Cd Concentrations In Roots Research Articles

Cadmium, Chromium, and Lead Uptake Associated Health Risk Assessment of Alternanthera sessilis: A Commonly Consumed Green Leafy Vegetable.

Green leafy vegetables are becoming increasingly popular in the developing countries due to their high nutritious value, common availability, and low cost. However, no studies have assessed the health risks associated with consumption of fresh green leafy vegetables. The present study assessed Cd, Cr, and Pb associated health risks in a commonly consumed green leafy vegetable in developing countries, Alternanthera sessilis. The Cd, Cr, and Pb concentrations in roots, leaves, and root zone soil of Alternanthera sessilis harvested from organic and non-organic cultivations were measured. The results indicated that Cd, Cr, and Pb concentrations in roots and leaves of Alternanthera sessilis exceeded the WHO/FAO safe limits for human consumption. Further, bioconcentration factor, soil to root, and root to leaf translocation factors indicated a potential of hyperaccumulating Cd in roots and leaves of Alternanthera sessilis. However, the target hazard quotients for Cd, Cr, and Pb were less than 1 indicating negligible health hazard associated with long time consumption of Alternanthera sessilis.

Metabolic regulation in soil microbial succession and niche differentiation by the polymer amendment under cadmium stress

Cadmium (Cd) contamination seriously threatens the agricultural production, so exploring the response of soil microenvironment to amendments in Cd-contaminated soils is of importance. In this study, the mechanism of remediation of Cd-contaminated soil using the polymer amendment was studied in cotton flowering stage. The results showed that the concentration of Cd in cotton root and various Cd forms in Cd-contaminated soils were obviously high. High concentration of Cd, especially exchangeable Cd, could seriously affect the soil microenvironment. The root growth of cotton could be promoted, the carbon and nitrogen concentration and storage in soil were increased by 21.72–50.00%, while the exchangeable Cd concentration in soil were decreased by 41.43%, after applying the polymer amendment. In addition, the polymer amendment affected the soil microbial niche, increased the relative abundance of soil bacteria (Flaviaesturariibacter, Rubellimicrobium, and Cnuella), fungi (Verticillium and Tricharina), actinomycetes (Blastococcus and Nocardioides), and fungivores nematodes (Aphelenchus), and improved soil microbial metabolic functions (metabolism of nucleotides and carbohydrates). Therefore, this polymer amendment could be used to remediate severe Cd-contaminated soils, and the changes in the microbial and nematode communities help us understand the detoxification mechanism of the polymer amendment in Cd-contaminated soils.

Effect of exogenous silicon and methyl jasmonate on the alleviation of cadmium-induced phytotoxicity in tomato plants.

In the present study, a hydroponic experiment was performed to evaluate the effect of exogenous silicon (Si) and methyl jasmonate (MeJA) on the mitigation of Cd toxicity in tomato seedlings. The results revealed that Cd-stressed plants exhibited growth inhibition, increased lipid peroxidation, and impaired photosynthetic pigment accumulation. However, Si and MeJA applied alone or in combination significantly ameliorated the above-mentioned adverse effects induced by Cd. Among all treatments, Cd+Si+MeJA treatment elevated the dry mass of roots, stems, and leaves by 317.39%, 110.85%, and 119.71%, respectively. The chlorophyll a, chlorophyll b, and carotenoid contents in Cd+Si+MeJA-treated group were dramatically elevated (p < 0.05). Meanwhile, the malondialdehyde content in roots and shoots were reduced by 32.24% and 69.94%, respectively. The Si and MeJA applied separately or in combination also resulted in a prominent decrease of Cd influxes in tomato roots; therefore, a reduction of Cd content in tomato tissues were detected, and the Cd concentration in tomato roots were decreased by 27.19%, 25.18%, and 17.51% in Cd+Si, Cd+MeJA and Cd+Si+MeJA-treated plants, respectively. Moreover, in Cd+Si+MeJA-treated group, the percentage of Cd in cell wall fraction was enhanced while that in organelle fraction was decreased as compared with Cd-stressed plants. Collectively, our findings indicated that Si and MeJA application provide a beneficial role in enhancing Cd tolerance and reducing Cd uptake in tomato plants.

