Community Bureau of Reference (BCR) continuous extraction method [27].
2.4. Statistical Analysis
SPSS version 20.0.0 (IBM, Chicago, IL, USA) was used for the statistical analyses. The data, which included triplicates, were normalized and then tested for homogeneity before undergoing a one-way analysis of variance and Duncan’s multiple range test (p < 0.05).
3. Results
3.1. Biomass
Intercropping with different densities of S. nigrum had various effects on the biomass of young grapevines (Figure 2A,B). Compared with the monoculture, the 40 × 40 treatment increased the root biomass of young grapevines, while intercropping with other densities of S. nigrum did not have such an effect. The 40 × 80 and 40 × 40 treatments increased the shoot biomass of young grapevines by 11.28% and 19.36%, respectively, compared with the monoculture. However, the 20 × 40 treatment did not have an effect on the shoot biomass of young grapevines, while the 20 × 20 treatment decreased it.
After intercropping with young grapevines, the biomass of S. nigrum varied (Figure 2C,D). Its root biomass among the treatments ranked as 20 × 40 > 20 × 20 > 40 × 40 ≈ 40 × 80, while that of the shoots ranked as 20 × 40 ≈ 20 × 20 > 40 × 40 ≈ 40 × 80.
3.2. Photosynthetic Pigment Contents
Compared with the monoculture, only the 40 × 40 treatment increased the photosynthetic pigment contents in young grapevines, which increased by 62.68%, 35.55% and 43.85%, respectively (Table 2). The 40 × 80 treatment had no effect on these photosynthetic pigments in young grapevines, while those of the 20 × 40 and 20 × 20 treatments decreased.
The photosynthetic pigment content in S. nigrum increased when the planting density of S. nigrum was no higher than 20 × 40. Then, it decreased when the density was higher than 20 × 40 (Table 2). The order of the chlorophyll a content in S. nigrum among the treatments was 20 × 40 > 20 × 20 > 40 × 40 > 40 × 80, while for chlorophyll b, it was 20 × 40 > 20 × 20 ≈ 40 × 40 > 40 × 80 and for carotenoid, it was 20 × 40 ≈ 20 × 20 ≈ 40 × 40 > 40 × 80.
3.3. Gas Exchange Parameters
Compared with the monoculture, the 40 × 40 treatment increased the gas exchange parameters of young grapevines by 6.89%, 45.28%, 11.71% and 40.94%, respectively (Table 3). The 40 × 80 treatment had no effect on the Pn, while it increased the Gs, Ci and Tr by 18.87%, 8.74% and 17.45%, respectively, compared with the monoculture. The 20 × 40 and 20 × 20 treatments had no effect on the Pn, Gs, Ci and Tr in young grapevines.
In S. Nigrum, the 20 × 40 treatment had the highest Pn, Gs and Ci among the different treatments (Table 3). The Pn in the 20 × 20 treatment was higher than in the 40 × 80 and 40 × 40 treatments, while no significant difference was found between the 40 × 80 and 40 × 40 treatments. The ranked order of the Gs among the treatments was 20 × 40 > 20 × 20 ≈ 40 × 80 ≈ 40 × 40, and that of the Ci was 20 × 40 > 20 × 20 ≈ 40 × 40 ≈ 40 × 80. The Tr was not significantly different among the 20 × 20, 20 × 40 and 40 × 80 treatments, while the Tr in the 20 × 20 and 20 × 40 treatments was higher than in the 40 × 40 treatment.
3.4. Antioxidant Enzyme Activity
Compared with the monoculture, the 40 × 40, 20 × 40 and 20 × 20 treatments increased the CAT activity of young grapevines by 42.59%, 62.59% and 78.10%, respectively, while the 40×80 treatment had no effect (Table 4). The 40 × 80, 40 × 40, 20 × 40 and 20 × 20 treatments increased the SOD activity by 3.80%, 12.67%, 21.51% and 19.57%, respectively, compared with the monoculture. Only the POD activity in the 20 × 40 and 20 × 20 treatments increased, while the 40 × 80 and 40 × 40 treatments had no effect.
