Growth, physiological, and temperature characteristics in chinese cabbage pakchoi as affected by Cd- stressed conditions and identifying its main controlling factors using PLS model.

BACKGROUND: Although hormesis induced by heavy metals is a well-known phenomenon, the involved biological mechanisms are not fully understood. Cadmium (Cd) is a prevalent heavy metal in the environment. Exposure of Cd, via intake or consumption of Cd-contaminated air or food, poses a huge threat to human health. Chinese cabbage pakchoi (Brassica chinensis L.) is widely planted and consumed as a popular vegetable in China. Therefore, studying the response of Chinese cabbage pakchoi to Cd- stressed conditions is critical to assess whether cabbage can accumulate Cd and serve as an important Cd exposure pathway to human beings. In this study, we investigated the influence of Cd stress on growth, photosynthetic physiology, antioxidant enzyme activities, nutritional quality, anatomical structure, and canopy temperature in Chinese cabbage pakchoi. A partial least squares (PLS) model was used to quantify the relationship between physical and chemical indicators with Cd accumulation in cabbage, and identify the main controlling factors. RESULTS: Results showed that Cd stress significantly inhibited cabbage's growth and development. When Cd stress was increased, the phenotypic indicators were significantly reduced. Meanwhile, Cd stress significantly enhanced the oxidative stress response of cabbage, such as the activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and the content of malondialdehyde (MDA) in leaves. Such a change tended to increase fenestrated tissues' thickness but decrease the thickness of leaf and spongy tissues. Moreover, Cd stress significantly increased soluble sugar, protein, and vitamin C contents in leaves as well as the temperature in the plant canopy. The PLS model analysis showed that the studied phenotypic and physicochemical indicators had good relationships with Cd accumulation in roots, shoots, and the whole plant of cabbage, with high coefficient of determination (R2) values of 0.891, 0.811, and 0.845, and low relative percent deviation (RPD) values of 3.052, 2.317, and 2.557, respectively. Furthermore, through analyzing each parameter's variable importance for projection (VIP) value, the SOD activity was identified as a key factor for indicating Cd accumulation in cabbage. Meanwhile, the effects of CAT on Cd accumulation in cabbage and the canopy mean temperature were also high. CONCLUSION: Cd stress has significant inhibitory effects and can cause damage cabbage's growth and development, and the SOD activity may serve as a key factor to indicate Cd uptake and accumulation in cabbage.

Negative pressure irrigation on water use efficiency, yield and quality of Brassica chinensis L.

BACKGROUND: Water is critical to the production of crops, especially when faced with seasonal drought or freshwater scarcity. We compared the effect of negative pressure irrigation (NPI) on water use efficiency (WUE), nutrient uptake, yield and quality of Brassica chinensis L. using a greenhouse plot experiment. Three different water supply pressures (-5, -10 and -15 kPa), and a conventional irrigation (CK) treatment, were arranged in a randomized design with three replications. RESULTS: Our results suggest that plant height, leaf area, number of leaves and ratio of root to shoot were significantly correlated with water supply pressure. Specifically, our results show that B. chinensis L. yield was increased 50% with NPI versus CK. Water supply pressure had a significant effect on N and P nutrient uptake and no significant effect on K. The average concentration of vitamin C was greatest with -5 kPa treatment and consecutively declined. According to our results, NPI can save up to 36.8% of water used and improve WUE by 61.3% during growth of B. chinensis L. Our results suggest that the optimum irrigation management strategy is -5 kPa treatment. CONCLUSION: NPI versus CK can provide more stable irrigation water and retain soil moisture during plant growth, resulting in an increased WUE and yield with suitable water supply pressure. While our results suggest that NPI can enhance B. chinensis L. yield and perhaps also quality, future research should explore the mechanism of NPI in relation to yield and water use efficiency. © 2021 Society of Chemical Industry.

Study on the Dynamic Difference between Single and Mixed Residues of Three Neonicotinoids in Brassica chinensis L.

