Effects of arbuscular mycorrhizal fungi on the reduction of arsenic accumulation in plants: a meta-analysis

Arsenic (As) accumulation in plants is a global concern. Although the application of arbuscular mycorrhizal fungi (AMF) has been suggested as a potential solution to decrease As concentration in plants, there is currently a gap in a comprehensive, quantitative assessment of the abiotic and biotic factors influencing As accumulation. A meta-analysis was performed to quantitatively investigate the findings of 76 publications on the impacts of AMF, plant properties, and soil on As accumulation in plants. Results showed a significant dose-dependent As reduction with higher mycorrhizal infection rates, leading to a 19.3% decrease in As concentration. AMF reduced As(V) by 19.4% but increased dimethylarsenic acid (DMA) by 50.8%. AMF significantly decreased grain As concentration by 34.1%. AMF also improved plant P concentration and dry biomass by 33.0% and 62.0%, respectively. The most significant reducing effects of As on AMF properties were seen in single inoculation and experiments with intermediate durations. Additionally, the benefits of AMF were significantly enhanced when soil texture, soil organic carbon (SOC), pH level, Olsen-P, and DTPA-As were sandy soil, 0.8%-1.5%, ≥7.5, ≥9.1 mg/kg, and 30-60 mg/kg, respectively. AMF increased easily extractable glomalin-related soil protein (EE-GRSP) and total glomalin-related soil protein (T-GRSP) by 23.0% and 28.0%, respectively. Overall, the investigated factors had significant implications in developing AMF-based methods for alleviating the negative effects of As stress on plants.

Comprehensive evaluation of factors influencing selenium fertilization biofortification

BACKGROUND

Dietary selenium (Se) deficiency, stemming from low Se concentrations in agricultural products, threatens human health. While Se-containing fertilizers can enhance the Se content in crops, the key factors governing Se biofortification with Se fertilization remain unclear.

RESULTS

This study constructed a global meta-analysis dataset based on field experiments comprising 364 entries on Se content in agricultural products and 271 entries on their yield. Random forest models and mixed effects meta-analyses revealed that plant types (i.e., cereals, vegetables, legumes, and forages) primarily influenced Se biofortification, with Se fertilization rates being the next significant factor. The random forest model, which included variables like plant types, Se fertilization rates, methods and types of Se application, initial soil conditions (including Se content, organic carbon content, and pH), soil types, mean annual precipitation, and temperature, explained 82.14% of the variation in Se content and 48.42% of the yield variation in agricultural products. For the same agricultural products, the increase in Se content decreased with higher rates of Se fertilization. The increase in Se content in their edible parts will be negligible for cereals, forages, legumes, and vegetable crops, when Se fertilization rates were 164, 103, 144, and 147 g Se ha-1 , respectively. Conversely, while low Se fertilization rates enhanced yields, high rates led to a yield reduction, particularly in cereals.

CONCLUSION

Our findings highlight the need for balanced and precise Se fertilization strategies to optimize Se biofortification benefits and minimize the risk of yield reduction. © 2024 Society of Chemical Industry.

Effects of Amount and Chemical Form of Selenium Amendments on Forage Selenium Concentrations and Species Profiles

Selenium (Se) agronomic biofortification of plants is effective for alleviating Se deficiencies in human and livestock populations. Less is known about how higher selenate amendment rates, or how foliar compared with granular selenate amendments affect forage Se concentrations. Therefore, we compared the effects of a higher sodium selenate foliar amendment rate (900 vs. 90 g Se ha-1), and two selenate amendment methods (liquid foliar sodium selenate vs. granular slow-release Selcote Ultra® at 0, 45, and 90 g Se ha-1) on Se concentrations and Se species in forages across Oregon. The 10 × amendment rate (900 g Se ha-1) resulted in 6.4 × higher forage Se concentrations in the first cut (49.19 vs. 7.61 mg Se kg-1 plant DM, respectively) compared with the 90 g ha-1 amendment rate, indicating that forages can tolerate higher selenate amendment rates. Most Se was incorporated as SeMet (75%) in the harvested portion of the forage (37 mg Se kg-1 forage DM of the first cut) and only a limited amount was stored in the selenate reserve pool in the leaves (~ 5 mg Se kg-1 forage DM). Higher application rates of selenate amendment increased forage Se concentrations in first and second cuts, but carry over in subsequent years was negligible. Application of foliar selenate vs. granular Selcote Ultra® amendments, between 0 and 90 g Se ha-1, both resulted in a linear, dose-dependent increase in forage Se concentration. Amendments differed in their Se incorporation pattern (Se%), in that, first cut forage Se concentrations were higher with foliar selenate amendment and second, third, and residual (following spring) cut forage Se concentrations were higher with granular Selcote Ultra® amendment. Given the linear relationship between forage Se concentrations and whole-blood Se concentrations in livestock consuming Se-biofortified forage, we conclude that targeted grazing or other forage feeding strategies will allow producers to adapt to either selenate-amendment form.