As the intercropping density increased, the antioxidant enzyme activity of S. nigrum also increased (Table 4). The ranked order of the CAT and SOD activity among the treatments was 20 × 20 > 20 × 40 > 40 × 40 > 40 × 80, and that of the POD activity was 20 × 20 > 20 × 40 > 40 × 40 ≈ 40× 80.
3.5. Cd Content in Plants
Intercropping with S. nigrum decreased the Cd content in young grapevines (Table 5). Compared with the monoculture, the 40 × 80, 40 × 40, 20 × 40 and 20 × 20 treatments decreased the root Cd content by 66.05%, 68.92%, 72.94% and 77.27%, respectively, and decreased the shoot Cd content by 20.89%, 26.11%, 38.12% and 45.95%, respectively. Intercropping with S. nigrum increased the translocation factor of young grapevines compared with the monoculture, while no differences were observed among the different S. nigrum planting densities.
The Cd content in S. nigrum increased with the increasing intercropping density (Table 5). The ranked order of the Cd content in S. nigrum among the treatments was 20 × 20 > 20 × 40 > 40 × 40 > 40 × 80. The translocation factor decreased with increasing intercropping density and ranked as 40 × 80 > 40 × 40 ≈ 20 × 20 > 20 × 40.
3.6. Cd Extraction in S. nigrum
As the intercropping density increased, the Cd extraction in S. nigrum also increased (Figure 3A,B). The Cd extraction in the roots ranged from 15.2 to 46.0 μg/plant, while that of the shoots varied between 251.2 and 648.4 μg/plant. The ranked order of the Cd extraction in roots among the treatments was 20 × 20 > 20 × 40 > 40 × 40 > 40 × 80, and that of the shoots was 20 × 20 > 20 × 40 > 40 × 40 ≈ 40 × 80.
3.7. Chemical Forms of Soil Cd and Soil pH
Intercropping young grapevines with S. nigrum decreased soil acid-extractable Cd content (Table 6). The 40 × 80, 40 × 40, 20 × 40 and 20 × 20 treatments decreased the acid-extractable Cd content by 23.47%, 14.08%, 8.61% and 6.26%, respectively, compared with the monoculture. Only the 40 × 80, 40 × 40 and 20 × 40 treatments decreased the reducible Cd content, while the 20 × 20 treatment had no effect, compared with the monoculture. The 40 × 80 and 40 × 40 treatments did not affect the oxidizable Cd content, while the 20 × 40 and 20 × 20 treatments decreased it by 9.23% and 14.06%, respectively, compared with the monoculture. The 40 × 40, 20 × 40 and 20 × 20 treatments decreased the residue Cd content by 5.88%, 22.06% and 22.06%, respectively, compared with the monoculture, while the 40 × 80 treatment had no effect.
In terms of proportions, the 40 × 80 and 40 × 40 treatments decreased that of soil acid-extractable and reducible Cd contents and increased those of the oxidizable and residue Cd contents (Figure 4A). The 20 × 40 and 20 × 20 treatments increased the proportions of the acid-extractable and reducible Cd contents and decreased that of the residue Cd content. The 20 × 40 treatment slightly increased the proportion of the oxidizable Cd content, while the 20 × 20 treatment decreased it.
Compared with the young grapevine monoculture, intercropping young grapevine with different planting densities of S. nigrum reduced soil pH (Figure 4B). As the intercropping density increased, the soil became more acidic. The ranked order of soil pH among the treatments was monoculture 40 × 80 ≈ 40 × 40 ≈ 20 × 40 ≈ 20 × 20.
