Next Article in Journal
WRKY36–PIL15 Transcription Factor Complex Negatively Regulates Sheath Blight Resistance and Seed Development in Rice
Next Article in Special Issue
Recent Advances in Transcriptome Analysis Within the Realm of Low Arsenic Rice Breeding
Previous Article in Journal
Medicinal Potential of Broussonetia papyrifera: Chemical Composition and Biological Activity Analysis
Previous Article in Special Issue
Effects of Nitrogen Fertilizer Types and Planting Density on the Yield and Nitrogen Use Efficiency of Salt-Tolerant Rice Under Salt Stress Conditions
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Plants
Volume 14
Issue 4
10.3390/plants14040524
plants-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Effects of Modified Biochar on Growth, Yield, and Quality of Brassica chinensis L. in Cadmium Contaminated Soils

by
Guojun Pan
1,
Shufang Geng
1,
Liangliang Wang
1,
Jincheng Xing
2,
Guangping Fan
1,
Yan Gao
1,
Xin Lu
1,3,* and
Zhenhua Zhang
1,2,4,*
1
Key Laboratory for Saline-Alkali Soil Improvement and Utilization, Ministry of Agriculture and Rural Affairs/Institute of Agricultural Resources and Environment, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China
2
Institute of Jiangsu Coastal Agricultural Sciences, Yancheng 224002, China
3
School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang 212013, China
4
The School of Agriculture and Environment, The University of Western Australia, Crawley, WA 6009, Australia
*
Authors to whom correspondence should be addressed.
Plants 2025, 14(4), 524; https://doi.org/10.3390/plants14040524
Submission received: 21 January 2025 / Revised: 4 February 2025 / Accepted: 6 February 2025 / Published: 8 February 2025
(This article belongs to the Special Issue Physiological and Genetic Mechanisms of Abiotic Stress Tolerance in Crops, Third Edition)
Browse Figures
Versions Notes

Abstract

:
Cadmium (Cd) pollution in farmland soil leads to excessive Cd in vegetables, which can be transferred to humans through the food chain, posing a significant threat to human health, and requires urgent measures to combat it. Modified biochar may have the potential to remediate Cd pollution in farmland soils. In this experiment, bulk biochar (YC) derived from reed straw or modified biochar by ball milling (Q) either alone or combined with a combination of several passivation agents {potassium hydroxide (K), attapulgite (A), calcium magnesium phosphate fertilizer (M), and polyacrylamide (P)} was applied to soils polluted with Cd, to investigate the growth, yield, and quality of pakchoi (Brassica chinensis L.). The results showed that bulk biochar (YC) provided pakchoi with plenty of nitrogen, phosphorus, and potassium, while passivation agents enhance macronutrient accumulation. Compared to YC, modified biochar improved pakchoi yields and nutritional quality. Among them, concentrations of nitrates in pakchoi significantly decreased by 51.8% and 51.0%, while vitamin C levels increased by 29.6% and 19.0%, respectively, in QKAMP and QKAM treatments. The contents of Cd in pakchoi significantly decreased by 21.6% and 18.6%, respectively, in QKAMP and QKAM treatments. The implementation of QKAMP led to the cadmium contents in edible vegetables being lower than the maximum stipulated content as defined by the national standard, but QKAM failed to accomplish it. In conclusion, QKAMP effectively reduced the bioavailability of Cd in the middle to slightly Cd-polluted alkaline soils, making it a suitable soil amendment to improve the yield and quality and mitigate Cd accumulation in vegetables.

1. Introduction

Agricultural soil pollution, especially cadmium (Cd), is becoming increasingly severe because of industrialization and population growth [1,2,3]. Cd is highly toxic, reducing soil quality and crop yields, and accumulating in humans through the food chain, posing significant health risks [4]. Given that Cd contaminated agricultural soils are predominantly mild to moderate in China, in situ immobilization techniques are being widely applied to ensure the safety of crops grown on contaminated soils [5,6]. Passivation agents used in in situ remediation are mainly classified into inorganic and organic types. Through adsorption, precipitation, ion exchange, or complex with heavy metals, the bioavailability of Cd in soil can be reduced, which will result in a reduction in the absorption and accumulation of heavy metals by crops [7].
Under limited-oxygen conditions, biochar is produced by pyrolyzing agricultural residues, including straw and manure [8]. As the material has a well-developed porous structure, it is capable of forming clusters that can complex with metal ions, in turn reducing both the bioavailability and mobility of heavy metals in soil [9]. Additionally, biochar contains nutrients that improve soil fertility and boost crop growth [10,11]. However, due to the complexity of soil environments, the sole application of biochar often requires large quantities and incurs high costs. Furthermore, bulk biochar exhibits a limited adsorption ability [12,13]. The adsorption performance of biochar can be significantly enhanced by physically, chemically, or biologically modified biochar [14].
Pakchoi, Brassica chinensis L. is a widely cultivated leafy vegetable in China characterized by a short growth cycle, strong environmental adaptability, and high yield. More importantly, pakchoi contains various vitamins and mineral elements essential for human health; thus, it is highly favored by consumers [15]. Heavy metal contamination is more common in leafy vegetables than in other vegetables, according to previous studies [16]. Cultivating pakchoi in cadmium-contaminated soil possibly inhibits its growth while leading to nutrient loss and reduced nutritional quality. Prolonged consumption of pakchoi with elevated cadmium levels poses potential health risks to human beings.
In our previous study, we identified that reed straw biochar modified with either potassium hydroxide or potassium hydroxide combined with attapulgite exhibited favorable effects on the immobilization of Cd in soils [17]. Building upon this foundation, the current study optimizes mechanical ball-milling modifications by incorporating additional functional passivation agents into reed straw biochar. Our study investigated the effects of modified biochar on the growth, nutritional quality, and accumulation of Cd in pakchoi, a model plant for safe vegetable production in soils polluted with Cd.

2. Materials and Methods

2.1. Preparation of Modified Biochar

Based on reed straw, biochar was prepared for this study [17]. To prepare the straw for use in the future, small sections were cut into smaller pieces, filled with inert nitrogen by heating at the rate of 20 °C per minute and stayed at 600 °C for 30 min, then cooled, ground, and sieved through 60 meshes. Passivating agents used in the experiment included potassium hydroxide (Xilong Chemical Company, Shantou, China), attapulgite (Xuyi Xinyuan Company, Huai’an, China), calcium magnesium phosphate fertilizer (Sanheng Company, Nanning, China), and polyacrylamide (PAM1200-; Xinbang Company, Changzhou, China). The bulk biochar was mixed either alone or combined with the various passivation agents in a specific ratio (see Table 1) and ball-milled at 300 rpm for 4 h. The modified biochar was bagged and stored for use.

2.2. Pot Experiment

The tested soil was collected from 0 to 20 cm layers of cadmium-contaminated lands in Shanghu Town, Changshu City, Jiangsu Province, China (120°37′ E, 31°43′ N). A 2 mm screen was used to grind and remove impurities from the soil after it was air-dried and screened. Soil properties are summarized below: pH, 7.07; soil bulk density, 1.32 g·cm3; soil organic matter, 24.8 g·kg−1; available nitrogen, 41.5 mg·kg−1; available phosphorus, 34.8 mg·kg−1; available potassium, 74 mg kg−1; total Cd, 1.75 mg kg−1.
The pot experiment was conducted in the greenhouse of the Jiangsu Academy of Agricultural Sciences (118°52′ E, 32°2′ N). Cylindrical plastic pots (0.15 m in diameter, 0.12 m in height) were used, each filled with 1.5 kg of soil to a depth of 0.10 m. In total, 2% of the modified biochar or bulk biochar (YC) was added to the tested soil (weight percentage) based on our previous studies [17]. Soil without added biochar served as the control (CK). Each treatment was replicated three times. For each pot, 70% of the field water capacity was kept, ensuring uniform mixing while adding water, followed by a two-week stabilization period. After this period, 30 uniformly sized pakchoi seeds, purchased from Mingtian Seed Company in Nanjing, Jiangsu Province, were planted in each pot. After germination, 10 evenly spaced seedlings were retained for further growth. During the cultivation period, watering was performed quantitatively to ensure adequate moisture content (70%) in the soil. After sixty days of growth, plants were harvested to measure both aerial and root fresh weights. Subsequently, representative fresh samples were taken for quality assessment before being dried and ground through a 100-mesh sieve for analysis.