Contribution of Nano-Zero-Valent Iron and Arbuscular Mycorrhizal Fungi to Phytoremediation of Heavy Metal-Contaminated Soil.

Soil pollution with heavy metals has attracted increasing concern, which calls for the development of new remediation strategies. The combination of physical, chemical, and biological techniques can achieve more efficient remediation. However, few studies have focused on whether nanomaterials and beneficial microbes can be jointly used to facilitate phytoremediation. Therefore, we studied the role of nano-zero-valent iron (nZVI) and arbuscular mycorrhizal (AM) fungi in the phytoremediation of an acidic soil polluted with Cd, Pb and Zn, using sweet sorghum. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and mapping analyses were conducted to explore the mechanisms of metal immobilization by nZVI. The results showed that although both bare nZVI (B-nZVI) and starch-stabilized nZVI (S-nZVI) inhibited root mycorrhizal colonization, Acaulospora mellea ZZ successfully colonized the plant roots. AM inoculation significantly reduced the concentrations of DTPA-Cd, -Pb, and -Zn in soil, and the concentrations of Cd, Pb, and Zn in plants, indicating that AM fungi substantially facilitated heavy metal immobilization. Both B-nZVI and S-nZVI, ranging from 50 mg/kg to 1000 mg/kg, did not impede plant growth, and generally enhanced the phytoextraction of heavy metals. XRD, EDS and mapping analyses showed that S-nZVI was more susceptible to oxidation than B-nZVI, and thus had more effective immobilization effects on heavy metals. Low concentrations of nZVI (e.g., 100 mg/kg) and AM inoculation had synergistic effects on heavy metal immobilization, reducing the concentrations of Pb and Cd in roots and enhancing root Zn accumulation. In conclusion, our results showed that AM inoculation was effective in immobilizing heavy metals, whereas nZVI had a low phytotoxicity, and they could jointly contribute to the phytoremediation of heavy metal-contaminated soils with sweet sorghum.

Effects of Pseudomonas TCd-1 on rice (Oryza sativa) cadmium uptake, rhizosphere soils enzyme activities and cadmium bioavailability under cadmium contamination

Microbial remediation is a promising technique to reduce Cd accumulation in rice (Oryza sativa). In present study, a set of pot experiments were conducted to evaluate the effects of Cd-tolerate Pseudomonas TCd-1 inoculation on rice Cd uptake, soil enzyme activities and Cd bioavailability in the rhizosphere soils under Cd contaminated conditions. The results showed that at the ripening stage, with the inoculation of TCd-1, Cd contents in root, culm, leaf, hull and brown rice significantly reduced by 60.7%, 47.7%, 50.6%, 58.1% and 47.9%, respectively, and the cadmium bioconcentration factor (BCF) of rice lowered by 66.2% under 5 mg kg−1 Cd treatment. At the meantime, in the rhizosphere soils, pH increased by 0.05, the contents of exchangeable Cd (EX-Cd) and Fe-Mn oxides (OX-Cd) increased by 107.8% and 33.5%, whereas organic matter (OM-Cd) and residual (Res-Cd) decreased by 31.9% and 60.0%, respectively. The activity of acid phosphatase (ACP) increased by 28.3%, catalase (CAT), saccharase (SUC) activity decreased by 28.5% and 26.0%. Similarly, the Cd contents in root, culm, leaf, hull and brown rice reduced by 42.1%, 42.5%, 58.0%, 50.3%, and 68.8%, respectively, and the BCF lowered by 57.1%, under 10 mg kg−1 Cd treatment. Simultaneously, the soil pH increased by 0.06, the activities of CAT, SUC, urease (URE), ACP decreased by 26.4%, 34.6%, 63.8% and 15.3%, respectively. Furthermore, the correlation analysis showed that the inoculation of TCd-1 changed the correlation between rice Cd content and the biomass of roots, leaves, soil pH, CAT, PPO, URE activities, OM-Cd in rhizosphere soils. It suggested that Pseudomonas TCd-1 effectively reduced Cd uptake and Cd accumulation in rice was closely linked to the changes of soil pH, enzyme activities and Cd availability.

Foliage application of chitosan alleviates the adverse effects of cadmium stress in wheat seedlings (Triticum aestivum L.)