4. Discussion
Plant species and planting density affect the effectiveness of intercropping systems [21]. Intercropping can alter the available heavy metal and nutrient contents in the soils, thus affecting plant growth [28]. When the soil is contaminated by Cd, intercropping food crops with hyperaccumulators can increase, decrease or have no effect on crop biomass [14,15,16]. Different intercropping densities also affect the biomass and growth of crops [20,29]. In the present study, the 40 × 40 and 40 × 80 treatments led to an increase in shoot biomass of young grapevine, while the 20 × 40 and 20 × 20 treatments resulted in a decrease or showed no impact. These findings align with those of a previous study [29], indicating that intercropping with a low S. nigrum planting density could promote young grapevine growth while intercropping with a high S. nigrum planting density could have an inhibitory effect. When intercropped with a high density of S. nigrum, competition for resources between the two plant species may be the main factor hindering the growth of young grapevines. Specifically, S. nigrum, which is an herb plant, grew faster than the woody grapevine, thereby likely inhibiting the young grapevine’s growth. In addition, the biomass of each S. nigrum plant in the 20 × 40 and 20 × 20 treatments was higher than in the 40 × 40 and 40 × 80 treatments in this experiment, which was consistent with the previous studies [20,29]. These results indicate that high-density planting could promote S. nigrum growth when intercropped with young grapevine, which is beneficial for enhancing S. nigrum phytoremediation capability in the Cd-contaminated soils. In the field, the biomass and height of mature grapevines surpass those of S. nigrum. Consequently, the growth of S. nigrum might be restrained. Therefore, the results of the current study are only applicable to young grapevines.
Intercropping can affect the amount of sunlight received and utilized by each plant species, which, in turn, changes their chlorophyll content, Gs and Pn [30,31]. When planted in the Cd-contaminated soils, intercropping with a hyperaccumulator was shown to increase the photosynthetic pigment content, Pn, Tr, Ci and Gs of the common plant [32]. Other studies have shown that intercropping with hyperaccumulators could increase or decrease crop photosynthetic pigment contents [13,23]. In this study, the photosynthetic pigment content in young grapevines was increased by the 40 × 40 treatment, whereas the other treatments either decreased it or had no effect. The 40 × 80 and 40 × 40 treatments increased the gas exchange parameters of young grapevines, while the other treatments decreased or did not affect them. These results are consistent with a previous study [31], indicating that intercropping with a low density of S. nigrum could be beneficial to young grapevine photosynthetic pigment biosynthesis and improve its photosynthetic capacity, while intercropping with a high density of S. nigrum could inhibit the young grapevine’s photosynthesis. In addition, the photosynthetic pigment content in S. nigrum among the treatments was ranked as 20 × 40 > 20 × 20 > 40 × 40 > 40 × 80 in this study. The gas exchange parameters of S. nigrum in the 20 × 40 and 20 × 20 treatments were higher than in the 40 × 40 and 40 × 80 treatments to some extent. These results align with the previous studies [20,29], indicating that high-density planting could enhance photosynthesis in S. nigrum when intercropped with young grapevine.
In plants, to ensure normal cellular metabolism, a dynamic redox balance exists between reactive oxygen species (ROS) and the antioxidant system by regulating the relative composition of oxidizing and reducing electron carriers to control ROS accumulation [33]. When plants take up heavy metals, ROS are produced, which alters the antioxidant system and leads to oxidative stress [34]. In the antioxidant system, antioxidant enzymes play a crucial role, where the SOD disproportionates superoxide anions to H2O2 and O2, while the CAT and POD convert the generated H2O2 to H2O and O2, thereby effectively attenuating intracellular oxidative-stress-related damage [35]. In this study, intercropping with a high density of S. nigrum increased the antioxidant enzyme activity in young grapevines, while intercropping with a low density of S. nigrum did not affect that. As the intercropping density increased, the antioxidant enzyme activity in young grapevines also increased. These findings were in line with the prior research [19,20,29], indicating that intercropping with a high density of S. nigrum could induce additional stress by S. nigrum. Meanwhile, as the intercropping density increased, the antioxidant enzyme activity in S. nigrum also increased, indicating that the additional stress from crowding the plants could also be inducing stress responses in S. nigrum. The mechanism of the above phenomena needs to be further studied.