2.3. Measurement Methods

2.3.1. Soil Analysis

A pH meter (FE28, Mettler Toledo, Changzhou, China) was used to measure the pH values of these solutions [18]. Based on Kjeldahl’s method, we determined the soil’s nitrogen content. According to Qian et al. [19], volumetric potassium dichromate analysis was used to assess organic matter content; using molybdenum–antimony colorimetry, we measured the phosphorus availability, while flame photometry was used to determine the potassium availability. The soil available Cd concentration (DTPA−Cd) was determined following national standards of China (GB/T 23739-2009) [20].

2.3.2. Plant Parameters

An instrument was used to measure plant height, starting at the soil surface and extending to the highest point of the leaves of the pakchoi plant. Pakchoi was harvested, cleaned with deionized water, air-dried, and divided into aerial parts and roots. Fresh weight was measured using a precision balance. Following 30 min of enzyme deactivation at 105 °C, samples were dried at 70 °C to a constant weight. Measured were the dry masses of aerial parts and roots.

2.3.3. Nutrition Contents in Plants

Plant samples underwent digestion using H2SO4-H2O2 to prepare them for analysis. According to Pandey et al. [21], Kjeldahl’s method semi-micro was used to quantify total nitrogen content; molybdenum–antimony colorimetry and flame photometry were used to measure the total phosphorus and potassium levels, respectively.

2.3.4. Plant Quality

The chlorophyll content was measured using spectrophotometric methods [22]. The soluble protein level was evaluated employing Coomassie Brilliant Blue G-250 staining [23]. Nitrate concentration was determined utilizing salicylic acid methods [24]. Soluble sugar content was analyzed through anthrone colorimetric techniques [25]. Vitamin C level was quantified via titration with 2,6-dichlorophenol indophenol [26].

2.3.5. Cadmium Content in Plants

The determination of the total Cd concentration in plants followed the national standards of China (GB 5009.15-2023) [27], which involved sample digestion utilizing a pressure digestion vessel. In a pressure vessel, 0.5 g of dried plant matter was sealed, soaked, and sealed in nitric acid overnight. Cd content was measured via inductively coupled plasma mass spectrometry (PerkinElmer Syngistix, Waltham, MA, USA) after the sample was digested at a constant temperature.

2.4. Data Statistical Analysis

Data processing was performed using Microsoft Excel 2019. One-way analysis of variance (ANOVA) was conducted via SPSS 20. Duncan method was used to statistically analyze the significant differences between treatments (p < 0.05). The graphs were created using Origin 2021.

3. Results and Discussions

3.1. Physicochemical Properties and Cd Bioavailability in Soils

Using modified biochar as a soil amendment, Table 2 summarizes its results on physicochemical properties. Soil pH, a fundamental indicator of soil chemistry, greatly influences the form and availability of heavy metals [28]. This study used soil that was mildly alkaline. Compared to CK, the soil pH significantly (p < 0.05) increased by 0.20−0.71 units after addition of the biochar. The pH values for soils treated with QKAMP, QKAM, QKM, and QK increased by 0.71, 0.65, 0.63, and 0.69 units, respectively. Furthermore, the pH values were significantly (p < 0.05) higher in the biochar treatments including ball milling with the agents than in both Q and YC treatments. The alkali ions of biochar, such as Ca2+, Mg2+, and K+, are released into the soil in the form of carbonates and oxides, which are exchanged with acidic ions to increase the soil pH [29]. Furthermore, the carboxyl, hydroxyl, and phenolic groups on the surface of the biochar can interact with acidic ions, thus helping to reduce the concentration of H+ [30]. The passivation agents used in the experiment contain a rich variety of basic functional groups, resulting in a significantly higher pH value in the soil treated with the passivation agents compared to Q and YC.
Compared to CK, total nitrogen contents significantly (p < 0.05) increased by 5.3−8.5% among the biochar treatments. In biochar-treated soils, nitrogen was provided, though the effect was not considerable, and the higher nitrogen content may be due to a reduction in nitrogen loss [31]. Soil organic matter contents were also significantly increased by 126.3−146.1% in the biochar treatments, though the modification of biochar did not further enhance organic matter levels. The results of our study are in agreement with those of Mohamed et al. [32], which showed that the organic matter contents in the treatments with 1.5% biochar added to the soil were more than twice that of CK. Moreover, soil available potassium contents were significantly increased by 22.9−489.8% among the different treatments, with addition of KOH being a key factor in enhancing potassium availability. The soil available phosphorus content was 34.86 mg/kg in CK treatment; while bulk biochar (YC) and ball-milled biochar (Q) did not significantly improve the available phosphorus levels. However, the available phosphorus increased by 66.9%, 49.9%, 22.3%, and 20.3%, respectively, in soils treated with QM, QKM, QKAM, and QKAMP, due to the phosphorus in the modifying agents. Previous studies have found that calcium magnesium phosphate, potassium hydroxide, and other modifiers work together with the ball-milled biochar to slow down the loss of nutrients, increased the utilization rate, and ensured the effective growth of subsequent plants [33,34,35]. In addition, bulk biochar reduced available Cd by 10.4%; however, the modified biochar reduced it by 14.4% to 25.5%, when compared with CK. Qin et al. [36], who found that pH and organic matter affect heavy metal bioavailability, a finding that is consistent with our results.

3.2. Growth of Pakchoi

3.2.1. Effects of Modified Biochar on Chlorophyll Contents in Pakchoi

Chlorophyll directly participates in photosynthesis and thus influences plant growth and yield [37]. The chlorophyll a and b content of pakchoi in this experiment was shown in Figure 1a,b. Modified biochar increased chlorophyll a and b contents to varying degrees. Compared to CK, only chlorophyll a contents in QKAM significantly increased by 14.6%, while bulk biochar, ball milling alone, or with various passivation agent treatments showed insignificant effects. By comparison, chlorophyll b contents in QM, QKM, and QKAM significantly increased by 21.9%, 22.6%, and 34.6%, respectively, compared to CK. Total chlorophyll contents (chlorophyl a + b) increased by 4.3−20.6% compared to CK, and the addition of modifying agents showed a tendency to enhance the photosynthetic capacity of pakchoi, with only QKAM producing a significant effect. (Figure 2c). The chlorophyll a/b ratio, as shown in Figure 2d, was significantly different between QKAM and CK treatments. Biochar has been demonstrated to increase chlorophyll content in plants in previous studies [38,39]. The modifying agents further enhanced the photosynthetic capacity of pakchoi, with QKAM showing the greatest improvement in chlorophyll contents. Cadmium stress inhibits photosynthesis in plants, and the reduction of cadmium accumulation in plants may be an important factor in the elevated chlorophyll content of pakchoi. Several studies have reported that insufficient phosphorus in plants affects the photosynthesis process and thus reduces the chlorophyll contents in plants [40,41]. Battie-Laclau et al. [42] reported adequate potassium enhances carbon dioxide transport within leaves, promoting photosynthesis. Generally, adding modified biochar to soil improved the nutrient content and promoted photosynthesis.

3.2.2. The Effects of Modified Biochar on Plant Height, Root Length and Biomass of Pakchoi

Table 3 shows the response of pakchoi to modified biochar in terms of growth and biomass. The application of biochar significantly improved plant growth compared to the application of CK, which was in line with previous studies that had been conducted [43,44]. The plant height significantly increased in QKAMP, QKAP, QKM, QM, Q, and YC treatments, compared to CK. The root length significantly increased by 1.03−2.07 cm after application of the modified biochar, compared to YC, representing a growth increase of 12.1−24.4%. Compared with the YC treatment, the ball-milled biochar treatment had significantly (p < 0.05) longer roots than the YC treatment. Due to its porous structure and high surface area, biochar is able to absorb nutrients and retain water, thus promoting the development of roots [45,46]. The fresh and dry weight of plant roots ranged from 12.54−13.78 g and 1.87−2.07 g, respectively, representing increases of 6.6−17.2% and 9.3−21.1% compared to CK. The fresh and dry weights of arial parts also increased by 10.2−20.7% and 12.9−22.5%, respectively, with significant biomass improvements across the biochar treatments. The biochar in nature contains a variety of nutrients, such as nitrogen, phosphorus, and potassium, all of which improve plant growth and are useful for use as a soil fertilizer when applied to the soil. No additional fertilizers were added in this study aside from the modified biochar materials. Rasul et al. [47] concluded that biochar modulates soil microbial communities to improve plant resistance to stress, thereby increasing crop yields. In addition, the raw materials used in biochar preparation, as well as its application, can significantly affect plant growth.