Multiple insecticides' residues after the mixed application of several neonicotinoids cause combined pollution and bring new challenges to food safety and pest control during agricultural production. In this study, three neonicotinoid insecticides, namely imidacloprid (IMI), acetamiprid (ACE), and thiamethoxam (TMX), were mixed and evenly sprayed on Brassica chinensis L. in the field. Then, the insecticides' residues were dynamically monitored to determine the differences in their rates of dissipation and final residues after 10 days. The results showed that the dissipation kinetics of neonicotinoids still conformed to the first-order kinetic model for binary or ternary application of neonicotinoid mixtures, with all determination coefficients (R2) being above 0.9 and the dissipation half-life (DT50) being 2.87-6.74 d. For treatment groups with five times the recommended dosages (IMI 300 g·hm-2, ACE 900 g·hm-2, and TMX 600 g·hm-2), mixed insecticides had a slower dissipation rate, and the DT50 values of mixtures were longer than those of single insecticides. Moreover, the final insecticide residues with mixed application were higher than those of single compounds at 10 d after spraying. Thus, mixed applications of neonicotinoids may increase food safety risks as they increase the final insecticide residues in Brassica chinensis L., and care should therefore be taken when considering the combined use of such compounds.

LC-QTOF/MS-based non-targeted metabolomics to explore the toxic effects of di(2-ethylhexyl) phthalate (DEHP) on Brassica chinensis L.

Di(2-ethylhexyl) phthalate (DEHP) is a widely used plasticizer known to pose health risks to humans upon exposure. Recognizing the toxic nature of DEHP, our study aimed to elucidate the response mechanisms in Brassica chinensis L. (Shanghai Qing) when subjected to varying concentrations of DEHP (2 mg kg-1, 20 mg kg-1, and 50 mg kg-1), particularly under tissue stress. The findings underscored the substantial impact of DEHP treatment on the growth of Brassica chinensis L., with increased DEHP concentration leading to a notable decrease in chlorophyll levels and alterations in the content of antioxidant enzyme activities, particularly superoxide dismutase (SOD) and peroxidase (POD). Moreover, elevated DEHP concentrations correlated with increased malondialdehyde (MDA) levels. Our analysis detected a total of 507 metabolites in Brassica chinensis L., with 331 in shoots and 176 in roots, following DEHP exposure. There was a significant difference in the number of metabolites in shoots and roots, with 79 and 64 identified, respectively (VIP > 1, p < 0.05). Metabolic pathway enrichment in Brassica chinensis L. shoots revealed significant perturbations in valine, leucine, and isoleucine biosynthesis and degradation, aminoacyl-tRNA, and glucosinolate biosynthesis. In the roots of Brassica chinensis L., varying DEHP levels exerted a substantial impact on the biosynthesis of zeatin, ubiquinone terpenoids, propane, piperidine, and pyridine alkaloids, as well as glutathione metabolic pathways. Notably, DEHP's influence was more pronounced in the roots than in the shoots, with higher DEHP concentrations affecting a greater number of metabolic pathways. This experimental study provides valuable insights into the molecular mechanisms underlying DEHP-induced stress in Brassica chinensis L., with potential implications for human health and food safety.

Soil microorganisms play an important role in the detrimental impact of biodegradable microplastics on plants.

