Se Availability Research Articles

Selenium availability in tea: Unraveling the role of microbiota assembly and functions

Tea (Camellia sinensis (L.) O. Kuntze) plants have a strong ability to accumulate selenium (Se). However, the question of how tea plants affect Se availability has received little attention. In this study, five tea cultivars, including Soubei (SB), Aolǜ (AL), Longjing43 (LJ), Zhaori (ZR) and Fenglǜ (FL), were chosen for the study. Quantitative Microbial Ecology Chip and high-throughput sequencing were used to explore the effects of five tea cultivars on soil functions, microbial community structures and Se availability. The results showed that the total soil Se content in the FL garden was lower compared to LJ and SB gardens, whereas available Se was highest in the FL garden. Based on the Bray-Curtis distances, tea cultivar was the main factor affecting bacterial and fungal community structures. The abundance of functional genes concerning carbon, nitrogen, phosphorus and sulfur cycling processes varied among tea gardens. The higher soil NH4+ and NO3− contents, and higher abundance of functional genes like nifH, amoA1 and narG, whereas lower total nitrogen in the FL garden than in the AL and LJ tea gardens demonstrated that the FL tea plants induced microbes to accelerate soil nitrogen cycling processes. Dominant microbes that positively related with functional genes like nifH, narG, and amoA1 were also positively related with the available Se content. In conclusion, tea cultivars could regulate soil functions through affecting microbial community structures and then affecting the soil Se availability. The soil nitrogen cycle processes are suggested to be closely related with Se transformation in tea gardens.

Genetic Determinants of Selenium Availability, Selenium-Response, and Risk of Polycystic Ovary Syndrome.

Selenium is a trace element and its deficiency has been associated with the risk of PCOS, a multifactorial syndrome that affects a large number of women worldwide. Several databases and literature were searched to find out genetic variants of the genes involved in selenium uptake, metabolism, and regulation which may be significantly associated with the risk of PCOS through Se-related pathways. Genes that require selenium for their biological actions to perform were also shortlisted. A total of eighteen significantly associated genes with forty-four variants were identified as candidate variants that could play a potential role in the modulation of PCOS risk among the study population. The genetic variant distribution data was available in-house and was obtained through a GWAS study of the North India population. In silico tools were applied to understand the functional impact of these variants. Three variants namely LDLR (rs2228671), TNF (rs1041981), and SAA2 (rs2468844) are strongly associated with PCOS risk and have a functional impact on encoded protein. Certain variants of Se uptake genes such as DIO1, GPX2, TXNRD1,DIO2and GPX3 are also significantly associated with the risk of PCOS development. "C" allele of the Se transporter gene SELENOP (rs9686343) significantly increases PCOS risk. Other potential genes require selenium for their biological actions and are involved in the inflammatory, antioxidant response, and energy homeostasis signaling pathways. Thus, genetic variants of the population may affect the Se availability in the body. Also, deficiency of Se effects may get modulated due to underlying genetic polymorphism of Se-associated genes. This information may be helpful in dosage adjustment of Se supplementation for a population in order to get maximum benefits.

Impact of selenium fertilisation of ‘Red Jonaprince’ apple trees on selenium nutrition and fruit quality and storability

Selenium (Se) malnutrition in humans is caused by low soil Se availability, leading to an insufficient content of this nutrient in food. In this study, we examined the effect of Se fertilisation on the absorption and distribution of Se in apple (Malus domestica Borkh.) trees, as well as fruit quality and storability. The experiment was carried out on mature ‘Red Jonaprince’ apple trees grown in medium-textured soil. Fertilisation of Se (as sodium selenate) was applied as: (i) summer sprays, 4 times in a season at a rate of 50 g Se ha−1, (ii) a fall spray, 2 weeks before harvest at a rate of 200 g Se ha−1, (iii) soil application at a rate of 500 g Se ha−1, and (iv) fertigation at a rate of 100 g Se ha−1. Trees that were not fertilised with Se served as controls. The results revealed that the fall Se spray caused leaf burns and defoliation, but it did not affect tree vigour and fruit yield. The highest leaf Se concentration was found on Se-sprayed trees in the fall. Most Se in fruit was recorded on Se-sprayed trees in the fall and on Se-fertigated trees; fruit Se amounts from these combinations covered about 30 % of the recommended daily intake. None of the Se treatments affected fruit appearance (mean weight, skin russeting, and colour), flesh firmness, and acidity at harvest. Apart from the fall Se spray, the other treatments decreased the soluble solid concentration (SSC), starch index values, ethylene evolution, and increased Streif index values in apples at harvest. After storage, Se-enriched apples were firmer, contained more organic acids, and produced less ethylene than the control fruit. We conclude that Se fertigation or a fall Se spray can be recommended in apple orchards, at least for late season and winter varieties, to biofortify fruit with Se and delay their ripening process.