Excessive cadmium (Cd) causes toxic effects on crops. The effects of chitosan (CTS) with different molecular weight (MW) (5 kDa, 3 kDa, and 1 kDa) on the growth and biochemical parameters, as well as Cd concentrations in Cd-treated wheat plants were examined in a pot experiment. The results demonstrated that foliar spraying with CTS significantly improve the wheat growth, reduce malondialdehyde content and reactive oxygen species accumulation in leaves and decrease Cd concentrations in roots and shoots of wheat seedling under Cd stress. The alleviation of Cd toxicity by CTS is probably related with the activity of antioxidant enzymes, osmotic adjustment matter and root morphology. The application of CTS enhanced the activities of superoxide dismutase, peroxidase, and catalase in Cd-stressed wheat seedling leaves by 6.6%–13.1%, 17.2%–33.0%, and 19.6%–25.5%, respectively. Besides, exogenously applied CTS also increased the soluble protein and soluble sugar contents by 17.6%–33.8% and 30.1%–36.1% in the leaves of wheat under Cd stress. Furthermore, CTS with a molecular weight of 1 kDa was the most effective in mitigating Cd toxicity in wheat seedlings, which indicates that the activity of CTS is dependent on its molecular weight. It can be concluded that the use of foliar spraying, especially with 1 kDa CTS, could have potential in reducing the damage of Cd stress.

Efficacy of Indole Acetic Acid and Exopolysaccharides-Producing Bacillus safensis Strain FN13 for Inducing Cd-Stress Tolerance and Plant Growth Promotion in Brassica juncea (L.)

Untreated wastewater used for irrigating crops is the major source of toxic heavy metals and other pollutants in soils. These heavy metals affect plant growth and deteriorate the quality of edible parts of growing plants. Phytohormone (IAA) and exopolysaccharides (EPS) producing plant growth-promoting rhizobacteria can reduce the toxicity of metals by stabilizing them in soil. The present experiment was conducted to evaluate the IAA and EPS-producing rhizobacterial strains for improving growth, physiology, and antioxidant activity of Brassica juncea (L.) under Cd-stress. Results showed that Cd-stress significantly decreased the growth and physiological parameters of mustard plants. Inoculation with Cd-tolerant, IAA and EPS-producing rhizobacterial strains, however, significantly retrieved the inhibitory effects of Cd-stress on mustard growth, and physiology by up regulating antioxidant enzyme activities. Higher Cd accumulation and proline content was observed in the roots and shoot tissues upon Cd-stress in mustard plants while reduced proline and Cd accumulation was recorded upon rhizobacterial strains inoculation. Maximum decrease in proline contents (12.4%) and Cd concentration in root (26.9%) and shoot (29%) in comparison to control plants was observed due to inoculation with Bacillus safensis strain FN13. The activity of antioxidant enzymes was increased due to Cd-stress; however, the inoculation with Cd-tolerant, IAA-producing rhizobacterial strains showed a non-significant impact in the case of the activity of superoxide dismutase (SOD), peroxidase (POX) and catalase (CAT) in Brassica juncea (L.) plants under Cd-stress. Overall, Bacillus safensis strain FN13 was the most effective strain in improving the Brassica juncea (L.) growth and physiology under Cd-stress. It can be concluded, as the strain FN13 is a potential phytostabilizing biofertilizer for heavy metal contaminated soils, that it can be recommended to induce Cd-stress tolerance in crop plants.

Different sources of phosphorus fertilizers and soil amendments affected the phosphorus and cadmium content in soil, roots and seeds of maize (Zea mays L.)

Phosphorus (P) fertilizers contain cadmium (Cd) as a contaminant at levels varying from trace amounts to high levels and therefore, can be a major source of Cd to agricultural systems. This study was designed to assess the impact on application of Eppawala rock phosphate (ERP) and triple super phosphate (TSP) as P fertilizers and different soil amendments on P and Cd uptake in maize (Zea mays L.). The field trial was carried out at Field Crop Research and Development Institute at Mahailluppallama, Sri Lanka. A randomized complete block design was employed with three replicates as ERP and TSP separately applied with arbuscular mycorrhizal fungi (AMF) and three types of amendments (biochar, compost and dolomite) and the control without adding P fertilizers. Phosphorus content and Cd content of soil, maize roots and seeds were quantified. Results revealed that available soil Cd and total accumulated root and seed Cd amounts were significantly higher in TSP added treatments with and without amendments compared with ERP added soil. Considering soil available P, root and seed P, there was no significant difference observed in different treatments of TSP and ERP added treatments. A similar phenomenon was also observed in growth and yield parameters with both fertilizers added and with the added amendments. There was no colonization of AMF in maize roots in TSP applied soil while 25-60% of colonization was recorded with ERP. Synthetic fertilizer (TSP) must have inhibited the AMF colonization and thereby increasing the Cd content in maize seeds. AMF colonization increased with comparatively low soil available P in ERP added treatments. The results revealed that TSP could be effectively substituted by ERP as a source of P for maize soils. The addition of AMF, compost and biochar further increased the effect.

The combined use of arbuscular mycorrhizal fungi, biochar and nitrogen fertilizer is most beneficial to cultivate Cichorium intybus L. in Cd-contaminated soil

We assessed Cichorium intybus L. (chicory) growth, nutrients and Cd uptake in the presence of arbuscular mycorrhizal fungi (AMF), biochar (BC) and nitrogen (N) fertilizer applications in experimental pot studies. Mycorrhizal colonization was improved by BC addition but not N addition. However, in the presence of AMF, BC and N had positive effects on shoot biomass and plants grown in the presence of all 3 components yielded the highest levels of shoot biomass compared to pair-wise combinations or individual components singly added. AMF inoculation also increased root biomass and this effect was apparent in the combinations that included AMF without BC. Fungal inoculation also led to increased contents of phosphorus (P), magnesium (Mg) and copper (Cu) in both chicory shoots and roots and potassium (K) and manganese (Mn) in roots. Moreover, in the presence of BC, AMF inoculation evidently enhanced the shoot Ca content. In contrast, the presence of AMF inhibited plant Cd absorption and BC addition further inhibited root Cd concentration following the AMF inoculation. Applying N fertilizer alone increased Cd transfering from soil to plants. However, when combined with use of AMF and BC, Cd toxicity to plants was reduced. This study demonstrated that AMF inoculation combined with BC and N fertilizer could improve chicory growth, nutrient absorption and reduction of Cd uptake in Cd-contaminated soil.

The use of mercapto-modified palygorskite prevents the bioaccumulation of cadmium in wheat

In this study, the mechanism by which mercapto-modified palygorskite (MPAL) mediates Cd and Mn absorption by wheat was elucidated. In the aqueous phase, MPAL can react with Cd to form Cd-thiol complexes and CdO and with Mn to form MnO. In the wheat-soil system, 0.1–0.3% MPAL application increased the biomass of wheat by 18.6–29.4% and decreased the Cd concentration in shoots and roots by 19.4–51.8% and 35.9–64%, respectively; however, MPAL application did not decrease the diethylenetriaminepentaacetic acid (DTPA)-extracted Cd concentration in soil, probably because the formed Cd-thiol complexes and CdO could not be taken up by plants but could be extracted by DTPA. MPAL appeared to increase the Mn concentration in plants and the DTPA-extracted Mn concentration in soil, possibly because of the reduction in soil Mn oxides to more soluble Mn(Ⅱ) by the thiol groups in MPAL. MPAL enriched plant growth-promoting rhizobacteria and Cd-immobilizing bacteria and strengthened the sulfate reduction metabolism in rhizosphere soil, which partly contributed to the improvement in plant growth and the reduction in Cd bioaccumulation in wheat. These findings highlight the importance of the thiol group in MPAL and the regulation of the rhizosphere bacterial community in mediating Cd and Mn bioaccumulation in wheat.

Effects of plant growth regulator and chelating agent on the phytoextraction of heavy metals by Pfaffia glomerata and on the soil microbial community

Pfaffia glomerata is a candidate for the remediation of heavy metal-contaminated soil, but phytoremediation efficiency requires enhancement. In this study, we evaluated how application of DA-6, EDTA, or CA affected the growth and heavy metal accumulation of P. glomerata and soil microorganisms. We found that P. glomerata removed more Cd and Zn than Pb or Cu from contaminated soil. When compared to the control, application of DA-6, CA, or CA + DA-6 increased plant biomass and increased stem Cd concentration by 1.28-, 1.20-, and 1.31-fold respectively; increased leaf Cd concentration by 1.25-, 1.28-, and 1.20-fold, respectively; and increased the total quantity of Cd extracted by 1.37-, 1.37-, and 1.38-fold, respectively. When compared to the control, application EDTA or EDTA + DA-6 significantly increased the soil available metal and Na concentrations, which harmed plant growth. Application of EDTA or EDTA + DA-6 also significantly decreased the Cd concentration in roots and stems. 16S rRNA high-throughput sequencing analysis revealed that application of EDTA or CA alone to soil significantly reduced the richness and diversity of soil bacteria, while foliar spraying of DA-6 combined with EDTA or CA slightly alleviated this reduction. EDTA or CA addition significantly changed the proportion of Actinobacteria and Proteobacteria. In addition, EDTA or CA addition caused changes in soil properties (e.g. heavy metal availability, K concentration, Na concentration, soil pH, soil CEC, and soil DOC concentration) that were associated with changes in the bacterial community. EDTA addition mainly affected the soil bacterial community by changing soil DOC concentration, the soil available Pb and Na concentration, and CA addition mainly affected the soil bacterial community by changing the soil available Ca concentration.

Cell wall modification induced by an arbuscular mycorrhizal fungus enhanced cadmium fixation in rice root

The chemistry of root cell wall of rice could be changed by inoculation of arbuscular mycorrhizal fungi (AMF). Hydroponic experiments were conducted to investigate the roles of such changes on cadmium (Cd) uptake and distribution in rice. Results showed that inoculation of AM fungus Rhizophagus intraradices (RI) significantly enhanced (p < 0.05) shoot biomass, plant height and root length of rice, and decreased Cd concentration in shoot and root under Cd stress. Moreover, Cd in root was mainly found in pectin and hemicellulose 1 (HC1) components of root cell wall. Inoculation of RI increased the levels of pectin, HC1 and lignin content, accompanied by the increments of L-phenylalanine ammonia-lyase (PAL) and pectin methylesterase (PME) activities. Results of Fourier transform infrared spectroscopy further showed that more hydroxyl and carboxyl groups in root cell wall were observed in mycorrhizal treatment, compared with control. This study demonstrates that cell wall components could be the locations for Cd fixation, which reduced Cd transportation from root to shoot. Inoculation of AMF may remodel root cell wall biosynthesis and affect the characteristics of Cd fixation. The entering and fixing mechanisms should be further studied.

Comparative responses of cadmium accumulation and subcellular distribution in wheat and rice supplied with selenite or selenate.

Cadmium (Cd) contamination of crop plants has aroused a worldwide concern because of the threats posed to human health through accumulation in the food chains. Selenium (Se) can alleviate the Cd-induced phytotoxicity, but the relevant underlying mechanisms are not fully understood. Therefore, with wheat (Triticum aestivum L.) and rice (Oryza sativa L.) chosen as the target plants in this study, the effects of selenite or selenate on Cd accumulation and subcellular distribution were investigated through greenhouse hydroponic experiments; and simultaneously, the effects of pre-Se treatment with selenite or selenate on Cd accumulation and root-to-shoot translocation in the studied plants were also included. Results showed the addition of Se slightly changed the Cd content in plant roots in a time-dependent manner; however, with the obvious decreasing trend on the Cd transfer factor (TF), its content in plant shoots was significantly reduced by selenite or selenate in a plant species-dependent manner. At 48 h of exposure, the supplementation of selenite and selenate significantly decreased the Cd content by 40.4% and 38.0% in wheat shoots, and by 72.2% and 40.9% in rice shoots, respectively. Additionally, the order of Cd proportion distributed to the different subcellular fractions of plant tissues was as follows: cell wall > soluble cytosol > organelle, irrespective of the Se treatments or the plant species. However, selenate increased the Cd percentage in soluble cytosol of wheat shoots, while selenite increased that percentage in the cell wall of rice shoots; and the Cd proportion in soluble cytosol of the studied plant roots was significantly enhanced owing to selenite or selenate addition. Moreover, similar to the co-application, the pre-Se treatment with inorganic Se also reduced the Cd accumulation and translocation both in wheat and rice. Our results proved that the inorganic Se could decline the Cd accumulation and translocation in the crop plants, although selenite was found more effective than selenate regarding such effects.