3.3. Contents of Macronutrients in Pakchoi

Figure 2 illustrates the variations in nitrogen, phosphorus, and potassium contents in aerial parts and roots. The total nitrogen contents decreased in the aerial parts treated with biochar (Figure 2a), with significant differences being observed between QKAMP, QKAM, QKA, and CK (p < 0.05). Nitrogen is a critical factor in protein and nucleic acid synthesis in plants, and nitrogen deficiency can inhibit normal plant growth [48]. In this experiment, all biochar-treated plants showed a varying degree of reduced nitrogen contents, compared to CK. Biochar contains high levels of carbon, which might immobilize nitrogen and reduce nitrogen loss from the soils [49,50]. However, a high C/N ratio lead to competition between soil microbes and plant roots for available nitrogen, potentially reducing nitrogen uptake by plants [51]. Additionally, biochar has fertilizer retention properties that reduce the rate of nitrogen released from the soil, which could result in inadequate nitrogen supply for short-cycle vegetables like pakchoi. Total phosphorus contents in the aerial parts of biochar-treated plants increased by 5–40%, compared to CK (Figure 2b), with significant (p < 0.05) differences being observed in treatments containing calcium magnesium phosphate fertilizer (M). As seen in Table 3, the yield of QKM was also the highest among all the treatments, indicating that calcium magnesium phosphorus fertilizers have a positive effect in promoting higher yields of pakchoi. The potassium contents in pakchoi significantly increased among the biochar treatments, compared to CK (Figure 2c), with QK-treated plants showing a 1.5-fold increase. The nutrient supply capacity of biochar itself is relatively limited, which can be remedied by the addition of modified materials. Nutrient contents in the roots followed a similar trend, with total nitrogen decreasing by 2.3–11.1%, and total phosphorus and potassium increasing by 10.5–33.2% and 17.0–77.6%, respectively. Compared to CK, YC increased total phosphorus and potassium by 10.5% and 21.5%, respectively. Biochar not only supplied nutrients for plant growth but also reduced nutrient losses from modifying agents, improving nutrient uptake efficiency [52,53].
The total nitrogen accumulation in both the aerial parts and roots parts in biochar application treatments did not differ significantly from CK, indicating that bulk/modified biochar did not increase total nitrogen accumulation in pakchoi (Figure 2d). In contrast, total phosphorus and potassium accumulation increased significantly compared to CK (Figure 2e,f). Total phosphorus accumulation in the aerial parts of biochar-treated plants ranged from 2.14 to 2.88 g pot−1, representing increases of 42.7−92.0%, compared to CK. The total potassium accumulation in the aboveground portion of pakchoi was also augmented by 29.7–79.0% as a consequence of the incorporation of modified biochar in comparison with CK. Total phosphorus and total potassium accumulation in the roots increased by 23.1–61.5% and 31.1–108.8%, respectively, compared with CK. The addition of modifying agents enhanced phosphorus and potassium contents in the plants, leading to increased nutrient accumulation. Based on the above results, we found that the nutrient supply capacity of biochar itself was relatively limited, and the addition of modified materials could make up for this defect. Compared with YC, ball-milling modification of biochar further improved nutrient utilization and nutrient accumulation in pakchoi.

3.4. Nutritional Quality of Pakchoi

3.4.1. Effects of Modified Biochar on Soluble Protein Contents in Pakchoi

Soluble proteins play a vital role in osmotic regulation and nutrient supply in plants. Their exceptional water-holding capacity not only helps maintain the integrity of plant cell membranes but also promotes plant growth. Increasing soluble protein content could enhance plant stress resistance [54]. The effects of the different modified biochar treatments on soluble protein contents in pakchoi were shown in Figure 3a. Bulk/modified biochar and CK did not exhibit any significant differences in soluble protein content, implying that the supplementation of biochar or biochar incorporating with inactivation agent did not conspicuously enhance the soluble protein content of pakchoi. Nitrogen levels in the environment directly influence soluble protein content [55]. As determined by this experiment, biochar-treated soils contained significantly more nitrogen than control soils, even though the amount of nitrogen accumulated in aerial parts and roots was not statistically significant. This indicated that it was not readily absorbed and utilized by the plants, as biochar increased nitrogen contents in the soil. According to Bi et al. [56], biochar and organic fertilizers can reduce soil N loss and increase vegetable soluble protein levels by a significant amount.

3.4.2. Effects of Modified Biochar on Nitrate Content in Pakchoi

Human health may be compromised by prolonged consumption of foods with high nitrate levels [57]. Moreover, 80% of the nitrates ingested by humans are obtained from vegetables; thus, reducing the nitrate levels in vegetables is of paramount importance [58]. According to Figure 3b, modified biochar affects the nitrate content of pakchoi. Pakchoi’s nitrate content was significantly reduced by the addition of modified biochar, and the order of magnitude of nitrate contents in aerial parts of plants among the treatments was QKAMP < QKAM < QKAP < QKA < QM < QK < Q < QKM < YC < CK. Compared to CK, nitrate contents decreased by 46.7% and 32.1%, respectively, in YC and Q treatments, indicating that ball-milled biochar more effectively reduced nitrate uptake in pakchoi. It was found that the treatments differed significantly, with QKAMP, QKAM, QKAP, and QKA treatments having significantly low nitrate contents. The unique layered structure of attapulgite enhanced biochar adsorption capacity, allowing nutrients like nitrogen to be slowly released into the soil [59]. The nitrate contents in treatments of QKAMP and QKAM were recorded at 1954 mg kg−1 and 1964 mg kg−1, respectively, with reductions of 100.4% and 99.3%, compared to CK (3916 mg kg−1), demonstrating that these treatments substantially decreased nitrate accumulation within pakchoi. Previous studies have shown that nitrate contents in crops was closely associated with nitrogen fertilizer application, with an excessive application of nitrogen fertilizer resulting in a sharp increase in nitrate contents in leafy vegetables [60,61,62]. In this experiment, no additional nitrogen fertilizer was applied, and the modified materials used had low nitrogen content, which explained why no significant increase in nitrate contents was observed. Furthermore, the rich functional groups and porous structure in QKAMP and QKAM treatments provided more binding sites for ammonium and nitrate nitrogen [63], ensuring a stable nitrogen absorption rate by the plants, thereby reducing nitrate accumulation. Yao et al. [64] demonstrated that increasing the pyrolysis temperature of biochar to 600 °C enhances nitrate adsorption, reducing nitrate uptake by plants, which is agreeable with our results. Additionally, as a consequence of Cd stress, nitrate reductase, an enzyme that is crucial in nitrogen assimilation, may experience reducing activity under Cd stress, affecting nitrate reduction and assimilation [65,66]. Both Marousek et al. [67] and Cao et al. [68] concluded that adding biochar to the soil could increase nitrate reductase activity in plant roots, lowering nitrate concentration in plants.

3.4.3. Effects of Modified Biochar on Soluble Sugar Contents in Pakchoi

Soluble sugars are essential sources of energy and carbon for plants, playing a role in energy transfer and regulation during plant growth [69]. Based on Figure 3c, there were no significant (p > 0.05) differences in soluble sugar contents between CK and YC or Q, indicating that bulk biochar (YC) and ball milling alone could not enhance soluble sugar contents in pakchoi. By comparison, the treatments with modified biochar increased soluble sugar contents to varying degrees, with QM treatment showing a significant (p < 0.05) increase by 29.9% and 28.6% in contrast to YC and CK. The different modifications of biochar, however, did not show any significant differences. Zhang et al. [70] reported that applying calcium magnesium phosphate fertilizer increased soluble sugar contents in bananas. Wang et al. [71] applied calcium fertilizer to two different varieties of apples, finding that soluble sugar content in the harvested fruit increased by 6.3% and 12.0% compared to the control. The application of calcium magnesium phosphate fertilizer enhances nutrient contents in plants and promotes the transport of photosynthetic products and the accumulation of carbohydrates, resulting in the increase in soluble sugar contents [72]. In this study, the modifier—magnesium phosphate fertilizer—played a key role in increasing soluble sugar contents, with QM performing best because of the addition of the highest amount of calcium magnesium phosphate. Bulk biochar also contributed by providing numerous adsorption sites, reducing the loss of mineral elements, and improving nutrient uptake efficiency in pakchoi.