Insight into the availability and desorption kinetics of Se and Cd in naturally-rich soils using diffusive gradients in thin-films technique

Cadmium (Cd) contamination of selenium (Se)-rich soils may jeopardize the nutritional benefits of Se-biofortified crops. This study employed diffusive gradients in thin-films (DGT) technique and DIFS (DGT-induced fluxes in soils) model to understand the interdependency and driving factors of Se and Cd distribution and desorption kinetics across 50 soils from south China with naturally elevated levels. DGT-labile Se was the highest (up to 2.66 μg L−1) in non-carbonate/shale-derived soils, while Cd was maximal (5.53 μg L−1) in carbonate-based soils, reflecting soil background concentrations and soil characteristics. Over one-third of the soils showed labile Se:Cd molar ratio below 0.7, suggesting Cd phytotoxicity risks. The DIFS-derived response times (Tc) and desorption rate constants (k−1) suggested that Se was resupplied to the soil solution faster than Cd in soils with higher pH and SOM level, but Se resupply was still restricted due to the rapid depletion of its labile pool. As the first study of Se and Cd release kinetics in soils, our results reveal dependence on soil parent materials, with low labile Se:Cd soils presenting greater Cd hazards. By elucidating Se and Cd lability and interactions in soils, our findings help to inform management strategies to balance reduced Cd risk with adequate Se availability.

Agronomic and Genetic Strategies to Enhance Selenium Accumulation in Crops and Their Influence on Quality.

Selenium (Se) is an essential trace element that plays a crucial role in maintaining the health of humans, animals, and certain plants. It is extensively present throughout the Earth's crust and is absorbed by crops in the form of selenates and selenite, eventually entering the food chain. Se biofortification is an agricultural process that employs agronomic and genetic strategies. Its goal is to enhance the mechanisms of crop uptake and the accumulation of exogenous Se, resulting in the production of crops enriched with Se. This process ultimately contributes to promoting human health. Agronomic strategies in Se biofortification aim to enhance the availability of exogenous Se in crops. Concurrently, genetic strategies focus on improving a crop's capacity to uptake, transport, and accumulate Se. Early research primarily concentrated on optimizing Se biofortification methods, improving Se fertilizer efficiency, and enhancing Se content in crops. In recent years, there has been a growing realization that Se can effectively enhance crop growth and increase crop yield, thereby contributing to alleviating food shortages. Additionally, Se has been found to promote the accumulation of macro-nutrients, antioxidants, and beneficial mineral elements in crops. The supplementation of Se biofortified foods is gradually emerging as an effective approach for promoting human dietary health and alleviating hidden hunger. Therefore, in this paper, we provide a comprehensive summary of the Se biofortification conducted over the past decade, mainly focusing on Se accumulation in crops and its impact on crop quality. We discuss various Se biofortification strategies, with an emphasis on the impact of Se fertilizer strategies on crop Se accumulation and their underlying mechanisms. Furthermore, we highlight Se's role in enhancing crop quality and offer perspective on Se biofortification in crop improvement, guiding future mechanistic explorations and applications of Se biofortification.

Replacing dietary sodium selenite with biogenic selenium nanoparticles improves the growth performance and gut health of early-weaned piglets

