Mo Accumulation Research Articles

Chemical speciation and availability of molybdenum in soils to wheat uptake.

Molybdenum (Mo) is an essential micronutrient for plants, yet it also poses potential environmental risks when present in excess. This study investigated the Mo speciation in soils with varying properties and their influences on Mo uptake by wheat (Triticum aestivum L.), a staple crop with significant implications for global food security. Mo K-edge X-ray absorption spectroscopy (XAS), combined with a sequential extraction method, was employed to analyze the chemical speciation and fractionation of Mo in the soils before and after wheat cultivation. The predominant Mo species identified were sorbed molybdate (Mo(VI)) and Ca- and Fe-Mo(VI) precipitates. After wheat cultivation, sorbed Mo(VI) and Ca-Mo(VI) decreased while Fe-Mo(VI) increased, with the most notable changes observed in the alkaline soil. These changes indicated that the desorption of sorbed Mo(VI) and dissolution of Ca-Mo(VI) contributed to soil Mo availability, while Fe-Mo(VI) precipitation restricted it. Bioaccumulation and translocation factors revealed efficient Mo uptake and transport within wheat plants, with shoots being the primary site of Mo accumulation. Elevated Mo concentrations in wheat grains raise potential human health concerns due to dietary exposure. These findings underscore the critical role of soil Mo speciation in controlling Mo dynamics in soil-wheat systems, providing valuable insights for managing Mo in agricultural soils to balance its nutritional benefits with the risks of excessive crop accumulation.

Exploring the impact of fulvic acid and humic acid on heavy metal availability to alfalfa in molybdenum contaminated soil

Humic substances, such as Fulvic acid (FA) and humic acid (HA), are widely used for the remediation of heavy metal-contaminated soils due to their ability to enhance metal mobility and facilitate plant uptake. In this study, we conducted a pot experiment with alfalfa to investigate the effects of FA and HA amendments on the mobility of molybdenum (Mo) in the soil, its uptake by alfalfa plants, and subsequent changes in the microbial community. The results demonstrated that both FA and HA influence Mo accumulation in the soil and plants. Specifically, HA treatment increased Mo concentrations in alfalfa shoots and roots by 1.08–1.19 times and 1.19–2.43 times, respectively, compared to the control. In contrast, FA enhanced Mo concentrations in alfalfa roots (1.05–1.58 times) but reduced Mo levels in the shoots (0.78–0.85 times). Furthermore, the addition of FA and HA altered the chemical speciation of Mo in the soil, promoting the conversion of reducible and oxidizable fraction to more exchangeable and residual fraction. As a result, the proportion of non-residual Mo fractions (exchangeable, reducible, and oxidizable) decreased from 87.48% to 80.30-87.35%, while residual fractions increased from 12.52% to 12.65–19.70%. Additionally, the structure of the soil bacterial community was primarily influenced by changes in soil properties such as cation exchange capacity, available phosphorus, and ammonium nitrogen levels. This finding highlight the potential of FA and HA to enhance Mo availability, uptake, and translocation in alfalfa, suggesting that their application could be an effective strategy for phytoremediation of Mo-contaminated soils, particularly when alfalfa is used as a hyperaccumulator.

Features of seasonal biogeochemical element migration in the "soil-plant" system: A case study of Bambusoideae in the Bidoup-Nui Ba National Park (Central Vietnam)

The article presents unique research conducted in Bidoup-Nui Ba National Park, Vietnam, focusing on the biogeochemical element migration in soil and plants. The study aimed to identify element content changes, biological accumulation, and biogeochemical mobility during wet and dry seasons across different landscape conditions. The research revealed the active elements involved in migration and accumulation, assessed mobility and accumulation in bamboo organs, and highlighted the peculiarities within the "soil-plant" system. The study found that the uptake of certain microelements by plants is influenced by landscape facies and moisture conditions. For example, Zn, Cu, and Co were introduced through plant litter during the wet season and accumulated, while Mo accumulation was more pronounced in the dry season. Furthermore, the research observed variations in biological uptake by bamboo organs, with different landscape conditions and seasons playing a role. The biogeochemical mobility of elements in bamboo organs increased significantly with soil moisture during the wet season. Overall, the research provided insights into element accumulation and biogeochemical migration. Notably, the accumulation of element B was found to increase with soil moisture, while its reduction was associated with slope process activation during the wet season.