Impact of selenium biofortification on production characteristics of forages grown following standard management practices in Oregon

INTRODUCTION

Low selenium (Se) concentrations in soils and plants pose a health risk for ruminants consuming locally-grown forages. Previous studies have shown that Se concentrations in forages can be increased using soil-applied selenate amendments. However, the effects of foliar selenate amendments applied with traditional nitrogen-phosphorus-potassium-sulfur (NPKS) fertilizers on forage yields, and nutrient contents, and agronomic efficiencies are unknown.

METHODS

Using a split plot design, we determined the effects of springtime sodium selenate foliar amendment rates (0, 45, and 90 g Se ha^-1) and NPKS application (none, NPK for grasses/PK for alfalfa, and NPKS/PKS fertilization at amounts adapted to meet local forage and soil requirements) on forage growth and N, S, and Se concentrations, yields, and agronomic efficiencies. This 2-year study was conducted across Oregon on four representative forage fields: orchardgrass (Dactylis glomerata L.) in Terrebonne (central Oregon), grass-clover mixture in Roseburg (southwestern Oregon), and both grass mixture and alfalfa (Medicago sativa L.) fields in Union (eastern Oregon).

RESULTS

Grasses grew poorly and were low in N content without NPK fertilization. Fertilization with NPK/PK promoted forage growth, increased forage N concentrations, and had to be co-applied with S when plant available S was low. Without Se amendment, forage Se concentrations were low and further decreased with NPKS/PKS fertilization. Selenate amendment linearly increased forage Se concentration without adversely affecting forage yields, N and S concentrations, or N and S agronomic efficiencies.

DISCUSSION

Importantly, S fertilization did not interfere with Se uptake in Se amended plots. In conclusion, co-application of NPKS/PKS fertilizers and foliar sodium selenate in springtime is an effective strategy to increase forage total Se concentrations, while maintaining optimal growth and quality of Oregon forages.

Salsola soda as selenium biofortification crop under high saline and boron growing conditions

In California, there is a shortage of good quality water available for irrigated agriculture due to severe drought. Consequently, saline groundwaters and drainage waters containing natural-occurring selenium (Se) and boron (B) salts are being considered as alternative sources of water for irrigation on salt and B tolerant crops like the edible halophyte-agretti (Salsola soda L.). In this multi-year field study, we evaluated agretti grown as a Se-biofortification crop in typical saline/B-laden soils (10 dS m^-1 and 12 mg B/L) and irrigated with saline (3-8 dS m^-1) and low-saline water (<1 d/S m) containing B (3-6 mg B/L) and Se (0.02-0.25 mg Se/L) at different evaporation transpiration (Et _o ) rates (100, 75, and 50 %, respectively). During the four-year study, fresh biomass yields ranged from 1 to 3 kg/m² and were generally highest with irrigation at 100 % Et _o with either saline or low-saline water. Tissue Se concentrations ranged from 2 to 3.2 mg Se / kg DW and 0.4-0.5 mg Se/kg DW with saline and low-saline irrigation, respectively. Selenium speciation in plant tissue showed the following: selenomethionine (SeMet) > selenate (SeO₄) > methylselenocysteine (MeSeCy _s ), irrespective of any treatment (i.e., year of planting, saline or low saline irrigation, rate of water application, direct seeding or transplanted). Agretti did not exhibit any toxicity symptoms as indicated by changes in total phenolic concentrations. Total phenolics ranged from 180 to 257 GAE/L and showed no significant differences among all treatments, although they were generally higher at the lowest water treatment (50% Et _o ). In regard to toxic ion accumulation, agretti tolerated excessive sodium (Na) and boron (B) and tissue concentrations ranging from 5.5 to 8.8% Na and 60 to 235 mg B/kg DW, respectively. Results from this multi-year study have identified a unique Se-biofortification strategy for producing Se-enriched agretti using saline, B- and Se-laden soil and irrigating with saline and low-saline water, respectively. Successful production of this crop may promote Se- biofortification strategies in poor quality regions where natural- occurring Se is present in soils and in waters used for irrigation.

Soil and foliar selenium application: Impact on accumulation, speciation, and bioaccessibility of selenium in wheat (Triticum aestivum L.)

