Iron Plaque Research Articles

Sediment arsenic remediation by submerged macrophytes via root-released O2 and microbe-mediated arsenic biotransformation

Arsenic (As)-contaminated water restoration is extremely challenging because As remobilization from sediments can result in episodic or long-term release of As to the overlying water. In this study, by combining high-resolution imaging techniques with microbial community profiling, we examined the feasibility of utilizing the rhizoremediation of submerged macrophytes (Potamogeton crispus) to decrease As bioavailability and regulate its biotransformation in sediments. Results showed that P. crispus considerably decreased the rhizospheric labile As flux to lower than 4 pg cm−2 s−1 from larger than 7 pg cm−2 s−1, suggesting its effectiveness in promoting As retention in sediments. Iron plaques induced by radial oxygen loss from roots decreased the mobility of As by sequestering it. Additionally, Mn-oxides may act as an oxidizer for the oxidation of As(III) to As(V) in the rhizosphere, which can further increase the As adsorption owing to the strong binding affinity between As(V) and Fe-oxides. Furthermore, microbially mediated As oxidation and methylation were intensified in the microoxic rhizosphere, which decreased the mobility and toxicity of As by changing its speciation. Our study demonstrated that root-driven abiotic and biotic transformation contribute to As retention in sediments, which lays a foundation for applying macrophytes to the remediation of As-contaminated sediments.

Elevated CO2 may increase the health risks of consuming leafy vegetables cultivated in flooded soils contaminated with Cd and Pb.

Elevated CO2 levels threat the crop quality by altering the environmental behavior of heavy metals (HMs) in soils. In reality, multiple HMs often co-exist in field, while details regarding coexisting HMs migration in flooded soil at elevated CO2 levels remain unclear. A pot experiment in open-top chambers (CO2 at 400 and 600μmolmol-1) was conducted to explore the uptake and transfer of cadmium (Cd) and lead (Pb) in water dropwort (Oenanthe javanica DC.) grown in flooded soils contaminated with Cd and Pb. Results showed that elevated CO2 significantly reduced soil pH, promoting the release of Cd and Pb (by 63.64-106.90% and 10.66-30.99%, respectively) into soil porewater. In the harvested O. javanica, elevated CO2 decreased the root uptake of Cd but promoted that of Pb. Further mechanism analysis showed that elevated CO2 promoted the formation of iron plaque on root surface by 44.60-139.57%, with lower adsorption capacity to HMs (0-34.93% and 63.61-67.69% for Cd and Pb, respectively). Meanwhile, Pb showed lower adsorbability in iron plaque but higher transfer capacity when compared with Cd. Ultimately, elevated CO2 increased the target hazard quotient values of Pb in O. javanica. These findings provide new insights on the effects of elevated CO2 on the transfer of coexisting HMs in soil-plant system, and the risk of HMs pollution under climate changes needs to be more fully assessed.

Speciation and distribution of chromium (III) in rice root tip and mature zone: The significant impact of root exudation and iron plaque on chromium bioavailability

Evidence on the contribution of root regions with varied maturity levels in iron plaque (IP) formation and root exudation of metabolites and their consequences for uptake and bioavailability of chromium (Cr) remains unknown. Therefore, we applied combined nanoscale secondary ion mass spectrometry (NanoSIMS) and synchrotron-based techniques, micro-X-ray fluorescence (µ-XRF) and micro-X-ray absorption near-edge structure (µ-XANES) to examine the speciation and localisation of Cr and the distribution of (micro-) nutrients in rice root tip and mature region. µ-XRF mapping revealed that the distribution of Cr and (micro-) nutrients varied between root regions. Cr K-edge XANES analysis at Cr hotspots attributed the dominant speciation of Cr in outer (epidermal and sub-epidermal) cell layers of the root tips and mature root to Cr(III)-FA (fulvic acid-like anions) (58–64%) and Cr(III)-Fh (amorphous ferrihydrite) (83–87%) complexes, respectively. The co-occurrence of a high proportion of Cr(III)-FA species and strong co-location signals of 52Cr16O and 13C14N in the mature root epidermis relative to the sub-epidermis indicated an association of Cr with active root surfaces, where the dissolution of IP and release of their associated Cr are likely subject to the mediation of organic anions. The results of NanoSIMS (poor 52Cr16O and 13C14N signals), dissolution (no IP dissolution) and µ-XANES (64% in sub-epidermis >58% in the epidermis for Cr(III)-FA species) analyses of root tips may be indicative of the possible re-uptake of Cr by this region. The results of this research work highlight the significance of IP and organic anions in rice root systems on the bioavailability and dynamics of heavy metals (e.g. Cr).

Iron plaque crystallinity, heavy metal toxicity, and metal translocation in Kandelia obovata seedlings as altered by an iron-reducing bacterium under different flooding regimes

Iron plaque crystallinity, heavy metal toxicity, and metal translocation in Kandelia obovata seedlings as altered by an iron-reducing bacterium under different flooding regimes

Shade and iron plaque of Sesbania affect cadmium accumulation in rice: A new strategy for safe production in contaminated soil

Shade and iron plaque of Sesbania affect cadmium accumulation in rice: A new strategy for safe production in contaminated soil

Effects of sulfur supply on cadmium transfer and concentration in rice at different growth stages exposed to sulfur-deficient but highly cadmium-contaminated soil

BackgroundSulfur (S) has been widely used to alleviate cadmium (Cd) toxicity and control Cd accumulation in rice under waterlogging conditions. However, the results are contradictory, and the reasons remain unclear. This could be because most studies rarely simultaneously monitor the processes of S-induced soil Cd bioavailability and Cd accumulation in rice throughout its growth period. A pot experiment was conducted to investigate the influence of two sulfur levels (0, and 30 mg S kg−1) on Cd concentration and translocation in rice at three growth stages (booting, filling and maturity) under waterlogging conditions. Paddy soil deficient in S but contaminated with Cd (10.16 mg Cd kg−1) was used for the pot experiment.ResultsS application increased concentrations of Cd in grain at the filling stage partially because S induced the promotion of Cd transfer from roots to stems, leaves, and grains, and S induced the accumulation and fixation of Cd in iron plaques at the filling stage. However, the application of S significantly reduced Cd concentrations in brown rice at the maturity stage, which could be attributed to three aspects, as described below. First, S supply reduced the availability of Cd in soil and iron plaque on the root surface by reducing dissolved Cd in soil pore water and transferring Cd from iron plaque on the root surface to roots. Second, S supply inhibited the transfer of Cd in other tissues to brown rice based on Cd transfer factors from roots, stems, leaves, and husks to brown rice, which were obviously lower with S supply than without S supply at the maturity stage. Third, S induced the dilution of Cd in brown rice because the application of S significantly increased brown rice biomass by 215%.ConclusionsA S-induced decline in Cd accumulation in brown rice was related to S-regulated Cd transfer among rice plants, S-induced promotion of rice growth and a decrease in Cd bioavailability in S-deficient but Cd-contaminated paddy soil under waterlogging conditions. This study provides valuable information for growing rice in low-S and Cd-contaminated paddy soil and reducing the risk of Cd in rice to humans.Graphical abstract

Crucial role of iron plaque on thallium uptake by rice plant

Iron plaque is a Fe-containing oxide film produced by the oxidation of Fe(II) in the rice root system under the combined action of oxygen infiltration and other microorganisms. Owing to its special surface structure and physio-chemical properties, the iron plaque has a strong absorption capacity for a variety of heavy metal ions. This study aimed to first investigate the effects of Fe species on the geochemical fractionation of Tl in typical paddy soil systems affected by industrial activities, followed by pot culture experiments to probe the effects of Fe species on the uptake and translocation of Tl in rice plants. The results of field work preliminarily showed that iron at different valences affected the conversion of the Tl geochemical fraction in the soil. Oxidizable Tl exerted significant positive correlation relationships with Fe2+ and negative correlation relationships with Fe3+, while reducible Tl only displayed a positive correlation with Fe3+. Further analysis by pot culture experiments revealed that the contents of Fe were significantly positively correlated with Tl contents in Fe plaque (R2 = 0.529). In contrast, the water-soluble Tl contents in the soil were significantly negatively correlated with the contents of Fe (R2 = – 0. 90, p < 0.05). It suggests that the iron plaque promoted the absorption and fixation of Tl on the root surface of rice plants, causing Tl to accumulate in the iron plaque. Besides, the Tl content in the Fe plaque on the root surface of rice plants was greater than that in the above-ground tissues, which indicates that most Fe plaque exerts a certain degree of inhibition on Tl migration into the above-ground tissues of rice plants. All these findings indicate that Fe film is also an important carrier of Tl transfer in the soil–rice plant system, which provides new scientific support for the remediation of typical Tl-contaminated rice fields.

Iron-based nanomaterials reduce cadmium toxicity in rice (Oryza sativa L.) by modulating phytohormones, phytochelatin, cadmium transport genes and iron plaque formation

Rice is known to accumulate cadmium (Cd) in its grains, causing a severe threat to billions of people worldwide. The possible phytotoxicity and mechanism of 50–200 mg/L hydroxyapatite NPs (nHA), iron oxide NPs (nFe2O3) or nano zero valent iron (nZVI) co-exposed with Cd (100 μM) in rice seedlings were investigated. Three types of nanoparticles significantly reduced the bioaccumulation of Cd in rice shoots by 16–63%, with nZVI showing the greatest effect, followed by nHA and nFe2O3. A decrease in Cd content in the roots was observed only in the nZVI treatment, with values ranging from 8 to 19%. Correspondingly, nZVI showed the best results in promoting plant growth, increasing rice plant height, shoot and root biomass by 13%, 29% and 42%. In vitro studies showed that nZVI reduced the content of Cd in the solution by 20–52% through adsorption, which might have contributed to the immobilization of Cd in root. Importantly, the nZVI treatment resulted in 267% more iron plaques on the root surface, which acted as a barrier to hinder the entry of Cd. Moreover, all three nanoparticles significantly reduced the oxidative stress induced by Cd by regulating phytohormones, phytochelatin, inorganic homeostasis and the expression of genes associated with Cd uptake and transport. Overall, this study elucidates for the first time the multiple complementing mechanisms for some nanoparticles to reduce Cd uptake and transport in rice and provides theoretical basis for applying nanoparticles for reducing Cd accumulation in edible plants.

Effects of elevated CO2 on the Cd uptake by rice in Cd-contaminated paddy soils.

The rising atmospheric CO2 is a major driver for climate change, directly affects rice production. Cadmium (Cd) in paddy soils also serves as a persistent concern. Currently, few studies consider the rice response to coupled stresses of elevated CO2 (eCO2) and soil Cd. Experimental evidence understanding the effects and mechanisms of eCO2 on Cd uptake by rice is lacking yet. In a free-air CO2 enrichment (FACE) system, a 3-year pot experiment was conducted to explore the Cd uptake by rice under two CO2 conditions (ambient and ambient + 200µmol·mol-1) using combinations of in-situ Cd-contaminated soils and associated rice varieties. Results showed that more low-crystalline Fe oxides (Feh) in iron plaque (IP) were deposited on root surface with the increased dissolved Fe2+ due to lower soil redox status under eCO2. The Cd accumulation in rice was hindered due to more Cd associated with Feh (Feh-Cd) rather than uptake by roots. Taken together, the relative effects of eCO2 on Cd uptake by rice were consistent across years under different Cd-contaminated soils. Our findings will help to better understand the Cd uptake by rice under future climate conditions, and thus push the development of climate-crop-soil models and accurate prediction for food security.

Датировка железных пряжек, накладок и крючков эпохи Средневековья из Среднего Поволжья (по материалам Остолоповского селища в Татарстане)

The article deals with iron buckles, plaques on the belt and hooks from the excavations of the Ostolopovo settlement in Tatarstan. It existed in the 11th — 12th centuries. The Ostolopovo settlement was one of the settlements in the central part of the Volga Bulgaria, located on the way from the center of the state to the Kama River, which was the most important trade route of Bulgaria. The settlement was investigated in 1969 and 1997–2013. It is distinguished by a unique stratigraphy, which is associated with the peculiarities of the functioning of the settlement. This settlement existed for a short time — from the end of the 10th century to the second half of the 12th century. The heyday of the settlement fell on the second half of the 11th — the fi rst half of the 12th century. During the excavations, 40 iron buckles, plaques on the belt and hooks were found. The peculiarity of these artifacts was that they were made according to samples that came to the Bulgars from Southern Siberia. Their prototypes were items of the Askiz archaeological culture. Such fi nds are typical for the Bulgar archaeological sites of the pre-Mongol period. In addition, Bulgar copies of Askiz originals spread beyond the borders of Volga Bulgaria. They are found among the medieval Mari, Udmurts, Permians, Mordovians. Th erefore, finding out the time of existence of such items is very important for dating the archaeological materials of the entire Volga-Kama region. Well-dated layers of the Ostolopovsky settlement allow this to be done. The analysis of the finds showed that they begin to occur in the third stratigraphic layer, which dates back to no earlier than the middle — second half of the 11th century. It contained a few items from a belt with an iron buckle and plaques on the belt that adorned it. Most of the finds come from the second layer, which was formed from the turn of the 11th–12th centuries until the second third of the 12th century. They are notable for their improved form design, which also included decoration of the surface with ornaments and possibly silver inlay. Finds of this type are no longer found in the upper horizon of the second layer. Thus, the period of the use of the Bulgar derivatives of Askiz products in the Ostolopovo settlement is the second half of the 11th — the second third of the 12th century. According to stratigraphy, the greatest use of such artifacts was in the first half of the 12th century.

Effects of topdressing silicon fertilizer at key stages on uptake and accumulation of arsenic in rice.

The booting stage and filling stage have been considered as the key stages for arsenic (As) uptake in rice. In this study, a field study was conducted to investigate the influence of the topdressing different amounts of silicon (Si) fertilizer at the key stages on rice As uptake and accumulation. The results showed that topdressing of a low amount of Si fertilizer at the booting stage and filling stage could increase rice yield, promote the formation of iron plaque and the retention of As on iron plaque, and reduce inorganic As content in brown rice. Compared with the control, the rice grain yield was increased by 22.60% with the topdressing of 20kg·hm-2 Si fertilizer at the grain filling stage. As compared with the control, the Fe and As content in iron plaque under the topdressing of 20kg·hm-2 Si fertilizer at the booting stage and filling stage was significantly (p < 0.05) increased by 84.34% and 87.78% (Fe content) and 70.96% and 63.80% (As content), respectively. Meanwhile, contents of As in rice roots, stems, and husks at the topdressing of 20kg·hm-2 Si fertilizer at the booting stage were significantly (p < 0.05) reduced by 45.10%, 33.34%, and 31.23%, respectively, relative to the control. The lowest inorganic As content (0.21mg·kg-1) in brown rice was obtained at the topdressing of 20kg·hm-2 Si fertilizer at the booting stage, which was close to the National Food Limit Standard of 0.20mg·kg-1 (GB 2762-2017). Therefore, topdressing of 20kg·hm-2 Si fertilizer at the booting stage might be considered as an effective method to reduce inorganic As content in brown rice.

The role of nickel in cadmium accumulation in rice

Rice is one of the world's staple foods. Cadmium (Cd) levels in paddy soil are still increasing, and “Cd-contaminated rice” is a frequent occurrence, posing a serious threat to human health. Therefore, Cd contamination in rice is a key issue in agricultural production that needs to be addressed urgently. The Cd accumulation in rice is closely related to other elements. In this study, the impact of nickel (Ni) on the uptake and accumulation of Cd in rice was revealed, and the mechanism was discussed. Statistical analysis of field data showed that Cd concentration in rice grains decreased exponentially with increasing Ni concentration in paddy soils, which was verified by the hydroponic experiments. Under 5 μmol/L Cd exposure conditions, the addition of Ni (100 μmol/L) reduced the Cd contents in roots, stems, and leaves by 81.6 %, 60.6 %, and 65.9 %, respectively. With the presence of Ni, the amount of iron plaque decreased, and the Cd content in the iron plaque was reduced due to the competition between Ni and Cd for adsorption sites. In addition, the migration of Cd from stems to leaves was reduced. At the same time, the distribution of Cd in the cell was altered, and the concentration of Cd in the root cell walls increased with increasing Ni addition under 5 μmol/L Cd exposure. These findings highlight the critical role of Ni in inhibiting Cd accumulation in rice, and provide important information for understanding the effects of coexisting elements in Cd-contaminated soils on Cd accumulation in crops.

Cadmium-induced iron deficiency is a compromise strategy to reduce Cd uptake in rice

Expose of cadmium (Cd) leads to severe leaf chlorosis and reducing nutrient uptake. It is unclear how plants responded to Cd stress in the roots, and its relation to the leaf chlorosis. Our results showed Cd disturbed the homeostasis of multiple nutrient element at different levels. The most reduced elements were Mn, Fe, with 96 %, 89 % decline in the leaves, that caused leaf chlorosis. The plants actively downregulated the expression of metal transporters to reduce Cd uptake, but consequently reducing Fe and Mn uptake. Moreover, Cd stress promoted the formation of iron plaque and significantly reduced the exchangeable ions on root surface. Importantly, ethylene plays an essential role in regulating iron plaque formation and the existent forms of Cd. Blocking ethylene biosynthesis significantly increased exchangeable Cd on the root surface and decreased the percentage of iron oxides bound Cd, thus leading to increase of Cd in the shoots. Above all, our results revealed plants actively control the expression of metal transporter and the ethylene-dependent iron plaque formation to reduce Cd uptake, but sacrificed iron nutrition. The mechanism of sequester Cd on rhizosphere by ethylene in response to Cd stress may provide guidelines for the mitigation of Cd accumulation in rice via ethylene-dependent rhizosphere regulation.

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.

Silkworm excrement reduces cadmium and arsenic accumulation in rice grains by altering soil chemical properties, microbial community, and promoting iron plaque formation

Rice (Oryza sativa L.) consumption represents a major route for the exposure to cadmium (Cd) and arsenic (As). Compared with un-amendment soil, silkworm excrement (SE) amendment at a rate of 0.20 % (m/m) reduced the rice grains Cd and As concentrations by 15.99 % and 8.70 %, respectively, with the following mechanisms: 1) increasing the soil pH, electrical conductivity, and organic matter content (for Cd); 2) regarding the total soil bacteria (16S rRNA), SE-0.2 increased the abundances of Chloroflexi and decreased the abundances of Firmicutes, Bacillus, and Clostridium_sensu_stricto_1. Regarding the microorganisms involved in As methylation (arsM) in soil, SE-0.2 increased the abundances of Actinobacteria_d__bacteria, Firmicutes, Chloroflexi, and Rubriviva (for Cd and As); 3) promoting the formation of the iron plaque (for Cd and As). Collectively, SE can remediate Cd- and As-polluted soil and prevent the migration of Cd and As, thus ultimately resulting in decreased Cd and As in rice grains. This provides a new way to improve the utilization rate of agricultural waste resources and ensure the safe production of food.

Soil inorganic amendments produce safe rice by reducing the transfer of Cd and increasing key amino acids in brown rice

The digestibility of cadmium (Cd) in brown rice is directly related to amino acid metabolism in rice and human health. In our field study, three kinds of alkaline calcium-rich soil inorganic amendments (SIAs) at three dosages were applied to produce safe rice and improve the quality of rice in Cd-contaminated paddy. With the increased application of SIA, Cd content in iron plaque on rice root significantly increased, the transfer of Cd from rice root to grain significantly decreased, and then Cd content in brown rice decreased synchronously. The vitro digestibility of Cd in brown rice was estimated by a physiologically based extraction test. Results showed that more than 70% of Cd in brown rice could be digested by simulated gastrointestinal juice. Based on the total and digestible Cd contents in brown rice to evaluate the health risk, the application of 2.25 ton SIA/ha could produce safe rice in acidic slightly Cd-contaminated paddy soils. The amino acids (AAs) in brown rice were determined by high-performance liquid chromatography. The contents of 5 key AAs (KAAs) that actively respond to environmental changes increased significantly with the increased application of SIA. The structural equation model indicated that KAAs could be affected by the Cd translocation capacity from rice root to grain, and consequently altered the ratio of indigestible Cd in brown rice. The formation of indigestible KAAs-Cd complexes by combining KAAs (phenylalanine, leucine, histidine, glutamine, and asparagine) with Cd in brown rice could be considered a potential mechanism for reducing the digestibility of Cd.

Exogenous iron alters uptake and translocation of CuO nanoparticles in soil-rice system: A life cycle study.

The abundant iron in farmland soil may affect the environmental fate of metal-based nanoparticles (MNPs). In this study, the effect of FeSO4 and nano-zero-valent iron (nZVI) as exogenous iron on the uptake and translocation of CuO nanoparticles (NPs) in soil-rice system was performed in a life cycle study. The results show that exogenous iron basically elevated the soil pH and electrical conductivity but lowered the redox potential. Moreover, the Cu bioavailability in soil was significantly increased by 86-269% with exogenous iron at the tillering stage, while was reduced by 15-45% with medium and high concentrations of Fe(II) at the maturation stage. Meanwhile, the addition of exogenous iron resolved the unfilling of grains caused by CuO NPs. Notably, except for highest Fe(II) treatment, both Fe(II) and nZVI reduced Cu accumulation from 31% to 84% in roots and leaves due to more iron plaque. Especially, medium Fe(II) level markedly decreased the Cu content in the brown rice. μ-XRF analysis suggests that high intensity of Cu was primarily located in the rice hull and embryo under Fe(II) treatment. The reduction of CuO NPs to Cu2O caused by Fe(II) can explain the positive effect of exogenous iron on controlling the environmental risk of MNPs.

Alleviative effects of ferrous sulfate on arsenic toxicity in Lens culinaris Medik. by enhancing iron plaque formation on roots

Alleviative effects of ferrous sulfate on arsenic toxicity in Lens culinaris Medik. by enhancing iron plaque formation on roots

Effect of Iron Plaque on Gaseous Elemental Mercury Uptake, Translocation, and Volatilization by Paddy Rice.

Paddy rice is a typical wetland plant species, and mercury (Hg) accumulation in this rice has received much attention over the last two decades. The role of root iron plaque on rice Hg accumulation is not well understood. The effects of iron plaque on Hg0 uptake, translocation, and volatilization in rice seedlings were investigated under hydroponic conditions using different rice genotypes. After induction of iron plaque on rice roots with pretreatment solutions containing 0, 15 and 30mg Fe2+L-1, rice seedlings were transplanted into specially designed airtight culture chambers, where roots were separated from the aerial parts and exposed to saturated Hg0 vapor. The results showed the following: (1) There were significant differences in the amount of iron plaque formed on the rice roots among the three genotypes. (2) A significant correlation was observed between the concentrations of Hg and Fe in the iron plaque of the root surface for the three genotypes (R2 = 0.933, p < 0.01). (3) Iron plaque may act as a barrier for Hg0 behavior, i.e., inhibiting the process of Hg0 uptake and translocation from the rhizosphere.

Effects of biochar-based silicate fertilizer on iron reduction by bacteria and root iron plaque formation in subtropical paddy soils

Effects of biochar-based silicate fertilizer on iron reduction by bacteria and root iron plaque formation in subtropical paddy soils