Selenium nanoparticles (SeNPs) are proposed as a safer and more effective selenium delivery system than sodium selenite (Na2SeO3). Here, we investigated the effects of replacing dietary Na2SeO3 with SeNPs synthesized by Lactobacillus casei ATCC 393 on the growth performance and gut health of early-weaned piglets. Seventy-two piglets (Duroc × Landrace × Large Yorkshire) weaned at 21 d of age were divided into the control group (basal diet containing 0.3 mg Se/kg from Na2SeO3) and SeNPs group (basal diet containing 0.3 mg Se/kg from SeNPs) during a 14-d feeding period. The results revealed that SeNPs supplementation increased the average daily gain (P = 0.022) and average daily feed intake (P = 0.033), reduced (P = 0.056) the diarrhea incidence, and improved (P = 0.013) the feed conversion ratio compared with Na2SeO3. Additionally, SeNPs increased jejunal microvilli height (P = 0.006) and alleviated the intestinal barrier dysfunction by upregulating (P < 0.05) the expression levels of mucin 2 and tight junction proteins, increasing (P < 0.05) Se availability, and maintaining mitochondrial structure and function, thereby improving antioxidant capacity and immunity. Furthermore, metabolomics showed that SeNPs can regulate lipid metabolism and participate in the synthesis, secretion and action of parathyroid hormone, proximal tubule bicarbonate reclamation and tricarboxylic acid cycle. Moreover, SeNPs increased (P < 0.05) the abundance of Holdemanella and the levels of acetate and propionate. Correlation analysis suggested that Holdemanella was closely associated with the regulatory effects of SeNPs on early-weaned piglets through participating in lipid metabolism. Overall, replacing dietary Na2SeO3 with biogenic SeNPs could be a potential nutritional intervention strategy to prevent early-weaning syndrome in piglets.

Irrigation leads to new Se-toxicity paddy fields in and around typical Se-toxicity area

Although the issue has been of much concern and has subsequently been controlled for years, the environmental risk of excess selenium (Se) in farmlands still has not been eliminated in Se-toxicity areas. Different types of farmland utilization can change Se behavior in soil. Thus, located field monitoring and surveys of various farmland soils in and around typical Se-toxicity areas spanning eight years were conducted in the tillage layer and deeper soils. The source of new Se contamination in farmlands was traced along the irrigation and natural waterway. This research indicated that 22 % of paddy fields increased to Se-toxicity in surface soil led by irrigation with high-Se river water. Selenate is the dominant Se species in rivers (90 %) originating from geological background areas with high Se. Both soil organic matter (SOM) and amorphous iron content played important roles in the fixation of input Se. Thus, available Se was increased by more than twofold in paddy fields. The release of residual Se and eventual bounding by organic matter is commonly observed, thus suggesting that stable soil Se availability seems sustainable for a long time. This study is the first report in China that shows how new soil Se-toxicity farmland is caused by high-Se water irrigation. This research warns that external attention should be paid to the selection of irrigation water in high-Se geological background areas to avoid new Se contamination.

Effects of microorganisms on soil selenium and its uptake by pak choi in selenium-enriched lateritic red soil

Data on selenium (Se) transformation, specifically the mineralization or activation of Se bound by microorganisms in natural Se-enriched soil, is limited. Therefore, this study investigates the effects of microorganisms on Se availability of Se-enriched lateritic red soil and Se uptake by pak choi. Following the incubation of Stenotrophomonas maltophilia S1 and arbuscular mycorrhizal (AM) fungi agent, the available Se content of soils increased from 35 to 66.69–117.04 μg/kg, corresponding to an increase of 90.50–234.40%. The Se bioconcentration and translocation factors in pak choi increased after adding the AM fungi agent and strain S1. The soil acid phosphatase activity, and pak choi root length, surface area, and diameter also increased. Moreover, the soil acid phosphatase activity showed a significant positive correlation with soil available Se and phosphorus content (p < 0.01). Overall, the AM fungi agent and strain S1 increased Se bioavailability by enhancing soil acid phosphatase and promoting root activity, ultimately increasing pak choi’s ability to absorb available Se.

Modelling Leverage of Different Soil Properties on Selenium Water-Solubility in Soils of Southeast Europe

Selenium (Se) is a nonmetal that is essential for humans and other animals, and is considered beneficial for plants. The bioavailability of Se strongly influences its content in the food chain. Soils are the main source of Se, and their Se content primarily influences its availability, along with other soil properties. A field survey was conducted on soils of Southeast Europe, specifically in Croatia (Osijek), Bosnia and Herzegovina (Sarajevo, Banja Luka, Mostar, and Prud), and Serbia (Novi Sad). Soil samples were taken from the arable soil layer (0–30 cm depth), and two types of Se availability were measured: Se extracted using pure HNO3 (SeTot) and Se readily extracted in water (SeH2O). Only soils from the Mostar area had Se concentrations above deficit levels (0.5 mg kg−1), with the highest values of cation exchange capacity (CEC), soil organic matter (SOM) measured as loss of ignition (LOI), total C, total N, ZnTot and CdTot. The connections between the chemical characteristics of the soil and SeH2O were investigated. Principal component analysis (PCA) explained 73.7% of the variance in the data set in the first three principal components (PCs). Using the provided data, we developed a partial least squares (PLS) regression model that predicted the amount of SeH2O in the soil, with an accuracy ranging from 77% to 90%, depending on the input data. The highest loadings in the model were observed for LOI, CEC, total C, total N, and SeTot. Our results indicate the need for biofortification in these key agricultural areas to supplement the essential dietary requirements of humans and livestock. To efficiently and economically implement biofortification measures, we recommend utilizing regression models to accurately predict the availability of Se.

Increasing selenium concentration in Finnish organic milk using participatory action approach

Selenium (Se) is an essential trace element for animals. In Finland, Se supplementary feeding and Se-enriched macronutrient fertilisers are used in conventional farming because the Se availability from soil is extremely low. The objective of this study was to improve Se concentration in organic milk by replacing sodium selenite (SS) in mineral-vitamin mixture with selenium yeast (SY) either completely or partly (50/50). The feeding experiment was conducted on 15 certified organic dairy farms in Eastern Finland during spring 2008. The cross-over design consisted of three treatments (SS treatment, SY treatment, and SS/SY treatment), three experimental periods (28 days each), and three farm groups (different order of treatments). Replacing SS with the same amount (0.2 mg Se kg-1 feed dry matter) of SY more than doubled Se concentration in organic milk and their mixture resulted in slightly lower Se concentrations. In conclusion, SY supplementary feeding is needed to improve Se concentration in organic milk and Se supply to cows, their calves, and consumers.

Se(IV)/Se(VI) adsorption mechanisms on natural and on Ca-modified zeolite for Mediterranean soils amended with the modified zeolite: prospects for agronomic applications

In the present study, the ability of a modified CaCl2 zeolite (Ca-Z) to both increase Se(IV) availability and restrict Se(VI) mobility in soils is examined. As it was resulted from batch experiments and verified by X-ray absorption fine structure (XAFS) and X-ray fluorescence (XRF) spectroscopies, higher amounts of both Se species adsorbed on Ca-Z compared to natural zeolite (Z-N) forming outer-sphere complexes while the oxidation state did not alter during agitation of samples. Thereafter, Ca-Z was incorporated in six Greek soils, divided into acid and alkaline, at a 20% (w/w) rate and a series of equilibrium batch experiments were performed with soils alone and soils-Ca-Z mixtures to investigate sorption and desorption processes and mechanisms. The acid soils, either treated with Ca-Z or not, adsorbed higher amounts of Se(IV) than alkaline ones, whereas soils alone did not adsorb Se(VI) but impressively high adsorption of Se(VI) occurred in the Ca-Z-treated soils. Desorption of Se(IV) was higher from the Ca-Z-treated soils and especially from the acid soils. Higher distribution coefficients of desorption than the distribution coefficients of sorption were observed, clearly pointing to a hysteresis mechanism. The experimental data fitted with Langmuir and Freundlich isotherms. In the presence of Ca-Z, the Langmuir qm values increased indicating higher Se(IV) retention while Langmuir bL values decreased suggesting lower bonding strength and higher Se(IV) mobility. Overall, treating the soils with Ca-Z increased Se(IV) adsorption and mobility whereas it provided sites for Se(VI) adsorption that did not exist in the studied soils.

Impacts of P inputs on availability of Fe, Mn, Zn and Se in soils

Impacts of P inputs on availability of Fe, Mn, Zn and Se in soils

Selenium species transforming along soil-plant continuum and their beneficial roles for horticultural crops.

Selenium (Se) acquirement from daily diet can help reduce the risk of many diseases. The edible parts of crop plants are the main source of dietary Se, while the Se content in crops is determined by Se bioavailability in soil. We summarize recent research on the biogeochemical cycle of Se driven by specific microorganisms and emphasize the oxidizing process in the Se cycle. Moreover, we discuss how plant root exudates and rhizosphere microorganisms affect soil Se availability. Finally, we cover beneficial microorganisms, including endophytes, that promote crop quality and improve crop tolerance to environmental stresses. Se availability to plants depends on the balance between adsorption and desorption, reduction, methylation and oxidation, which are determined by interactions among soil properties, microbial communities and plants. Reduction and methylation processes governed by bacteria or fungi lead to declined Se availability, while Se oxidation regulated by Se-oxidizing microorganisms increases Se availability to plants. Despite a much lower rate of Se oxidization compared to reduction and methylation, the potential roles of microbial communities in increasing Se bioavailability are probably largely underestimated. Enhancing Se oxidation and Se desorption are crucial for the promotion of Se bioavailability and uptake, particularly in Se-deficient soils. Beneficial roles of Se are reported in terms of improved crop growth and quality, and enhanced protection against fungal diseases and abiotic stress through improved photosynthetic traits, increased sugar and amino acid contents, and promoted defense systems. Understanding Se transformation along the plant-soil continuum is crucial for agricultural production and even for human health.