3.4.4. Effects of Modified Biochar on Vitamin C Content in Pakchoi

A natural antioxidant, vitamin C, is present in many plant-based products and is important for human health [73]. Figure 3d illustrates how modified biochar affects the vitamin C content of pakchoi. Compared to CK, the addition of modified biochar increased vitamin C contents in pakchoi. Specifically, the vitamin C contents increased by 36.0%, 24.9%, 22.1%, and 22.6%, respectively, in QKAMP, QKAM, QKAP, and QKA treatments compared to CK. The vitamin C contents increased by 29.6%, 19.0%, 16.3%, and 16.8%, respectively, in QKAMP, QKAM, QKAP, and QKA treatments compared to YC. Although QKM, QK, QM, and Q treatments showed a tendency to increase vitamin C contents, there no significant differences were observed compared to CK. The addition of attapulgite and polyacrylamide might have promoted vitamin C accumulation in pakchoi. Yang et al. [74] suggested that biochar improves soil enzyme activity in the rhizosphere, as well as improving the root environment. Root growth, which plays a crucial role in nutrient uptake, significantly influences vitamin C contents in plants [75]. Besides providing trace elements, the unique crystalline structure of attapulgite can reduce soil permeability while improving water retention capacity [76,77]. In previous studies, polyacrylamide was found to improve soil water retention [78] and reduce phosphorus-leaching losses [79]. Additionally, polyacrylamide applied in combination with biochar in the soil could possibly boost the growth of plants and increase soil nutrient retention [80]. On the basis of the other growth indicators, it seems evident that biochar with attapulgite and polyacrylamide significantly improved both the nutritional quality and growth performance of pakchoi.

3.5. Effects of Modified Biochar on Cd Accumulation in Pakchoi

As shown in Figure 4, both aerial parts and roots of pakchoi accumulate less Cd when 2% biochar is added to Cd-contaminated soil than when CK is added to the soil. Specifically, Cd contents in the aerial parts reduced by 36.1% and 33.6%, respectively, compared to CK (p < 0.05), and by 21.6% and 18.6%, respectively, compared to YC (p < 0.05) in QKAMP and QKAM treatments. Similarly, Cd contents in the roots treated with QKAMP and QKAM were reduced by 32.8% and 34.5%, respectively, compared to CK (p < 0.05), and by 19.5% and 21.5%, respectively, compared to YC (p < 0.05). Zhang et al. [81] reported that adding 5% ball-milled phosphorus-loaded biochar to Cd-contaminated soil significantly reduced the cadmium content in maize plants. According to other studies, chemical modification of biochar can enhance electrostatic interaction, thereby increasing its adsorption capacity for cadmium and reducing the transfer of cadmium to plants over bulk biochar [82]. In this study, QKAMP-modified biochar application at 2% in the Cd-contaminated alkaline soils (1.75 mg Cd kg−1) reduced Cd contents in both aerial and root parts of pakchoi to below 0.2 mg/kg, meeting the maximum Cd limit for leafy vegetables as set by the Chinese national Food Safety Standard for Contaminants in Food (GB 2762-2022) [83], which ensures safe vegetable production.

4. Conclusions

The results of this study showed that the application of modified biochar significantly increased soil pH and nutrient contents and reduced the bioavailable Cd in soils. The plant growth, nutrients content, and accumulation were also improved to varying degrees by the addition of modified biochar. Although the soluble sugar content and soluble protein contents in plants did not differ significantly from other treatments, QKAMP and QKAM significantly reduced nitrate levels and enhanced vitamin C concentrations in pakchoi compared to bulk biochar and CK. More importantly, modified biochar could reduce the accumulation of Cd in pakchoi, among which the Cd content in pakchoi for QKAMP treatment was within the safe range specified by the national standard. Based on the above results, QKAMP was recommended to be the optimal modified biochar for the safe production of pakchoi in the mild to moderate Cd-contaminated soils under weakly alkaline soil pH conditions. Further studies will explore the feasibility and stability of modified biochar across diverse soil types and varying cadmium contamination levels as well as various vegetable types in order to optimize operational and economical parameters for large-scale applications.

Author Contributions

All authors contributed to the study conception and design. G.P.: writing—original draft, methodology, investigation, formal analysis, data curation. S.G.: investigation, data curation, software. L.W.: investigation, formal analysis, visualization. J.X.: writing—review and editing, validation. G.F.: writing—review and editing. Y.G.: supervision, writing—review and editing, project administration. X.L.: supervision, writing—review and editing, resources, project administration. Z.Z.: supervision, writing—review and editing, methodology. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by Jiangsu Provincial Agricultural Science and Technology Independent Innovation Fund [SCX(24)1132] and National Natural Science Foundation of China (32273137).

Data Availability Statement

The datasets used or analyzed during the current study are available from the corresponding author upon reasonable request.

