Soil Se Research Articles

Effects of different selenium forms on selenium accumulation, plant growth, and physiological parameters of wild peach

In order to better understand the transformation and distribution of different Se forms in wild peach. Se2−, Se0, Se4+ and Se6+ (from selenomethionine, Se powder, sodium selenite, and sodium selenate, respectively) were added to 4.1-L plastic pots with 15-cm high wild peach seedlings, for a final soil Se concentration of 1.0 mg/kg soil. Growth parameters, Se transaction factors (TFS) and bioconcentration factor, as well as the leaf sugar content and antioxidant ability were determined. We found that all four forms of Se increased shoot length, stem diameter, and dry weight, whereby treatment with Se4+ and Se6+ especially promoted the dry weight. The wild peach seedlings showed different Se enrichment ability, whereby the Se bioconcentration factor (BCF) and total Se uptake per plant were in the same order of Se2– > Se6+> Se4+> Se0 > Control. However, the transaction factors (TFS) in the control and Se6+ treatment groups were significantly higher than in the groups treated with other Se forms. The control and the Se forms Se0, Se4+ and Se2− showed the same trend of Se distribution, with the largest Se concentration in the roots, followed by the leaves and stems. No significant differences were observed in leaf pigment concentration of the seedlings treated with all Se forms except for Se0. Treatment with different Se forms significantly reduced the leaf malondialdehyde (MDA) concentration, obviously increased the reducing power, insignificantly increased the content of reducing sugars, and decreased the content of total sugars. Overall, different Se forms effected the growth and physiological parameters of wild peach seedlings to different extent, whereby Se6+ and Se2– led to the highest Se accumulation, which may be beneficial for the production of Se-enriched fruits.

Arbuscular mycorrhizal fungi increase the bioavailability and wheat (Triticum aestivum L.) uptake of selenium in soil

The interaction between arbuscular mycorrhizal (AM) fungi and selenium (Se) bioavailability in rhizosphere soils of host plants is still unclear. Pot trials were conducted to investigate the effects of inoculation of AM fungi on Se uptake in winter wheat growing on selenite (Se (IV)) or selenate (Se (VI)) spiked soils (2.5 mg kg−1) and on Se bioavailability in the rhizosphere soils. Inoculation of Funneliformis mosseae (F.m) and Glomus versiforme (G.v) significantly (P < 0.05) increased concentration of available Se (SOL–Se or EXC–Se) in the rhizosphere soils by 30.21 %–189.19 % and 12.03 %–76.35 % in Se (IV)- or Se (VI)- spiked soils, and the effect of inoculatingF.m was better than G.v. Se content in winter wheat was significantly (P < 0.05) enhanced by 24.11–56.06 % and 20.27-56.49 % in Se (IV)- or Se (VI)- spiked soils inoculated with F.m and G.v. The present results also showed that Se availability in rhizosphere soils of wheat was apparently influenced by speciation of exogenous Se. In addition, correlation analysis showed that soil organic matter (SOM), dissolved organic carbon (DOC), easily extractable glomalin-related soil protein (EE-GRSP), fungi and actinomyces abundance were significantly positively correlated with available Se in the rhizosphere soils, while were negatively correlated with pH. The present study indicated that inoculation of AM fungi could increase Se bioavailability in the rhizosphere soils via influencing partial soil chemical properties including pH, SOM, DOC, EE-GRSP and microbial quantities, consequently enhancing Se uptake in winter wheat. This study can provide a theoretical basis for the study of AM fungi on Se biofortification of winter wheat.