Intercropping can affect the composition of soil organic acids and pH and thus change soil available Cd content, which ultimately decreases the uptake of Cd by crops [36,37]. In this study, intercropping young grapevine with S. nigrum decreased the soil pH. As the intercropping density with S. nigrum increased, the soil pH decreased. These results were in line with the previous studies [38]. This may be due to the organic acids from S. nigrum roots [39]. In addition, it has been observed that soil pH is strongly associated with soil chemical forms of Cd [40]. In this study, intercropping young grapevine with different densities of S. nigrum decreased the acid-extractable and reducible Cd contents in the soil to some extent. This is beneficial for decreasing the Cd uptake by grapes. Moreover, the high intercropping density also decreased the oxidizable Cd and residue Cd content in the soils, while low intercropping density had no effect. The above results suggest that when more S. nigrum plants are planted, more soil Cd can be removed, resulting in low levels of the different forms.
Intercropping with suitable hyperaccumulators can reduce crop Cd level, thus promoting safe agricultural production [15]. However, intercropping with hyperaccumulators also can increase or have no effect on Cd accumulation in crops [14,15,16]. Therefore, using different combinations of plant species for intercropping may have different effects on Cd accumulation in crops. In this study, intercropping with S. nigrum decreased the Cd content in young grapevines, while it increased the translocation factor of young grapevines. With increasing intercropping density, the Cd content in young grapevines decreased. In addition, with increasing intercropping density, S. nigrum Cd content increased, while the translocation factor of S. nigrum decreased, similar to previous studies [20,29]. These results indicate that intercropping young grapevine with S. nigrum may produce the “rhizosphere talks” between two plant species [41]. The root secretions from each of the two plant species may be absorbed by both species and improve the tolerance of both species to Cd. For grapevines, when S. nigrum plants took up more Cd from the soil, the lower available soil Cd content resulted in lower Cd uptake by young grapevines. The mechanism of their interaction needs to be further investigated. Moreover, with increasing intercropping density, the Cd extraction in S. nigrum increased, suggesting that intercropping young grapevine with higher densities of S. nigrum could improve the effectiveness of S. nigrum to remediate the Cd-contaminated soils.
5. Conclusions
The effects of different planting densities of S. nigrum on young grapevine growth and Cd uptake were studied to screen the best planting density of S. nigrum. The 40 × 80 and 40 × 40 treatments promoted young grapevine growth by increasing its biomass, photosynthetic pigment content and photosynthesis, while the 20 × 40 and 20 × 20 treatments were inhibitory toward these traits. S. nigrum in the 20 × 40 and 20 × 20 treatments had higher biomass, photosynthetic pigment content and photosynthesis than in the 40 × 80 and 40 × 40 treatments. With increasing intercropping density, the antioxidant enzyme activity in both plant species increased, and the Cd content in young grapevines decreased while in S. nigrum, it increased. In addition, with increasing intercropping density, S. nigrum phytoremediation capacity for the Cd-contaminated soils improved. Therefore, intercropping young grapevine with S. nigrum can decrease Cd accumulation in young grapevines while remediating the Cd-contaminated soil. Future work should investigate the effects of intercropping with S. nigrum on the Cd accumulation of grape berries in the field and also study the mechanism of grape and S. nigrum interactions in relation to Cd uptake.
Author Contributions
Conceptualization, Y.Y., R.L. and L.L.; investigation, Y.Y., Q.Z., J.W. and X.L.; data analysis, Q.Z., J.W., X.L. and D.L.; data interpretation, J.W., X.L., D.L., R.L. and L.L.; writing—original draft preparation, Y.Y. and Q.Z.; writing—review and editing, D.L., R.L. and L.L.; supervision, L.L. All authors have read and agreed to the published version of the manuscript.
Funding
This work was financially supported by the National Natural Science Foundation of China (32271697).
Informed Consent Statement
We all declare that manuscript reporting studies do not involve any human participants, human data or human tissue. Plant samples were collected from the university research area. Study protocol must comply with relevant institutional, national and international guidelines and legislation. Our experiment follows the relevant institutional, national and international guidelines and legislation.
Data Availability Statement
The raw data supporting the conclusions of this article will be made available by the authors on request.
Conflicts of Interest
The authors declare no conflicts of interest.
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Figure 1.
Experimental design diagram. Mon. = monoculture of grapevine; 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of Solanum nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum.
Figure 1.
Experimental design diagram. Mon. = monoculture of grapevine; 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of Solanum nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum.