Cd accumulation characteristics of Salvia tiliifolia and changes of rhizospheric soil enzyme activities and bacterial communities under a Cd concentration gradient

This study aimed to explore the phytoremediation potential of Salvia tiliifolia for cadmium (Cd)-contaminated soils and to understand the interactions in soil-Cd-plant systems. We assessed the Cd tolerance and accumulation characteristics of S. tiliifolia grown in soils with 0, 5, 25, and 50 mg kg− 1 Cd for 3 months. We also analysed the changes in physicochemical properties, enzyme activities, and bacterial community composition in the rhizosphere soils of S. tiliifolia. S. tiliifolia could tolerate all Cd concentrations with unchanged biomass. Cd concentrations (21.50–189.50 mg kg− 1) in roots of S. tiliifolia and corresponding bioconcentration factors (3.79–4.30) were much higher than those in shoots, and Cd translocation factors (0.03–0.23) were thereby very low. Rhizosphere pH decreased with increasing concentrations of Cd. Soil pH and rich organic matter may jointly affect the soil available Cd. Ultimately, soil enzyme activities involved in carbon, nitrogen, and phosphorus cycles were affected to varying degrees, and bacterial diversity and richness were slightly influenced by Cd stress. Interestingly, bacterial ABC transporters were induced by Cd stress during this process. S. tiliifolia can be designed as a Cd excluder. The induced soil bacterial ABC transporters may contribute to Cd detoxification and accumulation in both soil microbial communities and S. tiliifolia plants.

Remediation potential of spent mushroom substrate on Cd pollution in a paddy soil.

To investigate the remediation potential of spent mushroom substrate (SMS) on Cd pollution in a paddy soil, a rice pot experiment was conducted to study the effects of SMS addition on the availability of Cd in soil and the uptake of Cd in rice tissues. Five percent of SMS from Pleurotus eryngii (SMS-A, treatment: A), SMS from Agaricus bisporus (SMS-B, treatment: B), or SMS-A plus SMS-B (1:1, treatment: A+B) were added into a Cd-contaminated paddy soil before planting, respectively. The treatment of no SMS amendment was set up as the control (CK). At the four main growth stages of rice, the soils and plant samples were collected to detect the soil properties, Cd concentration in soils and rice tissues, and Cd fractions in soils. Results indicated that the application of SMS-A, SMS-B, and A+B significantly increased soil pH by 14.0-22.9, 23.9-32.9, and 22.7-30%, organic matter (OM) contents by 12.9-31.5, 22.1-34.5, and 26.1-36.9% comparing with CK. While cation exchange capacities (CECs) were increased by 3.6-8.5, 4.9-13.1, and 0.4-10.0% in A, B, and A+B treatments, respectively, except those at the maturation stage in A and B treatments. However, the CaCl2-Cd concentrations in soils were significantly decreased by 64.8-77.9, 76.1-98.9, 73.2-98.9% in A, B, and A+B treatments, respectively, comparing with CK. The reduced availability of Cd was attributed to the changes of Cd from soluble to insoluble fractions in soils amended with SMS and resulted in the decreased Cd uptake in rice tissues. The Cd concentrations in roots significantly decreased by 22.8-36.9, 28.6-36.6, and 26.8-42.6%, while the Cd concentrations in straw decreased by 20.1-46.4, 9.3-41.6, and 16.0-49.1% in A, B, and A+B treatments, respectively. At the maturation stage, the Cd concentrations in brown rice were reduced by 17.7, 15.9, and 19.4% in A, B, and A+B treatments, respectively. Correlation analysis revealed that the Cd concentrations in rice roots, straws, and brown rice were all positively correlated with CaCl2-Cd concentrations of soils. Moreover, soil pH and OM were significantly negatively correlated with the Cd concentration in rice tissues, except that between soil pH and the Cd concentration in rice straws. Therefore, the reduced Cd availability in soil and uptake in rice plant tissues together with better soil nutrient conditions by SMS application improved the biomass of root and straw at heading, filling, and maturation stages and the rice production by 32.9-38.8% at the maturation stage. The combined application of SMS-A and SMS-B can be used as a potential method for remediation of Cd-contaminated paddy soil.