Sulfate availability and soil selenate adsorption alleviate selenium toxicity in rice plants

Selenium (Se) is a micronutrient for humans and other animals; however, it can cause severe toxicity at high concentrations. Selenium and sulfur (S) present a strict relationship in plants and soils, affecting their uptake and accumulations. Thus, addressing selenium-sulfur interaction is important to understand selenium nutrition and toxicity in plants, which could influence crop composition and production, and the toxicity risk to humans and animals. Here, we aimed to evaluate the impact of selenium exposure on rice plants grown under different sulfur supplies at tillering and grain ripening phases. We studied the effects of selenate and sulfate doses on rice plants grown hydroponically or in soils with varying clay contents. In the hydroponic experiment (short-term experiment), rice plants were grown until tillering stage under combinations of two concentrations of Se (0 and 20 µM Se) and S (0.1 and 0.5 mM S) in the nutrient solution. In the long-term, rice plants were grown until the ripening stage in two Oxisols with different clay contents (240 and 620 g kg−1 clay) under combinations of five doses of Se (0; 0.5; 1.0; 2.0 and 4.0 mg dm−3 Se) and three doses of S (0; 45; and 90 mg dm−3 S). We also performed sorption assays to evaluate the influence of soil clay content (240 and 620 g kg−1 clay) and S doses (0; 45; and 90 mg dm−3 S) on selenate adsorption and desorption at exposure to 4.0 mg kg−1 Se. Sulfate supply alleviated selenate toxicity in both short-term and long-term experiments. Selenate treatment up-regulated the expression of sulfate transporters (OsSULTR1;1 and OsSULTR1;2), leading to increased sulfur contents in rice seedlings, which enhanced the antioxidant system (catalase and ascorbate peroxidase activities and glutathione content) and alleviated selenate toxicity. However, this enhanced mechanism is absent in seedlings grown under a low sulfur supply, presenting severe Se toxicity. Moreover, soil clay contents strongly influenced selenate availability. The higher clay content promoted a high selenate adsorption capacity (67% of Se added), resulting in lower selenium contents in shoots and grains and the absence of toxicity symptoms. In contrast, a lower clay content presented a low selenate adsorption capacity (24% of Se added), increasing the Se availability, which can favor the biofortification of crops. However, high selenate doses caused growth and yield impairment in rice cultivated in the soil with lower selenate adsorption, which exhibited higher Se concentrations in shoots and grains, increasing the risk of Se toxicity for humans and animals.

Selenium Uptake by Lettuce Plants and Se Distribution in Soil Chemical Phases Affected by the Application Rate and the Presence of a Seaweed Extract-Based Biostimulant

To tackle selenium (Se) malnutrition, biofortification is among the proposed strategies. A biostimulant application in soils is thought to support a plant’s growth and productivity. Biofortification with Se(VI) may lead to a leaching hazard due to the high mobility of Se(VI) in the soil environment. In this study, the effect of the application of two Se(VI) rates—5 and 10 mg kg−1 soil—and a biostimulant on the Se uptake by lettuce plants and on the Se(VI) distribution in soil fractions following the plants harvest, was investigated. Phosphorus (P) and sulfur (S) concentrations in plants were also determined. A high Se(VI) rate suppressed plant growth, leading to a significant fresh weight decrease from 12.28 to 7.55 g and from 14.6 to 2.43 g for the control and high Se(VI) without and with biostimulants, respectively. Impaired plant growth was verified by the SPAD, NDVI and NDRE measurements. The significantly highest Se concentration in plants, 325 mg kg−1, was recorded for the high Se(VI) rate in the presence of the biostimulant. Compared to controls, the low Se(VI) rate significantly decreased P and increased the S concentrations in plants. The post-harvest soil fractionation revealed that, in the presence of the biostimulant, the Se(VI) soluble fraction increased from 0.992 to 1.3 mg kg−1 at a low Se(VI) rate, and decreased from 3.T85 to 3.13 mg kg−1 at a high Se(VI) rate. Nevertheless, at a low Se(VI) rate, 3.6 and 3.1 mg kg−1 of the added Se(VI) remained in the soil in less mobile forms, in the presence or absence of the biostimulant, respectively. This study indicated that the exogenous application of Se in soil exerted dual effects on lettuce growth and Se availability, depending on the level of selenate applied.