Chemical speciation and rice uptake of soil molybdenum-Investigation with X-ray absorption spectroscopy and isotope fractionation

Molybdenum (Mo) contamination of farmland soils poses health risks due to Mo accumulation in crops like rice. However, the mechanisms regulating soil availability and plant uptake of Mo remain poorly understood. This study investigated Mo uptake by rice plants, focusing on Mo speciation and isotope fractionation in soil and rice plants. Soil Mo species were identified as sorbed Mo(VI) and Fe-Mo(VI) using X-ray absorption spectroscopy (XAS). Soil submergence during rice cultivation led to the reductive dissolution of Fe-associated Mo(VI) while increasing sorbed Mo(VI) and Ca-Mo(VI). Soil Mo release to soil solution was a dynamic process involving continuous dissolution/desorption and re-precipitation/sorption. Mo isotope analysis showed soil solution was consistently enriched in heavier isotopes during rice growth, attributed to re-sorption of released Mo and the uptake of Mo by rice plants. Mo was significantly associated with Fe in rice rhizosphere as sorbed Mo(VI) and Fe-Mo(VI), and around 60 % of Mo accumulated in rice roots was sequestrated by Fe plaque of the roots. The desorption of Mo from Fe hydroxides to soil solution and its subsequent diffusion to the root surface were the key rhizosphere processes regulating root Mo uptake. Once absorbed by roots, Mo was efficiently transported to shoots and then to grains, resulting in heavier isotope fractionation during the translocation within plants. Although Mo translocation to rice grains was relatively limited, human exposure via rice consumption remains a health concern. This study provides insights into the temporal dynamics of Mo speciation in submerged paddy soil and the uptake mechanisms of Mo by rice plants.

The trade-off regulation of arbuscular mycorrhiza on alfalfa growth dose-dependent on gradient Mo exposure

Molybdenum (Mo) is an essential nutrient for leguminous plants, but the effects of Mo exposure on plant growth, especially in relation to soil microorganisms, are not fully understood. This study employed alfalfa (Medicago sativa L.) to evaluate the physiochemical responses to gradient soil Mo variations and explore the potential regulatory role of rhizosphere microorganism - arbuscular mycorrhizal fungi (AMF) in modulating Mo's impact on plant physiology, with a focus on metabolic pathways. The results showed that Mo exerted hormetic effect (facilitation at low doses; inhibition at high doses) on alfalfa growth, promoting biomass (below 90.94 mg/kg, with a 63.98 % maximum increase), root length (below 657.11 mg/kg, with a 39.29 % maximum increase), and plant height (below 304.03 mg/kg, with an 18.4 % maximum increase). Excess Mo (1000 mg/kg) resulted in a reduction in photosynthesis and biomass growth due to increased oxidative stress (p < 0.05). Within the stimulatory zones, AMF enhanced Mo accumulation in alfalfa, augmenting its phytological effects. Exceed the stimulatory zones, AMF enhanced alfalfa Fe uptake and reduced the generation of reactive oxygen species (ROS) induced by excess Mo by shifting the redox homeostasis-controlled enzyme from peroxidase (POD) to superoxide dismutase (SOD), thereby improving alfalfa's tolerance to Mo. Metabolomic analysis further revealed that AMF promoted the biosynthesis of indole acetic acid (IAA) and various amino acids in Mo-stressed alfalfa (p < 0.05), which accelerated alfalfa growth and mitigated Mo-induced phytotoxicity. These insights provide a foundation for developing sustainable management strategies for Mo-exposed soils using AMF inoculants, such as minimizing Mo fertilizer application in Mo-deficient soils and facilitating the reclamation of Mo-contaminated soils.

Potential Use of Biochar as a Mitigation Strategy for Salinity-Related Issues in Tomato Plants (Solanum lycopersicum L.)