Figure 2.
Biomass. (A): root biomass of young grapevines; (B): shoot biomass of young grapevines; (C): root biomass of S. nigrum; (D): shoot biomass of S. nigrum. Different lowercase letters indicate significant differences among the treatments (Duncan’s multiple range test, p < 0.05). Mon. = monoculture of young grapevine; 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of S. nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum.
Figure 2.
Biomass. (A): root biomass of young grapevines; (B): shoot biomass of young grapevines; (C): root biomass of S. nigrum; (D): shoot biomass of S. nigrum. Different lowercase letters indicate significant differences among the treatments (Duncan’s multiple range test, p < 0.05). Mon. = monoculture of young grapevine; 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of S. nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum.
Figure 3.
Cd extraction in S. nigrum. (A): root Cd extraction in S. nigrum; (B): shoot Cd extraction in S. nigrum. Different lowercase letters indicate significant differences among the treatments (Duncan’s multiple range test, p < 0.05). Cd extraction = plant biomass × plant Cd content. 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of S. nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum.
Figure 3.
Cd extraction in S. nigrum. (A): root Cd extraction in S. nigrum; (B): shoot Cd extraction in S. nigrum. Different lowercase letters indicate significant differences among the treatments (Duncan’s multiple range test, p < 0.05). Cd extraction = plant biomass × plant Cd content. 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of S. nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum.
Figure 4.
Chemical forms of soil Cd proportion and soil pH. (A): chemical form of soil Cd proportion; (B): soil pH. Different lowercase letters indicate significant differences among the treatments (Duncan’s multiple range test, p < 0.05). Mon. = monoculture of young grapevine; 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of S. nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum.
Figure 4.
Chemical forms of soil Cd proportion and soil pH. (A): chemical form of soil Cd proportion; (B): soil pH. Different lowercase letters indicate significant differences among the treatments (Duncan’s multiple range test, p < 0.05). Mon. = monoculture of young grapevine; 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of S. nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum.
Table 1.
Soil physicochemical properties.
| pH | Organic Matter (g/kg) | Total N (g/kg) | Total P (g/kg) | Total K (g/kg) | Available N (mg/kg) | Available P (mg/kg) | Available K (mg/kg) | Total Cd (mg/kg) |
|---|---|---|---|---|---|---|---|---|
| 7.55 | 12.09 | 0.49 | 0.58 | 11.55 | 42.95 | 12.39 | 41.33 | 0.23 |
Table 2.
Photosynthetic pigment contents.
| Treatment | Chlorophyll a (mg/g) | Chlorophyll b (mg/g) | Carotenoid (mg/g) |
|---|---|---|---|
| Grapevine | |||
| Mon. | 1.313 ± 0.027 b | 0.602 ± 0.039 b | 0.545 ± 0.021 b |
| 40 × 80 | 1.334 ± 0.066 b | 0.622 ± 0.018 b | 0.556 ± 0.023 b |
| 40 × 40 | 2.136 ± 0.107 a | 0.816 ± 0.032 a | 0.784 ± 0.030 a |
| 20 × 40 | 1.157 ± 0.019 c | 0.462 ± 0.020 c | 0.494 ± 0.008 c |
| 20 × 20 | 1.111 ± 0.046 c | 0.457 ± 0.032 c | 0.481 ± 0.024 c |
| S. nigrum | |||
| 40 × 80 | 1.314 ± 0.041 d | 0.451 ± 0.017 c | 0.454 ± 0.012 c |
| 40 × 40 | 1.509 ± 0.040 c | 0.541 ± 0.006 b | 0.520 ± 0.014 b |
| 20 × 40 | 1.702 ± 0.036 a | 0.611 ± 0.032 a | 0.534 ± 0.020 ab |
| 20 × 20 | 1.620 ± 0.041 b | 0.560 ± 0.031 b | 0.558 ± 0.017 a |
Different lowercase letters indicate significant differences among the treatments (Duncan’s multiple range test, p < 0.05). Mon. = monoculture of young grapevine; 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of S. nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum.
Table 3.