Insights into the accumulation and transformation of Ch-SeNPs by Raphanus sativus and Brassica juncea: Effect on essential elements uptake

Selenium (Se) at very low doses has important functions for humans. Unfortunately, the low levels of Se in soils in various regions of the world have implemented the agronomic biofortification of crops by applying Se-enriched fertilizers (mainly based on selenate). Lately, the use of nanofertilizers is growing in interest as their low size reduces the amount of chemicals and minimizes nutrient losses in comparison with conventional bulk fertilizers. However, the knowledge on their fate and environmental impact is still scarce. This study aims to evaluate the biotransformation of chitosan-modified Se nanoparticles (Ch-SeNPs) as well as their effect on the metabolism of essential metals (Fe, Cu, Zn and Mo) when applied to hydroponic cultivation of R. sativus and B. juncea. In house-synthesized Ch-SeNPs were characterized in both synthesis and hydroponic culture media by transmission electron microscopy (TEM), dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA). The composition of one-tenth strength Hoagland's solution did not affect the size, shape and concentration in number of particles per mL of Ch-SeNPs. The plants were grown inside a box at 25 °C during the months of May–July in 2018. After a week of treatment with Ch-SeNPs, plants were harvested and divided into roots and aerial part. The biotransformation of Ch-SeNPs was evaluated through a process of enzymatic hydrolysis and subsequent analysis by HPLC-ICP-MS and HPLC-ESI-MS/MS. The results confirmed the transformation of Ch-SeNPs to seleno-amino acids: Selenomethionine (SeMet), Semethylselenocysteine (SeMetSeCys) and ɣ-glutamyl-Se-MetSeCys. Moreover, Multiple-way analysis of variance (ANOVA) and principal component analysis (PCA) showed that, regardless the plant species, Ch-SeNPs supplementation affected the absorption of Zn.

Sources, Fraction Distribution and Health Risk Assessment of Selenium (Se) in Dashan Village, a Se-Rich Area in Anhui Province, China.

Soil, rock, potable water, animal food and human hair samples were collected from the Dashan village, a typical selenium (Se)-rich area of China. Se content and fraction distribution were determined to trace the source of soil Se and evaluate the potential health risk to humans. Total Se contents in soils ranged from 0.60 to 10.46 mg kg- 1. The fractions of soil Se followed the order: residual Se (R-Se) > organic-bound Se (O-Se) > acid soluble Se (A-Se) > exchangeable Se (E-Se) > water soluble Se (W-Se). Total Se contents in rocks ranged from 0.07 to 24.8 mg kg- 1. The dietary Se intake of local residents was estimated to be 261.2 µg day- 1 and hair Se content varied from 0.34 to 1.35 mg kg- 1, suggesting that the potential health risk should be concerned. Weathering of carbonaceous rock was speculated to be the primary source of soil Se according to the contents of Se in rocks, the distribution of Se in soil profiles and the relationships between Se and other elements in soils and parent rocks.

Selenium biofortification of crops on a Malawi Alfisol under conservation agriculture

Biofortification with selenium (Se) may rely on rapid uptake by crops, following application, to offset progressive fixation into unavailable organic forms of Se in soil. A biofortification study was conducted on an Alfisol within a long-term conservation agriculture (CA) field trial at Chitedze Research Station, Malawi. The aim was to assess the dynamics of selenium bioavailability to a staple cereal (Zea mays) and a range of legumes (cowpeas, groundnuts, pigeon peas and velvet beans) under CA management, as well as residual Se effects in the year following biofortification. Isotopically labelled selenate (>99% enriched 77SeVI) was applied to each plot, in solution, at a rate of 20 g ha−1, at maize flowering (75 days after planting), in February 2017. Samples of grain and stover from maize and legumes, and topsoil, were collected at harvest in May 2017 and May 2018. Plant and soil samples were analyzed by ICP-MS for selenium isotopes (77Se and 78Se). The concentration of 77Se in the grain of maize and single-cropped legumes exceeded 200 µg kg−1 in all the treatments. This would contribute approximately 56–64 µg day−1 to the Malawi diet, as refined maize flour. The fertilizer derived Se concentration ratio of maize grain-to-stover Se were >1 in 2017 but <1 in 2018; which followed the same trend as the native soil-derived Se in the residual year. In legumes the grain-to-stover concentration ratio was consistently <1 in both years, except for the velvet beans. Differences in CA management had minimal influence on 77Se concentration in plant grain but the low yield in the single conventional treatment reduced 77Se uptake. Residual 77Se in the soil (35% of the applied) measured at harvest in 2017 was still present at harvest in the residual year (2018) but was completely unavailable to any of the crops. Almost none of the remaining 77Se was present in soluble or phosphate-extractable forms and virtually all was present in the ‘organic’ (TMAH-extractable) fraction. Thus, annual Se applications to maize would be necessary to maintain concentrations which could improve dietary supply and reduce current Se deficiency in Malawi.