Selenium status in adults and children in Lusaka, Zambia

BackgroundSelenium (Se) is a trace element found in many foodstuffs and critical for antioxidant and immune functions. Widespread Se deficiency has been noted in populations of some sub-Saharan African countries including Ethiopia and Malawi. As a first step towards developing a fuller understanding of problems with the availability of Se in the diet in Lusaka province, Zambia, we measured plasma Se in adults and children in this geographic area. MethodsTotal plasma Se was measured using inductively coupled plasma optical emission spectrometry (ICP-OES) in several groups of adults recruited to various pre-existing studies, including those of high and low socioeconomic status (SES) and pregnant women, and children with a range of nutritional states (healthy, stunted or wasted). ResultsA total of 660 plasma samples from 391 adults and 269 children were included. Adults had a median plasma Se concentration of 0.27 μmol/l (IQR 0.14–0.43). Concentrations consistent with deficiency (<0.63 μmol/l) were found in 83% of adults. Low SES was associated with low plasma Se among adults, [OR 0.1; 95% CI 0.1–0.3, p < 0.0001]. Among the children, 24% had plasma Se less than 0.41 μmol/l. There was a statistically significant positive correlation between plasma Se and age among children, Spearman's rho 0.47, p < 0.0001. ConclusionsThese data suggest that Se deficiency is widespread in Lusaka province and could in part be related to socio-economic status. Supplementation or agronomic biofortification may therefore be needed.

Effects of different forms and application methods of selenium fertilizers on wheat selenium uptake and utilization and its residual availability

<p id="C3">A two-year positioning field experiment was conducted to determine the reasonable regulation measures of selenium (Se) fertilizer for improving wheat grain Se nutrition, and to explore the feasibilities of different Se application approaches in Se agronomic biofortification of wheat grown in the typical Se-deficient soils of Yongshou County, Shaanxi Province. To study the effects of different forms and application methods of Se fertilizers on wheat yield, Se concentration and its accumulation and utilization, with the goal of producing wheat grain with Se concentration of 100 μg kg ^-1, five Se application rates of 0, 15, 18, 700, and 45 g hm^-2 were calculated for the treatments of no Se application (control), soil- and foliar-sodium selenate, and soil- and foliar-sodium selenite in the first year, respectively. In the following wheat season, for further investigating the residual Se availability, no Se fertilizer was applied and each plot was divided into straw removal and straw return. These results showed that the wheat grain yield and straw biomass were not influenced by Se forms and application methods. For the first wheat season, grain Se concentration reached the expected target value with a range of 109-397 μg kg ^-1, and the flour Se concentration varied from 101 μg kg ^-1 to 356 μg kg ^-1 for all the Se application treatments. In the next year, both grain and white flour Se concentrations were 100 μg kg ^-1 higher than under the treatment of soil-sodium selenite, and there was no significant difference of straw removal and straw return. Grain Se biofortification index was 4.7, 16, 0.3, 8.0 (μg kg^-1) (g hm^-2)^-1 for soil- and foliar-sodium selenate, and soil- and foliar-sodium selenite, respectively. The Se use efficiency was the highest for foliar-sodium selenate (7.3%), whereas its cumulative use efficiency was only 0.3% in soil-sodium selenite treatment with the long-term residue effects. At wheat harvest, the highest soil available Se was observed for soil-sodium selenite, with 91 μg kg ^-1 and 107 μg kg ^-1 for the straw removal and straw return, respectively. In conclusion, both soil- and foliar-sodium selenate /selenite were beneficial for producing wheat grain with target Se concentration of 100 μg kg ^-1, and the sodium selenite requirement was the highest, and its residual availability should be taken into consideration for Se biofortification in wheat production in the Se-deficient area of Chinese Loess Plateau.