Acknowledgments

This work was supported by Jiangsu Provincial Agricultural Science and Technology Independent Innovation Fund [SCX(24)1132] and National Natural Science Foundation of China (32273137).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Ahmad, M.; Rajapaksha, A.U.; Lim, J.E.; Zhang, M.; Bolan, N.; Mohan, D.; Vithanage, M.; Lee, S.S.; Ok, Y.S. Biochar as a sorbent for contaminant management in soil and water: A review. Chemosphere 2014, 99, 19–33. [Google Scholar] [CrossRef] [PubMed]
  2. Han, L.F.; Gao, B.; Hao, H.; Zhou, H.D.; Lu, J.; Sun, K. Lead Contamination in Sediments in the Past 20 Years: A Challenge for China. Sci. Total Environ. 2018, 640, 746–756. [Google Scholar] [CrossRef] [PubMed]
  3. Park, J.H.; Lamb, D.; Paneerselvam, P.; Choppala, G.; Bolan, N.; Chung, J.W. Role of Organic Amendments on Enhanced Bioremediation of Heavy Metal (loid) Contaminated Soils. J. Hazard. Mater. 2011, 185, 549–574. [Google Scholar] [CrossRef] [PubMed]
  4. Albert, H.A.; Li, X.; Jeyakumar, P.; Wei, L.; Huang, L.X.; Huang, Q.; Kamran, M.; Shaheen, S.M.; Hou, D.Y.; Rinklebe, J.; et al. Influence of Biochar and Soil Properties on Soil and Plant Tissue Concentrations of Cd and Pb: A Meta-Analysis. Sci. Total Environ. 2021, 755, 142582. [Google Scholar] [CrossRef]
  5. He, L.Z.; Zhong, H.; Liu, G.X.; Dai, Z.M.; Brookes, P.C.; Xu, J. Remediation of Heavy Metal Contaminated Soils by Biochar: Mechanisms, Potential Risks and Applications in China. Environ. Pollut. 2019, 252, 846–855. [Google Scholar] [CrossRef]
  6. Xu, D.M.; Fu, R.B.; Wang, J.X.; Shi, Y.X.; Guo, X.P. Chemical Stabilization Remediation for Heavy Metals in Contaminated Soils on the Latest Decade: Available Stabilizing Materials and Associated Evaluation Methods—A Critical Review. J. Clean. Prod. 2021, 321, 128730. [Google Scholar] [CrossRef]
  7. Younis, U.; Qayyum, M.F.; Shah, M.H.R.; Danish, S.; Shahzad, A.N.; Malik, S.A.; Mahmood, S. Growth, Survival, and Heavy Metal (Cd and Ni) Uptake of Spinach (Spinacia oleracea) and Fenugreek (Trigonella corniculata) in a Biochar-Amended Sewage-Irrigated Contaminated Soil. J. Plant Nutr. Soil Sci. 2015, 178, 209–217. [Google Scholar] [CrossRef]
  8. Qi, F.J.; Lamb, D.; Naidu, R.; Bolan, N.S.; Yan, Y.B.; Ok, Y.S.; Rahman, M.M.; Choppala, G. Cadmium Solubility and Bioavailability in Soils Amended with Acidic and Neutral Biochar. Sci. Total Environ. 2018, 610, 1457–1466. [Google Scholar] [CrossRef]
  9. Abou Jaoude, L.; Castaldi, P.; Nassif, N.; Pinna, M.V.; Garau, G. Biochar and Compost as Gentle Remediation Options for the Recovery of Trace Elements-Contaminated Soils. Sci. Total Environ. 2020, 711, 134511. [Google Scholar] [CrossRef]
  10. Pandit, N.R.; Mulder, J.; Hale, S.E.; Martinsen, V.; Schmidt, H.P.; Cornelissen, G. Biochar Improves Maize Growth by Alleviation of Nutrient Stress in a Moderately Acidic Low-Input Nepalese Soil. Sci. Total Environ. 2018, 625, 1380–1389. [Google Scholar] [CrossRef]
  11. You, X.W.; Yin, S.J.; Suo, F.Y.; Xu, Z.C.; Chu, D.P.; Kong, Q.X.; Zhang, C.S.; Li, Y.Q.; Liu, L. Biochar and Fertilizer Improved the Growth and Quality of the Ice Plant (Mesembryanthemum crystallinum L.) Shoots in a Coastal Soil of Yellow River Delta, China. Sci. Total Environ. 2021, 775, 144893. [Google Scholar] [CrossRef] [PubMed]
  12. Fang, W.; Yang, Y.; Wang, H.L.; Yang, D.X.; Luo, J.; Williams, P.N. Rice Rhizospheric Effects on the Bioavailability of Toxic Trace Elements during Land Application of Biochar. Environ. Sci. Technol. 2021, 55, 7344–7354. [Google Scholar] [CrossRef] [PubMed]
  13. Zhang, D.; Ding, A.F.; Li, T.; Wu, X.X. Effects of Passivators on Artemisia selengensis Yield and Cd Stabilization in a Contaminated Soil. Pol. J. Environ. Stud. 2021, 30, 1903–1912. [Google Scholar] [CrossRef]
  14. Trifunovic, B.; Gonzales, H.B.; Ravi, S.; Sharratt, B.S.; Mohanty, S.K. Dynamic Effects of Biochar Concentration and Particle Size on Hydraulic Properties of Sand. Land Degrad. Dev. 2018, 29, 884–893. [Google Scholar] [CrossRef]
  15. Zou, L.; Tan, W.K.; Du, Y.Y.; Lee, H.W.; Liang, X.; Lei, J.J.; Striegel, L.; Weber, N.; Rychlik, M.; Ong, C.N. Nutritional Metabolites in Brassica Rapa Subsp. Chinensis Var. Parachinensis (Choy sum) at Three Different Growth Stages: Microgreen, Seedling and Adult Plant. Food Chem. 2021, 357, 129535. [Google Scholar] [CrossRef]
  16. Yang, J.X.; Guo, H.T.; Ma, Y.B.; Wang, L.Q.; Wei, D.P.; Hua, L.O. Genotypic Variations in the Accumulation of Cd Exhibited by Different Vegetables. J. Environ. Sci. 2010, 22, 1246–1252. [Google Scholar] [CrossRef]
  17. Pan, G.J.; Lu, X.; Yang, Z.Q.; Chen, B.F.; Geng, S.F.; Fan, G.P.; Gao, Y.; Ying, X.L. Adsorption Characteristics of Composite Modified Biochar and Its Passivation Effect on Farmland Soil with Light to Moderate Cadmium Pollution. Jiangsu J. Agric. Sci. 2024, 40, 457–468. (In Chinese) [Google Scholar]
  18. Luo, S.S.; Tian, L.; Chang, C.L.; Wang, S.J.; Zhang, J.F.; Zhou, X.; Li, X.J.; Tran, L.S.P.; Tian, C.J. Grass and Maize Vegetation Systems Restore Saline-Sodic Soils in the Songnen Plain of Northeast China. Land Degrad. Dev. 2018, 29, 1107–1119. [Google Scholar] [CrossRef]
  19. Qian, M.J.; Zhou, W.X.; Wang, S.F.; Li, Y.T.; Cao, Y.G. The Influence of Soil Erodibility and Saturated Hydraulic Conductivity on Soil Nutrients in the Pingshuo Opencast Coalmine, China. Int. J. Environ. Res. Public Health 2022, 19, 1762. [Google Scholar] [CrossRef]
  20. GB/T 23739-2009; Soil Quality—Analysis of Available Lead and Cadmium Contents in Soils—Atomic Absorption Spectrometry. Standards Press of China: Beijing, china, 2009.
  21. Pandey, V.; Patel, A.; Patra, D.D. Biochar Ameliorates Crop Productivity, Soil Fertility, Essential Oil Yield and Aroma Profiling in Basil (Ocimum basilicum L.). Ecol. Eng. 2016, 90, 361–366. [Google Scholar] [CrossRef]
  22. Richardson, A.D.; Duigan, S.P.; Berlyn, G.P. An Evaluation of Noninvasive Methods to Estimate Foliar Chlorophyll Content. New Phytol. 2002, 153, 185–194. [Google Scholar] [CrossRef]
  23. Deans, C.A.; Sword, G.A.; Lenhart, P.A.; Burkness, E.; Hutchison, W.D.; Behmer, S.T. Quantifying Plant Soluble Protein and Digestible Carbohydrate Content, Using Corn (Zea mays) as an Exemplar. Jove-J. Vis. Exp. 2018, 138, e58164. [Google Scholar] [CrossRef]
  24. Neata, G.; Hoza, G.; Teodorescu, R.I.; Basaraba, A.; Petcuci, A.; Sima, R. Phosphorus, Potassium and Nitrate Contents in Fruit of Pickling Cucumbers Grown in a High Tunnel. Notul. Bot. Horti Agrobot. Cluj-Napoca. 2016, 44, 541–547. [Google Scholar] [CrossRef]
  25. Salehi, A.; Tasdighi, H.; Gholamhoseini, M. Evaluation of Proline, Chlorophyll, Soluble Sugar Content and Uptake of Nutrients in the German Chamomile (Matricaria chamomilla L.) under Drought Stress and Organic Fertilizer Treatments. Asian Pac. J. Trop. Biomed. 2016, 6, 886–891. [Google Scholar] [CrossRef]
  26. Stevens, R.; Buret, M.; Garchery, C.; Carretero, Y.; Causse, M. Technique for Rapid, Small-Scale Analysis of Vitamin C Levels in Fruit and Application to a Tomato Mutant Collection. J. Agric. Food Chem. 2006, 54, 6159–6165. [Google Scholar] [CrossRef] [PubMed]