Bioaccumulation of Hg in Rice Leaf Facilitates Selenium Bioaccumulation in Rice (Oryza sativa L.) Leaf in the Wanshan Mercury Mine.

Mercury (Hg) bioaccumulation in rice poses a health issue for rice consumers. In rice paddies, selenium (Se) can decrease the bioavailability of Hg through forming the less bioavailable Hg selenides (HgSe) in soil. Rice leaves can directly uptake a substantial amount of elemental Hg from the atmosphere, however, whether the bioaccumulation of Hg in rice leaves can affect the bioaccumulation of Se in rice plants is not known. Here, we conducted field and controlled studies to investigate the bioaccumulation of Hg and Se in the rice-soil system. In the field study, we observed a significantly positive correlation between Hg concentrations and BAFs of Se in rice leaves (r2 = 0.60, p < 0.01) collected from the Wanshan Mercury Mine, SW China, suggesting that the bioaccumulation of atmospheric Hg in rice leaves can facilitate the uptake of soil Se, perhaps through the formation of Hg-Se complex in rice leaves. This conclusion was supported by the controlled study, which observed significantly higher concentrations and BAFs of Se in rice leaf at a high atmospheric Hg site at WMM, compared to a low atmospheric Hg site in Guiyang, SW China.

Distributions of selenium and related elements in high pyrite and Se-enriched rocks from Ziyang, Central China

Pyrite-bearing volcanic tuff and carbonaceous slates of the Lower Cambrian Lujiaping Formation have been considered the source of selenium (Se) in high-Se soils in the area of the Naore Village of the Ziyang County, China, where acute Se toxicity occurred in the 1980s. For geochemical exploration, the accumulation and distribution of Se and trace elements within the pyrite grains are of great indicative significance for understanding the possible origin and forming mechanism of the Se enrichment. In this work, 7 rock samples and 89 pyrite grains were collected and analysed to investigate the element micro-distribution within the pyrite grains using EPMA and LA-ICP-MS. The whole-rock analysis shows that the pyrite-bearing Lower Cambrian rocks in Ziyang are commonly enriched in Se, As, Mo, Cd, Cr, Ni, Sb, Cu and Ba. In situ microanalysis indicates that Se (30–1880 μg/g) and As (160–2960 μg/g) concentrations within the pyrite grains are 1–2 orders of magnitude higher than those in the host rocks (Se: 0.56–73.1 μg/g, As: 2.56–195 μg/g) and that the Se contents are negatively correlated with pyrite mineral sizes. Grain-scale element mappings of fresh Se-enriched pyrites reveal two types of Se and As distribution patterns (type-I: high-Se 120–1870 μg/g and low-As <150–1580 μg/g cores, type-II: low-Se 60–680 μg/g and low-As <150–1310 μg/g cores) with alternating Se or As contents during the growth of zoned pyrite. The texture of pyrite element zoning reflects multi-stage hydrothermal pulses with changing trace element concentrations. Type-II pyrite formed later than type-I pyrite. Genetic analysis confirms that Se-enriched strata were strongly affected by hydrothermal submarine deposition and that Se in pyrite was mainly derived from hydrothermal fluids. Secondary hydrothermal erosion led to the formation of high-Se “fractures” (Se content 19.3 wt%). In summary, utilizing pyrite as an indicator for the Lower Cambrian Lujiaping Formation Se-bearing strata extends our understanding of selenium geochemical processes and highlights the mechanistic aspects of Se.