Co-application of biochar and microorganisms improves soybean performance and remediate cadmium-contaminated soil

Sole biochar addition or microbial inoculation as a soil amendment helps to reduce cadmium (Cd) toxicity in polluted agricultural soils. Yet the synergistic effects of microorganisms and biochar application on Cd absorption and plant productivity remain unclear. Therefore, a pot experiment was conducted to investigate the combined effect of microorganisms (Trichoderma harzianum L. and Bacillus subtilis L.), biochar (maize straw, cow manure, and poultry manure), and Cd (0, 10, and 30 ppm) on plant physiology and growth to test how biochar influences microbial growth and plant nutrient uptake, and how biochar ameliorates under Cd-stressed soil. Results showed that in comparison to non-Cd polluted soil, the highest reduction in chlorophyll content, photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency, and intercellular CO2 were observed in Cd2 (30 ppm), which were 9.34%, 22.95%, 40.45%, 29.07%, 20.67%, and 22.55% respectively less than the control Cd0 (0 ppm). Among sole inoculation of microorganisms, highest stomatal conductance, water use efficiency, and intercellular CO2 were recorded with combined inoculation of both microorganisms (M3), which were 5.92%, 7.65%, and 7.28% respectively higher than the control, and reduced the Cd concentration in soil, root, and shoot by 21.34%, 28.36%, and 20.95%, respectively, compared to the control. Similarly, co-application of microorganisms and biochar ameliorated the adverse effect of Cd in soybean as well as significantly improved plant biomass, photosynthetic activity, nutrient contents, and antioxidant enzyme activities, and minimized the production of reactive oxygen species and Cd content in plants. Soil amended with poultry manure biochar had significantly improved the soil organic carbon, total nitrogen, total phosphorous, and available potassium by 43.53%, 36.97%, 22.28%, and 4.24%, respectively, and decreased the concentration of Cd in plant root and shoot by 34.68% and 47.96%, respectively, compared to the control. These findings indicate that the combined use of microorganisms and biochar as an amendment have important synergistic effects not only on the absorption of nutrients but also on the reduction of soybean Cd intake, and improve plant physiology of soybean cultivated in Cd-polluted soils as compared to sole application of microorganisms or biochar.

Effects of Water Management and Silicon Application on Iron Plaque Formation and Uptake of Arsenic and Cadmium by Rice

To explore the effects of water management and silicon application on the bioavailability of soil arsenic (As) and cadmium (Cd), and the accumulation of As and Cd in rice, pot experiments were carried out using As/Cd co-contaminated paddy soil from a field in Kaiyang County, Guizhou Province. The experimental treatments had the following five water application modes with and without silicon addition:flooding during the entire growth period (T1); flooding for three weeks (0-105 d) after transplanting with wet irrigation (moisture content 50%-60%) during other growth periods (T2); flooding for three weeks before heading (0-65d), three weeks after heading (84-105d), and wet irrigation during other growth periods (T3); flooding from heading to three weeks after heading (84-105d) and wet irrigation during the other growth periods (T4); and wet irrigation during the entire growth period (T5). The results showed that compared with flooding and wet irrigation, flooding combined with wet irrigation was more conducive to the formation of iron plaque (DCB-Fe) on the surfaces of roots. As and Cd content increased with an increasing of content of DCB-Fe. Silicon application increased soil pH and the content of DCB-As but decreased available As and Cd in the soil and, with the exception of the flooding treatment, the DCB-Fe/Cd content. The shorter the flooding time, the higher the accumulation of Cd and the lower the accumulation of As in each part of the rice. Silicon application increased the biomass of rice but decrease the Cd content of roots, stems, leaves, and grain by 4.23%-31.06%, 11.41%-52.90%, 1.74%-35.73%, and 19.25%-39.76%, respectively. Silicon application also decreased the As content of roots, stems, leaves, and grain by 1.47%-52.60%, 6.12%-63.02%, 2.97%-28.41%, and 16.33%-61.23%, respectively. Among the five modes of water application tested, silicon application combined with the T3 mode achieved the highest rice biomass and lowest rice As and Cd contents. Therefore, it is suggested that selecting water management and silicon application regimes according to the level of As/Cd pollution can effectively decrease the bioavailability of As/Cd in the soil, thereby reducing the accumulation of As/Cd in rice.