Gas exchange parameters.
| Treatment | Pn (µmol CO2/m2/s) | Gs (mol H2O/m2/s) | Ci (µmol CO2/mol) | Tr (mmol H2O/m2/s) |
|---|---|---|---|---|
| Grapevine | ||||
| Mon. | 14.51 ± 0.24 b | 0.053 ± 0.003 c | 198.23 ± 9.25 b | 1.49 ± 0.03 c |
| 40 × 80 | 14.64 ± 0.54 b | 0.063 ± 0.004 b | 215.55 ± 8.88 a | 1.75 ± 0.10 b |
| 40 × 40 | 15.51 ± 0.50 a | 0.077 ± 0.005 a | 221.44 ± 11.03 a | 2.10 ± 0.09 a |
| 20 × 40 | 12.92 ± 0.26 c | 0.050 ± 0.003 cd | 191.15 ± 5.66 bc | 1.43 ± 0.03 c |
| 20 × 20 | 12.07 ± 0.16 d | 0.045 ± 0.004 d | 180.55 ± 10.13 c | 1.46 ± 0.08 c |
| S. nigrum | ||||
| 40 × 80 | 18.19 ± 0.80 c | 0.132 ± 0.003 bc | 129.89 ± 2.58 c | 3.78 ± 0.27 ab |
| 40 × 40 | 19.54 ± 1.11 c | 0.126 ± 0.002 c | 133.93 ± 1.41 bc | 3.53 ± 0.24 b |
| 20 × 40 | 24.64 ± 0.70 a | 0.168 ± 0.007 a | 170.71 ± 8.08 a | 4.15 ± 0.21 a |
| 20 × 20 | 21.96 ± 0.60 b | 0.137 ± 0.004 b | 143.94 ± 9.80 b | 4.07 ± 0.10 a |
Different lowercase letters indicate significant differences among the treatments (Duncan’s multiple range test, p < 0.05). Mon. = monoculture of young grapevine; 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of S. nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum.
Table 4.
Antioxidant enzyme activity.
| Treatment | CAT Activity (mg/g/min) | SOD Activity (U/g) | POD Activity (U/g/min) |
|---|---|---|---|
| Grapevine | |||
| Mon. | 0.580 ± 0.030 d | 402.6 ± 6.58 d | 13.00 ± 1.00 b |
| 40 × 80 | 0.610 ± 0.020 d | 417.9 ± 8.00 c | 14.63 ± 1.00 b |
| 40 × 40 | 0.827 ± 0.038 c | 453.6 ± 7.24 b | 15.28 ± 0.06 b |
| 20 × 40 | 0.943 ± 0.042 b | 489.2 ± 6.52 a | 23.27 ± 1.90 a |
| 20 × 20 | 1.033 ± 0.040 a | 481.4 ± 1.40 a | 20.97 ± 1.68 a |
| S. nigrum | |||
| 40 × 80 | 5.812 ± 0.066 d | 393.3 ± 0.65 d | 1907 ± 86.63 c |
| 40 × 40 | 6.089 ± 0.115 c | 407.9 ± 9.00 c | 2013 ± 60.01 c |
| 20 × 40 | 6.311 ± 0.052 b | 465.5 ± 2.11 b | 2269 ± 63.89 b |
| 20 × 20 | 6.618 ± 0.110 a | 491.1 ± 2.89 a | 2459 ± 70.11 a |
Different lowercase letters indicate significant differences among the treatments (Duncan’s multiple range test, p < 0.05). Mon. = monoculture of young grapevine; 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of S. nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum. CAT = catalase; SOD = superoxide dismutase; POD = peroxidase.
Table 5.