Safe utilization and zoning on natural selenium-rich land resources: a case study of the typical area in Enshi County, China.

Selenium (Se) is an essential trace element. However, Se in soil is often accompanied by heavy metals, such as cadmium (Cd), because of geological background. The safe utilization of such Se-rich land resources remains a challenge. A typical Se-rich area located in Enshi County, China, was systematically investigated with geochemical and epidemiological methods. The results show that Se in the topsoil is 0.84 ± 1.39μg/g, whereas that of Cd is 0.93 ± 1.63μg/g. And the concentration of Se and Cd in corn is 0.22 ± 0.96μg/g and 0.15 ± 0.32μg/g, respectively, which is mainly related to the high concentrations in soil. The benchmark dose limit of urinary Cd for β2-microglobulin in subjects (n = 160) was calculated as 3.27µg/g Cr. In view of crop-human dose effect and combining the relationship among the concentrations of crops and human biomarkers and the concentrations of crops and topsoil, this study established the models of land resource safety zoning. With that, the risk screening value of Cd in the soil could be obtained as 0.98μg/g in this typical area. The proportions of priority utilization, safe utilization, and strict management of agricultural land area were 58.85%, 22.90%, and 18.25%, respectively, in Enshi, China. These results could provide scientific support for local agricultural development and ecological sustainability.

The interaction of phosphate and selenite in alkaline soil and accumulation by alfalfa (Medicago sativa L.)

ABSTRACT Selenium (Se) is an essential nutrient for humans and animals, but is toxic at high concentrations in leaves. It is chemically similar to phosphorus (P), an essential plant macronutrient. The objective of this pot experiment was to investigate the effects of P- and Se-application rate on alfalfa growth and P and Se uptake in loessial soil, and reveal the changing processes of soil P and Se fractions. The results indicated that Se concentration in alfalfa was significantly influenced by the interaction of P- and Se-application rate. In the loessial soil, an optimal P- and Se-application rate is 5 mg kg−1 and 2 mg kg−1, respectively for plant growth and the maximum P and Se accumulation in alfalfa. Besides, concentrations of exchangeable Se and organic-matter-bound Se in soil decreased, as the P-application rate increased, whereas concentrations of soluble Se and iron oxide-bound Se increased. The addition of P fertilizer reduced soil pH, affecting the changing processes of soil P and Se fractions, thus promoting the activation of Fe-P and the transformation of exchangeable Se to iron oxide-bound Se. These findings will help in understanding of forage P and Se accumulation and provide the guide for cultivating Se-enriched forage.

Mapping the drivers of uncertainty in atmospheric selenium deposition with global sensitivity analysis

