Fe Plaque Formation Research Articles

Controlling factors of iron plaque formation and its adsorption of cadmium and arsenic throughout the entire life cycle of rice plants

Iron (Fe) plaque, which forms on the surface of rice roots, plays a crucial role in immobilizing heavy metal(loids), thus reducing their accumulation in rice plants. However, the principal factors influencing Fe plaque formation and its adsorption capacity for heavy metal(loid)s throughout the rice plant's lifecycle remain poorly understood. Thus, this study investigated the dynamics of Fe plaque formation and its ability to adsorb cadmium (Cd) and arsenic (As) across different growth stages, aiming to identify the key drivers behind these processes. The findings reveal that the rate of radial oxygen loss (ROL) and the abundance of plaque-associated microbes are the primary drivers of Fe plaque formation, with their relative importance ranging from 1.4% to 81%. Similarly, the adsorption of As by Fe plaque is principally determined by the rate of ROL and the quantity of Fe plaque, with subsequent effects from the total Fe in rhizospheric soil, arsenate-reducing bacteria, and organic matter-degrading bacteria. The relative importance of these factors ranges from 6.0% to 11.7%. By contrast, the adsorption of Cd onto Fe plaque is primarily affected by competition for adsorption sites with ammonium in soils and the presence of organic matter-degrading bacteria, contributing 25.5% and 23.5% to the adsorption process, respectively. These findings provide significant insights into the development of Fe plaque and its absorption of heavy metal(loid)s throughout the lifecycle of rice plants.

Rainwater-borne H2O2 accelerates roxarsone degradation and reduces bioavailability of arsenic in paddy rice soils

Contamination of rice by arsenic represents a significant human health risk. Roxarsone -bearing poultry manure is a major pollution source of arsenic to paddy soils. A mesocosm experiment plus a laboratory experiment was conducted to reveal the role of rainwater-borne H2O2 in the degradation of roxarsone in paddy rice soils. While roxarsone could be degraded via chemical oxidation by Fenton reaction-derived hydroxyl radical, microbially mediated decomposition was the major mechanism. The input of H2O2 into the paddy soils created a higher redox potential, which favored certain roxarsone-degrading and As(III)-oxidizing bacterial strains and disfavored certain As(V)-reducing bacterial strains. This was likely to be responsible for the enhanced roxarsone degradation and transformation of As(III) to As(V). Fenton-like reaction also tended to enhance the formation of Fe plaque on the root surface, which acted as a filter to retain As. The dominance of As(V) in porewater, combined with the filtering effect of Fe plaque significantly reduced the uptake of inorganic As by the rice plants and consequently its accumulation in the rice grains. The findings have implications for developing management strategies to minimize the negative impacts from the application of roxarsone-containing manure for fertilization of paddy rice soils.

Evaluation of iron-modified biochar on arsenic accumulation by rice: a pathway to assess human health risk from cooked rice.

Arsenic (As) contamination of rice grain poses a serious threat to human health. Therefore, it is crucial to reduce the bioavailability of As in the soil and its accumulation in rice grains to ensure the safety of food and human health. In this study, mango (Mangifera indica) leaf-derived biochars (MBC) were synthesized and modified with iron (Fe) to produce FeMBC. In this study, 0.5 and 1% (w/w) doses of MBC and FeMBC were used. The results showed that 1% FeMBC enhanced the percentage of filled grains/panicle and biomass yield by 17 and 27%, respectively, compared to the control. The application of 0.5 and 1% FeMBC significantly (p < 0.05) reduced bioavailable soil As concentration by 33 and 48%, respectively, in comparison to the control. The even higher As flux in the control group as compared to the biochar-treated groups indicates the lower As availability to biochar-treated rice plant. The concentration of As in rice grains was reduced by 6 and 31% in 1% MBC and 1% FeMBC, respectively, compared to the control. The reduction in As concentration in rice grain under 1% FeMBC was more pronounced due to reduced bioavailability of As and enhanced formation of Fe-plaque. This may restrict the entry of As through the rice plant. The concentrations of micronutrients (such as Fe, Zn, Se, and Mn) in brown rice were also improved after the application of both MBC and FeMBC in comparison to the control. This study indicates that the consumption of parboiled rice reduces the health risk associated with As compared to cooked sunned rice. It emphasizes that 1% MBC and 1% FeMBC have great potential to decrease the uptake of As in rice grains.