Phytochelatins formation kinetics and Cd-induced growth inhibition in Lolium perenne L. at elevated CO2 level under Cd stress.

Elevated CO2 levels may alleviate toxicities induced by environmental stresses in plants, such as heavy metals. To assess this possibility, seedlings of Lolium perenne L. were exposed to different Cd stress and CO2 levels during hydroponic culture. The kinetics of growth, Cd accumulation, and thiol formation were investigated. Elevated CO2 levels increased the growth rate from 30 to 75%, and decreased the Cd accumulation rate from 36 to 42%, leading to a decrease of Cd content in root and shoot. However, an increase in Cd transport from root to shoot was observed at elevated CO2 under Cd stress. The production of phytochelatins (PCs) occurred earlier at elevated CO2 level than at ambient CO2 level after exposure to Cd stress. The mean SH/Cd ratio was relatively higher at elevated CO2 level, but elevated CO2 level significantly decreased thiol contents. The reduction of Cd contents, earlier production of PCs, and relatively higher SH/Cd ratio at the elevated CO2 level alleviated Cd toxicity in root and shoot to some extent, causing significant yield increase of L. perenne after exposure to Cd stress. This study could provide an important data support and theoretical basis in understanding the effects of elevated CO2 on plant growth, heavy metal accumulation, and thiol formation.

Mechanisms of Enterobacter bugandensis TJ6 immobilization of heavy metals and inhibition of Cd and Pb uptake by wheat based on metabolomics and proteomics

Microbial passivation remediation of heavy metal-contaminated farmland has attracted increasing attention. However, the molecular mechanism by which heavy metal-immobilizing bacteria inhibit the uptake of Cd and Pb by wheat is not clear. Herein, a heavy metal-immobilizing bacterium, Enterobacter bugandensis TJ6, was used to reveal its immobilization mechanisms of Cd and Pb and inhibition of Cd and Pb uptake by wheat using metabolomics and proteomics. Compared with the control, strain TJ6 significantly reduced (44.7%–56.6%) the Cd and Pb contents of wheat roots and leaves. Strain TJ6 reduced the Cd and Pb concentrations by adsorption, intracellular accumulation, and bioprecipitation in solution. Untargeted metabolomics showed that strain TJ6 produced indole-3-acetic acid (IAA), betaine, and arginine under Cd and Pb stress, significantly improving the resistance of strain TJ6 and wheat to Cd and Pb. Label-free proteomics showed that 143 proteins were upregulated and 61 proteins were downregulated in wheat roots in the presence of strain TJ6. The GO items of the differentially expressed proteins (DEPs) involved in protein-DNA complexes, DNA packaging complexes, and peroxidase activity were enriched. In addition, the ability of wheat roots to synthesize abscisic acid and jasmonic acid was improved. In conclusion, strain TJ6 reduced Cd and Pb uptake in wheat through its own adsorption of Cd and Pb and regulation of wheat root DNA repair ability, plant hormone levels, and antioxidant activities. These results provide new insights and a theoretical basis for the application of heavy metal-immobilizing bacteria in safe wheat production.

Iron and copper micronutrients influences cadmium accumulation in rice grains by altering its transport and allocation.

Cadmium (Cd) contamination in rice paddy fields constitutes a serious health issue in some parts of China. Here we study the potential for remediation of Cd contaminated alkaline paddy soil with low iron (Fe) and high copper (Cu) background by altering the concentrations of Fe and Cu in the growing media, which has been only seldom considered. We assessed how these two micronutrients (Cu and Fe) affect the absorption and transport of Cd in rice. Adding Cu significantly increased rice biomass and grain yield by reducing root Cd influx and Cd upward transport which, consequently, lowered Cd concentrations in roots, culms and leaves. However, excessive Cu also promoted a relatively higher Cd allocation in grains, especially under Fe deficiency, likely because Cu significantly increased the proportion of bioavailable Cd in leaves. Contrastingly, Fe did not alleviate the toxic effects of Cd on rice growth and yield, but it significantly reduced Cd transfer towards grains, which might be attributed to a sharp decrease in the proportion of bioavailable Cd in leaves. Our results demonstrated that Cd remediation may be achieved through altering Fe and Cu inputs, such that Cd accumulation in rice grains is reduced.