Selenium adsorption and desorption capacity and its influence on selenium uptake by green spinach

Selenium is important to human health and must be consumed in adequate amounts through a variety of food sources, particularly vegetables. In order to identify availability of soil Se to crops, Se adsorption-desorption process in soil must be understood. In this study, an adsorption-desorption study of inorganic Se in soils of various textural classes was performed with the following concentration of Se (0–2 mg L−1) applied as Se(VI) and Se(IV). A glasshouse experiment was then conducted in a factorial (2 × 5) completely randomized design, with two Se form—Se(IV) and Se(VI)—and Se at five rates (0–60 g ha−1 Se in solution form) to green spinach. First, soil texture appeared to be the main factor controlling Se adsorption in soils. Selenite was adsorbed more, however, Se(VI) was desorbed at higher rate compared to Se(IV). Contrary to other soil types, in peat, Se(IV) was desorbed at higher level compared to Se(VI), where more than 70% was retained. Higher retention of Se(IV) was found in clayey soil. Meanwhile, from glasshouse experiment, Se uptake was higher in plants when treated with Se(VI) than with Se(IV). However, higher dry matter and antioxidant activity of green spinach was observed when Se(IV) was applied. Selenium applied as Se(IV) had greater benefits to spinach yield and antioxidant activity than Se(VI) or conventionally grown spinach (0 g ha−1), even though plants treated with Se(VI) had greater Se uptake.

Geochemical characteristics and ecological effects of Se and Zn in topsoil in Western Fuling of Chongqing

A large area of soil in China is deficient in selenium (Se) and zinc (Zn)，meanwhile, Se and Zn are essential trace elements for human body, so it is of great significance to find Se and Zn rich soil to cultivate crops. Based on the data of Se and Zn in topsoil, crops and root soil obtained from 1:50000 land quality geochemical survey, this paper taking the western area of Fuling in Chongqing as the research area, studies the content and spatial distribution characteristics of Se and Zn in soil and crops, and analyzes the enrichment law of Se and Zn in agricultural crops. The results show that the average values of Se and Zn in the topsoil of the study area are 0.265mg/kg and 77.56mg/kg respectively. There are some differences in the contents of Se and Zn in different geological backgrounds, soil parent materials and soil types. The high value areas of Se and Zn are mainly distributed in the exposed areas of Triassic carbonate; in the study area, the average contents of Se and Zn in maize seeds are 0.029mg/kg and 20.752mg/kg respectively, and the enrichment rates are 96% and 82% respectively. The average contents of Se and Zn in rice seeds are 0.032mg/kg and 11.463mg/kg respectively, and the enrichment rates are 13.3% and 5% respectively. The bioaccumulation coefficients of Se and Zn in maize are higher than that in rice, and the availability of Se and Zn elements in maize root soil is higher.The results can provide geochemical basis for developing characteristic land resources, functional agriculture and promoting rural revitalization in Fuling District.

Arbuscular mycorrhizal fungi reverse selenium stress in Zea mays seedlings by improving plant and soil characteristics

Selenium (Se) is a beneficial trace element for certain animals including humans, while remaining controversial for plants. High Se concentration in soil is toxic to plants especially at seedling stage of the plants. Although, arbuscular mycorrhizal fungi (AMF) are important for plant stress resistance; but the mechanisms by which AMF alleviate Se stress in crop seedlings are unclear. Therefore, we investigated the potential strategies of AMF symbiosis to alleviate Se stress in maize (Zea mays) from plants and soil perspectives. Results showed that Se stress (Se application level > 5 mg kg−1) significantly inhibited leaf area, shoot dry weight, and root dry weight of maize (P < 0.05). In contrast, AM symbiosis significantly improved root morphology, increased nitrogen and phosphorus nutrition, promoted shoot growth, inhibited the transport of Se from soil/roots to shoots, and then diluted the concentration of Se in shoots (32.65–52.80%). In general, the response of maize growth to AMF was mainly observed in shoots rather than roots. In addition, AMF inoculation significantly increased the easily extractable glomalin-related soil protein and organic matter contents and decreased the availability of soil Se to the plant. Principal component analysis showed that AMF promoted growth and nutrition uptake of maize was the most dominant effect of Se stress alleviation, followed by the decrease of soil Se availability, limiting Se transport from soil/roots to shoots. Moreover, the expression of Se uptake-related ion transporter genes (ZmPht2, ZmNIP2;1, and ZmSultr1;3) in maize roots were down-regulated upon AM symbiosis which resultantly inhibited the uptake and transport of Se from soil to maize roots. Thus, AMF could impede Se stress in maize seedlings by improving plant and soil characteristics.