The utilization of Lysinibacillus bacterial powder to induce Fe plaque formation mitigates cadmium and chromium levels in rice

The presence of cadmium (Cd) and chromium (Cr) contamination in soil poses an environmental risk to food safety. Microorganisms are crucial for biotransforming heavy metals, but their limited survival in contaminated soils hinders their application in bioremediation. Here, we isolated Lysinibacillus sp. OR-15, which effectively removed Cd(II) and reduced Cr(VI) from the culture. Proteomic analyses and heterologous expression assays showed that QueF, an NADPH-dependent reductase, enhanced bacterial resistance to Cd(II) and Cr(VI), enhancing metal removal capacity. The dry bacterial powder, produced through deep liquid fermentation and spray drying, contained 2.3 × 1010 viable cells per gram. It effectively reduced Cd and Cr levels in rice grains and maintained a concentration of 105 per gram in soils even after 60 days of cultivation following one application. Scanning and microscopy analysis revealed that Lysinibacillus sp. OR-15 facilitated the formation of iron plaque on rice roots. The formation of iron plaque on the root surface serves as a protective barrier against the upward translocation of heavy metals. Our findings suggest that Lysinibacillus sp. OR-15 exhibits stable and effective properties as a factor for Cd and Cr adsorb on rice iron plaque, thus mitigating the levels of Cd and Cr in rice grains.

The influence of phosphorus availability on rice root traits driving iron plaque formation and dissolution, and implications for phosphorus uptake

Background and aimsIron (Fe) plaque which normally coats rice roots has a strong affinity for phosphorus (P), with a debated effect on plant P uptake. Furthermore, plant responses to P availability shape the rhizospheric environment, possibly affecting the rates of Fe plaque formation and dissolution. The role of Fe plaque to serve as a sink or source of available P may depend on root traits, themselves influenced by P availability. However, the underlying mechanism regulating these interactions remains unclear. In this study, we investigated the effects of P availability on root traits, Fe plaque dynamics and their implications for P uptake and rice plant growth.MethodsPlants were hydroponically grown for 60 days under P-sufficiency or P-deficiency, with or without Fe plaque. Root traits, rhizosphere acidification, and the rates of Fe plaque formation and dissolution were investigated and linked to differences in rice P content and growth.ResultsP-deficient conditions stimulated root development and promoted Fe plaque formation on the root surface compared to P-sufficient conditions. However, P limited plants exhibited a faster Fe plaque dissolution, along with increased net proton exudation. After 60 d, P-deficient plants showed higher P uptake in the presence of Fe plaque, whereas the opposite was observed in P-sufficient plants, where Fe plaque limited plant P uptake.ConclusionsThe role of Fe plaque in regulating P uptake highly depends on the dynamic nature of this Fe pool that is strictly linked to P availability and regulated by plant responses to P deficiency.

Phytoavailability of cadmium in rice amended with organic materials and lime: Effects of rhizosphere chemical changes and cadmium sequestration in iron plaque

Excessive Cd in rice grains produced with acidic paddy soil is receiving increasingly widespread attention because it endangers human health. Applying organic materials (OM) and lime (L) is a common technique used to reduce Cd concentration in grains (CdG). Nevertheless, the mechanism by which their simultaneous application affects the Cd phytoavailability in soilrice systems remains ambiguous. In the current study, we adopted a rhizobag pot culture test to explore the influences of single application of OM [rice straw (RS), milk vetch (MV)], L, and their co-utilization on Cd phytoavailability and the associated mechanisms. The results showed that the application of RS, MV, L, L + RS (LRS), and L + MV (LMV) significantly decreased CdG by 26.9%, 38.2%, 48.6%, 50.0%, and 53.0%, respectively. Fe plaque (IP) formation was not affected by these treatments; however, Cd sequestration in IP (CdIP) was significantly reduced. CdIP was significantly reduced by 18.3%, 23.6%, 43.8%, 33.1%, and 41.4%, after RS, MV, L, LRS, and LMV treatments, respectively. Additionally, available Cd concentrations in rhizospheric soil (RHS) were significantly reduced by 11.5%, 14.8%, 15.1%, and 18.4%, after MV, L, LRS, and LMV treatments, respectively. Cd availability in RHS was significantly influenced by pH, dissolved organic carbon concentration, and Zn, Fe, and Mn availability. The results of the structure equation mode showed that CdG was mainly affected by CdIP, followed by Cd availability and the pH of RHS. In conclusion, the reduction of CdG by OM, L, and their co-utilization was the results of their combined effects of reducing Cd availability in RHS, CdIP, and Cd uptake by the roots. This study emphasizes that the reduction of CdG is a result of the dual effects of reducing Cd availability in RHS and CdIP after amendments application. L application alone or in conjunction with OM is an efficient practice to reduce CdG in acidic Cd-contaminated paddy fields.