Abstract. An estimated 0.5–1 billion people globally have inadequate intakes of selenium (Se), due to a lack of bioavailable Se in agricultural soils. Deposition from the atmosphere, especially through precipitation, is an important source of Se to soils. However, very little is known about the atmospheric cycling of Se. It has therefore been difficult to predict how far Se travels in the atmosphere and where it deposits. To answer these questions, we have built the first global atmospheric Se model by implementing Se chemistry in an aerosol–chemistry–climate model, SOCOL-AER (modeling tools for studies of SOlar Climate Ozone Links – aerosol). In the model, we include information from the literature about the emissions, speciation, and chemical transformation of atmospheric Se. Natural processes and anthropogenic activities emit volatile Se compounds, which oxidize quickly and partition to the particulate phase. Our model tracks the transport and deposition of Se in seven gas-phase species and 41 aerosol tracers. However, there are large uncertainties associated with many of the model's input parameters. In order to identify which model uncertainties are the most important for understanding the atmospheric Se cycle, we conducted a global sensitivity analysis with 34 input parameters related to Se chemistry, Se emissions, and the interaction of Se with aerosols. In the first bottom-up estimate of its kind, we have calculated a median global atmospheric lifetime of 4.4 d (days), ranging from 2.9 to 6.4 d (2nd–98th percentile range) given the uncertainties of the input parameters. The uncertainty in the Se lifetime is mainly driven by the uncertainty in the carbonyl selenide (OCSe) oxidation rate and the lack of tropospheric aerosol species other than sulfate aerosols in SOCOL-AER. In contrast to uncertainties in Se lifetime, the uncertainty in deposition flux maps are governed by Se emission factors, with all four Se sources (volcanic, marine biosphere, terrestrial biosphere, and anthropogenic emissions) contributing equally to the uncertainty in deposition over agricultural areas. We evaluated the simulated Se wet deposition fluxes from SOCOL-AER with a compiled database of rainwater Se measurements, since wet deposition contributes around 80 % of total Se deposition. Despite difficulties in comparing a global, coarse-resolution model with local measurements from a range of time periods, past Se wet deposition measurements are within the range of the model's 2nd–98th percentiles at 79 % of background sites. This agreement validates the application of the SOCOL-AER model to identifying regions which are at risk of low atmospheric Se inputs. In order to constrain the uncertainty in Se deposition fluxes over agricultural soils, we should prioritize field campaigns measuring Se emissions, rather than laboratory measurements of Se rate constants.

Comparison of selenium accumulation in three Solanum species

In order to compare the difference of selenium (Se) accumulation in three Solanum species, the Se accumulation characteristics of Solanum nigrum L., Solanum alatum Moench and Solanum nigrum L. var. humile (Bernh.) C. Y. Wu et S. C. Huang were studied by pot experiment at a Se concentration of 10 mg/kg. The results showed that the biomass of all parts of Solanum species was as follows: S. nigrum > S. alatum > S. nigrum var. humile. Interestingly, contrary to the order of Solanum species biomass, the Se content of all parts of Solanum species was as follows: S. nigrum var. humile > S. alatum > S. nigrum. Furthermore, the amount of Se extracted by leaves and shoots was significantly higher than that of other Solanum species, and reached 38.73 and 51.40 μg/plant, respectively. Among the three Solanum species, S. nigrum var. humile has the strongest enrichment ability for soil Se and is an ideal Se-enriched vegetable.

Shifts in microbial communities and networks are correlated with the soil ionome in a kiwifruit orchard under different fertilization regimes

This study investigated the shifts in the community composition and co-occurrence networks of soil microbiota in relation to the soil ionome in a kiwifruit orchard under different fertilization regimes. A 9-year split-plot field experiment (2009–2018) was conducted in Meixian county, Shaanxi province, China. Two main plots were assigned to bio-organic fertilization (0 vs. 8000 kg ha−1 y−1), each containing two subplots assigned to chemical fertilization (0 vs. 300 kg N ha−1 y−1, 225 kg P ha−1 y−1, and 150 kg K ha−1 y−1). High-throughput sequencing and inductively coupled plasma-mass spectrometry were used to analyze soil microbial community composition and ion concentrations, respectively. Results showed that bio-organic fertilization increased soil Ni, Se, total C, total N, and pH levels, whereas soil Mg, Cu, Zn, and Sr concentrations were decreased. Mantel testing indicated that bacterial community composition was influenced more easily by the availability of soil ions (e.g., Zn, Ni, Co, Cu) than fungal community composition. Bio-organic fertilization also increased bacterial α-diversity indices that were strongly correlated with the availability of soil ions (e.g., Fe, Mn, and Ca). Network analysis revealed that bio-organic fertilization generated more links (especially positive links) between microbial taxa in the community. Fewer but highly interconnected modules were found in the network formed under bio-organic fertilization, for which fewer nodes and negative links occurred concurrently. After selecting putative keystone species, the network with bio-organic fertilization was characterized by more generalists than the network without bio-organic fertilization. In contrast to the network without bio-organic fertilization, none of the generalists in the network with bio-organic fertilization were correlated with soil total C and N contents; however, high correlations were found with soil ions (e.g., Fe, Mn, Co, and Al). These results demonstrate that a better-organized and more stable network of soil microbial communities can assemble in a kiwifruit orchard under bio-organic fertilization, as mediated by alterations to the soil ionome. This study highlights that the less-commonly researched soil ions (e.g., Ni, Mo, Se, Sr) may play a crucial role in the response of soil microbial communities to bio-organic fertilization in agricultural ecosystems.

Interactive effects of earthworm Eisenia fetida and bean plant Phaseolus vulgaris L on the fate of soil selenium

Selenium (Se) is an essential micronutrient for animals with a narrow margin between essentiality and toxicity. Se toxicity is largely related to inorganic forms of Se in soil, i.e., selenite and selenate that enter food chains through plant uptake, threatening higher trophic level organisms. This experiment investigated effects of earthworm activity on Se bioavailability in soil and the subsequent plant uptake, using earthworm Eisenia fetida and bean plant Phaseolus vulgaris L, both exposed to either selenite or selenate at 1 or 4 mg Se kg−1 for 16 weeks. Plants took up selenate (up to 221-fold) faster than selenite, with up to 84% of the Se rapidly transported to shoots. In the presence of earthworms, Se accumulation obviously increased for selenate-supplied plants, leading to an up to 4% increase in Se translocation factor for all treatments except for 1 mg kg−1 selenite treatment. Earthworms also concentrated Se faster in tissues (up to 274 mg kg−1 DW) at exposure to selenate. For Se toxicity, Se speciation analysis was conducted on the plants and earthworms using XAS. Compared to worm-free treatments, the percentage of organo-Se, i.e., SeMet and CysSeSeCys, increased in beans (up to 34%) in the presence of earthworms for selenate, while the elemental Se portion was significantly reduced or absent, opposite to the results for selenite. Surprisingly, elemental Se (up to 65%) dominated earthworms, regardless of the form of Se supplied. In conclusion, earthworms clearly enhanced Se uptake and translocation in plants, leading to elevated Se levels in shoots. To prevent resulting hazards to humans and other animals, caution should be taken while consuming the shoots, particularly beans, harvested from the Se contaminated soil where earthworm activity is high. Finally, the significant reduction in soil Se suggests phytoextraction of Se from the soil could be improved using earthworms as an aid to plants.

DOM derivations determine the distribution and bioavailability of DOM-Se in selenate applied soil and mechanisms

Straw amendment and plant root exudates modify the quality and quantities of soil dissolved organic matter (DOM) and then manipulate the fractions of soil selenium (Se) and its bioavailability. Two typical soils with distinct pH were selected to investigate the effect of different contributors on DOM-Se in soil. The mechanisms relying on the variation in DOM characteristics (quality, quantity and composition) were explored by UV–Vis, ATR-FTIR and 3D-EEM. Straw amendment significantly (p < 0.05) suppressed the selenate bioavailability. The reduction in wheat Se content was greater in krasnozems than in Lou soil, as more HA fraction appeared in krasnozems. The root exudates of wheat mainly elevated the low molecular hydrophilic compounds (Hy) in soil, which contributed to the SOL-Hy-Se fractions and thus grain Se in soils (p < 0.01). However, straw amendment promoted DOM transforming from small molecules (Hy and FA) to aromatic large molecules (HA), when accompanied with the reduction and retention of Se associated with these molecules. As a result, selenium bioavailability and toxicity reduced with DOM amendment and DOM-Se transformation.

Screening and evaluation of selenium-rich maize cultivars in Ziyang area

To study selenium (Se)-enriched characteristics of maize in Ziyang area and to select cultivars, six cultivars were planted on three different soils with high-Se, middle-Se and low-Se. The Se content of grain, stalk &amp; leaf and cob were tested separately, and the relationship between Se content in soil and the capability of Se-enrichment in different organs of six cultivars were analyzed. The result showed that the Se content of maize organs is positively correlated with the Se in soil. Meanwhile, on the soil with different Se content, the trends of Se-enriching capacity in different organs of maize cultivars were as follows: stalk &amp; leaf &gt; grain &gt; cob. Further comparison of the ratio of the Se content of various organs to the Se content of soil showed that, the maize planted on the middle-Se soil has the highest capability of Se-enrichment. Considering the biomass, the accumulation of Se in the grains of sweet maize Shaan K512 and waxy maize Shaan K818 were relatively higher. This study has implications for Se-rich maize and comprehensive utilization of Se in Ziyang.

Selenium Fractionation and Speciation in Paddy Soils and Accumulation in Rice Under Field Conditions in Jinhua Zhejinang Province, China

Soils, as well as paddy tissue samples, were collected in the Se-rich area of Jinhua County, Zhejiang Province, China. Sequential extraction procedure was used for selenium (Se) fractionation, including soluble Se, exchangeable Se, carbonate-bound Se, iron and manganese oxide-bound Se, humic acids-bound Se, organic matter-bound Se, and the residual Se fraction. The results showed that soluble Se, exchangeable Se, carbonate-bound Se, iron and manganese oxide-bound Se fractions accounted for less than 2% of the total Se, respectively. Organic matter-bound Se was the dominant fractions. The average concentrations (mg kg−1) of Se in the paddy tissues were 0.069 in seed, 0.263 in root, 0.09 in stalk, and 0.17 in leaf. The organic matter-bound Se had a significant indirect effect on Se accumulation in paddy tissues. In conclusion, organic matter-bound Se was an important fraction and source of plant Se in agricultural soil.

Selenium deficiency risk in central Kenya highlands: an assessment from the soil to the body.

Selenium (Se) deficiency is associated with increased risk of clinical disorders. Yet, it has not been considered as an important public health issue in Africa. The health burden of this 'hidden hunger' remains largely unknown. Using a case study of central Kenya highlands, a cross-sectional survey assesses Se status of agricultural soils, foods, hair, and actual average dietary Se intake of the local population and investigates the soil-food Se concentration and Se intake-individual Se status relationships. The survey examines eight locations characterized by different agricultural soil types and assesses average dietary Se intake among 159 children and 111 women based on 24-h dietary recall data. Soil Se concentration does not explain Se concentration in foods, which instead is associated with soil's pH, organic matter, and P and Fe content. Cereal grains, beans and potato/green banana form a large portion of the local diet while intake of animal-based foods is limited. This results in Se intake of 15 and 33µgp-1d-1 for children and women, respectively. On average, 87% of children and 97% of women have inadequate average daily dietary Se intake, and the hair Se concentration of 92% children and 94% women is below the reference values. Soil's characteristics contribute to variation in Se concentration in foods and consequently the dietary Se intake. A low diversified diet is a key contributing factor to inadequate dietary Se intake in the region. These findings call for the need to investigate potential intervention measure and the health burden of Se deficiency.

Agronomic biofortification of leafy vegetables grown in an Oxisol, Alfisol and Vertisol with isotopically labelled selenium (77Se)

Selenium biofortification of crops is a proven technology for improving dietary nutrition. This study used isotopically labelled selenate (>99% enriched 77Se) to assess uptake and Se availability to two green vegetables, Brassica napus L (B. napus) and Amaranthus retroflexus L (A. retroflexus) grown in three contrasting Malawi soils: a Vertisol (calcareous), Alfisol (moderately acidic) and Oxisol (acidic). Plants were grown under glasshouse conditions (4 replicates; 6 kg soil per pot) following application of 77Se-enriched selenate at rates equivalent to 0, 10 and 20 g ha−1. Leaves were harvested at fortnightly intervals and the plants were then allowed to re-grow, to simulate cultivation practice. Leaf samples were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) for selenium isotopes (77Se and 78Se). The isotopic data were processed to quantify the contribution to plant Se concentration from the fertilizer and the soil. Both concentration and uptake of the fertilizer 77Se declined sharply with sequential harvests due to progressive fixation of 77Se in the soil rather than exhaustion (by uptake) of the Se applied. Initially the bioavailability of fertilizer Se was three orders of magnitude greater than the soil Se but this declined to the same order of magnitude by the end of the trial. Application of 77Se had no effect on uptake of soil-derived Se. There were marked differences between the three soils studied. The relative bio-availability of the fertilizer Se followed the sequence (Vertisol > Alfisol > Oxisol) but the two crops showed the same trend in decline of fertilizer Se uptake. Thus, fixation of selenium in the soils studied was sufficiently rapid that Se biofortification of green vegetables subject to several harvests would require multiple applications during the growing season.

Identification and physiological comparison of plant species that show positive or negative co-occurrence with selenium hyperaccumulators.

In these studies we identified and compared the properties of plant species that showed positive or negative co-occurrence with selenium (Se) hyperaccumulators in their natural habitat. The main questions addressed were: which species are most abundant directly adjacent to hyperaccumulators, and which are absent? How do Se accumulation and tolerance compare in species found to positively or negatively co-occur with hyperaccumulators? Approaches included field surveys, X-ray microprobe analysis of field samples, and a lab Se tolerance and accumulation study. When 54 hyperaccumulators across two naturally seleniferous sites were surveyed for their five nearest neighboring species, and the relative abundance of these species around hyperaccumulators compared to that in the overall vegetation, some species were identified to positively or negatively co-occur with hyperaccumulators. Several positively co-occurring species showed high Se accumulation capability (up to 900 mg Se per kg dry weight), which may reflect Se tolerance. Leaf X-ray microprobe analysis found relatively more organic forms of Se in two positively co-occurring species than in a negatively co-occurring one. There were elevated soil Se levels around Se hyperaccumulators, and neighbors of Se hyperaccumulators had a higher tissue Se concentration as compared to when the same species grew elsewhere in the area. The elevated soil Se levels around Se hyperaccumulators - likely resulting from litter deposition- may significantly affect the local plant community, facilitating Se-tolerant plant community members but lowering the fitness of Se-sensitive members.

The origin of soil selenium in a typical agricultural area in Hamatong River Basin, Sanjiang Plain, China

The origin of soil selenium (Se) is relatively complex, and analysis of the origin of soil Se is of great significance in clarifying the cause of its richness and the impact of human activities on soil environmental quality, as well as assisting in the scientific planning of Se-rich land use, improving land use value, and promoting regional economic development. In this study, in order to identify and clarify the origin of soil Se and the causes of its richness in a typical agricultural area in the Hamatong River Basin of the Sanjiang Plain, we tested the Se concentrations in soil, atmospheric deposition, irrigation water, chemical fertilizer, rock, and rice crop samples from the study area. Geostatistical analysis indicated that the soil Se is mainly controlled by natural factors such as soil parent material. Elemental geochemical analysis indicated the soil Se is mainly derived from the granite occurring in the Wanda Mountains. Elemental mass balance analysis indicated that the atmospheric deposition is the most important source of soil Se input, with a contribution of 84.90%, followed by irrigation and fertilization. Deep percolation is the main pathway of soil Se output, with a contribution of 74.17%, followed by rice crop harvest and volatilization. In addition, the soil Se is derived from a natural source, its richness can be attributed to the effect of anthropogenic factors, such as fossil fuel combustion and fertilization, superimposed on the high natural background value of soil Se.