Pyrolysis of exhausted biochar sorbent: Fates of cadmium and generation of products.

Biochar is a promising sorbent for Cd removal from water, while the disposal of the exhausted Cd-enriched biochar remains a challenge. In this study, pyrolysis was employed to treat the exhausted biochar under N2 and CO2 atmospheres at 600-900 °C, and the fate of Cd during pyrolysis and characteristics of high-valued products were determined. The results indicated that higher temperature and CO2 atmosphere favored the volatilization of Cd. Based on the toxicity characteristic leaching procedure (TCLP) results, the pyrolysis treatment under both atmospheres enhanced the stability of Cd, and the leached Cd concentration of regenerated biochar obtained at high temperatures (>800 °C) was lower than 1 mg/L. Compared with the pristine biochar, the regenerated biochar demonstrated higher carbon content and pH, whereas the contents of oxygen and hydrogen declined, and exhibited promising sorption properties (35.79 mg/g). The atmosphere played an important role in modifying biochar properties and syngas composition. The N2 atmosphere facilitated CH4 production, whereas the CO2 atmosphere increased the proportion of CO. These results implied that pyrolysis can be a valuable and environmental-friendly strategy for the treatment and reuse of exhausted biochar sorbent.

The toxicological effect on pak choi of co-exposure to degradable and non-degradable microplastics with oxytetracycline in the soil.

Microplastics and antibiotics are emerging as ubiquitous contaminants in farmland soil, harming crop quality and yield, and thus threatening global food security and human health. However, few studies have examined the individual and joint effects of degradable and/or non-degradable microplastics and antibiotics on crop plants. This study examined the individual and joint effects of polyethylene (PE) and polylactic acid (PLA) microplastics and the antibiotic oxytetracycline (OTC) on pak choi by measuring its growth, photosynthesis, antioxidant enzyme activity, and metabolite levels. Microplastics and/or oxytetracycline adversely affected root weight, photosynthesis, and antioxidant enzyme (superoxide dismutase, catalase, and ascorbate peroxidase) activities. The levels of leaf metabolites were significantly altered, causing physiological changes. Biosynthesis of plant secondary metabolites and amino acids was altered, and plant hormones pathways were disrupted. Separately and together, OTC, PE, and PLA exerted phytotoxic and antagonistic effects on pak choi. Separately and together with OTC, degradable microplastics altered the soil properties, thus causing more severe impacts on plant performance than non-degradable microplastics. This study elucidates the effects on crop plants of toxicity caused by co-exposure to degradable or non-degradable microplastic and antibiotics contamination and suggests mechanisms.

Single and combined effect of tetracycline and polyethylene microplastics on two drought contrasting cultivars of Oryza sativa L. (Rice) under drought stress.

Co-exposure of tetracycline (TC) and polyethylene microplastic (MP-PE) pollution might result in more intricate effects on rice growth and grain quality. In present study, two different rice cultivars of contrasting drought tolerance, Hanyou73 (H73, drought-resistant) and Quanyou280 (Q280, drought-sensitive) were grown on MP-PE and TC-contaminated soils under drought. It was found that drought stress had different influence on TC accumulation in the two rice cultivars. H73 accumulated more TC in leaves and grains without drought stress while Q280 accumulated more TC under drought stress. Furthermore, metabolomics results demonstrated that under drought stress, about 80 % of metabolites in H73 and 95 % in Q280 were down-regulated as compared to non-drought treatments. These findings provide insights into the effects of TC and MP-PE with and without drought stress on potential risks to rice growth and grain quality, which has implications on rice production and cultivar election under multiple-stress conditions.

Impact of polystyrene microplastics with combined contamination of norfloxacin and sulfadiazine on Chrysanthemum coronarium L.

Antibiotics and microplastics including nanoplastics are emerging contaminants which have become global environmental issues. The application of antibiotics along with microplastics in soil and their entrance in food chain may pose a major threat to human health. The single and combined exposure of polystyrene microplastic (MPS), norfloxacin (NF) and sulfadiazine (SFD) on Chrysanthemum coronarium L. a medicinal food crop, were investigated. Accumulation of nutrient element contents (Fe, Mn, Mg, Zn, K) differentially responded to the single or combined treatments compared to the control. Scanning electron microscopy and transmission electron microscopy analysis indicated that MPS, NF and SFD accumulated in roots, shoots, and leaves and affected their ultrastructure. Compared with that of the single contamination, the co-contamination of microplastics and antibiotics had a greater effect on leaf metabolites due to combination of multiple abiotic stresses. MPS, NF and SFD accumulated from roots and transported to shoots and leaves which ultimately impacts plant metabolites and, nutritional value. They subsequently impact agricultural sustainability and food safety of medicinal food plants. This investigation suggests the possible ecological risks of microplastics to medicinal food plants, especially in co-exposure with organic pollutants like antibiotics and help to reveal potential mechanisms of phytotoxicity of different antibiotics with polyethylene microplastic.

Comparison of cadmium adsorption by hydrochar and pyrochar derived from Napier grass.

Biochar (e.g. pyrochar and hydrochar) is considered a promising adsorbent for Cd removal from aqueous solution. Considering the vastly different physicochemical properties between pyrochar and hydrochar, the Cd2+ sorption capacity and mechanisms of pyrochars and hydrochars should be comparatively determined to guide the production and application of biochar. In this study, the hydrochars and pyrochars were prepared from Napier grass by hydrothermal carbonization (200 and 240 °C) and pyrolysis (300 and 500 °C), respectively, and the physicochemical properties and Cd2+ sorption performances of biochars were systematically determined. The pyrochars had higher pH and ash content as well as better stability, while the hydrochars showed more oxygen-containing functional groups (OFGs) and greater energy density. The pseudo second order kinetic model best fitted the Cd2+ sorption kinetics data of biochars, and the isotherm data of pyrochar and hydrochar were well described by Langmuir and Freundlich models, respectively. In comparison with hydrochar, the pyrochar exhibited better Cd2+ sorption capacity (up to 71.47 mg/g). With increasing production temperature, the Cd2+ sorption capacity of pyrochar elevated, while the reduction was found for hydrochar. The mineral interaction, complexation with surface OFGs, and coordination with π electron were considered the main mechanisms of Cd2+ removal by biochars. The minerals interaction and the complexation with OFGs was the dominant mechanism of Cd2+ removal by pyrochars and hydrochars, respectively. Therefore, the preparation technique and temperature have significant impacts on the sorption capacity and mechanisms of biochar, and pyrochar has better potential for Cd2+ removal than the congenetic hydrochar.

Pyrolysis of exhausted hydrochar sorbent for cadmium separation and biochar regeneration.

Sorption is considered a cost-effective technique for cadmium (Cd) removal from water, while the exhausted Cd-enriched sorbent should be properly disposed of. In this study, pyrolysis of exhausted hydrochar sorbent was conducted at 300-900 °C, and the behavior of Cd and the physicochemical properties and environmental applications of the regenerated biochar were investigated. The vaporization of adsorbed Cd in hydrochar was greatly enhanced by elevating pyrolysis temperature, and almost no Cd was observed in the regenerated biochars obtained at 700-900 °C. In comparison with the raw hydrochar, the regenerated biochars showed higher pH, ash content, and carbon content, while the contents of hydrogen and oxygen decreased. According to the toxicity characteristic leaching procedure result, the toxicity and mobility of Cd in hydrochar were greatly reduced after pyrolysis. Notably, the regenerated biochar showed much higher Cd sorption capacity (26.05-30.24 mg/g) than the raw hydrochar (6.70 mg/g). Surface complexation with oxygen-containing functional groups was the dominant Cd sorption mechanism for hydrochar, and precipitation between Cd2+ and carbonates dominated the Cd removal by the regenerated biochars. These results illuminated that pyrolysis can be an effective technique for the harmless disposal of exhausted hydrochar sorbent and the regeneration of valuable biochar.

Phytotoxic effects on chloroplast and UHPLC-HRMS based untargeted metabolomic responses in Allium tuberosum Rottler ex Sprengel (Chinese leek) exposed to antibiotics.

Introduction of antibiotics into agricultural fields poses serious health risks to humans. This study investigated the uptake of antibiotics, their effects on metabolic pathways, and chloroplast structure changes of Allium tuberosum exposed to norfloxacin (NFL), oxytetracycline (OTC), and tetracycline (TC). Among all the antibiotic treatments, the highest accumulation of antibiotics in roots (4.15 mg/kg) and leaves (0.29 mg/kg) was TC, while in bulbs it was NFL (5.94 mg/kg). OTC was with the lowest accumulation in roots: 0.19 mg/kg, bulbs: 0.18 mg/kg, and leaves: 0.11 mg/kg. The number of mitochondira and the number of plastoglobulli increased. The chloroplast structure was disturbed under the stress of NFL, OTC, and TC. Disturbance in the chloroplast ultrastructure leads to altered chlorophyll fluorescence variables. Simultaneously, metabolomic profiling of leaves demonstrated that NFL stress regulated more of metabolic pathways than OTC and TC. Differences in metabolic pathways among the antibiotic treatments showed that each antibiotic has different impact even under the same experimental conditions. TC and NFL have more toxic effects than OTC antibiotic. Metabolic variations induced by antibiotics stress highlighted pools of metabolites that affect the metabolic activities, chlorophyll fluorescence, ultrastructural adjustments, and stimulate defensive impact in A. tubersoum. These findings provide an insight of metabolic destabilization as well as metabolic changes in defensive mechanism and stress response of A. tuberosum to different antibiotics.

A scientometric analysis of agricultural pollution by using bibliometric software VoSViewer and Histcite™.

While modern agriculture brings more food to people, it causes environmental pollution as well. Agricultural pollution has attracted extensive public attention. A lot of reviews on agricultural research were conducted from different research aspects, but there is a lack of work on analyzing the research trend from large volumes of publications in the field of agricultural pollution. In the present work, a scientometric analysis of agricultural pollution was conducted to fill the gap by using the software of VoSviewer and HistCite™. The datasets are collected from the core database of Web of Science from 1991 to 2019, totally 1338 records on the topic of agricultural pollutions. In most years (1996, 1999, 2002, 2006, 2009, 2011, and 2013), the total local citation score (TLCS) and total global citation score (TGCS) have coincident peaks. Zhang, Ju, and Zhu have the highest TLCS and TGCS. In terms of institutes, Chinese Acad Sci and China Agr Univ are the leading institutes in this field. The Univ Calif Davis, INRA, and USDA ARS have very high global impacts. From the research hot topics, the representative words include "soil," "agriculture," "contamination," "environment," "lead," and "balance." Representative words like "heavy-metals," "groundwater," "land-use," and "water" are emerging in the latter time period. Five leading research co-cited reference clusters are identified, including environment management, underground water, monitoring and alarming for the agriculture-environment standards, intrinsic mechanism to the circulatory system, and ecology system and land use. The recent trend is revealed from the bibliographical-coupling network, focusing on classical and old-fashion research, like pollution chemicals including N management, pesticides, and heavy metal. This work provides a holistic picture on the research in the field of agriculture pollution.

Biochar from constructed wetland biomass waste: A review of its potential and challenges.

Constructed wetland is considered a promising approach for water remediation due to its high efficiency, low operation costs, and ecological benefits, but the large amounts of wetland plant biomass need to be properly harvested and utilized. Recently, wetland plant derived biochar has drawn extensive attention owing to its application potential. This paper provides an updated review on the production and characteristics of wetland plant derived biochar, and its utilization in soil improvement, carbon sequestration, environmental remediation, and energy production. In comparison to hydrothermal carbonization and gasification, pyrolysis is a more common technique to convert wetland plant to biochar. Characteristics of wetland plant biochars varied with plant species, growth environment of plant, and preparation conditions. Wetland plant biochar could be a qualified soil amendment owing to its abundant nutrients. Notably, wetland plant biochar exhibited considerable sorption capacity for various inorganic and organic contaminants. However, the potentially toxic substances (e.g. heavy metal and polycyclic aromatic hydrocarbons) retained in wetland plant biochar should be noticed before large-scale application. To overcome the drawbacks from the scattered distribution, limited productivity, and seasonal operation of constructed wetlands, the economic feasibility of wetland plant biochar production system could be improved via using mobile pyrolysis unit, utilizing local waste heat, and exploiting all the byproducts. Future challenges in the production and application of wetland plant derived biochar include the continuous supply of feedstock and proper handling of potentially hazardous components in the biochar.

Effects of antibiotics stress on growth variables, ultrastructure, and metabolite pattern of Brassica rapa ssp. chinensis.

Antibiotics frequently contaminate agricultural fields and through plant uptake enter into the food chain. This study aimed to explore the effects of antibiotics; tetracycline (TC), oxytetracycline (OTC) and norfloxacin (NF) on the growth, cell ultrastructure, and metabolite pattern of Brassica rapa ssp. chinensis. Oxytetracycline accumulated more than other antibiotics followed by TC and NF. Plant growth, chlorophyll fluorescence, and antioxidant activities were negatively affected under all antibiotic treatments. Ultrastructural investigation of mesophyll of leaves performed by transmission electron microscopy indicated that antibiotic stress caused the changes in thylakoid orientation, number of plastoglobuli, and starch grains. Identification of functional groups through Fourier transform infrared analysis indicated that carboxyl group, carbonate and ammonium ions are involved in the adsorption of antibiotics. The metabolic profiling of B. rapa leaves demonstrated that all of the antibiotics treatments distorted phenylalanine, tyrosine and tryptophan biosynthesis, d-glutamine and d-glutamate metabolism, alanine, aspartate and glutamate metabolism, phenylalanine metabolism and TCA cycle. Metabolic alterations as a result of antibiotics stress provide insights of metabolites that affect the physiological changes attributed to antibiotic stress. These results will improve the understanding of antibiotic contamination effects on plants.

Metal accumulation potential, human health risks, and yield attributes of hundred bread wheat genotypes on irrigation with municipal and remediated wastewater.

This study was carried out to screen historical diversity panel of bread wheat against municipal wastewater (MW) and remediated wastewater (RW) irrigation to find tolerant and sensitive genotypes and their impact on yield attributes. The experiment was conducted in randomized complete block design (RCBD) with three water treatments, i.e., tap water (TW), RW, and MW. Yield attributes, health risk assessment, water and soil chemistry were recorded. Principal component analysis (PCA) was used to identify tolerant and sensitive genotypes of wheat on the basis of metal accumulation. Metal accumulation in grains increased in pattern K > Fe > Zn in all irrigation treatments. Tolerant genotypes in MW showed lowest hazard quotient (HQ) and hazard index (HI) values (adults 0.62; children 0.67) for Fe and Zn as compared to sensitive genotypes (adults 1.53; children 1.70). However, HI values in sensitive and tolerant genotypes of RW were recorded < 1. Mean values of yield attributes, i.e., plant height, spike length, spikelet per spike, grains per plant, biological yield, grain yield, and thousand kernel weight, were recorded in pattern, i.e., MW > RW > TW. In this study, yield attributes and human health are affected in both cases of higher and lower concentration of Fe and Zn metal. It is suggested that tolerant genotypes can prove useful for cultivation in areas receiving MW and also provide molecular breeding opportunities for seeking tolerance against metal stresses.

Heavy metal phyto-accretion, biochemical responses and non-carcinogenic human health risks of genetically diverse wheat genotypes cultivated with sewage of municipal origin.

Current study explored the effects of municipal sewage (MS) irrigation on heavy metal phyto-accretion, biochemical responses and human health risks of diverse wheat genotypes along with recycled municipal sewage (RMS). Mean concentrations of PO43-, NO3--N, chemical oxygen demand, biological oxygen demand, K, Co, Cu, Cd, Cr and Ni were found higher in MS than irrigation criteria. This led to significant increase in heavy metal contents in roots, stem and grains of MS irrigated wheat genotypes compared to RMS and control treatments. No adverse health risk effects for individual or multiple metals were recorded in RMS irrigated wheat genotypes on grounds of lowest heavy metal accumulation. Multivariate techniques i.e. principal component analyses (PCA) and hierarchical agglomerative cluster analyses (HACA) identified tolerant (inefficient metal accumulators) and sensitive (efficient metal accumulators) wheat genotypes in MS and RMS. Tolerant wheat genotypes showed lowest accumulation of heavy metals, efficient biochemical mechanisms to combat oxidative stress and lower health risks to adults/children. Cultivation of identified tolerant wheat genotypes is recommended in areas receiving municipal wastes to reduce human and environmental health risks. Moreover, genetic potential of identified tolerant wheat genotypes from MS and RMS can be utilized in breeding heavy metal tolerant wheat germplasm worldwide.

A review on the thermal treatment of heavy metal hyperaccumulator: Fates of heavy metals and generation of products.

Phytoremediation is perceived as a promising technique for remediation of heavy metal (HM) contaminated soils, while the harvested HM-enriched hyperaccumulator biomass should be appropriately disposed. Recently, various thermal treatments of hyperaccumulator have drawn increasing attention. After thermal treatment, the hyperaccumulator was converted to bio-oil, bio-gas, biochar, or ash in accordance with the corresponding conditions, and the HMs were separated, immobilized, or trapped. The migration and transformation of HMs during the thermochemical conversion processes are critical for the safe disposal and further utilization of HM hyperaccumulator. This paper provides a systematic review on the migration and transformation of typical HMs (Cd, Ni, Mn, As, and Zn) in hyperaccumulator during various thermochemical conversion processes, and special emphasis is given to the production and application of targeted products (e.g. biochar, hydrochar, bio-oil, and syngas). Besides, future challenges and perspectives in the thermal treatment of hyperaccumulator are presented as well. The distribution and speciation of HMs were influenced by thermal technique type and reaction conditions, thereby affecting the utilization of the derived products. This review suggests that speciation and availability of HMs in hyperaccumulator are tunable by varying treatment techniques and reaction conditions. This information should be useful for the selective conversion of hyperaccumulator into green and valuable products.

Study amino acid contents, plant growth variables and cell ultrastructural changes induced by cadmium stress between two contrasting cadmium accumulating cultivars of Brassica rapa ssp. chinensis L. (pak choi).

Cadmium (Cd) is an inauspicious abiotic traction that not only influences crop productivity and its growth parameters, but also has adverse effects on human health if these crops are consumed. Among crops, leafy vegetables which are the good source of mineral and vitamins accumulate more Cd than other vegetables. It is thus important to study photosynthetic variables, amino acid composition, and ultrastructural localization of Cd differences in response to Cd accumulation between two low and high Cd accumulating Brassica rapa ssp. chinensis L. (pak choi) cultivars, differing in Cd accumulation ability. Elevated Cd concentrations significantly lowered plant growth rate, biomass, leaf gas exchange and concentrations of amino acids collated to respective controls of both cultivars. Electron microscopy indicated that the impact of high Cd level on ultrastructure of leaf cells was associated to affecting cell functionalities, i.e. irregular cell wall, withdrawal of cell membrane, and chloroplast structure which has negative impact on photosynthetic activities, thus causing considerable plant growth suppression. Damage in root cells were observed in the form of enlargement of vacuole. The energy dispersive micro X-ray spectroscopy of both cultivars leaves indicated that cellular structure exhibited exudates of Cd-dense material. Ultrastructural damages and phytotoxicity were more pronounced in high accumulator cultivar as compared to the low accumulator cultivar. These findings are useful in determining the mechanisms of differential Cd-tolerance among cultivars with different Cd tolerance abilities at cellular level.

Production of ingredient type flavoured white enzyme modified cheese.

Enzyme modified white cheese (EMWC) was produced to use as flavouring ingredient. White cheese curd coupled with low fat was hydrolysed using combination of proteinases/peptidase to produce a range of proteolysed products followed by lipolysis. The results revealed that lowering pH 5.6 known to impart flavour strength of cheese. The inclusion of enzyme preparations significantly elevated free amino acids and free fatty acids. Developed EMWC had relatively higher levels of volatiles and improved sensory characteristics including less negative attributes such as, astringent, bitter, pungent, rancid, smoky, and more positive attributes, such as the strength of buttery, sweaty, caramel and nutty notes. Spray-dried EMWC powders had low moisture content and water activity values whereas, scanning electron micrographs showed spherical with a uniform distribution and large microparticles size. Because consumers like low fat products with cheese flavour, EMWCs are important products. Thus, process demonstrates the potential to be a cost-effective to produce EMWC flavour as ingredient and may suited to the products in which added.

Variations in cadmium and nitrate co-accumulation among water spinach genotypes and implications for screening safe genotypes for human consumption.

Vegetables are important constituents of the human diet. Heavy metals and nitrate are among the major contaminants of vegetables. Consumption of vegetables and fruits with accumulated heavy metals and nitrate has the potential to damage different body organs leading to unwanted effects. Breeding vegetables with low heavy metal and nitrate contaminants is a cost-effective approach. We investigated 38 water spinach genotypes for low Cd and nitrate co-accumulation. Four genotypes, i.e. JXDY, GZQL, XGDB, and B888, were found to have low co-accumulation of Cd (<0.71 mg/kg dry weight) and nitrate (<3100 mg/kg fresh weight) in the edible parts when grown in soils with moderate contamination of both Cd (1.10 mg/kg) and nitrate (235.2 mg/kg). These genotypes should be appropriate with minimized risk to humans who consume them. The Cd levels in the edible parts of water spinach were positively correlated with the concentration of Pb or Zn, but Cd, Pb, or Zn was negatively correlated with P concentration. These results indicate that these three heavy metals may be absorbed into the plant in similar proportions or in combination, minimizing the influx to aerial parts. Increasing P fertilizer application rates appears to prevent heavy metal and nitrate translocation to shoot tissues and the edible parts of water spinach on co-contaminated soils.

Soymilk-Cow's milk ACE-inhibiting enzyme modified cheese.

In present study, we developed and optimized soymilk-cow's milk enzyme-modified cheese with angiotensin-I converting enzyme inhibitory activity. Bioactive peptide production was found to be a multivariable-dependent process. Maximum bioactivity of hydrolysates was obtained with prolonged curd proteolysis at an increased enzyme concentration. This bioactive cheese paste was subsequently spray-dried under different drying conditions to determine the powder sorption isotherm properties. Higher drying temperatures resulted in cheese powder with weak thermal stability and lower browning indices. Experiments aimed at optimizing thermal stability and physical properties revealed that optimal conditions for producing cheese powder were an inlet air temperature of 150°C, a feeding rate of 10%, and an air flow rate of 600Lh-1. Moreover, in addition to flavour, the bioactive cheese powders produced from a combination of soymilk-cow's milk are of potential source and can be used in the dietary management of hypertension.

Simultaneous sorption and catalytic oxidation of trivalent antimony by Canna indica derived biochars.

The simultaneous sorption and oxidation of Sb(III) on biochars were investigated using batch experiments. The biochars were derived from Canna indica at different pyrolysis temperatures (300-600 °C, referred as CIB300-CIB600), and characterized by FTIR, BET, XRD, SEM-EDS, EPR and Boehm titration. The Sb(III) sorption data could be well fitted by both the Langmuir and Freundlich models, and the pseudo-second order model is best for describing the kinetic data. The maximum Sb(III) sorption capacity of CIB300 was 16.1 mg g-1, which was greater than that of other biochars. Inner-sphere complexation with oxygen-containing functional groups and coordination with π electrons are the possible sorption mechanisms. It is worthwhile to note that 4.7-32.3% of Sb(III) was oxidized to Sb(V) after sorption equilibration, demonstrating the occurrence of Sb(III) oxidation during the sorption process. Further study of oxidation under anoxic condition confirmed the catalytic role of biochar for Sb(III) oxidation, and free radicals in biochars were crucial for electron transfer. CIB400 exhibited the highest catalytic oxidative ability for Sb(III), which could be ascribe to its reserve of more electroactive polyphenolic macromolecule and less electroinactive cellulose. These results imply that biochars have good potential as a green effective sorbent for remediation of Sb(III) contaminated water, and simultaneously reduce the toxicity of Sb(III) by catalytic oxidation.

Imitation of soymilk-cow's milk mixed enzyme modified cheese: their composition, proteolysis, lipolysis and sensory properties.

Combined use of soymilk-cow's milk is a novel approach in food industry and has great potential to developed products with numerous health benefits. This study aimed to develop the enzyme-modified cheeses (EMCs) using soymilk-cow's milk. The curd was hydrolysed using combination of proteinases/peptidase to produce a range of proteolysed products followed by lipolysis to create flavoured EMCs. Results showed that enzymes led to an increase in amino acids (AA), free fatty acids (FFA), complex volatiles, and improved sensory attributes. The EMCs showed higher mean values of AA, FFA and volatile compounds when prepared using Flavourzyme® in combination with Lipases AY30 and DF15. EMCs were less eggy, bitter, pungent, more buttery, saltier, nutty, and had sweet sensory characteristics. Overall, results demonstrated the potential of combined matrix to create a range of flavoured EMCs for a wider range of consumers.

Enhanced Cd extraction of oilseed rape (Brassica napus) by plant growth-promoting bacteria isolated from Cd hyperaccumulator Sedum alfredii Hance.

Four plant growth-promoting bacteria (PGPB) were used as study materials, among them two heavy metal-tolerant rhizosphere strains SrN1 (Arthrobacter sp.) and SrN9 (Bacillus altitudinis) were isolated from rhizosphere soil, while two endophytic strains SaN1 (Bacillus megaterium) and SaMR12 (Sphingomonas) were identified from roots of the cadmium (Cd)/zinc (Zn) hyperaccumulator Sedum alfredii Hance. A pot experiment was carried out to investigate the effects of these PGPB on plant growth and Cd accumulation of oilseed rape (Brassica napus) plants grown on aged Cd-spiked soil. The results showed that the four PGPB significantly boosted oilseed rape shoot biomass production, improved soil and plant analyzer development (SPAD) value, enhanced Cd uptake of plant and Cd translocation to the leaves. By fluorescent in situ hybridization (FISH) and green fluorescent protein (GFP), we demonstrated the studied S. alfredii endophytic bacterium SaMR12 were able to colonize successfully in the B. napus roots. However, all four PGPB could increase seed Cd accumulation. Due to its potential to enhance Cd uptake by the plant and to restrict Cd accumulation in the seeds, SaMR12 was selected as the most promising microbial partner of B. napus when setting up a plant-microbe fortified remediation system.