Iron plaque formation and its influences on the properties of polyethylene plastic surfaces in coastal wetlands: Abiotic factors and bacterial community

Iron (Fe) plaques in coastal wetlands are widely recognized because of their strong adsorption affinity for natural particles, but their interaction behaviors and mechanisms with plastics remain unknown. Through laboratory incubation experiments, paired with multiple characterization methods and microbial analysis, this work focused on the characteristics of Fe plaques on low-density polyethylene plastic surfaces and their relationship with environmental factors in coastal wetlands (Mangrove and Spartina alterniflora soil). The results showed that iron plaques increased the adhesive force of the plastic surface from 65.25 to 300 nN and promoted the oxidation of the plastic surface. Fe plaque formation was stimulated by salinity, anaerobic conditions, natural organic matter, and a weak alkaline scenario (pH 8.0–8.3). The Fe content showed a stable positive correlation with heavy metals loading (i.e., As, Mn, Co, Cr, Pb, and Zn). Furthermore, we revealed that Fe plaque was positively regulated by Nitrospirae through 16S rRNA high-throughput sequencing analysis. Meanwhile, Verrucomicrobia and Kiritimatiellaeota. may act as depressants by consuming salt. This work illustrated that iron plaques could enhance the role of plastics in contaminant migration by altering their adsorption performance, providing new insights into plastic interface behavior and potential ecological effects in coastal wetlands.

Iron plaque effects on selenium and cadmium stabilization in Cd-contaminated seleniferous rice seedlings.

Dietary intake of selenium (Se)-enriched rice has benefit for avoiding Se-deficient disease, but there is a risk of excessive cadmium (Cd) intake. Through hydroponic culture and adsorption-desorption experiments,this paper focused on Se and Cd uptake in rice seedlings associated with the interactive effects of Se (Se4+ or Se6+), Cd,and iron (Fe) plaque. The formation of Fe plaque was promoted by Fe2+ and inhibited by Cd but not related with Se species. Shoot Se (Se4+ or Se6+) uptake was not affected by Fe plaque in most treatments, except that shoot Se concentrations were decreased by Fe plaque when Se4+ and Cd co-exposure. Shoot Cd concentrations were always inhibited by Fe plaque, regardless of Se species. Inhibiting Cd adsorption onto root surface (Se4+ + Cd) or increased Cd retention in Fe plaque (Se6+ + Cd) is an important mechanism for Fe plaque to reduce Cd uptake by rice. However, we found that DCB Cd concentrations (Cd adsorbed by Fe plaque) were not always positively correlated with Fe plaque amounts and always negatively correlated with the distribution ratios of Cd mass in root to that in Fe plaque (abbreviated as DRCMRF; r = - 0.942**); meanwhile, with the increase of DCB Fe concentration, the directions of variations of DCB Cd concentration and DRCMRF were affected by Se species. It indicated that the root system is also an important factor to affect DCB Cd concentration and inhibit Cd uptake, which is mediated by Se species. This paper provides a new understanding of Fe plaque-mediated interactive effect of Se and Cd uptakes in rice, which is beneficial for the remediation of Cd-contaminated and Cd-contaminated seleniferous areas.

Visualization and quantification of carbon "rusty sink" by rice root iron plaque: Mechanisms, functions, and global implications.