Biodegradable plastics were developed to mitigate environmental pollution caused by conventional plastics. Research indicates that biodegradable microplastics still have effects on plants and microorganisms as their non-biodegradable counterparts, yet the effects on vegetable crops are not well-documented. Additionally, the function of soil microorganisms affected by biodegradable microplastics on the fate of microplastics remains unverified. In this study, Brassica chinensis was cultivated in soil previously incubated for one year with low-density polyethylene (LDPE-MPs) and poly (butylene adipate-co-terephthalate) microplastics (PBAT-MPs) at 0.05 % and 2 % concentrations. High concentrations of PBAT-MPs significantly reduced the biomass to 5.83 % of the control. The abundance of Methyloversatilis, IS-44, and UTCFX1 in the rhizosphere bacterial community increased significantly in the presence of PBAT-MPs. Moreover, these microplastics significantly enhanced soil enzyme activity. Incubation tests were performed with three PBAT plastic sheets to assess the function of the altered bacterial community in the soil of control (Control-soil) and soil treated with high concentrations of PBAT-MPs (PBAT-MPs-soil). Scanning Electron Microscopy and Atomic Transfer Microscopy (SEM/ATM) results confirmed enhanced PBAT degradation in the PBAT-MPs-soil. PICRUST2 analysis revealed that pathways related to substance degradation were upregulated in the PBAT-MPs-soil. Furthermore, a higher percentage of strains with PBAT-MPs-degrading ability was found in PBAT-MPs-soil. Our results confirm that PBAT-MPs significantly inhibit the growth of vegetable crops and that soil bacterial communities affected by PBAT-MPs are instrumental in degrading them.

Assessing Seasonal Effects on Identification of Cultivation Methods of Short-Growth Cycle Brassica chinensis L. Using IRMS and NIRS.

Seasonal (temporal) variations can influence the δ13C, δ2H, δ18O, and δ15N values and nutrient composition of organic (ORG), green (GRE), and conventional (CON) vegetables with a short growth cycle. Stable isotope ratio mass spectrometry (IRMS) and near-infrared spectroscopy (NIRS) combined with the partial least squares-discriminant analysis (PLS-DA) method were used to investigate seasonal effects on the identification of ORG, GRE, and CON Brassica chinensis L. samples (BCs). The results showed that δ15N values had significant differences among the three cultivation methods and that δ13C, δ2H, and δ18O values were significantly higher in winter and spring and lower in summer. The NIR spectra were relatively clustered across seasons. Neither IRMS-PLS-DA nor NIRS-PLS-DA could effectively identify all BC cultivation methods due to seasonal effects, while IRMS-NIRS-PLS-DA combined with Norris smoothing and derivative pretreatment had better predictive abilities, with an 89.80% accuracy for ORG and BCs, 88.89% for ORG and GRE BCs, and 75.00% for GRE and CON BCs. The IRMS-NIRS-PLS-DA provided an effective and robust method to identify BC cultivation methods, integrating multi-seasonal differences.

Comparative effects of copper nanoparticles and copper oxide nanoparticles on physiological characteristics and mineral element accumulation in Brassica chinensis L.

In this study, the short-term toxicity of Cu NPs, CuO NPs, and CuSO4 on bok choy (Brassica chinensis L.) under hydroponic conditions was evaluated using indicators such as biomass, net photosynthesis rate, root morphology, enzyme activity, and Cu accumulation and subcellular distribution. Results showed that CuO NPs exposure notably increased the biomass, root length, and root tip number by 22.0%, 22.7%, and 82.9%, respectively, whereas Cu NPs and CuSO4 significantly reduced root biomass, net photosynthetic rate (PN), and root length by 31.2% and 44.2%, 24.5% and 32.2%, and 43.4% and 40.6%, respectively. In addition, Cu NPs, CuO NPs and CuSO4 exposure increased the distribution of Cu in soluble component and cell wall. Moreover, short-term exposure to different Cu forms significantly affected mineral element accumulation in bok choy. For instance, Cu NPs exposure reduced the concentrations of Mg, Ca and Mn in edible part by 21.7%, 16.1% and 23.2%, respectively. CuSO4 exposure reduced the concentrations of Mg and Ca in edible part by 12.3% and 50.1%, respectively. CuO NPs caused a significant increase of 30.4% for Ca concentration in root, 34.5% and 34.5% for K and Mn concentration in edible part. Over all, CuO NPs exposure was beneficial for plant growth. These findings help understand the phytotoxic effect of different Cu forms on bok choy, and CuO NPs has the potential to be applied to improve nutrition and prompt growth in edible plants.

Fabrication and design of poly(l-lactic acid) membrane for passive MAP packaging of Brassica chinensis L.