  27. GB 5009.15-2023; National Food Safety Standard—Determination of Cadmium in Foods. Standards Press of China: Beijing, China, 2023.
  28. Rees, F.; Simonnot, M.O.; Morel, J.L. Short-Term Effects of Biochar on Soil Heavy Metal Mobility Are Controlled by Intra-Particle Diffusion and Soil pH Increase. Eur. J. Soil. Sci. 2014, 65, 149–161. [Google Scholar] [CrossRef]
  29. Bashir, S.; Zhu, J.; Fu, Q.L.; Hu, H.Q. Cadmium Mobility, Uptake and Anti-Oxidative Response of Water Spinach (Ipomoea aquatic) under Rice Straw Biochar, Zeolite and Rock Phosphate as Amendments. Chemosphere 2018, 194, 579–587. [Google Scholar] [CrossRef]
  30. Tang, J.Y.; Zhang, L.H.; Zhang, J.C.; Ren, L.H.; Zhou, Y.Y.; Zheng, Y.Y.; Luo, L.; Yang, Y.; Huang, H.L.; Chen, A.W. Physicochemical Features, Metal Availability and Enzyme Activity in Heavy Metal-Polluted Soil Remediated by Biochar and Compost. Sci. Total Environ. 2020, 701, 134751. [Google Scholar] [CrossRef]
  31. Rashid, M.; Hussain, Q.; Hayat, R.; Ahmad, M.; Azeem, M.; Alvi, S.; Chaudhry, A.N.; Masood, S.; Khalid, R.; Jehan, S.; et al. Deashed Biochar as N-Carrier Extended the N-Release by Inhibiting N-Losses in Calcareous Soils. Biomass Convers. Bior. 2023, 13, 9549–9564. [Google Scholar] [CrossRef]
  32. Mohamed, I.; Zhang, G.S.; Li, Z.G.; Liu, Y.; Chen, F.; Dai, K. Ecological Restoration of an Acidic Cd Contaminated Soil Using Bamboo Biochar Application. Ecol. Eng. 2015, 84, 67–76. [Google Scholar] [CrossRef]
  33. Wang, M.; Wang, J.J.; Wang, X.D. Effect of KOH-Enhanced Biochar on Increasing Soil Plant-Available Silicon. Geoderma 2018, 321, 22–31. [Google Scholar] [CrossRef]
  34. Wang, M.; Wang, J.; Park, J.H.; Wang, J.; Wang, X.D.; Zhao, Z.P.; Song, F.M.; Tang, B. Pyrolysis Temperature Affects Dissolved Phosphorus and Carbon Levels in Alkali-Enhanced Biochar and Its Soil Applications. Agronomy 2022, 12, 1923. [Google Scholar] [CrossRef]
  35. Zhou, L.; Su, L.Z.; Zhang, L.Y.; Zhang, L.; Zheng, Y.; Tang, L. Effect of Different Types of Phosphate Fertilizer on Phosphorus Absorption and Desorption in Acidic Red Soil of Southwest China. Sustainability 2022, 14, 9973. [Google Scholar] [CrossRef]
  36. Qin, J.M.; Li, J.X.; Pei, H.H.; Li, Q.H.; Cheng, D.M.; Zhou, J.; Pei, G.P.; Wang, Y.Y.; Liu, F.W. Effective Remediation and Phytotoxicity Assessment of Oxytetracycline and Cd Co-Contaminated Soil Using Biochar. Environ. Technol. Innov. 2024, 35, 103649. [Google Scholar] [CrossRef]
  37. Makino, A. Photosynthesis, Grain Yield, and Nitrogen Utilization in Rice and Wheat. Plant Physiol. 2011, 155, 125–129. [Google Scholar] [CrossRef]
  38. Feng, W.Y.; Yang, F.; Cen, R.; Liu, J.; Qu, Z.Y.; Miao, Q.F.; Chen, H.Y. Effects of Straw Biochar Application on Soil Temperature, Available Nitrogen and Growth of Corn. J. Environ. Manag. 2021, 277, 111331. [Google Scholar] [CrossRef]
  39. Jabborova, D.; Wirth, S.; Halwani, M.; Ibrahim, M.F.M.; El Azab, I.H.; El-Mogy, M.M.; Elkelish, A. Growth Response of Ginger (Zingiber officinale), Its Physiological Properties and Soil Enzyme Activities after Biochar Application under Greenhouse Conditions. Horticulturae 2021, 7, 250. [Google Scholar] [CrossRef]
  40. Loudari, A.; Mayane, A.; Zeroual, Y.; Colinet, G.; Oukarroum, A. Photosynthetic Performance and Nutrient Uptake under Salt Stress: Differential Responses of Wheat Plants to Contrasting Phosphorus Forms and Rates. Front. Plant Sci. 2022, 13, 1038672. [Google Scholar] [CrossRef]
  41. Naciri, R.; Chtouki, M.; Oukarroum, A. Mechanisms of Cadmium Mitigation in Tomato Plants under Orthophosphate and Polyphosphate Fertilization Regimes. Ecotoxicol. Environ. Saf. 2024, 274, 116219. [Google Scholar] [CrossRef]
  42. Battie-Laclau, P.; Laclau, J.P.; Beri, C.; Mietton, L.; Muniz, M.R.A.; Arenque, B.C.; Piccolo, M.D.C.; Jordan-Meille, L.; Bouillet, J.P.; Nouvellon, Y. Photosynthetic and Anatomical Responses of Eucalyptus grandis Leaves to Potassium and Sodium Supply in a Field Experiment. Plant Cell Environ. 2014, 37, 70–81. [Google Scholar] [CrossRef]
  43. Agbna, G.H.D.; She, D.L.; Liu, Z.P.; Elshaikh, N.A.; Shao, G.C.; Timm, L.C. Effects of Deficit Irrigation and Biochar Addition on the Growth, Yield, and Quality of Tomato. Sci. Hortic. 2017, 222, 90–101. [Google Scholar] [CrossRef]
  44. Wang, M.; Wu, J.; Zhou, T.; Liang, Y.; Zheng, L.X.; Sun, Y.X. Effects of Copper and Florfenicol on nirS- and nirK-Type Denitrifier Communities and Related Antibiotic Resistance in Vegetable Soils. Ecotoxicol. Environ. Saf. 2021, 213, 112001. [Google Scholar] [CrossRef] [PubMed]
  45. Oguntunde, P.G.; Abiodun, B.J.; Ajayi, E.A.; van de Giesen, N. Effects of charcoal production on soil physical properties in Ghana. J. Plant Nutr. Soil Sci. 2008, 171, 591–596. [Google Scholar] [CrossRef]
  46. Wang, L.; Wang, Y.J.; Ma, F.; Tankpa, V.; Bai, S.S.; Guo, X.M.; Wang, X. Mechanisms and reutilization of modified biochar used for removal of heavy metals from wastewater: A review. Sci. Total Environ. 2019, 668, 1298–1309. [Google Scholar] [CrossRef]
  47. Rasul, M.; Cho, J.; Shin, H.S.; Hur, J. Biochar-induced priming effects in soil via modifying the status of soil organic matter and microflora: A review. Sci. Total Environ. 2022, 805, 150304. [Google Scholar] [CrossRef]
  48. Diaz, U.; Saliba-Colombani, V.; Loudet, O.; Belluomo, P.; Moreau, L.; Daniel-Vedele, F.; Morot-Gaudry, J.F.; Maselaux-Daubresse, U. Leaf yellowing and anthocyanin accumulation are two genetically independent strategies in response to nitrogen limitation in Arabidopsis thaliana. Plant Cell Physiol. 2006, 47, 74–83. [Google Scholar] [CrossRef]
  49. Gul, S.; Whalen, J.K.; Thomas, B.W.; Sachdeva, V.; Deng, H.Y. Physico-chemical properties and microbial responses in biochar-amended soils: Mechanisms and future directions. Agric. Ecosyst. Environ. 2015, 206, 46–59. [Google Scholar] [CrossRef]
  50. Lehmann, J. A handful of carbon. Nature 2007, 447, 143–144. [Google Scholar] [CrossRef]
  51. Sahebdelfar, N.; Khorasani, R.; Astaraei, A. Effect of some additives on heavy metals behavior and phytoavailability in municipal solid waste compost-amended soil. Int. J. Environ. Sci. Technol. 2022, 19, 307–318. [Google Scholar] [CrossRef]
  52. Peng, X.; Ye, L.L.; Wang, C.H.; Zhou, H.; Sun, B. Temperature- and duration-dependent rice straw-derived biochar: Characteristics and its effects on soil properties of an Ultisol in southern China. Soil. Tillage Res. 2011, 112, 159–166. [Google Scholar] [CrossRef]
  53. Sani, M.N.H.; Hasan, M.; Uddain, J.; Subramaniam, S. Impact of application of Trichoderma and biochar on growth, productivity and nutritional quality of tomato under reduced N-P-K fertilization. AOAS 2020, 65, 107–115. [Google Scholar] [CrossRef]
  54. Sytar, O.; Kumari, P.; Yadav, S.; Brestic, M.; Rastogi, A. Phytohormone priming: Regulator for heavy metal stress in plants. J. Plant Growth Regul. 2019, 38, 739–752. [Google Scholar] [CrossRef]
  55. Monterumici, C.M.; Rosso, D.; Montoneri, E.; Ginepro, M.; Baglieri, A.; Novotny, E.H.; Kwapinski, W.; Negre, M. Processed vs. non-processed biowastes for agriculture: Effects of post-harvest tomato plants and biochar on radish growth, chlorophyll content and protein production. Int. J. Mol. Sci. 2015, 16, 8826–8843. [Google Scholar] [CrossRef]