Paddies contain 78% higher organic carbon (C) stocks than adjacent upland soils, and iron (Fe) plaque formation on rice roots is one of the mechanisms that traps C. The process sequence, extent and global relevance of this C stabilization mechanism under oxic/anoxic conditions remains unclear. We quantified and localized the contribution of Fe plaque to organic matter stabilization in a microoxic area (rice rhizosphere) and evaluated roles of this C trap for global C sequestration in paddy soils. Visualization and localization of pH by imaging with planar optodes, enzyme activities by zymography, and root exudation by 14 C imaging, as well as upscale modeling enabled linkage of three groups of rhizosphere processes that are responsible for C stabilization from the micro- (root) to the macro- (ecosystem) levels. The 14 C activity in soil (reflecting stabilization of rhizodeposits) with Fe2+ addition was 1.4-1.5 times higher than that in the control and phosphate addition soils. Perfect co-localization of the hotspots of β-glucosidase activity (by zymography) with root exudation (14 C) showed that labile C and high enzyme activities were localized within Fe plaques. Fe2+ addition to soil and its microbial oxidation to Fe3+ by radial oxygen release from rice roots increased Fe plaque (Fe3+ ) formation by 1.7-2.5 times. The C amounts trapped by Fe plaque increased by 1.1 times after Fe2+ addition. Therefore, Fe plaque formed from amorphous and complex Fe (oxyhydr)oxides on the root surface act as a "rusty sink" for organic matter. Considering the area of coverage of paddy soils globally, upscaling by model revealed the radial oxygen loss from roots and bacterial Fe oxidation may trap up to 130 Mg C in Fe plaques per rice season. This represents an important annual surplus of new and stable C to the existing C pool under long-term rice cropping.

Effects of Iron Intensity-regulated Root Microbial Community Structure and Function on Cadmium Accumulation in Rice

Exploring the effects of exogenous iron (Fe) on cadmium (Cd) in rice is of great significance for ensuring food security. The accumulation of Cd and the changes in the microbial community structure in rice roots under three Fe concentrations (5, 50, and 500 μmol·L-1 EDTA-Na2Fe) were studied through a hydroponic experiment. The results showed that the increase in the environmental Fe concentration promoted the formation of iron plaque on the rice roots, and both Fe-deficiency and Fe-sufficiency would enhance the adsorption and fixation of Cd on the root surface. Compared with that of normal Fe levels (50 μmol·L-1), Fe deficiency increased Cd accumulation in rice roots and shoots by 49.76% and 15.68%, respectively. Although Fe sufficiency also increased Cd accumulation in the roots by 18.39%, the Cd concentration in shoots was significantly reduced by 35.95% compared with that of the normal Fe. 16S rRNA high-throughput sequencing was used to determine the root microbial community structure, and through PCA, LEfSe, and RDA analysis, it was found that compared with normal Fe, an Fe-deficient environment reduced the abundance and uniformity of root microbes. Proteobacteria and Bacteroidetes at the phylum level were the dominant flora, Fe deficiency inhibited the increase in the relative abundance of Bacteroidetes, and high-concentration Fe reduced the relative abundance of Proteobacteria. At the genus level, the relative abundance of functional microorganisms Ensifer, Rhodopila, Bdellovibrio, and Dyella were different under different Fe environments, which may have affected the absorption and accumulation of Cd by rice by affecting the formation of Fe plaque on the root and other biochemical processes. In addition, the effect of an Fe-deficient environment on microbial functions was higher than that of the Fe sufficient environment. This study investigated the changes in the rice root microbial community structure and the ability of rice to absorb and transport Cd under different Fe environments, which provided a theoretical basis and an important reference for the inhibition of Fe on Cd accumulation in rice in Cd-polluted paddy soil in southern China.

Effects of Red Mud on Cadmium Uptake and Accumulation by Rice and Chemical Changes in Rhizospheres by Rhizobox Method

Red mud (RM), a byproduct of aluminum production, is used as amendments to increase the pH and reduce the available Cd in soil, but the effects of RM treatments on rice and rhizosphere chemistry changes at different radial-oxygen-loss (ROL) rates and developmental stages remain unclear. To address this concern, a rhizobox trial was conducted to investigate the effect of 0%, 0.5%, and 1.0% RM, on Cd accumulation by rice cultivars differing in ROL rate (‘Zheyou12’ (ZY12), ‘Qianyou1’ (QY1), and ‘Chunjiangnuo2’ (CJN2)) at two growth stages (tillering and bolting). The results showed that mobility factors of Cd in the soil were decreased significantly at both stages. The Cd mobility factor (MF) of CJN2 was decreased by 33.01% under 1% RM treatment at bolting stage. The pH value was increased by 0.39–0.53 units at two stages. RM contains large amounts of metals, which can increase soil iron (Fe) and manganese (Mn) concentrations, reduce redox potential, and transform the available Cd into Fe/Mn oxide-bound Cd. In addition, the Fe plaque further increased to inhibit the transformation of Cd. These changes reduced the available Cd in the soil and further decreased Cd absorption by rice. With the increase in RM concentration, the shoot and root biomass increased, and Cd accumulation in the plant significantly decreased. Compared with that under 0% RM treatment, the shoot Cd concentrations of ZY12, QY1, and CJN2 under 1% RM treatment at the bolting stage decreased by 27.59%, 36.00%, and 46.03%, respectively. The relative Cd accumulation ability of the three rice cultivars was CJN2 &lt; QY1 &lt; ZY12. The ROL promotes Fe plaque formation on the root surface. The Fe plaque is an obstacle or buffer between Cd and rice, which can immobilize Cd in Fe plaque and further reduce Cd absorption by rice. The addition of RM, in combination with a high-ROL rice cultivar, is a potential strategy for the safe production of rice on Cd-contaminated soils.

The effect of silicon on the kinetics of rice root iron plaque formation

PurposeAquatic plants, including rice, develop iron (Fe) plaques on their roots due to radial oxygen loss (ROL), and these plaques accumulate both beneficial and toxic elements. Silicon is an important nutrient for rice and both accumulates in Fe plaque and can affect ROL. How these plaques form over time and how Si affects this process remains unclear.MethodsRice was grown in a pot study with 4 levels of added Si. Root Fe plaque formation was monitored weekly using vinyl films placed between the pot and soil. Plants were grown to maturity and then ratooned to also examine the formation of Fe plaque during the ratoon crop.ResultsIron plaque formation increased exponentially during the vegetative phase, peaked at the booting phase, then decreased exponentially – a pattern that repeated in the ratoon crop. While the highest Si treatment led to an earlier onset of Fe plaque formation, increasing Si decreased the amount of Fe plaque at harvest, resulting in a minimal net effect.ConclusionsThe kinetics of Fe plaque formation are dependent on rice growth stage, which may affect whether the Fe plaque is a source or sink of elements such as phosphorous and arsenic.

Application of Exogenous Iron Alters the Microbial Community Structure and Reduces the Accumulation of Cadmium and Arsenic in Rice (Oryza sativa L.).

Cadmium (Cd) and arsenic (As) contamination of soil has been a public concern due to their potential accumulation risk through the food chain. This study was conducted to investigate the performance of ferrous sulfate (FeSO4) and ferric oxide (Fe2O3) nanoparticle (Nano-Fe) to stabilize the concentrations of Cd and As in paddy soil. Both Fe treatments led to low extractable Cd and the contents of specifically sorbed As contents, increased (p < 0.05) the Shannon index and decreased (p < 0.05) the Simpson diversity indices compared with the control. Nano-Fe increased the relative abundances of Firmicutes and Proteobacteria and decreased the abundances of Acidobacteria and Chloroflexi. Moreover, the addition of both forms of Fe promoted the formation of Fe plaque and decreased the translocation factor index (TFs) root/soil, TFs shoot/root, and TFs grain/shoot of Cd and As. These results suggest that exogenous Fe may modify the microbial community and decrease the soil available Cd and As contents, inhibit the absorption of Cd and As by the roots and decrease the transport of Cd and As in rice grains and the risk intake in humans. These findings demonstrate that soil amendment with exogenous Fe, particularly Nano-Fe, is a potential approach to simultaneously remediate the accumulation of Cd and As from the soil to rice grain systems.

The potential of Croton lindheimeri to sequester different metals from different mediums: uptake essential element Fe from soils or sequester toxic metal Sr from solutions

Some metals are necessary nutrients for plant health while some are toxic pollutants. In this study, the ability of Croton lindheimeri to uptake essential element Fe or toxic metal Sr was assessed separately. The amounts of iron plaque on the root systems and the levels of Fe in C. lindheimeri collected from an iron-rich field were assessed. The results indicated that Translocation Factor (TF) of Fe in C. lindheimeri was around 1, with similar amounts of Fe in roots and shoots. C. lindheimeri seedlings were cultured in Sr solutions for 3 weeks to determine its potential to accumulate Sr. It was found that the roots of C. lindheimeri cultured in 20 mg/L Sr solutions sequestered 0.05 ± 0.01 mg Sr/g biomass. TF of Sr in C. lindheimeri was >1. Further research is worthwhile to evaluate the potential of C. lindheimeri to remediate Sr contaminated sites. Novelty statement No study related to the sequester of metals (either essential or non-essential metals) in Croton lindheimeri (goat weed) was found before. It was the first research about metal accumulation in goat weed. Fe plaque formation and iron sequester in the biomass of Croton lindheimeri were never studied in previous research. Very limited information about phytoremediation of Sr contaminated media was reported in previous studies, this study filled the gap by exploring the uptake of Sr in Croton lindheimeri.

Regulation of iron and cadmium uptake in rice roots by iron(iii) oxide nanoparticles: insights from iron plaque formation, gene expression, and nanoparticle accumulation

Fe2O3 nanoparticles alleviated Cd uptake mainly via down-regulation of OsNRAMP5, OsCd1, OsIRT1 and OsIRT2 in roots, while the contribution of the enhanced formation of Fe plaque was minor.

Influences of soil pH, iron application and rice variety on cadmium distribution in rice plant tissues

Cadmium (Cd) is a widespread environmental contaminant, and its increasing concentrations in rice poses significant risks to human health. Globally, rice is a staple food for millions of people, and consequently, effective strategies to reduce Cd accumulation in rice are needed. This study investigates the effect of soil pH (Soil 1: 4.6; Soil 2: 6.6) and iron (Fe) application (at 0, 1.0 and 2.0 g/kg) on Fe plaque formation, Cd sequestration in Fe plaques and Cd bioaccumulation in different parts of the rice plant for three different Cd-graded paddy soils (0, 1.0 and 3.0 mg/kg, respectively) using two Australian rice cultivars under glasshouse conditions. Results show that grain and straw yield declined as Cd toxicity increased, and the toxic effects of Cd were lower in the Quest cultivar than in the Langi cultivar. With applications of Cd at 1.0 mg/kg and 3.0 mg/kg, Cd concentrations in rice grown in Soil 1 were 1.09 mg/kg and 1.37 mg/kg, respectively, while those in rice grown in Soil 2 were 0.38 mg/kg and 0.52 mg/kg, respectively. Soil pH significantly affected the bioaccumulation of Cd in different parts of the rice plant. At both levels of Cd application, Cd concentration was highest in the root, followed by the stem, leaf, husk and grain. Cd was more concentrated in Fe plaques formed by the application of Fe than in rice plant tissues. The Quest cultivar had a higher ability to produce Fe plaques and a 1.3- and 1.4-times higher Cd concentration compared with the Langi cultivar in Soils 1 and 2, respectively.

Goethite modified biochar simultaneously mitigates the arsenic and cadmium accumulation in paddy rice (Oryza sativa) L

Cadmium (Cd) and arsenic (As) contamination of paddy soils is a serious global issue because of the opposite geochemical behavior of Cd and As in paddy soils. Rice plant (Oryza sativa L.) cultivation in Cd- and As- contaminated paddy soil is regarded as one of the main dietary cause of Cd and As entry in human beings. This study aimed to determine the impact of goethite-modified biochar (GB) on bioavailability of both Cd and As in Cd- and As- polluted paddy soil. Contrary to control and biochar (BC) amendments, the application of GB amendments significantly impeded the accumulation of both Cd and As in rice plants. The results confirmed an obvious reduction in Cd and As content of rice grains by 85% and 77%, respectively after soil supplementation with GB 2% amendment. BC 3% application minimized the Cd uptake by 59% in the rice grains as compared to the control but exhibited a little impact on As accumulation in rice grains. Sequential extraction results displayed an increase in immobile Cd and As fractions of the soil by decreasing the bioavailable fractions of both elements after GB treatments. Fe-plaque formation on the root surfaces was significantly variable (P ˂ 0.05) among all the amendments. GB 2% treatment significantly increased the Fe content (10 g kg−1) of root Fe-plaque by 48%, which ultimately enhanced the sequestration of Cd and As by Fe-plaque and minimized the transport of Cd and As in rice plants. Moreover, GB treatments significantly changed the relative abundance of the microbial community in the rice rhizosphere and minimized the metal(loid)s mobility in the soil. The relative abundance of Acidobacteria, Firmicutes and Verrucomicrobia increased with GB 2% treatment while those of Bacteroidetes and Choloroflexi decreased. Our findings confirmed improvement in the rice grains quality regarding enhanced amino acid contents with GB application. Overall, the results of this study demonstrated that GB amendment simultaneously alleviated the Cd and As concentrations in edible parts of rice plant and provided a new valuable method to protect the public health by effectively remediating the co-occurrence of Cd and As in paddy soils.