PLDx L copolymers were synthesized from physically stable rigid poly(l-lactic acid) (PLLA) and a few different molecular weights of polydimethylsiloxane (PDMS) to increase the O2 and CO2 permeabilities of PLLA films and make them acceptable for packaging highly respirable products. The effect of PDMS on the morphology, mechanical properties, and gas permeability of PLDx L was investigated. Copolymers showed approximately 10 times the fracture strain and 1.7 times the CO2 and O2 permeabilities of neat PLLA. Additionally, PLDx L maintained an increased CO2 /O2 perm-selectivity consistent between 5 and 40°C. Passive modified atmosphere packaging of Brassica chinensis L was developed to assess the membrane's impact on headspace gas inside the package. The results showed that poly(amide)/poly(ethylene) packaging with 48 cm2 PLD1.8 L membrane as a breathing window can provide 50 g B. chinensis L. with a healthy atmosphere of 3%-8% O2 and 5%-8% CO2 between 6 and 22 days. Vegetables packaged in PLD1.8 L had the lower respiration rate, lower nitrite contents, and less proliferation of microorganisms. Moreover, a suitable atmosphere kept vegetables with higher ascorbic acid and a good appearance after more than 2 weeks of storage at 5°C. PRACTICAL APPLICATION: The permeability of the PLLA-based membrane can be adjusted for the breathable window membrane of sealed fresh products. In the future, several types of film could be developed to match the respiratory and metabolic characteristics of different kinds of products. Such PLLA-based specialized membranes can refine the fresh-keeping function and be more attractive to the customer.

[Effects of Nano-copper Oxide on Physiobiochemical Properties of Brassica chinensis L. and Its Heavy Metal Accumulation Under Cadmium Stress].

To investigate the effects of nano-copper oxide (CuO NPs) on plant growth, physio-biochemical characteristics, and heavy metal content under cadmium stress, a hydroponics experiment was conducted on the effects of single and combined treatments of CuO NPs (0, 10, 20, and 50 mg·L-1) and Cd (0, 1, and 5 µmol·L-1) on the fresh weight, photosynthetic pigment content, MDA content, antioxidant enzyme activity (CAT, POD, SOD, and GR), and Cu and Cd contents in Brassica chinensis L. The results showed that under the single addition of CuO NPs, the fresh weight and activities of CAT, POD, and GR were inhibited as a whole. Photosynthetic pigment content and SOD activity increased first and then decreased with the increase in CuO NPs concentration, whereas MDA content in leaves and roots, and Cu content in subcells of B. chinensis L. increased with the increasing of CuO NPs. As compared with that in the control, CuO NPs promoted the growth of B. chinensis L., and the fresh weight increased by 8.70%-44.87% at 1 µmol·L-1 Cd. When the content of Cd was up to 5 µmol·L-1, a low content (10 mg·L-1) of CuO NPs promoted the growth of B. chinensis L., whereas a high concentration (50 mg·L-1) showed an inhibitory effect. The addition of CuO NPs could increase photosynthetic pigment and MDA contents under different Cd stress, and MDA content in leaves and roots of B. chinensis L. increased by 4.34%-36.27% and 13.43%-131.04%, respectively, than that in the control groups. Under the same concentration of 1 µmol·L-1 Cd, the addition of CuO NPs decreased the activities of CAT and GR, whereas the activity of POD increased. When the content of Cd was up to 5 µmol·L-1, CuO NPs increased the POD activity and inhibited the activity of SOD and GR. The activities of CAT and CAT in the leaves of B. chinensis L. initially showed an increasing and then decreasing trend. CuO NPs and Cd showed antagonistic effects, the maximum reduction of Cd content in leaves and roots of Brassica chinensis L. under 1 µmol·L-1 Cd treatment was 45.64% and 33.39%, and that under 5 µmol·L-1 Cd treatment was 18.25% and 25.35%, respectively. The content of Cu and Cd in subcellular organs of the plants decreased, but the proportion of soluble components increased. These results indicated that CuO NPs at low concentrations promoted plant growth under Cd stress and further inhibited the absorption of Cd but increased the oxidative damage to B. chinensis L.

Fate and health risk assessment of heavy metals in Brassica chinensis L. (pak-choi) and soil amended by sludge-based biochar.

Biochar is widely used in agriculture to efficiently solve the problem of sludge. In this study, sludge-based biochar (referred to as BC1, BC2, and BC3) was prepared by mixing sludge with FeCl3, Na2SiO3, and Ca (H2PO4)2, respectively. Then, it was mixed with fresh soil to plant Brassica chinensis L. The analysis of the effects of the three biochar types showed that all of them were beneficial to the growth of Brassica chinensis L. We added the biochar to the soil and found that the concentration of heavy metals did not exceed the recommended threshold. Additionally, the aboveground part of Brassica chinensis L. met the standard requirement for food safety (GB 2761-2017). Notably, BC3 stood out with the best effect on the growth of Brassica chinensis L. and resulted in the improvement of the physical and chemical properties of soil such as ammonium nitrogen, available phosphorus, and available potassium (BC3 was followed by BC2 and BC1). BC3 could efficiently inhibit the migration of heavy metals, thereby reducing the overall heavy metal pollution level and ameliorating the soil nutrients. BC3 could increase the organic carbon by 258.92%, available phosphorus by 234.45%, and available potassium by 37.12% compared with the CK group. The THQ and TTHQ estimates of Brassica chinensis L. were lower than one, indicating that the health risk of heavy metal intake was not prominent. Additionally, the application of the proposed biochar could reduce the form of F1 (acid extracted state) and increase the form of F4 (residue state) in soil. Overall, we conclude that the application of the proposed biochar can promote the root absorption of heavy metals and inhibit the migration of heavy metals.

Exopolysaccharide-producing bacteria enhanced Pb immobilization and influenced the microbiome composition in rhizosphere soil of pakchoi (Brassica chinensis L.).

Lead (Pb) contamination of planting soils is increasingly serious, leading to harmful effects on soil microflora and food safety. Exopolysaccharides (EPSs) are carbohydrate polymers produced and secreted by microorganisms, which are efficient biosorbent materials and has been widely used in wastewater treatment to remove heavy metals. However, the effects and underlying mechanism of EPS-producing marine bacteria on soil metal immobilization, plant growth and health remain unclear. The potential of Pseudoalteromonas agarivorans Hao 2018, a high EPS-producing marine bacterium, to produce EPS in soil filtrate, immobilize Pb, and inhibit its uptake by pakchoi (Brassica chinensis L.) was studied in this work. The effects of strain Hao 2018 on the biomass, quality, and rhizospheric soil bacterial community of pakchoi in Pb-contaminated soil were further investigated. The results showed that Hao 2018 reduced the Pb concentration in soil filtrate (16%-75%), and its EPS production increased in the presence of Pb2+. When compared to the control, Hao 2018 remarkably enhanced pakchoi biomass (10.3%-14.3%), decreased Pb content in edible tissues (14.5%-39.2%) and roots (41.3%-41.9%), and reduced the available Pb content (34.8%-38.1%) in the Pb-contaminated soil. Inoculation with Hao 2018 raised the pH of the soil, the activity of several enzymes (alkaline phosphatase, urease, and dehydrogenase), the nitrogen content (NH4 +-N and NO3 --N), and the pakchoi quality (Vc and soluble protein content), while also raising the relative abundance of bacteria that promote plant growth and immobilize metals, such as Streptomyces and Sphingomonas. In conclusion, Hao 2018 reduced the available Pb in soil and pakchoi Pb absorption by increasing the pH and activity of multiple enzymes and regulating microbiome composition in rhizospheric soil.

Bioorganic fertilizer promotes pakchoi growth and shapes the soil microbial structure.

As a functional probiotic, Bacillus subtilis can promote crop growth and improve nutrient utilization by various mechanisms, so it has been made into bioorganic fertilizer as a replacement for chemical fertilizer. However, the effects of B. subtilis bioorganic fertilizer application on the yield and quality of commercial crops of Brassica chinensis L., the soil physicochemical properties and the microflora have not been clarified. In this study, pot experiments were conducted using Brassica chinensis L. plants with four fertilization treatments: control without fertilization (CK), chemical fertilizer (CF), organic fertilizer (OF), and bioorganic fertilizer containing B. subtilis (BF). After 30 days of pot experiment, the results showed that BF efficiently improved plant height and biomass (1.20- and 1.93-fold, respectively); as well as significantly increasing soil available potassium and pH value. Using high-throughput sequencing, we examined the bacterial and fungal communities in the soil, and found that their diversity was remarkablely reduced in the BF treatment compared to CK group. A principal coordinate analysis also showed a clear separation of bacterial and fungal communities in the BF and CK groups. After application of B. subtilis bioorganic fertilizer, some beneficial bacteria (such as Bacillus and Ammoniphilus) and fungi (Trichoderma and Mortierella) were enriched. A network analysis indicated that bacteria were the dominant soil microbes and the presence of B. subtilis stimulated the colonization of beneficial microbial communities. In addition, predictive functional profiling demonstrated that the application of bioorganic fertilizer enhanced the function of mineral element metabolism and absorption and increased the relative abundance of saprotrophs. Overall, the application of bioorganic fertilizer effectively changed the soil microflora, improved the soil available potassium and pH value, and boosted the yield of Brassica chinensis L. This work has valuable implications for promoting the safe planting of facility vegetables and the sustainable development of green agriculture.

Incorporating in vitro bioaccessibility into human health risk assessment of heavy metals and metalloid (As) in soil and pak choi (Brassica chinensis L.) from greenhouse vegetable production fields in a megacity in Northwest China.

The rapid development of greenhouse vegetable production (GVP) in densely populated areas may cause the heavy metal/metalloid accumulation in soil and pose a threat to human health. In this study, 180 pairs of topsoil and pak choi (Brassica chinensis L.) samples were collected from GVP fields in Xi'an city in Northwest China to analyze health risks of Cd, Cr, Pb, and As in soil and pak choi combining in vitro bioaccessibility investigation. The results showed that Cd and Cr were common pollutants in both soil and pak choi. In the soil-pak choi system, the indexes of non-carcinogenic and carcinogenic risk for adults and children were 1.53, 2.68, and 1.37 × 10-4, 8.14 × 10-5, respectively, thereby indicating the presence of heavy metal/metalloid health risks for both groups. Based on the results, procedures to mitigate heavy metal/metalloid contamination risks should be discussed more during the development of GVP in the largest city in Northwest China.

Bacillus cereus liquid fertilizer was produced from Agaricus bisporus industrial wastewater.

During the Agaricus bisporus canning processes, a large number of water-soluble elements were dissolved into the processing hot water. This study was conducted to use the industrial wastewater of A. bisporus to prepare agricultural microbial fertilizer. In the work, the influence of 6 different liquid fermentation factors on the total biomass of living Bacillus cereus was evaluated with the one-factor-at-a-time method and the Plackett-Burman design. The total biomass of living B. cereus was most influenced by fermentation temperature, shaking speed, and inoculation volume, which were identified as the most critical independent variables for the B. cereus biomass. The approximate ranges of optimal fermentation conditions for the three key factors were identified by the path of steepest ascent. The center point of these factors were 24 ℃ of temperature, 250 rpm of shaking speed and 12 % inoculum amount, respectively. The Box-Behnken design was applied to derive a statistical model for optimizing the three fermentation factors for B. cereus biomass. After further optimizations based on statistical predictions, the optimum fermentation parameters for B. cereus cultured in the A. bisporus industrial wastewater were fermentation temperature of 24.8 °C, shaking speed of 234 rpm, inoculum dose of 12.2 % (v:v, %), industrial wastewater concentration of 4%, initial pH values of 6.5, loading liquid of 60 mL/250 mL, and culture time of 24 h. Culturing with the optimal fermentation conditions resulted in the biomass of B. cereus of 1.35 ± 0.02 × 109 Obj/mL (N = 3), which was consistent with the predicted values (1.32 × 109 Obj/mL) predicted by the corresponding regression models (p < 0.05), and more, was also far higher than that of the standard of agricultural bacterial fertilizers in People's Republic of China. Further, the results of field trial indicated that the of B. cereus liquid fertilizer can remarkably enhance the yield of Brassica chinensis L. It is practicable to make use of the industrial wastewater of A. bisporus to prepare the microbial fertilizer.

Effects of intercropping accumulator plants and applying their straw on the growth and cadmium accumulation of Brassica chinensis L.

Two pot experiments were conducted to study the effects of intercropping cadmium (Cd) accumulator plants (Stellaria media (L.) Villars, Cardamine hirsuta, Cerastium glomeratum Thuill, and Galium aparine L.) and applying their straw on the growth and Cd accumulation of Brassica chinensis L. Intercropping with four accumulator plants reduced the biomass, water content, and photosynthetic pigment content of B. chinensis compared with monoculture. Intercropping with accumulator plants increased the Cd content in the roots and shoot of B. chinensis, and the translocation factor (TF), root bioconcentration factor (root BCF), and shoot bioconcentration factor (Shoot BCF) increased. The soil pH decreased and the soil available Cd content increased by intercropping. Thus, intercropping with four accumulator plants can promote the Cd uptake of B. chinensis. The straw of four accumulator plants reduced the biomass, water content, and photosynthetic pigment content of B. chinensis compared with the control. The straw of S. media and C. hirsute increased the Cd content in the roots and shoots of B. chinensis, TF, root BCF, and shoot BCF. The straw of C. glomeratum and G. aparine decreased the Cd content in the roots and shoots of B. chinensis, TF, root BCF, and shoot BCF. The soil pH increased and the soil available Cd content decreased by application of straw. Thus, the straw of C. glomeratum and G. aparine can reduce the Cd uptake of B. chinensis.

Uptake and toxicity of di-(2-ethylhexyl) phthalate in Brassica chinensis L.

This work focuses on the bioaccumulation and toxic effects of di-(2-ethylhexyl) phthalate (DEHP) in the leafy vegetable Shanghaiqing (SHQ) (Brassica chinensis L.). The accumulated DEHP amount in the edible part and roots of SHQ increased as the DEHP concentration in the soil increased. DEHP accumulation was higher in the roots than in the edible part of the plant. The root concentration factors and bioaccumulation factors for DEHP in SHQ were 0.13-2.49 and 0.03-2.00, respectively. The DEHP translocation factors were below 1.0, indicating that DEHP preferentially accumulated in plant roots. The DEHP risk index in the edible part of SHQ in relation to the human body and in terms of dietary exposure risk assessment was also below 1.0, indicating a low health risk. High DEHP concentrations caused 1) inhibition of SHQ growth, 2) an increase in SHQ chlorophyll and malondialdehyde contents and 3) a decrease in soluble sugar and vitamin contents. Low DEHP concentrations stimulated total superoxide dismutase, peroxidase and catalase activities, while high DEHP levels showed an inhibitory effect. DEHP presence in soil affected not only SHQ growth but also quality. Our results provide the data needed for the proper assessment of food safety and the ecological impact of DEHP contamination in agricultural soils.

Lignin side chain region participates in Cd detoxification related to the cultivar-dependent Cd accumulation in Brassica chinensis L.

To investigate the effect of lignin in the cultivar-dependent Cd detoxification of Brassica chinensis L., Cd and lignin contents, lignin composition and laccase genes expressions in low-Cd-accumulating (LAJK) and high-Cd-accumulating (HAJS) cultivars grown under control (CK) and 25 µM Cd-treatment were determined. The results showed that lignin combined about 14 % of total Cd in both LAJK and HAJS. LAC genes were more up-regulated in HAJS than in LAJK, indicating that the LAC genes were involved in the cultivar-dependent lignin functions. Higher ß-aryl ether (A) proportion in the lignin side chain region in LAJK than in HAJS were observed, whereas resinol (B) and phenylcoumaran (C) constitute much higher proportions in HAJS than in LAJK. Chemical calculation to estimate Cd affinity associating with lignin side chain region displayed that i) ß-aryl ether (A) exhibited major coupling with lignin aromatic region; ii) resinol (B) and phenylcoumaran (C) displayed major participation in complexation with Cd. We therefore conclude that Cd compartmentalization in the secondary cell wall (SCW) by coupling with lignin side chain region is responsible for Cd detoxification related to cultivar-dependent Cd accumulation of Brassica chinensis. This is the first study on lignin composition in relation to Cd retention mechanisms in SCW.