  56. Bi, R.Y.; Zhang, Q.Q.; Zhan, L.P.; Xu, X.T.; Zhang, X.; Dong, Y.B.; Yan, X.Y.; Xiong, Z.Q. Biochar and organic substitution improved net ecosystem economic benefit in intensive vegetable production. Biochar 2022, 4, 46. [Google Scholar] [CrossRef]
  57. Devlamynck, R.; de Souza, M.F.; Bog, M.; Leenknegt, J.; Eeckhout, M.; Meers, E. Effect of the growth medium composition on nitrate accumulation in the novel protein crop Lemna minor. Ecotoxicol. Environ. Saf. 2020, 206, 111380. [Google Scholar] [CrossRef] [PubMed]
  58. Mohammadpour, A.; Tabatabaei, Z.; Rigi, A.M.; Shahsavani, S.; Shahsavani, E.; Derakhshan, Z.; Khaneghah, A.M. Nitrate levels in Iranian potatoes and tomatoes: Application of deterministic and probabilistic approaches potential health risks. J. Food Compos. Anal. 2023, 121, 105381. [Google Scholar] [CrossRef]
  59. Mu, B.; Wang, A.Q. One-pot fabrication of multifunctional superparamagnetic attapulgite/Fe3O4/polyaniline nanocomposites served as an adsorbent and catalyst support. J. Mater. Chem. A 2015, 3, 281–289. [Google Scholar] [CrossRef]
  60. Deng, R.; Huang, D.L.; Wan, J.; Xue, W.J.; Lei, L.; Wen, X.F.; Liu, X.G.; Chen, S.; Yang, Y.; Li, Z.H.; et al. Chloro-phosphate impregnated biochar prepared by co-precipitation for the lead, cadmium and copper synergic scavenging from aqueous solution. Bioresour. Technol. 2019, 293, 122102. [Google Scholar] [CrossRef]
  61. Kyriacou, M.C.; Soteriou, G.A.; Colla, G.; Rouphael, Y. The occurrence of nitrate and nitrite in Mediterranean fresh salad vegetables and its modulation by preharvest practices and postharvest conditions. Food Chem. 2019, 285, 468–477. [Google Scholar] [CrossRef]
  62. Wu, S.H.; Liu, Y.H.; Cui, X.; Zhang, Q.; Wang, Y.P.; Cao, L.P.; Luo, X.; Xiong, J.H.; Ruan, R.G. Assessment of potential nitrite safety risk of leafy vegetables after domestic cooking. Foods 2021, 10, 2953. [Google Scholar] [CrossRef]
  63. Rivelli, A.R.; Libutti, A. Effect of biochar and inorganic or organic fertilizer co-application on soil properties, plant growth and nutrient content in swiss chard. Agronomy 2022, 12, 2089. [Google Scholar] [CrossRef]
  64. Yao, Y.; Gao, B.; Zhang, M.; Inyang, M.; Zimmerman, A.R. Effect of biochar amendment on sorption and leaching of nitrate, ammonium, and phosphate in a sandy soil. Chemosphere 2012, 89, 1467–1471. [Google Scholar] [CrossRef] [PubMed]
  65. Taghavi, T.S.; Babalar, M. The effect of nitrate and plant size on nitrate uptake and in vitro nitrate reductase activity in strawberry (Fragaria × ananassa cv. Selva). Sci. Hortic. 2007, 112, 393–398. [Google Scholar] [CrossRef]
  66. Yang, Y.J.; Xiong, J.; Tao, L.X.; Cao, Z.Z.; Tang, W.; Zhang, J.P.; Yu, X.Y.; Fu, G.F.; Zhang, X.F.; Lu, Y.L. Regulatory mechanisms of nitrogen (N) on cadmium (Cd) uptake and accumulation in plants: A review. Sci. Total Environ. 2020, 708, 35186. [Google Scholar] [CrossRef] [PubMed]
  67. Marousek, J.; Kolár, L.; Vochozka, M.; Stehel, V.; Marousková, A. Biochar reduces nitrate level in red beet. Environ. Sci. Pollut. Res. 2018, 25, 18200–18203. [Google Scholar] [CrossRef]
  68. Cao, H.; Ning, L.F.; Xun, M.; Feng, F.; Li, P.; Yue, S.Q.; Song, J.F.; Zhang, W.W.; Yang, H.Q. Biochar can increase nitrogen use efficiency of Malus hupehensis by modulating nitrate reduction of soil and root. Appl. Soil. Ecol. 2019, 135, 25–32. [Google Scholar] [CrossRef]
  69. Rosa, M.; Prado, C.; Podazza, G.; Interdonato, R.; González, J.A.; Hilal, M.; Prado, F.E. Soluble sugars: Metabolism, sensing and abiotic stress: A complex network in the life of plants. Plant Signal. Behav. 2009, 4, 388–393. [Google Scholar] [CrossRef]
  70. Zhang, J.Z.; Li, B.S.; Zhang, J.L.; Christie, P.; Li, X.L. Organic fertilizer application and Mg fertilizer promote banana yield and quality in an Udic Ferralsol. PLoS ONE 2020, 15, e0230593. [Google Scholar] [CrossRef]
  71. Wang, G.P.; Wang, J.Z.; Han, X.P.; Chen, R.; Xue, X.M. Effects of spraying calcium fertilizer on photosynthesis, mineral content, sugar-acid metabolism and fruit quality of Fuji apples. Agronomy 2022, 12, 2563. [Google Scholar] [CrossRef]
  72. Cakmak, I.; Hengeler, C.; Marschner, H. Changes in phloem export of sucrose in leaves in response to phosphorus, potassium and magnesium-deficiency in bean-plants. J. Exp. Bot. 1994, 45, 1251–1257. [Google Scholar] [CrossRef]
  73. Giannakourou, M.C.; Taoukis, P.S. Effect of alternative preservation steps and storage on vitamin C stability in fruit and vegetable products: Critical review and kinetic modelling approaches. Foods 2021, 10, 2630. [Google Scholar] [CrossRef] [PubMed]
  74. Yang, S.H.; Chen, X.; Jiang, Z.W.; Ding, J.; Sun, X.; Xu, J.Z. Effects of biochar application on soil organic carbon composition and enzyme activity in paddy soil under water-saving irrigation. Int. J. Environ. Res. Public Health 2020, 17, 333. [Google Scholar] [CrossRef] [PubMed]
  75. Shi, L.R.; Zheng, W.; Lei, T.; Liu, X.S.; Hui, M.X. The effect of different soil amendments on soil properties and on the morphological and physiological characteristics of Chinese cabbage. J. Soil. Sci. Plant Nutr. 2021, 21, 1500–1510. [Google Scholar] [CrossRef]
  76. Khalifa, A.Z.; Cizer, Ö.; Pontikes, Y.; Heath, A.; Patureau, P.; Bernal, S.A.; Marsh, A.T.M. Advances in alkali-activation of clay minerals. Cement Concrete. Res. 2020, 132, 106050. [Google Scholar] [CrossRef]
  77. Yang, M.; Dai, J.H.; Wang, L.J.; Li, Y.; Song, Y. First principles study of structural stability against the distribution of Mg and Al atoms and adsorption behaviors of heavy metals of attapulgite. Comput. Mater. Sci. 2019, 169, 109106. [Google Scholar] [CrossRef]
  78. Wei, K.; Zhang, J.H.; Wang, Q.J.; Chen, Y.; Ding, Q. Effects of ionized brackish water and polyacrylamide application on infiltration characteristics and improving water retention and reducing soil salinity. Can. J. Soil Sci. 2021, 101, 324–334. [Google Scholar] [CrossRef]
  79. Jiang, T.; Teng, L.L.; Wei, S.Q.; Deng, L.L.; Luo, Z.B.; Chen, Y.P.; Flanagan, D.C. Application of polyacrylamide to reduce phosphorus losses from a Chinese purple soil: A laboratory and field investigation. J. Environ. Manag. 2010, 91, 1437–1445. [Google Scholar] [CrossRef]
  80. Awad, Y.M.; Blagodatskaya, E.; Ok, Y.S.; Kuzyakov, Y. Effects of polyacrylamide, biopolymer and biochar on the decomposition of 14C-labelled maize residues and on their stabilization in soil aggregates. Eur. J. Soil Sci. 2013, 64, 488–499. [Google Scholar] [CrossRef]
  81. Zhang, P.; Xue, B.; Jiao, L.; Meng, X.Y.; Zhang, L.Y.; Li, B.X.; Sun, H.W. Preparation of ball-milled phosphorus-loaded biochar and its highly effective remediation for Cd- and Pb-contaminated alkaline soil. Sci. Total Environ. 2022, 813, 152648. [Google Scholar] [CrossRef]
  82. Ghassemi-Golezani, K.; Farhangi-Abriz, S. Biochar related treatments improved physiological performance, growth and productivity of Mentha crispa L. plants under fluoride and cadmium toxicities. Ind. Crops Prod. 2023, 194, 116287. [Google Scholar] [CrossRef]
  83. GB 2762-2022; National Food Safety Standard—Limits of Contaminants in Food. Standards Press of China: Beijing, China, 2022.