The continuous growth of the population, along with climate change and the resulting surge in food demand, requires the development of alternative crop cultivation strategies that reduce the excessive use of freshwater for agricultural purposes. Biochar, which is a carbon-rich material made from organic waste through pyrolysis, has been recommended as a potential soil amendment to mitigate the negative effects of salinity. Biochar has unique properties such as high porosity, an ion exchange capacity, and the ability to retain water and nutrients. The purpose of this study was to evaluate the feasibility and effectiveness of using saline water for the cultivation of tomato plants (Solanum lycopersicum L.) and to investigate the potential use of biochar as a mitigation strategy for salinity-related issues in tomato cultivation. The concentration of NaCl during the experiment was 100 mM. We examined the impact of salt stress on plant growth, protein and chlorophyll content, the activation of the antioxidant response, and nutritional status. Our results indicated that salt treatments led to a significant accumulation of Na and Cl in shoots (regardless of the biochar addition) but did not result in a corresponding reduction in plant growth. However, the degree of oxidative damage caused by NaCl treatment, measured as malondialdehyde (MDA) accumulation, was reduced by biochar addition to the growth medium, most likely because of an increased guaiacol peroxidase (GPX) activity, which led to lower MDA accumulation. The strong positive effect of biochar on GPX activity could be reasonably attributed to increased Mo accumulation. In conclusion, the findings of this study represent a valuable starting point for developing crop management strategies based on biochar application to enhance plant performance under unfavorable conditions and reduce freshwater dependence in agriculture.

Effects of nano-molybdenum fertilizers on mo-inefficient winter wheat grown in acidic soil

Due to the essential role of nano-fertilizers in crop production, studies have yet to be conducted to evaluate nano-molybdenum (Mo) application on winter wheat (Triticum aestivum L.). The present study assessed the efficacy of nano-Mo on the Mo-uptake, plant growth, and winter wheat yield. Wheat was grown in the pot experiment using four experimental groups (deionized water: C, nano potassium molybdate: NMoK, potassium molybdate: MoK, and ammonium molybdate: MoA), each with six replicate samples applied-foliar three times in a 30-day interval. The results revealed that NMoK improved Mo accumulation in grains, stomatal conductance, root dry weight, yield, and the number of spikes per pot of wheat compared with MoK. Additionally, NMoK treatment significantly increased wheat grain yield by 46.29%, 13.94%, and 17.70% compared with C, MoK, and MoA treatments, respectively. These results demonstrated that the nano-Mo application may enhance Mo-inefficient wheat growth, thus, increasing its productivity under acidic soil conditions. The principal component analysis (PCA) elucidates that all variables reside within the positively correlated variable domain. This encompasses parameters related to yield, photosynthetic machinery, and Mo uptake by various plant organs. Through cluster analysis, the nano-Mo group exhibited a more pronounced influence on the variables than the without-Mo and non-nano-Mo groups. Based on our findings, nano-Mo could be a suitable alternative to non-nano molybdenum fertilizers. This recommendation is particularly relevant for enhancing the growth of winter wheat crops cultivated in acidic soil conditions.

Sedimentary molybdenum and uranium cycling under seasonally contrasting redox conditions on the Namibian Shelf

Sedimentary molybdenum (Mo) and uranium (U) enrichments have been widely used as a proxy for redox conditions in oxygen-depleted marine paleo-environments. However, in a dynamic upwelling system the seasonal fluctuations from oxic to completely anoxic-sulfidic bottom waters and lateral sediment transport can modify the primary Mo and U signal of the sediment, which in turn may impact paleo-redox interpretations. In this study we present pore water and solid phase data collected at two cross shelf transects during the ‘more oxygenated’ austral winter and ‘anoxic’ austral summer to study the influence of spatially and seasonally contrasting redox conditions on the formation of authigenic Mo and U enrichments in organic carbon (TOC) rich mud belt sediments on the Namibian shelf. A mass balance was established for each element based on diffusive fluxes and element mass accumulation rates to evaluate the respective mechanisms of trace metal delivery, accumulation and recycling.Mo is delivered to the sediment in its dissolved form via diffusion across the sediment–water interface, especially during austral summer when bottom waters are anoxic and surface sediments are highly sulfidic. In the center of the inner shelf mud belt, the benthic Mo fluxes of up to 37 nmol cm−2 yr−1 into sulfidic surface sediments are the highest ever reported for reducing sulfidic systems and agree with the rate of Mo accumulation in the solid phase. Concurrently, high sedimentation rates and low terrigenous input limit solid phase Mo accumulation on the Namibian shelf. In ancient marine sediments, this mode of Mo cycling can be identified by low Mo/TOC ratios of ∼2 similar to those found in sediments deposited below the perennial oxygen minimum zone on the Peruvian shelf and to those found in deposits of the Cretaceous Oceanic Anoxic Event 2. Diffusive U fluxes into the sediment are generally too low to account for the sedimentary enrichment leading to the conclusion that U is delivered mainly in particulate form. In areas with anoxic bottom water, shallow dissolved U maxima directly below the sediment water interface and rather low sedimentary U content indicate that particulate U is recycled and largely released back into the bottom water. At sites where bottom water oxygen concentrations vary from anoxic to completely oxic on seasonal timescales, the depth at which Mo and U are removed from pore waters moves vertically within the sediment column thus defining a layer between the sediment surface and ∼20 cm depth, in which Mo and U accumulate in the solid phase. Our results emphasize the importance of short-term redox fluctuations in the bottom waters and underlying sediments, as well as lateral sediment transport for the authigenic enrichment of redox-sensitive trace metals in reducing shelf sediments. The relative enrichment patterns identified might be useful for the reconstruction of open marine anoxia in the geological past.