Effect of selenium-enriched organic material amendment on selenium fraction transformation and bioavailability in soil.

To exploit the plant byproducts from selenium (Se) biofortification and reduce environmental risk of inorganic Se fertilizer, pot experiment was conducted in this study. The effects of Se-enriched wheat (Triticum aestivum L.) straw (WS + Se) and pak choi (Brassica chinensis L.) (P + Se) amendment on organo-selenium speciation transformation in soil and its bioavailability was evaluated by pak choi uptake. The Se contents of the cultivated pak choi in treatments amended with the same amount of Se-enriched wheat straw and pak choi were 1.7 and 9.7 times in the shoots and 2.3 and 6.3 times in the roots compared with control treatment. Soil respiration rate was significantly increased after all organic material amendment in soil (p < 0.05), which accelerated the mineralization of organic materials and thus resulted in soluble Se (SOL-Se), exchangeable Se (EX-Se), and fulvic acid-bound Se (FA-Se) fraction increasing by 25.2-29.2%, 9-13.8%, and 4.92-8.28%, respectively. In addition, both Pearson correlation and cluster analysis showed that EX-Se and FA-Se were better indicators for soil Se availability in organic material amendment soils. The Marquardt-Levenberg Model well described the dynamic kinetics of FA-Se content after Se-enriched organic material amendment in soil mainly because of the mineralization of organic carbon and organo-selenium. The utilization of Se in P + Se treatment was significantly higher than those in WS + Se treatment because of the different mineralization rates and the amount of FA-Se in soil. Se-enriched organic materials amendment can not only increase the availability of selenium in soil but also avoid the waste of valuable Se source.

The influence of particle size and feedstock of biochar on the accumulation of Cd, Zn, Pb, and As by Brassica chinensis L.

Biochar produced from rice straw (RC) and maize stalk (MC) was amended to the heavy metal-contaminated soil to investigate the effects of different biochar feedstock and particle size (fine, moderate, coarse) on the accumulation of Cd, Zn, Pb, and As in Brassica chinensis L. (Chinese cabbage). The concentrations of Cd, Zn, and Pb in shoot were decreased by up to 57, 75, and 63%, respectively, after biochar addition (4%). Only MC decreased As concentration in B. chinensis L. shoots by up to 61%. Biochar treatments significantly decreased NH4NO3-extractable concentrations of Cd, Zn, and Pb in soil by 47-62, 33-66, and 38-71%, respectively, yet increased that of As by up to 147%. Amendment of RC was more effective on immobilizing Cd, Zn, and Pb, but mobilizing soil As, than MC. A decrease in biochar particle size greatly contributed to the immobilization of Cd, Zn, and Pb in soil and thereby the reduction of their accumulations in B. chinensis L. shoots, especially RC. Increases in soil pH and extractable P induced by biochar addition contributed to the sequestration of Cd, Zn, and Pb and the mobilization of As. Shoot biomass, root biomass, and root system of B. chinensis L. were enhanced with biochar amendments, especially RC. This study indicates that biochar addition could potentially decrease Cd, Zn, Pb, and As accumulations in B. chinensis L., and simultaneously increase its yield. A decrease in biochar particle size is favorable to improve the immobilization of heavy metals (except As). The reduction in Cd, Zn, Pb, and As levels in B. chinensis L. shoots by biochar amendment could be mainly attributed to a function of heavy metal mobility in soil, plant translocation factor, and root uptake.