The mechanistic pathways of arsenic transport in rice cultivars: Soil to mouth

Rice cultivars are major conduit of arsenic (As) poisoning to human. We quantified transferability of fifteen rice cultivars representing three groups i.e., high yielding variety (HYV), local aromatic rice (LAR) and hybrid for As from soil to cooked rice and its ingestion led health risk, elucidating the processes of its unloading at five check points. Conducting a field experiment with those cultivars, we sampled roots and shoots at tillering, booting and maturity (with grains), separated the grains into husk, bran and polished rice, cooked it through different methods and analyzed for As. Of the tested groups, As restriction from root to grain followed the order: LARs (94%) > HYVs (88.3%) > hybrids (87.2%). The low As sequestration by LARs was attributed to their higher root biomass (10.20 g hill−1) and Fe-plaque formation (2421 mg kg−1), and lower As transfer coefficients (0.17), and higher As retention in husk and bran (84%). On average, based on calculated four major risk indices, LARs showed 4.7–6.8 folds less As toxicity than HYVs and hybrids. These insights are helpful in advocating some remedies for As toxicity of the tested rice cultivars.

Varietal variation and formation of iron plaques on cadmium accumulation in rice seedling

This study examined the impact of iron (Fe) plaque deposition and varietal variation on cadmium (Cd) accumulation in the rice plants (Oryza sativa L.) in a hydroponic experiment under controlled conditions. Fe was applied at the rate of 0, 50 and 100 mg L−1 to the nutrient solution to generate varying amounts of Fe plaque deposition around the root of the rice seedlings. The seedlings were then treated with Cd at the rate of 0, 0.5 and 1.0 mg L−1 in the nutrient solution. Reddish-brown colored Fe plaque is induced gradually on the roots of rice seedlings after Fe supplementation in the nutrient solution. Results showed that the biomass production differed markedly among the rice varieties due to the application of Fe with or without Cd stress. The Quest variety demonstrated the highest capacity of Fe plaque formation compared to the other varieties. The application of Fe and Cd significantly affected the Cd concentration in the citrate-bicarbonate-dithionite (CBD) extracts of roots and in the rice seedlings. The exogenous application of Cd significantly increased the root Cd content, which was greater than the shoot Cd content. The Fe plaque deposition capacity markedly varied among the examined varieties. The Cd concentrations in shoots declined by adding Fe. This study results demonstrated that boosted Fe plaque formation can minimize detrimental effects of Cd on rice shoot growth to some extent, but the root tissues are the main barrier to Cd accumulation and movements in the interior of the rice plants.

Effects of Water Management on Cadmium Accumulation by Rice (Oryza sativa L.) Growing in Typical Paddy Soil

In order to explore the effects of water management on the Cd accumulation of rice in paddy soils with different parent materials, a pot experiment with three paddy soils with different parent materials from Hunan Province (granite sandy soil, plate shale soil, and purple sandy shale soil) with different water management treatments ［flooding and alternate wetting and drying (AWD)］ was performed. The soil pH, DTPA-Cd, Fe plaque in the rice roots, and heavy metal concentration in the rice were determined. The results showed that the soil pH of the three paddy soils under the flooding treatment was increased by 0.17-1.33 units. During the filling and maturity periods, compared with that under AWD, the DTPA-Cd concentration in the three paddy soils was reduced by 14.39%-36.56% under the flooding treatment, but the DTPA-Fe concentration was increased by 35.35%-347.25%. In the three growth stages, the Cd and Mn concentrations in the Fe plaque (except for DCB-Fe) were in the order of tillering stage < filling stage < mature stage. Compared with that under AWD, the brown rice Cd concentration in the three soils was reduced by 57.84%-93.79% under flooding treatment. The Cd accumulation in rice was reduced under flooding treatment by reducing the DTPA-Cd via increasing the soil pH and DTPA-Fe and by decreasing the formation of Fe plaque. According to the results of the correlation and SEM analysis, the soil pH and DCB-Cd were the main factors affecting the Cd accumulation in rice grains, although the changes in the DTPA-Cd and DTPA-Fe also impacted the Cd in rice grains. In summary, our study demonstrated that water management had a significant impact on the Cd content in rice, and there were significant differences among the three paddy soils with different parent materials. In conclusion, the Cd content in rice grains was affected by the soil parent material, soil physicochemical properties, and Fe plaque on the surface of the rice roots. The granite sandy soil and plate shale soil with different water management treatments had significant impacts on the contents of heavy metals in rice. Continuous flooding is a valuable strategy for improving soil acidity and alkalinity and minimizing soil available Cd, but the soil parent materials must be considered.