Extremely light molybdenum isotope signature of sediments in the Mariana Trench

Molybdenum (Mo) isotope signature (δ98/95Mo) of marine sediments is a powerful proxy for constraining marine redox conditions and early diagenetic processes. Oxic pelagic sediments have been increasingly acknowledged as an important sink for Mo in its global cycling, however, the mechanisms controlling Mo enrichment and isotope fractionation during early diagenesis in this environment are not fully understood. In this study, four sedimentary cores were sampled by full-ocean-depth lander system in the Mariana Trench, aiming to explore the processes controlling Mo partitioning in the sediments of the deepest ocean in the world. Sediments from four locations exhibit a wide range of authigenic Mo contents (Moauth, relative to continental crust), varying from 1.98 to 43 μg/g. A positive relation between Mo and Mn contents was identified for these sediments, which suggests that Mo are mainly hosted in Fe-Mn (oxyhydr)oxides. In addition, negative correlations between δ98/95Mo values and Mo/Mn ratios are found at each site. The δ98/95Mo values of the sediments vary from −1.71 ± 0.05 to −0.15 ± 0.04‰, revealing similar trends towards lighter values with burial depth from three sites. However, throughout the sediment core TY41 obtained from Mariana Trench, the δ98/95Mo values of sediment remain nearly constant around −0.55‰. Supported by the abundant Fe (oxyhydr)oxides throughout this site, it is likely the sediment is affected by enhanced fluid exchange across sediment-seawater interface, and the δ98/95Mo values of dissolved Mo in pore water resemble seawater signature. Therefore, the Mo isotopic offset between dissolved Mo and sediment is similar to the expected fractionation during the adsorption to Mn oxides (~ + 3.0‰) and hematite (~ + 2.2‰), which suggests that most of the dissolved Mo is scavenged by Mn oxides and/or hematite. The extremely light δ98/95 Mo values of sediments in deeper parts of the cores coincide with enhanced Mo accumulation. This indicates an even lighter isotope signature of dissolved Mo in pore water during the re-precipitation of Fe-Mn (oxyhydr)oxides upon an isotopic equilibrium for Mo adsorption to metal oxides. Both the patterns of both dissolved oxygen and nitrate suggest that the study sites are located within the nitrate reduction zone and Mn reduction occur at deeper depths below the studied interval. Therefore, the source of the isotopically light dissolved Mo in pore water was explained by the preferential release of isotopically lighter Mo from Fe-Mn (oxyhydr)oxides during the enhanced dissolution at deeper depth. In contrast, at the shallower depths of these cores (expect for core TY41), the higher δ98/95 Mo values towards seawater-sediment interface suggest the dissolved Mo is more impacted by the seawater exchange. This study provides a deeper insight into the diagenetic Mo cycling in trench environments, with Fe-Mn (oxyhydr)oxides rich sediments as an important sink for Mo.

The Vacuolar Molybdate Transporter OsMOT1;2 Controls Molybdenum Remobilization in Rice.

Molybdenum (Mo) is an essential micronutrient for almost all living organisms. The Mo uptake process in plants has been well investigated. However, the mechanisms controlling Mo translocation and remobilization among different plant tissues are largely unknown, especially the allocation of Mo to rice grains that are the major dietary source of Mo for humans. In this study, we characterized the functions of a molybdate transporter, OsMOT1;2, in the interorgan allocation of Mo in rice. Heterologous expression in yeast established the molybdate transport activity of OsMOT1;2. OsMOT1;2 was highly expressed in the blades of the flag leaf and the second leaf during the grain filling stage. Subcellular localization revealed that OsMOT1;2 localizes to the tonoplast. Knockout of OsMOT1;2 led to more Mo accumulation in roots and less Mo translocation to shoots at the seedling stage and to grains at the maturity stage. The remobilization of Mo from older leaves to young leaves under molybdate-depleted condition was also decreased in the osmot1;2 knockout mutant. In contrast, overexpression of OsMOT1;2 enhanced the translocation of Mo from roots to shoots at the seedling stage. The remobilization of Mo from upper leaves to grains was also enhanced in the overexpression lines during grain filling. Our results suggest that OsMOT1;2 may function as a vacuolar molybdate exporter facilitating the efflux of Mo from the vacuole into the cytoplasm, and thus, it plays an important role in the root-to-shoot translocation of Mo and the remobilization of Mo from leaves to grains.