Plants 14 00524 g001
Figure 1. Effects of modified biochar on chlorophyll a (a), chlorophyll b (b), chlorophyll a + b (c), and chlorophyll a/b (d) contents in pakchoi. Note: Error bars represent the standard deviation of triplicate samples. Different letters above bars indicate a significant difference at p < 0.05.
Figure 1. Effects of modified biochar on chlorophyll a (a), chlorophyll b (b), chlorophyll a + b (c), and chlorophyll a/b (d) contents in pakchoi. Note: Error bars represent the standard deviation of triplicate samples. Different letters above bars indicate a significant difference at p < 0.05.
Plants 14 00524 g001
Plants 14 00524 g002
Figure 2. Effects of modified biochar on the content of total nitrogen (a), total phosphorus (b) and total potassium (c) in different parts of pakchoi and the total accumulation of nitrogen (d), total phosphorus (e), and total potassium (f) in different parts of pakchoi. Note: Error bars represent the standard deviation of triplicate samples. Different letters above bars indicate a significant difference at p < 0.05.
Figure 2. Effects of modified biochar on the content of total nitrogen (a), total phosphorus (b) and total potassium (c) in different parts of pakchoi and the total accumulation of nitrogen (d), total phosphorus (e), and total potassium (f) in different parts of pakchoi. Note: Error bars represent the standard deviation of triplicate samples. Different letters above bars indicate a significant difference at p < 0.05.
Plants 14 00524 g002
Plants 14 00524 g003
Figure 3. Effects of modified biochar on soluble protein content (a), nitrate content (b), soluble sugar content (c), and vitamin C content (d) in pakchoi. Note: Error bars represent the standard deviation of triplicate samples. Different letters above bars indicate a significant difference at p < 0.05.
Figure 3. Effects of modified biochar on soluble protein content (a), nitrate content (b), soluble sugar content (c), and vitamin C content (d) in pakchoi. Note: Error bars represent the standard deviation of triplicate samples. Different letters above bars indicate a significant difference at p < 0.05.
Plants 14 00524 g003
Plants 14 00524 g004
Figure 4. Effect of modified biochar on Cd contents in aerial parts and roots of pakchoi. Note: Error bars represent the standard deviation of triplicate samples. Different letters above or below bars, respectively, indicate a significant difference at p < 0.05.
Figure 4. Effect of modified biochar on Cd contents in aerial parts and roots of pakchoi. Note: Error bars represent the standard deviation of triplicate samples. Different letters above or below bars, respectively, indicate a significant difference at p < 0.05.
Plants 14 00524 g004
Table 1. Tested-treatments list.
Table 1. Tested-treatments list.
TreatmentBiochar Modification Ratio
(Mass Ratio)		Treatment Abbreviation
Untreated soil-CK
Bulk Biochar (unmodified)10:0YC
Biochar (ball-milled modified)10:0Q
Biochar + Potassium hydroxide modified by ball milling10:1QK
Biochar + Calcium magnesium phosphate fertilizer modified by ball milling10:1QM
Biochar + Potassium hydroxide + Attapulgite modified by ball milling10:0.5:0.5QKA
Biochar + Potassium hydroxide + Calcium magnesium phosphate fertilizer modified by ball milling10:0.5:0.5QKM
Biochar + Potassium hydroxide + Attapulgite + Calcium magnesium phosphate fertilizer modified by ball milling10:0.5:0.3:0.2QKAM
Biochar + Potassium hydroxide +Attapulgite + Polyacrylamide (PAM1200-) modified by ball milling10:0.5:0.5:0.005QKAP
Biochar + Potassium hydroxide +Attapulgite + Calcium magnesium phosphate + Polyacrylamide (PAM1200-) Modified by ball milling10:0.5:0.3:0.2:0.005QKAMP
Table 2. Effect of modified biochar on the physico-chemical properties and available Cd contents in soils.
Table 2. Effect of modified biochar on the physico-chemical properties and available Cd contents in soils.
TreatmentspHTotal Nitrogen
(g kg−1)		Organic Matter
(g kg−1)		Available
Potassium
(mg kg−1)		Available Phosphorus
(mg kg−1)		Available Cadmium
(mg kg−1)
QKAMP7.78 a1.98 ab77.09 b257.13 b42.10 c0.83 f
QKAM7.72 ab1.99 a76.00 b258.22 b42.63 c0.85 ef
QKAP7.46 d1.99 a78.48 ab246.25 b38.38 de0.88 ef
QKA7.49 d1.98 a76.47 b253.26 b38.99 d0.88 de
QKM7.71 b1.99 a79.86 ab255.67 b52.26 b0.87 de
QM7.63 c1.94 b82.65 a90.50 c58.18 a0.87 de
QK7.76 ab1.97 ab78.87 ab362.50 a35.93 ef0.90 d
Q7.25 e1.97 ab78.93 ab83.00 c35.82 ef0.95 c
YC7.28 e1.99 a80.21 ab91.00 c35.05 f1.00 b
CK7.07 f1.84 c33.58 c74.00 c35.41 f1.11 a
Note: Values with the different letters in the same columns are significantly different (p < 0.05).
Table 3. Effect of modified biochar on the growth and biomass of pakchoi.
Table 3. Effect of modified biochar on the growth and biomass of pakchoi.
TreatmentsPlant Height
(cm)		Root Length
(cm)		Arial Part Fresh Weight
(g pot−1)		Root Fresh Weight
(g pot−1)		Aerial Part Dry Weight
(g pot−1)		Root Dry Weight
(g pot−1)
QKAMP21.42 ± 0.91 a10.55 ± 0.35 a111.85 ± 5.59 ab12.54 ± 0.15 b9.14 ± 0.57 a1.97 ± 0.03 ab
QKAM21.20 ± 0.62 ab10.33 ± 1.06 a109.56 ± 3.15 ab13.78 ± 0.42 a9.09 ± 0.45 a2.07 ± 0.13 ab
QKAP21.54 ± 0.61 a10.06 ± 0.84 a110.34 ± 8.35 ab12.68 ± 0.30 b8.42 ± 0.36 a1.91 ± 0.11 abc
QKA20.89 ± 0.18 ab10.16 ± 1.01 a107.13 ± 3.14 b12.81 ± 0.33 b8.49 ± 0.35 a1.87 ± 0.08 bc
QKM21.32 ± 0.26 a9.56 ± 0.49 ab108.73 ± 2.79 ab13.69 ± 0.54 a8.92 ± 0.57 a2.11 ± 0.16 a
QM21.35 ± 0.48 a10.17 ± 0.58 a116.73 ± 4.18 a12.75 ± 0.30 b8.80 ± 0.47 a1.97 ± 0.13 ab
QK21.20 ± 0.43 ab9.75 ± 0.73 ab108.26 ± 5.54 ab13.23 ± 0.29 ab8.77 ± 0.24 a2.03 ± 0.12 ab
Q21.35 ± 0.48 a9.51 ± 0.67 ab110.93 ± 3.77 ab12.80 ± 0.40 b8.55 ± 0.47 a1.97 ± 0.09 ab
YC21.28 ± 1.50 a8.48 ± 1.00 bc106.53 ± 4.17 b12.73 ± 0.29 b8.72 ± 0.43 a1.91 ± 0.12 abc
CK19.70 ± 0.35 b7.96 ± 0.49 c96.70 ± 3.79 c11.76 ± 0.33 c7.46 ± 0.55 b1.71 ± 0.08 c
Note: Values with the different letters in the same columns are significantly different (p < 0.05).
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Pan, G.; Geng, S.; Wang, L.; Xing, J.; Fan, G.; Gao, Y.; Lu, X.; Zhang, Z. Effects of Modified Biochar on Growth, Yield, and Quality of Brassica chinensis L. in Cadmium Contaminated Soils. Plants 2025, 14, 524. https://doi.org/10.3390/plants14040524

AMA Style

Pan G, Geng S, Wang L, Xing J, Fan G, Gao Y, Lu X, Zhang Z. Effects of Modified Biochar on Growth, Yield, and Quality of Brassica chinensis L. in Cadmium Contaminated Soils. Plants. 2025; 14(4):524. https://doi.org/10.3390/plants14040524

Chicago/Turabian Style

Pan, Guojun, Shufang Geng, Liangliang Wang, Jincheng Xing, Guangping Fan, Yan Gao, Xin Lu, and Zhenhua Zhang. 2025. "Effects of Modified Biochar on Growth, Yield, and Quality of Brassica chinensis L. in Cadmium Contaminated Soils" Plants 14, no. 4: 524. https://doi.org/10.3390/plants14040524

APA Style

Pan, G., Geng, S., Wang, L., Xing, J., Fan, G., Gao, Y., Lu, X., & Zhang, Z. (2025). Effects of Modified Biochar on Growth, Yield, and Quality of Brassica chinensis L. in Cadmium Contaminated Soils. Plants, 14(4), 524. https://doi.org/10.3390/plants14040524

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop