Fe In Soils Research Articles

Iron oxides promote physicochemical stabilization of carbon despite enhancing microbial activity in the rice rhizosphere.

Rice rhizosphere soil is a hotspot of microbial activity and a complex interplay between soil abiotic properties, microbial community and organic carbon (C). The iron (Fe) plaque formation in the rice rhizosphere promotes Fe-bound organic C formation and increases microbial activity. Yet, the overall impact of Fe on C storage via physicochemical stabilization and microbial mineralization of rhizodeposits (rhizo-C) and soil organic C (SOC) in the rice rhizosphere remain unclear. We conducted a microcosm experiment using 13C-CO2 pulse labeling to grow rice (Oryza sativa L.) with four levels of α-FeOOH addition (Control, Fe-10%, Fe-20%, Fe-40% w/w of α-FeOOH per total Fe in soil). This study aimed to evaluate the impact of Fe oxides on rhizo-C mineralization, the rhizosphere priming effect, and Fe-OM formation. Microbial community composition and localization of enzyme activities were also quantified through 16S rRNA sequencing and zymography. The hotspot area, as being indicated by zymography, increased by 20-50% in the presence of Fe compared to the soil without Fe addition. Despite being a hotspot, strong coprecipitation of Fe-OM in the rhizosphere promoted C immobilisation. Fe-20% and Fe-40% resulted in a 41% and 33% decrease of rhizodeposits derived 13C-CO2 emission and increased 13C stabilization mainly in 0.25-2mm soil aggregates due to coprecipitation and aggregate formation with α-FeOOH. Moreover, Fe addition led to a dominance of Fe-oxidizing bacteria genera such as Pseudomonas, which fostered coprecipitation of Fe-OM formation. We highlight larger physicochemical stabilization of organic C by α-FeOOH addition despite raised hotspot area of microbial activity in the rice rhizosphere.

Transport, pollution, and health risk of heavy metals in “soil-medicinal and edible plant-human” system: A case study of farmland around the Beiya mining area in Yunnan, China

Heavy metals (HMs) pose a significant threat to soil quality, plant growth, and human health. However, the impacts (transport, pollution, and health risk) of HMs in medicinal and edible plants with rich value growing in high background soil for a long time remain unclear. So the effects of HMs on the “soil-medicinal and edible plant-human” system were comprehensively studied. Houttuynia cordata Thunb. (HCT) and growing soil were collected from the farmland around Beiya mining area located in Three Parallel Rivers of Yunnan Protected Areas, China. The transport, pollution, and health risks of HMs in the system were investigated by determining the content of active ingredients, HMs, and physicochemical properties in HCT and soil. The results of comprehensive analysis using various measurement and analysis methods showed that Zn, Cu, Mn, and Co in soil could affect the contents of available nutrients (available P (AP), available K (AK), and organic matter (OM)), while AP, OM, pH, Co, and Fe in soil were closely related to the formation of HCT quality. Cr and Fe had the strongest transport capacity in stems and leaves of HCT, respectively. Furthermore, it is worth noting that Cr, Pb, and Cu had caused serious pollution to HCT in the area. Pb and Cu are tolerable levels for human health and may pose a carcinogenic risk. Our study demonstrates that HCT is expected to be a marker of heavy metal pollution in the area and provides a scientific basis for making effective regulations on HMs control and scientific planting.

Fe(III) reduction mediates vanadium release and reduction in vanadium contaminated paddy soil under different organic amendments

Vanadium(V) contaminated soil is abundant in iron(Fe) oxides due to co-occurrence of V and Fe bearing minerals. However, biogeochemical transformation of redox-active V and Fe in soil, and the bacteria involved, has remained less investigated. This study explored the extent to which microbial mediated organic decomposition coupled to Fe(III) reduction contributed to V(V) release/reduction in V-contaminated paddy soil under different organic amendments. Soil flooding decreased toxic reducible V while increased less toxic oxidizable V. Glucose and straw promoted V(V) release with temporarily increasing V(V) concentration by 73.59–106.34 mg/kg compared to the control treatment and subsequently promoted V(V) reduction with decreasing V(V) to concentrations eventually similar to the control treatment. Biochar incorporation under glucose and straw amendments moderately alleviated V(V) release. The significantly positive correlation between Fe(II) and V(V) concentrations during the V solubilization process indicated a temporal coupling of Fe(III) reduction and V(V) release. Clostridium and Massilia mediated Fe(III) reductive dissolution and V(V) release, while Anaeromyxobacter, Sphingomonas, Bryobacter, Acidobacteriaceae and Anaerolineaceae contributed to V(V) reduction. This study provides a deeper understanding of V biotransformation coupled to Fe and C cycling and suggests a remediation strategy for V-contaminated soils via regulating Fe(III) reduction to weaken V(V) release or to promote V(V) reduction.

Metals geochemistry and ecological risk assessment in lateritic soils and their transfer to tea plants

ABSTRACT Tea plant cultivation has been demonstrated to change the physicochemical properties of soils and metal bioavailability. The present study reported the geochemistry of four selected metals (Fe, Mn, Cr, and Ni) in lateritic soil cores regarding various depths cultivated with tea plants of different ages (3, 6, and 10 years old). The ecological risk and bioaccumulation of these metals in tea plants were also evaluated. The results indicate the acidic property of tea plant cultivation soils (pH < 4.5) and highlight further soil acidification due to long-term cultivation. The soils were strongly affected by farming methods and showed high levels (average from all soil cores) of total organic carbon contents (4.0% w/w), total nitrogen (2806 mg kg−1), and total phosphorus (1730 mg kg−1). We suggest that the selected metals originated naturally, supported by a high percentage in residual fractions from the results of soil sequential extraction (over 95% for Mn, Fe, and Ni and ∼ 90% for Cr). These metals exhibited no ecological risk to the adjacent environment. Mn showed the highest bioavailability, possibly due to the acidic soils and nitrogen fertiliser applications, increasing the release of Mn from soils. Mn also exhibited the highest bioconcentration factor (BCF) among four metals and 2.4 ÷ 6.5-folds higher BCFs in tea leaves than in roots. Despite the dominant content of Fe in soils (average of 20% w/w), Fe indicated lower amounts in tea leaves than Mn (average of 513 mg kg−1 vs 1354 mg kg−1). This could be attributed to the formation of Fe-rich root coatings on the tea plant root surface as a barrier to prevent Fe from translocating to other higher tea plant parts. Ni and Cr, as potentially toxic metals, were found at the lowest contents in tea leaves with low BCFs, indicating consumer safety in terms of exposure by these metals.

Combined Application of Biochar and Silicon Fertilizer for Improved Soil Properties and Maize Growth

Biochar can be a good soil amendment to reduce the soil pH, increase crop growth rate, and improve the efficient use of fertilizer. Other than that, silicon fertilizer also would promote photosynthetic ability on plant development that would help to produce high yield. In this work, a series of experiments was conducted to observe the effect of rice husk biochar and silicon fertilizer on the maize growth rate and soil pH. A 45-day pot experiment in the greenhouse with three replicates of 9 experimental treatment combinations of RHB at two rates (5 and 2.5 t.ha-1) with silicon fertilizer at three rates (125%, 100%, 75%), sole biochar (10 t.ha-1), sole silicon fertilizer (100%) and control (NPK) to observe the best rate and combination to improve growth rate and change in soil chemical in acid soil. The result showed that the co-application of sole biochar and biochar with Silicon significantly improved growth development, increased photosynthesis rate, altered soil pH, and reduced Fe concentration compared to control. The plant height increased 88.35% from T4 (5 t.ha-1 RHB + 100% Si) compared to the control and the conductance was higher in T4 (0.53) followed by T8 (0.438) while T1 (0.071) recorded the lowest conductance. The shoot fresh weight was higher in T4 (127.83 g) followed by T8 (57.14 g). However, the weight increased by 343.7% at T4 followed by T8 (2.5 t.ha-1 RHB + 75% Si) at 98.33%. The highest pH increment of 1.24 units (T1 = 5.53, T4 = 6.77) of soil pH was noted from T4 (5 t.ha-1 RHB + 100% Si) compared to control (NPK), and the highest total Fe in soil was observed from T1 (442.30 mg.kg-1). The current study results showed that T4 (50% RHB + 100% Silicon) was the best treatment over the other rates of RHB and silicon increased plant height, photosynthetic rate, and biomass.

Human health risk assessment of microbial contamination and trace metals in water and soils of Chileka Township, Blantyre, Malawi

This study assessed nutrients and microbial contamination in water and soil samples from Chileka Township, Blantyre City, Malawi. Elevated total and fecal coliforms (1300 cfu/100 mL and 290 cfu/100 mL) in groundwater (GW), and (34,000 cfu/100 mL and 8000 cfu/100 mL) in surface water (SW) were found, representing a risk of exposure to water-borne disease. While the criteria in the Malawi Standard for raw groundwater was mostly met, water from only 20% of the boreholes complied with the WHO requirements. Nitrate (NO3─) and Cl─ (47.8 mg/L and 263 mg/L) exceeded the WHO limits in GW. Cadmium (Cd) occurred in a few cases at concentrations up to 0.217 mg/L and 0.138 mg/L in GW and SW. Lead (Pb) and Cr were below detection limits, while Mn (0.319 mg/L and 0.640 mg/L) in GW and SW, and Fe (6.92 mg/L) in SW compromised taste. Though bacteriologically unfit for raw consumption by humans, both GW and SW chemically met FAO-acceptable limits for irrigation, and standards for livestock watering. The NO3─ and PO43─ maximum concentrations in soil were 58.9 mg/kg and 506 mg/kg, respectively. Lead (Pb) and Cd were not detected whereas Cr, Zn, Cu, Mn and Fe in soil were 27.7 mg/kg, 190 mg/kg, 60.4 mg/kg, 1307 mg/kg and 6552 mg/kg, respectively. Magnesium (Mg), Ca, Na and K were 20,523 mg/kg, 22,334 mg/kg, 544 mg/kg and 5758 mg/kg, respectively in soil. The human health risk assessment results, on the other hand, showed that at least 30% (6 out of 20) of the GW samples and 60% (3 out 8) of the SW samples had HI > 1 for adults, children and infants, indicating existence of non-carcinogenic risk. Similarly, at least 15% (3 out 20) of the GW samples and 18% (1 out of 8) of the SW samples had CR > 0.001 for adults, children and infants, suggesting a risk of developing cancer during a lifetime due to Cd exposure. Though both GW and SW are generally of good chemical quality, chronic exposure to nitrate and cadmium is a health risk in the area. The current trace metal levels are not worrisome, but soil nitrate and phosphate may need regular monitoring.

Enhanced reduction of Cd uptake by wheat plants using iron and manganese oxides combined with citrate in Cd-contaminated weakly alkaline arable soils

Iron (Fe) and manganese (Mn) oxides can be used to remediate Cd-polluted soils due to their excellent performance in heavy metal adsorption. However, their remediation capability is rather limited, and a higher content of available Mn and Fe in soils can reduce Cd accumulation in wheat plants due to the competitive absorption effect. In this study, goethite and cryptomelane were first respectively used to immobilize Cd in Cd-polluted weakly alkaline soils, and sodium citrate was then added to increase the content of available Mn and Fe content for further reduction of wheat Cd absorption. In the first season, the content of soil-available Cd and Cd in wheat plants significantly decreased when cryptomelane, goethite and their mixture were used as the remediation agents. Cryptomelane showed a better remediation effect, which could be attributed to its higher adsorption performance. The grain Cd content could be decreased from 0.35 mg kg−1 to 0.25 mg kg−1 when the content of cryptomelane was controlled at 0.5%. In the second season, when sodium citrate at 20 mmol kg−1 was further added to the soils with 0.5% cryptomelane treatment in the first season, the content of soil available Cd was increased by 14.8%, and the available Mn content was increased by 19.5%, leading to a lower Cd content in wheat grains (0.16 mg kg−1) probably due to the competitive absorption. This work provides a new strategy for the remediation of slightly Cd-polluted arable soils with safe and high-quality production of wheat.

Physiological responses of young cacao trees to soil water deficiency as affected by Pb pollution and Fe availability

Plants are subject to various abiotic stresses such as water shortage and exposure to heavy metals, such as Pb in soil. These types of stress trigger a series of plant responses, ranging from a decrease in leaf gas exchange, an increase in lipid peroxidation, and even changes in the chemical composition of leaves and roots. As an essential micronutrient, Fe is involved in several physiological and biochemical processes in plants, such as photosynthetic activity, directly participating in chlorophyll synthesis and electron transport, being necessary for the maintenance of the structure and functioning of chloroplasts. The main objective of this work was to evaluate the action of Fe in mitigating Pb toxicity in young plants of the CCN 51 cacao genotype, subjected to water deficit in the soil, through photosynthetic responses and analysis of the chemical composition of different parts of the plant. Plants were grown with Pb (2 mmol Pb kg-1 soil) and different equimolar doses of Pb+Fe in the soil (2+0.5, 2+1, 2+1.5 and 2+2 mmol kg−1 soil), maintaining constant the Pb dose, whose soil was subjected to water deficit, with gradual reduction of water content, or its moisture was maintained near to field capacity, making a total of 12 treatments, together with the control treatment (without addition of Pb and Fe in soil). It was observed that the greater Fe absorbing, by the root system, mitigated the Pb toxicity. Fe application, in adequate dose in soil (2 mmol Pb kg-1 soil + 0.5 mmol Fe kg−1 soil), mitigated the toxic effects caused by Pb and water deficit in the plants, through the greater Fe taking up and translocation for the shoot in Pb detriment. Greater Pb translocation and accumulation in the leaves caused damage to leaf gas exchange and to the accumulation of carbohydrates in leaves. Fe and Pb applied in soil competed with each other for root absorbing regardless of soil water conditions.

BIOEXTRACTION OF IRON THROUGH Bacillus sp. SP10 FROM MINERAL OXIDE AND ITS APPLICATION AS PLANT MICRONUTRIENT

Iron is an essential micronutrient for all living organisms because of its critical &#x0D; role in metabolic processes. In plants it plays a key role in the synthesis of &#x0D; chlorophyll, some vital enzymatic and metabolic processese. However, most of &#x0D; the iron in nature is present as precipitates or in insoluble forms. Therefore, &#x0D; biological mechanism has been employed to mineralize Fe(III) oxides into &#x0D; Fe(II) through microbial action to increase the availability of soluble iron. An &#x0D; iron reducing bacterial strain was isolated based on its tolerant limits and iron &#x0D; mineralizing ability. The strain Bacillus sp. SP10 effectively mineralized iron &#x0D; in synthetic medium possessing 1% starch and pH 7. In a 25 day’s column &#x0D; study, the soluble Fe(II) as micronutrient showed a gradual increase in each &#x0D; seepage collected from different treatment columns. Similarly, the plants &#x0D; grown on soil obtained from treatment D (i.e. 1% starch + 1% Bacillus sp. &#x0D; SP10 inoculum + 0.25% anthraquinone-2,6-disulphonate) column displayed &#x0D; good growth and maximum shoot length, mainly due to the increased &#x0D; accessibility of iron through microbial mineralization. The mineralization of &#x0D; Fe in soil was established through SEM and EDX analysis.

Release, availability and geochemical interaction of Fe in soil after long‐term integrated nutrient management in wheat

AbstractWheat contributes to about one‐fifth of the total calories and protein consumption by humans but is found lower in total iron (Fe) concentration than the targeted nutritional requirement, leading to increasing cases of anaemia and malnutrition in humans, especially in the developing countries. Therefore, it is the need of the hour to understand the dynamics of Fe in soil and its supply in relation to wheat productivity and grain quality. The objectives of this study were to examine the impact of long‐term (54 years) annual and biannual application of different doses of farmyard manure (FYM) (0, 5, 10 and 15 Mg ha−1) and nitrogen (0, 60 and 120 kg ha−1) under integrated nutrient management on the dynamics of Fe in soil along with its relationship with total Fe uptake in wheat. Additionally, the release pattern of native soil Fe and risk of Fe toxicity were evaluated. The highest grain yield of wheat (6.08 Mg ha−1) was observed under biannual application of FYM and nitrogen at 10 Mg ha−1 and 120 kg ha−1, respectively, which was approximately 155% higher than the control plot (F0N0). Under the dual season application of 15 Mg ha−1 FYM and 120 kg ha−1 nitrogen, the total Fe content (48.48 mg kg−1) and its uptake (270.52 g ha−1) in wheat grains were found at maximum. The soil incubation study revealed that the rate of release of Fe increased up to 30 days of incubation followed by constant rates indicating the establishment of dynamic equilibrium among the different Fe fractions. Thus, the present study was conducted for the first time to improve the understanding of changes in Fe concentration and rate of release in soil, which directly influence the Fe uptake in wheat grain under the long‐term integrated nutrient management practices.

Antimony mobility in soil near historical waste rock at the world's largest Sb mine, Central China

Soil near waste rock often contains high concentrations of antimony (Sb), but the mechanisms that mobilize Sb in a soil closely impacted by the waste rock piles are not well understood. We investigated these mobility mechanisms in soils near historical waste rock at the world's largest Sb mine. The sequential extraction (BCR) of soil reveal that over 95 % Sb is present in the residual fraction. The leached Sb concentration is related to the surface protonation and deprotonation of soil minerals. SEM-EDS shows Sb in the soil is associated with Fe and Ca. Moreover, X-ray absorption spectroscopy (XAS) results show Sb is predominantly present as Sb(V) and is associated with Fe in the form of tripuhyite (FeSbO4) as well as edge- and corner-sharing complexes on ferrihydrite and goethite. Thus, Fe in soils is important in controlling the mobility of Sb via surface complexation and co-precipitation of Sb by Fe oxides. The initially surface-adsorbed Sb(V) or co-precipitation is likely to undergo a phase transformation as the Fe oxides age. In addition, Sb mobility may be controlled by small amounts of calcium antimonate. These results further the understanding of the effect of secondary minerals in soils on the fate of Sb from waste rock weathering and inform source treatment for Sb-contaminated soils.

Iron oxide nanoparticles as iron micronutrient fertilizer—Opportunities and limitations

AbstractIron (Fe) is necessary for plant growth and development. Iron deficiency disrupts major metabolic and cellular activities such as respiration, DNA synthesis, and chlorophyll synthesis. Iron also activates various metabolic pathways and is vital to numerous enzymes. Iron is widely distributed in soil, but plants do not readily absorb it. In addition to neutral pH, Fe also forms insoluble Fe complexes under alkaline conditions. The fundamental cause of Fe chlorosis is an imbalance between the solubility of Fe in soil and the demand for Fe by plants. Various Fe fertilizers, including organic, chelated, and inorganic, are administered to the soil and leaves to treat Fe deficiency and chlorosis. Currently, used Fe fertilizers are expensive, easily adsorb on soil particles, and cause Fe to leach out of the soil with water, thereby diminishing their efficiency. They also need to be applied repeatedly, resulting in an excessive Fe fertilizer concentration in the soil that can cause harm to the plants. The usage of Fe nanofertilizers in agricultural production has expanded to address the disadvantages of existing Fe fertilizers. The advantages of nanosized Fe fertilizers include their physical and chemical characteristics, such as the high surface area to volume ratio that aids in easy absorption by plants’ roots and leaves. Controlled‐release iron oxide nanofertilizers supply the regulated release of nutrients in a way that is coordinated with the nutritional needs of the crops. This improves the accumulation of nutrients in the plant, filling in the gap of nutrient deficiency and lowering environmental risks due to leaching. The possibility of iron oxide nanoparticles as Fe micronutrient fertilizers, their uptake and mechanism of action, advantages, and limitations are critically highlighted in this review article.

Growth response of clonal eucalyptus to varying levels of iron application and soil texture

Deficiency symptoms of iron (Fe) appear in eucalyptus (Eucalyptus spp.) plantations grown on different type of soils in Punjab, India. Therefore, a pot experiment was conducted to study the response of eucalyptus to application of Fe in soils of different textures. The treatments comprised of six levels of Fe as soil application (0, 15, 30, 45, 60, and 75 mg Fe kg−1 soil applied as chelated Fe through Fe-EDTA) and two foliar sprays (0.5% and 1% FeSO4·7H2O) replicated thrice in soils of three textures (loamy sand, sandy loam, and sandy clay) in a completely randomized design. Plant growth parameters, Fe concentration in soils, and Fe uptake by different plant parts were determined after nine months of eucalyptus growth. These parameters were significantly and positively influenced with the application of Fe. Dry weight of shoot and root was the highest at 30 mg Fe kg−1 whereas Fe concentration and uptake of Fe by shoot and root were the highest at 45 mg Fe kg−1. With 1% spray, the root dry weight, Fe concentration in leaves and its uptake by leaves and shoot were the highest. Loamy sand soil exhibited maximum shoot biomass and uptake response to applied Fe by eucalyptus. The Fe concentration in soil was positively and significantly related to Fe concentration (r = 0.436*–0.772**) and its uptake (r = 0.643**- 0.866**) by different plant parts. Conclusively, application of Fe to eucalyptus significantly increased the growth parameters, its uptake and response by the plants.

Variations in elemental composition of rice (Oryza sativa L.) with different cultivation areas of Ethiopia.

Variations in the elemental composition of rice (Oryza sativa L.) grains, and the link with the growing soil, were investigated across the major production areas of Ethiopia (Fogera, Metema and Pawe). The elements (Ca, Mg, Fe, Zn, Mn, Cu, Ni, Cr, Cd and Pb) were determined by using flame atomic absorption spectroscopy (FAAS), after digesting samples through an optimized procedure with respect to volumes of reagents (HNO3, HClO4 and H2O2), temperature and time. The accuracy of the FAAS method was in the range of 87‒113%. The most abundant element in rice was Mg (414‒561 mg kg-1) followed by Fe (49.4‒168 mg kg-1), while in soil was Fe (11674‒12917 mg kg-1) followed by Mg (619‒709 mg kg-1). Chromium, Cd and Pb were all below the limit of quantitation of the method. The concentrations of the elements, except Zn in rice and Fe in soil, varied significantly (p < 0.05) with the growing region. Notably, rice from Fogera contained more than double Fe, while from Pawe less than half Cu than from the other region. Soils from the rice fields of Pawe, generally, had lower levels of the elements than from the other regions. The order of the abundances of the elements in soil was reflected in the rice grains, except for the reversal between Fe and Mg. However, elemental concentrations were higher in soil than in rice, indicating the absence of bioaccumulation by the rice grains. Furthermore, only copper exhibited a strong positive correlation (r = 0.991) between the rice grain and soil.

Evidence That PbrSAUR72 Contributes to Iron Deficiency Tolerance in Pears by Facilitating Iron Absorption.

Iron is an essential trace element for plants; however, low bioactive Fe in soil continuously places plants in an Fe-deficient environment, triggering oxidative damage. To cope with this, plants make a series of alterations to increase Fe acquisition; however, this regulatory network needs further investigation. In this study, we found notably decreased indoleacetic acid (IAA) content in chlorotic pear (Pyrus bretschneideri Rehd.) leaves caused by Fe deficiency. Furthermore, IAA treatment slightly induced regreening by increasing chlorophyll synthesis and Fe2+ accumulation. At that point, we identified PbrSAUR72 as a key negative effector output of auxin signaling and established its close relationship to Fe deficiency. Furthermore, the transient PbrSAUR72 overexpression could form regreening spots with increased IAA and Fe2+ content in chlorotic pear leaves, whereas its transient silencing does the opposite in normal pear leaves. In addition, cytoplasm-localized PbrSAUR72 exhibits root expression preferences and displays high homology to AtSAUR40/72. This promotes salt tolerance in plants, indicating a putative role for PbrSAUR72 in abiotic stress responses. Indeed, transgenic plants of Solanum lycopersicum and Arabidopsis thaliana overexpressing PbrSAUR72 displayed less sensitivity to Fe deficiency, accompanied by substantially elevated expression of Fe-induced genes, such as FER/FIT, HA, and bHLH39/100. These result in higher ferric chelate reductase and root pH acidification activities, thereby hastening Fe absorption in transgenic plants under an Fe-deficient condition. Moreover, the ectopic overexpression of PbrSAUR72 inhibited reactive oxygen species production in response to Fe deficiency. These findings contribute to a new understanding of PbrSAURs and its involvement in Fe deficiency, providing new insights for the further study of the regulatory mechanisms underlying the Fe deficiency response.

ELONGATED HYPOCOTYL 5 regulates BRUTUS and affects Iron acquisition and homeostasis in Arabidopsis thaliana.

Iron (Fe) is an essential micronutrient for both plants and animals. Fe limitation significantly reduces crop yield and adversely impacts on human nutrition. Owing to limited bioavailability of Fe in soil, plants have adapted different strategies that not only regulate Fe uptake and homeostasis but also brings modifications in root system architecture to enhance survival. Understanding the molecular mechanism underlying the root growth responses will have critical implications for plant breeding. Fe uptake is regulated by a cascade of basic helix-loop-helix (bHLH) transcription factors in plants. In this study, we report that HY5 (Elongated Hypocotyl 5), a member of the basic leucine zipper (bZIP) family of TFs plays an important role in the Fe deficiency signalling pathway in Arabidopsis thaliana. The hy5 mutant failed to mount optimum Fe deficiency responses and displayed root growth defects under Fe limitation. Our analysis revealed that the induction of the genes involved in Fe uptake pathway (FIT-FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR, FRO2-FERRIC REDUCTION OXIDASE 2 and IRT1-IRON-REGULATED TRANSPORTER1) is reduced in the hy5 mutant as compared to the wild-type plants under Fe deficiency. Moreover, we also found that the expression of coumarin biosynthesis genes is affected in the hy5 mutant under Fe deficiency. Our results also showed that HY5 negatively regulates BRUTUS (BTS) and POPEYE (PYE). Chromatin Immunoprecipitation followed by qPCR revealed direct binding of HY5 to the promoters of BTS, FRO2 and PYE. Altogether, our results showed that HY5 plays an important role in regulation of Fe deficiency responses in Arabidopsis.

Contrasting Effects of Nitrogen and Organic Fertilizers on Iron Dynamics in Soil after 38–Year Fertilization Practice

Various environmental factors and anthropogenic practices can affect the Fe biogeochemical cycles in soils. Nitrogen and carbon states are closely associated with Fe dynamics. However, we still have a limited understanding of the complex response of Fe biogeochemical processes to long–term nitrogen– and organic–fertilization regimes. This study investigated the Fe fraction and distribution, as well as the link between Fe and nitrogen/carbon, in bulk soil and in soil aggregates. The results showed that the long–term application of the nitrogen fertilizer increased the contents of water–soluble iron (Ws–Fe) and carbonate–bound iron (Ca–Fe) in the bulk soil and various sizes of aggregates, as well as the iron contents in soybeans. The decreased pH and enhanced Feammox reaction in response to the nitrogen–fertilizer treatments were responsible for the increase in the Ws–Fe and Ca–Fe fractions. By contrast, the long–term application of the organic fertilizer decreased the contents of Ws–Fe and Ca–Fe, while it increased the contents of Ox–Fe and Or–Fe. Moreover, the contents of Ox–Fe and Or–Fe were positively correlated with the organic–carbon contents in the micro–aggregates of 0.053–0.25 mm and &lt;0.053 mm. These results indicated that the long–term use of the organic fertilizer encouraged Fe immobilization in organo–inorganic compounds. However, the application of the nitrogen fertilizer alleviated the Fe retention induced by the organic fertilizer. In conclusion, long–term nitrogen and organic fertilization have contrasting influences on the mineralogy and availability of Fe in soil. This study is useful for understanding the mechanism underlying the interaction between Fe and nitrogen/carbon, as well as Fe’s phytoavailability in response to different fertilization practices in brown soil.

Pollution and health-risk assessments of Cr-contaminated soils from a tannery waste lagoon, Hebei, north China: With emphasis on Cr speciation

In this paper, heavy metals (i.e., V, Cr, Co, Cu, Zn, Cd, Pb, and Sb) in soils from a tannery waste lagoon, Hebei, north China were investigated. Element concentrates were determined by a portable X-ray fluorescence in situ and an inductively coupled plasma mass spectrometry in the lab. Two sets of indexes, including geological accumulation index, contamination factor, and pollution load index, and hazard quotient and total carcinogenic risk were adopted to evaluate the pollution and health-risk of heavy metals. A scanning electron microscopy in conjunction with an energy dispersive X-ray spectroscopy and an X-ray photoelectron spectroscopy was used to observe chromium occurrence and speciation. With an average of 6493.11 mg/kg, chromium contents in the lagoon soils reached up to 12971.19 mg/kg, 211-times higher than the threshold of Chinese soils (61.00 mg/kg). Elevated Cr contents resulted in significantly high pollution and noncarcinogenic and carcinogenic risks in the studied area. Chromium in most soils occurred predominately as Cr3+ (60–74%), and to a lesser extent, Cr6+. The mechanism responsible for decreasing Cr6+ percentages in soils with increasing depth was summarized: Cr6+ favors aqueous environment; soil moisture decreased with increasing depth; in soils especially in the lower portion, Cr6+ was reduced by Fe0 and Fe2, transforming into Cr3+ and Fe3+. In addition, the alkaline condition promoted Cr3+ to precipitate, resulting more Cr3+ absorbing in soils. The intimate association of Cr and Fe in soils (i.e., Cr mainly occurred in Fe oxides and dolomite) further confirmed our assumptions. A combined application of microorganism (e.g., Aeromonas hydrophila) and biochar (prepared from maize stalk or peanut shells) were recommended to alleviate Cr pollution in the soils.

Roles of nanoparticles in arsenic mobility and microbial community composition in arsenic-enriched soils

Environmental effects of nano remediation engineering of arsenic (As) pollution need to be considered. In this study, the roles of Fe2O3 and TiO2 nanoparticles (NPs) on the microbial mediated As mobilization from As contaminated soil were investigated. The addition of Fe2O3 and TiO2 NPs restrained As(V) release, and stimulated As(III) release. As(V) concentration decreased by 94% and 93% after Fe2O3 addition, and decreased by 89% and 45% after TiO2 addition compared to the Biotic and Biotic+Acetate (amended with sodium acetate) controls, respectively. The maximum values of As(III) were 20.5 and 27.1 µg/L at 48 d after Fe2O3 and TiO2 NPs addition, respectively, and were higher than that in Biotic+Acetate control (12.9 µg/L). The released As co-precipitated with Fe in soils in the presence of Fe2O3 NPs, but adsorbed on TiO2 NPs in the presence of TiO2 NPs. Moreover, the addition of NPs amended with sodium acetate as the electron donor clearly promoted As(V) reduction induced by microbes. The NPs addition changed the relative abundance of soil bacterial community, while Proteobacteria (42.8%-70.4%), Planctomycetes (2.6%-14.3%), and Firmicutes (3.5%-25.4%) were the dominant microorganisms in soils. Several potential As/Fe reducing bacteria were related to Pseudomonas, Geobacter, Desulfuromonas, and Thiobacillus. The addition of Fe2O3 and TiO2 NPs induced to the decrease of arrA gene. The results indicated that the addition of NPs had a negative impact on soil microbial population in a long term. The findings offer a relatively comprehensive assessment of Fe2O3 and TiO2 NPs effects on As mobilization and soil bacterial communities.

DISTRIBUTION OF GROSS FORMS OF ELEMENTS IN SOILS AND DOMINANT PLANTS OF AGROCENOSIS TRITICUM AESTIVUM L.

The aim of this work was to study the distribution of gross forms of elements - Ca, Mg, Sr, Ni, Cr, Zn, Mn, Cu, Fe, Pb, Cd, Co, As in the soil and plants of roadside agrocenosis. Agrocenosis Triticum aestivum L. is located along the Federal highway P-404. Sonchus arvensis L. and Cirsium setosum (Willd) Bess. are dominant weed species of agrocenosis, have a similar elemental composition. Phytomass of these plants does not accumulate As, Cd, Co, Ni, Cr, Zn, Cu, Mn, Pb. The content of Ca, Mg, Sr, Fe does not depend on the removal of the roadbed. Triticum aestivum L. - the main crop of agrocenosis, does not accumulate in its phytomass As, Cd, Co, Ni, Cr, Zn. The concentrations of Ca, Mg, Sr, Mn, Cu, Fe, Pb in the phytomass of Triticum aestivum L. are not dependent on the location of the road and are in the same range over the entire area of the field. The approach to the roadbed at a distance of 15-200 m did not affect the salt composition of the soil; the pH of soil samples taken over the entire field area is neutral. As, Cd, Co in soil are not detected. The value of the gross forms of Cr, Cu, Sr, Zn, Fe in soil does not exceed the value of their clarkes in the lithosphere. The content of gross forms of Pb and Mn in soil does not exceed the maximum allowable concentration. The approach of the road did not have a critical impact on the elemental composition in the components of the roadside agrocenosis.