Genome-Wide Association Study Reveals Genomic Regions Associated With Molybdenum Accumulation in Wheat Grains.

Molybdenum (Mo) is an essential micronutrient for almost all organisms. Wheat, a major staple crop worldwide, is one of the main dietary sources of Mo. However, the genetic basis for the variation of Mo content in wheat grains remains largely unknown. Here, a genome-wide association study (GWAS) was performed on the Mo concentration in the grains of 207 wheat accessions to dissect the genetic basis of Mo accumulation in wheat grains. As a result, 77 SNPs were found to be significantly associated with Mo concentration in wheat grains, among which 52 were detected in at least two sets of data and distributed on chromosome 2A, 7B, and 7D. Moreover, 48 out of the 52 common SNPs were distributed in the 726,761,412–728,132,521 bp genomic region of chromosome 2A. Three putative candidate genes, including molybdate transporter 1;2 (TraesCS2A02G496200), molybdate transporter 1;1 (TraesCS2A02G496700), and molybdopterin biosynthesis protein CNX1 (TraesCS2A02G497200), were identified in this region. These findings provide new insights into the genetic basis for Mo accumulation in wheat grains and important information for further functional characterization and breeding to improve wheat grain quality.

A critical review of molybdenum sequestration mechanisms under euxinic conditions: Implications for the precision of molybdenum paleoredox proxies

The observed difference in molybdenum (Mo) mobility and isotopic fractionation under oxic versus euxinic (i.e., anoxic and sulfidic) aqueous conditions provides a sound operational basis for the use of Mo geochemical signatures in ancient sedimentary records to infer palaeoceanographic redox conditions . While Mo is known to exist predominantly as molybdate (MoO 4 2− ) in oxic waters and convert into thiomolybdate species (MoO x S 4-x 2− ) under euxinic conditions, the pathways that lead to Mo sequestration are highly debated. As mechanistic understanding of Mo sequestration is crucial for accurately reconstructing the chemistry of ancient oceans and constraining the timing and intensity of oxygenation events through Earth's history using Mo paleoproxies, we have closely examined the current proposed mechanisms for Mo sequestration across a wide range of euxinic conditions. Through compilation and comparison of such information, we aim to provide an integrated view of Mo sequestration processes, to identify the current controversies as well as the roots of such controversies, and importantly, to propose avenues for future research. Sequestration of Mo may occur through complexation with organic matter (OM), reactions with oxyhydroxide and sulfide mineral surfaces, incorporation into iron sulfide crystal structures, formation of Mo-sulfide, and cellular assimilation. However, several major questions remains unresolved, including whether OM complexation plays a significant role in overall sedimentary Mo accumulation, whether the reduction of Mo(VI) occurs during interaction with Fe-S clusters/precipitates and/or with OM, whether microbial enzymatic reduction of Mo(VI) is important in Mo sequestration, whether synergistic effects exist between the biological and abiotic processes in Mo sequestration, and whether differences in reactivity among the various thiomolybdate intermediate species and tetrathiomolybdate influence the Mo sequestration process. At the end of the review, the reliability of Mo paleoproxies is discussed and reevaluated.

Pulsed oxygenation events drove progressive oxygenation of the early Mesoproterozoic ocean

The Mesoproterozoic era has long been considered a time of relative environmental and biological stasis. However, emerging insight suggests that this period may have been more dynamic than previously considered, both in terms of oxygenation and potential consequences for biological evolution. Nevertheless, our understanding of this immense period of time remains limited. To provide more detailed constraints on oxygenation dynamics, we report a multiproxy geochemical study of an early Mesoproterozoic (∼1600–1540 million years ago, Ma) carbonate-dominated succession from the North China craton. We include inorganic carbon isotope (δ13Ccarb), iron-speciation, and major and trace element data, in addition to molybdenum isotopic compositions (δ98/95Mo). These geochemical data support previous inferences of persistent anoxic and ferruginous deeper water conditions in the earliest Mesoproterozoic ocean, with limited oxygenation of surface waters. However, the behaviour of these redox-sensitive geochemical proxies reveals pulsed oxygenation events, with each event increasing the maximum depth of oxygenation, leading to overall progressive oxygenation of the ocean. During these pulsed oxygenation events we find the lightest Mo isotope signatures ever measured in the rock record, which we attribute to initial drawdown of isotopically light Mo in association with extensive Mn and Fe (oxyhydr)oxide precipitation, followed by diagenetic recycling. However, shallower water sediments deposited after the pulses of deeper water oxygenation more faithfully record the Mo isotopic composition of coeval seawater. For these samples, we utilise a single reservoir Mo cycling model, constrained by an updated estimate of Mesoproterozoic seawater Mo concentration, and scaled using a function associated with differential organic carbon flux between the shelf and basin. When scaled to modern rates of Mo accumulation under variable marine redox conditions, our modelling estimates suggest a minimum oxic seafloor area of ∼30% of the total seafloor area at ∼1540 Ma. It remains unclear whether the oxygenation observed across this ∼60 million year interval represents a progressive transition to a more persistently oxygenated ocean, or whether oceanic oxygen levels fluctuated considerably through the later Mesoproterozoic.

The contribution of Cr and Mo to the passivation of Ni22Cr and Ni22Cr10Mo alloys in sulfuric acid

The beneficial effects of Mo on passive film formation were investigated for Ni22Cr10Mo with AESEC and XPS by comparison with Ni22Cr and pure Ni and Mo. Both spontaneous (E ≈ -0.2 VSCE) and anodic passivation (E = 0.3 VSCE) showed Cr surface accumulation, while significant Mo accumulation (as Mo(IV)) only occurred during spontaneous passivation with a markedly reduced open circuit corrosion rate as a consequence. Mo facilitated the active to passive transition in the low potential domain probably by favoring the oxidation of Cr to Cr2O3 over Cr(OH)3. At higher potential, Mo dissolved as Mo(VI) and did not accumulate in the film.

Arbuscular Mycorrhizal Fungi Improve the Performance of Sweet Sorghum Grown in a Mo-Contaminated Soil.

Arbuscular mycorrhizal fungi are among the most ubiquitous soil plant-symbiotic fungi in terrestrial environments and can alleviate the toxic effects of various contaminants on plants. As an essential micronutrient for higher plants, molybdenum (Mo) can cause toxic effects at excess levels. However, arbuscular mycorrhizal fungal impacts on plant performance and Mo accumulation under Mo-contamination still require to be explored. We first studied the effects of Claroideoglomus etunicatum BEG168 on plant biomass production and Mo accumulation in a biofuel crop, sweet sorghum, grown in an agricultural soil spiked with different concentrations of MoS2. The results showed that the addition of Mo produced no adverse effects on plant biomass, N and P uptake, and root colonization rate, indicating Mo has no phytotoxicity and fungitoxicity at the test concentrations. The addition of Mo did not increase and even decreased S concentrations in plant tissues. Arbuscular mycorrhizal inoculation significantly enhanced plant biomass production and Mo concentrations in both shoots and roots, resulting in increased Mo uptake by mycorrhizal plants. Overall, arbuscular mycorrhizal inoculation promoted the absorption of P, N and S by sweet sorghum plants, improved photosystem (PS) II photochemical efficiency and comprehensive photosynthesis performance. In conclusion, MoS2 increased Mo accumulation in plant tissues but produced no toxicity, while arbuscular mycorrhizal inoculation could improve plant performance via enhancing nutrient uptake and photochemical efficiency. Sweet sorghum, together with arbuscular mycorrhizal fungi, shows a promising potential for phytoremediation of Mo-contaminated farmland and revegetation of Mo-mine disturbed areas, as well as biomass production on such sites.

Streptozotocin (STZ)-Induced Diabetes Affects Tissue Trace Element Content in Rats in a Dose-Dependent Manner.

The objective of the present study was investigation of tissue trace element distribution in a streptozotocin model of DM1 in rats. DM1 was modeled in 2-month-old male Wistar rats (n = 30) using intraperitoneal injection of 45mg/kg b.w. (STZ1) and 55mg/kg b.w. streptozotocin (STZ2), whereas control animals were injected with physiological saline. The rats were subjected to oral glucose tolerance test (OGTT) and HbA1c level assessment at day 14. At day 30, blood serum, liver, kidney, and heart samples were collected for tissue trace element assessment using inductively coupled plasma mass spectrometry (ICP-MS). STZ-treated rats were characterized by lack of significant weight gain and elevated HbA1c and blood glucose levels. ICP-MS analysis demonstrated a dose-dependent accumulation of Cu, Mn, Mo, and Se levels in the liver. Correspondingly, the dose-dependent increase in renal Cu, Mn, V, and Zn levels was significant, whereas the observed trend for kidney V and Mo accumulation was nearly significant. The patterns of trace element content in the myocardium of STZ-exposed rats were quite different from those observed for liver and kidney. Only cardiac Zn content was characterized by a significant decrease. Serum Co, Cr, Cu, Se, V, and Mo levels were characterized by a significant decrease in response to STZ-induced diabetes. Generally, the obtained data demonstrate that diabetes is associated with altered copper, manganese, molybdenum, chromium, and vanadium handling. In turn, only altered Zn status may provide a link to diabetic cardiotoxicity. However, the particular mechanisms of both impaired metal handling in STZ diabetes and their potential anti-diabetic activity require further investigation.

Influence of particulate versus diffusive molybdenum supply mechanisms on the molybdenum isotope composition of continental margin sediments

The sedimentary concentration and stable isotope composition of molybdenum (Mo) is widely used as a proxy for paleo redox conditions in the marine environment. However, the behavior of Mo during early diagenesis is still not fully understood, which complicates the application of the Mo proxy in ancient continental margin environments. Here, we present Mo concentrations and isotope compositions of sediment and pore water samples from the Guaymas Basin in the Gulf of California. Our sample set covers a broad range of depositional environments, including sediments from within the eastern equatorial Pacific oxygen minimum zone (OMZ), from a semi-restricted oxic graben, and from near a hydrothermal vent-field. By investigating Mo cycling in these different settings, we provide new insights into different modes of Mo fixation and the associated isotope fractionation.Sediments from the OMZ have authigenic Mo concentrations (Moauth) between 3.3 and 17.2 µg/g and δ98Mo between +1.64 and +2.13‰. A linear decrease in pore water Mo concentrations to the depth where hydrogen sulfide accumulates, along with sedimentary authigenic δ98Mo values (δ98Moauth) close to seawater, indicate diffusion of Mo from the bottom water into the sediment with little isotope fractionation during quantitative Mo removal. Sediments from the site with oxic bottom water within the basin reveal Moauth concentrations ranging from 1.2 to 14.7 µg/g and δ98Moauth signatures between –1.39 to +2.07‰. Pore water Mo concentrations are generally higher than ambient bottom water concentrations and the light δ98Mo signatures of the pore waters between +0.50 and +0.80‰ and δ98Moauth signatures of the sediments indicate continuous Mo exchange between the pore water and Mn and Fe oxides during early diagenesis. Sediment samples from the vent field mainly consist of black smoker debris and are characterized by Moauth concentrations ranging from 8.6 to 33.2 µg/g and δ98Moauth values as high as +2.20‰. The relatively high Mo concentrations and seawater-like δ98Mo can be explained by near-quantitative Mo scavenging from hydrothermal solutions with little isotope fractionation at high temperatures. Comparison of our new data for the OMZ sediments in the Gulf of California with previously published data for sediments from the Peruvian OMZ highlights that Mo isotope compositions in this kind of setting strongly depend on how Mo is delivered to the sediment. If diffusive Mo delivery from the bottom water into the sediment significantly contributes to Mo accumulation in the solid phase, as is the case in the Guaymas Basin, sedimentary Moauth concentrations are relatively low but the isotope values are close to the δ98Mo signal of seawater. If Mo is exclusively delivered by particles, like on the Peruvian shelf, much higher sedimentary Moauth concentrations can be attained. In the latter case, Moauth isotope values will be lighter because the sediments preserve the isotopic offset that was generated during adsorption or uptake of Mo by particles. Our findings de-emphasize the role of dissolved Mo speciation in pore waters but highlight the importance of the mode of Mo delivery for the Mo concentration and isotope composition preserved in the paleo-record.

The identification of phytoextraction potential of Melilotus officinalis and Amaranthus retroflexus growing on copper- and molybdenum-polluted soils.

The contamination of soils by heavy metals from the mining industry nowadays is one of the greatest threats to environment and human health. The cleaning of polluted soils using cost-effective and eco-friendly methods such as phytoextraction has wide public recognition. Considering the above-mentioned ones, the objectives of the present study were the identification of Cu and Mo accumulation capability and the phytoextraction potential of Melilotus officinalis and Amaranthus retroflexus as well as the determination of the influence of ammonium nitrate and EDTA on phytoextraction effectiveness. The contaminated soil samples for phytoremediation experiments under ex situ conditions were collected from the surroundings of the Zangezur Copper and Molybdenum Combine, Armenia. During the studies, it was found out that M. officinalis and A. retroflexus are capable of growing in polluted soils. M. officinalis grown in polluted soil had greater ability to accumulate heavy metals in roots, while the ability to transport the copper to aboveground parts was more pronounced in A. retroflexus. During the growing of these plant species for phytoextraction of soils contaminated by copper, it is necessary to use chelates, in particular the EDTA, for the enhancement of the effectiveness of phytoextraction process. EDTA due to chelating influence increased the availability of copper for plants and its mobility in them that lead to greater accumulation of this metal in shoots. The application of chelates did not have a significant impact on molybdenum accumulation intensity in plants; therefore, in case of this metal, it is unreasonable to use additional chelating compounds.

Precipitation of molybdenum from euxinic waters and the role of organic matter

Molybdenum preserved in organic-rich shales is a key archive employed in studying Earth's past oxygenation and Life's evolution. In these shales, positive correlations between Mo and Corg are common and have been attributed to Mo scavenging from seawater by organic shuttles. Here, we argue that known organic ligands are too weak or too scarce to capture more than minor amounts of Mo from seawater, especially in competition with sulfide. Alternatively, we demonstrate that Mo-Corg correlations can arise simply from microbially mediated oxidation of Corg by SO42−. This process produces sulfide and lowers pH, triggering precipitation of FeMoS4, which soon transforms irreversibly to FeMoS2(S2). In euxinic basins, the extent of sulfate reduction progress increases with depth and can be modeled as an empirical function of biological productivity and water replacement time. The response of dissolved Mo to sulfate reduction progress occurs in three stages identified by a thermodynamic model. In Stage I, progress is too small to precipitate Mo from waters that are only mildly sulfidic. In Stage II, the flux of Mo to sediments is promoted by sulfate reduction progress, giving rise to positive Mo-Corg correlations in sediments due to fluctuations in biological productivity. In some cases, precipitation in this stage begins before MoS42− becomes the predominant dissolved Mo species, in which case FeMoS4 with negative δ98Mo can be produced. In Stage III, the flux of Mo becomes independent of further sulfate reduction progress and Mo-Corg correlations degrade, as reported in extremely Corg-rich shales. Even though the model omits a number of potentially important processes, its predicted Mo profiles in waters of several modern euxinic basins are qualitatively reasonable and are consistent with observed reduction of MoVI in water to MoIV in sediments. According to the model, spikes in atmospheric PCO2 will markedly increase Mo accumulation and lower δ98Mo in euxinic basin sediments. This appears to have occurred repeatedly during the Phanerozoic and may be commencing now as a result of fossil fuel combustion. Minimal deposition of Mo in organic-rich shales during the Archean has been attributed to low MoO42− in seawater but seems more likely to be due to low SO42−.

Axonopus compressus (Sw.) Beauv.: A potential biomonitor for molybdenum in soil pollution

Phytoremediation is an emerging technology that utilizes plants to remediate contaminated environments. In this study, Axonopus compressus (Sw.) Beauv, a fast-growing and hardy groundcover with wide geographical distribution, was exposed to soil Mo treatments ranging from 100 to 1000 mg/kg under tropical greenhouse conditions for five weeks. Generally, Mo accumulation increased as the concentration of Mo in the soil increased. The species was found to accumulate about 4000 mg/kg of Mo without exhibiting severe physiological stress at 600 mg/kg of soil Mo. Maximum accumulation of 6000 mg/kg Mo was observed at the 1000 mg/kg soil Mo treatment, though with severe necrosis and eventual plant mortality. The physiological observations, Mo accumulation behavior, and a bioconcentration factor of about 1 indicated that A. compressus could be a potential biomonitor of Mo.