Cd content in plants.
| Treatment | Root Cd Content (mg/kg) | Shoot Cd Content (mg/kg) | Translocation Factor |
|---|---|---|---|
| Grapevine | |||
| Mon. | 28.60 ± 0.72 a | 0.383 ± 0.015 a | 0.013 ± 0.001 b |
| 40 × 80 | 9.71 ± 0.36 b | 0.303 ± 0.006 b | 0.031 ± 0.002 a |
| 40 × 40 | 8.89 ± 0.37 c | 0.283 ± 0.015 b | 0.032 ± 0.002 a |
| 20 × 40 | 7.74 ± 0.23 d | 0.237 ± 0.012 c | 0.031 ± 0.002 a |
| 20 × 20 | 6.50 ± 0.30 e | 0.207 ± 0.006 d | 0.032 ± 0.002 a |
| S. nigrum | |||
| 40 × 80 | 5.22 ± 0.31 d | 15.03 ± 0.71 d | 2.88 ± 0.05 a |
| 40 × 40 | 7.74 ± 0.28 c | 16.86 ± 0.32 c | 2.18 ± 0.10 b |
| 20 × 40 | 9.30 ± 0.53 b | 18.58 ± 0.52 b | 2.00 ± 0.06 c |
| 20 × 20 | 13.13 ± 0.75 a | 29.55 ± 1.11 a | 2.25 ± 0.05 b |
Different lowercase letters indicate significant differences among the treatments (Duncan’s multiple range test, p < 0.05). Mon. = monoculture of young grapevine; 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of S. nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum.
Table 6.
Chemical forms of soil Cd content.
| Treatment | Acid Extraction Cd Content (mg/kg) | Reducible Cd Content (mg/kg) | Oxidizable Cd Content (mg/kg) | Residue Cd Content (mg/kg) |
|---|---|---|---|---|
| Mon. | 0.639 ± 0.009 a | 1.685 ± 0.023 a | 2.567 ± 0.013 a | 0.068 ± 0.003 a |
| 40 × 80 | 0.489 ± 0.020 d | 1.347 ± 0.088 c | 2.518 ± 0.013 a | 0.069 ± 0.002 a |
| 40 × 40 | 0.549 ± 0.016 c | 1.355 ± 0.068 c | 2.520 ± 0.061 a | 0.064 ± 0.002 b |
| 20 × 40 | 0.584 ± 0.008 b | 1.529 ± 0.016 b | 2.330 ± 0.095 b | 0.053 ± 0.002 c |
| 20 × 20 | 0.599 ± 0.012 b | 1.614 ± 0.060 ab | 2.206 ± 0.106 b | 0.053 ± 0.001 c |
Different lowercase letters indicate significant differences among the treatments (Duncan’s multiple range test, p < 0.05). Mon. = monoculture of young grapevine; 40 × 80 = density 40 cm (plant spacing) × 80 cm (row spacing) of S. nigrum; 40 × 40 = density 40 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 40 = density 20 cm (plant spacing) × 40 cm (row spacing) of S. nigrum; 20 × 20 = density 20 cm (plant spacing) × 20 cm (row spacing) of S. nigrum.
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Yang, Y.; Zheng, Q.; Wang, J.; Lv, X.; Liang, D.; Liao, R.; Lin, L. Effects of Different Planting Densities of Solanum nigrum L. on the Growth and Cadmium Uptake of Young Grapevines. Agronomy 2024, 14, 3056. https://doi.org/10.3390/agronomy14123056
AMA Style
Yang Y, Zheng Q, Wang J, Lv X, Liang D, Liao R, Lin L. Effects of Different Planting Densities of Solanum nigrum L. on the Growth and Cadmium Uptake of Young Grapevines. Agronomy. 2024; 14(12):3056. https://doi.org/10.3390/agronomy14123056
Chicago/Turabian StyleYang, Yuanxiang, Qinfeng Zheng, Jin Wang, Xiulan Lv, Dong Liang, Renyan Liao, and Lijin Lin. 2024. "Effects of Different Planting Densities of Solanum nigrum L. on the Growth and Cadmium Uptake of Young Grapevines" Agronomy 14, no. 12: 3056. https://doi.org/10.3390/agronomy14123056
APA StyleYang, Y., Zheng, Q., Wang, J., Lv, X., Liang, D., Liao, R., & Lin, L. (2024). Effects of Different Planting Densities of Solanum nigrum L. on the Growth and Cadmium Uptake of Young Grapevines. Agronomy, 14(12), 3056. https://doi.org/10.3390/agronomy14123056
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