A comprehensive study in selenium (Se) biofortification of staple food is vital for the prevention of Se-deficiency-related diseases in human beings. Thus, the roles of exogenous Se species, application methods and rates, and wheat growth stages were investigated on Se accumulation in different parts of wheat plant, and on Se speciation and bioaccessibility in whole wheat and white all-purpose flours. Soil Se application at 2 mg kg^-1 increased grains yield by 6% compared to control (no Se), while no significant effects on yield were observed with foliar Se treatments. Foliar and soil Se application of either selenate or selenite significantly increased the Se content in different parts of wheat, while selenate had higher bioavailability than selenite in the soil. Regardless of Se application methods, the Se content of the first node was always higher than the first internode. Selenomethionine (SeMet; 87-96%) and selenocystine (SeCys₂; 4-13%) were the main Se species identified in grains of wheat. The percentage of SeMet increased by 6% in soil with applied selenite and selenate treatments at 0.5 mg kg^-1 and decreased by 12% compared with soil applied selenite and selenate at 2 mg kg^-1, respectively. In addition, flour processing resulted in losses of Se; the losses were 12-68% in white all-purpose flour compared with whole wheat flour. The Se bioaccessibility in whole wheat and white all-purpose flours for all Se treatments ranged from 6 to 38%. In summary, foliar application of 5 mg L^-1 Se(IV) produced wheat grains that when grounds into whole wheat flour, was the most efficient strategy in producing Se-biofortified wheat. This study provides an important reference for the future development of high-quality and efficient Se-enriched wheat and wheat flour processing.

Synergistic Effect of Melatonin and Selenium Improves Resistance to Postharvest Gray Mold Disease of Tomato Fruit

Melatonin (MT) is a ubiquitous hormone molecule that is commonly distributed in nature. MT not only plays an important role in animals and humans but also has extensive functions in plants. Selenium (Se) is an essential micronutrient for animals and humans, and is a beneficial element in higher plants at low concentrations. Postharvest diseases caused by fungal pathogens lead to huge economic losses worldwide. In this study, tomato fruits were treated with an optimal sodium selenite (20 mg/L) and melatonin (10 μmol/L) 2 h and were stored for 7 days at room temperature simulating shelf life, and the synergistic effects of Se and MT collectively called Se-Mel on gray mold decay in tomato fruits by Botrytis cinerea was investigated. MT did not have antifungal activity against B. cinerea in vitro, while Se significantly inhibited gray mold development caused by B. cinerea in tomatoes. However, the interaction of MT and Se showed significant inhibition of the spread and growth of the disease, showing the highest control effect of 74.05%. The combination of MT with Se treatment enhanced the disease resistance of fruits by improving the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as increasing the gene expression level of pathogenesis-related (PR) proteins. Altogether, our results indicate that the combination of MT and Se would induce the activation of antioxidant enzymes and increase the expression of PR proteins genes that might directly enhance the resistance in tomato fruit against postharvest pathogenic fungus B. cinerea.

Mechanisms underlying mercury detoxification in soil-plant systems after selenium application: a review

Feasible countermeasures to mitigate mercury (Hg) accumulation and its deleterious effects on crops are urgently needed worldwide. Selenium (Se) fertilizer application is a cost-effective strategy to reduce Hg concentrations, promote agro-environmental sustainability and food safety, and decrease the public health risk posed by Hg-contaminated soils and its accumulation in food crops. This holistic review focuses on the processes and detoxification mechanisms of Hg in whole soil-plant systems after Se application. The reduction of Hg bioavailability in soil, the formation of inert HgSe or/and HgSe-containing proteinaceous complexes in the rhizosphere and/or roots, and the reduction of plant root uptake and translocation of Hg in plant after Se application are systemically discussed. In addition, the positive responses in plant physiological and biochemical processes to Se application under Hg stress are presented to show the possible mechanisms for protecting the plant. However, application of high levels Se showed synergistic toxic effect with Hg and inhibited plant growth. The effectiveness of Se application methods, rates, and species on Hg detoxification is compared. This review provides a good approach for plant production in Hg-contaminated areas to meet food security demands and reduce the public health risk.

Insights into uptake, accumulation, and subcellular distribution of selenium among eight wheat (Triticum aestivum L.) cultivars supplied with selenite and selenate

Selenium (Se)-enriched wheat can be improved by altering Se sources and selecting wheat cultivars. Such improvement can affect subcellular distribution and speciation of Se in wheat. Thus, a pot experiment was conducted to investigate Se uptake and distribution when Se was applied as selenite or selenate at low and high rates (1 and 10 mg kg^-1, respectively). Moreover, Se's impact on the grain and biomass yield of eight wheat cultivars was also investigated. The subcellular distribution and speciation of Se were also explored to elucidate Se metabolism and micro-distribution pattern in wheat. Results showed that biomass and grain yield were decreased with the application of both selenite and selenate in almost all the cultivars, regardless of the Se rate. Application high Se rate resulted in a significant (p < 0.05) decrease in grain yield and biomass compared with low rate of Se. Compared with the low rate of selenite application, the grain and the biomass yield of ZM-9023 significantly (p < 0.05) increased by about 15% for low rate of selenate application. In addition, both selenite and selenate treatment increased the uptake of Se in each part of wheat, compared with the control. Selenium was mostly accumulated in the grain and root of wheat under selenite treatment, while more Se accumulation was found in leaves and straw for selenate application. Further investigation on the subcellular distribution of Se showed that the proportion of Se in soluble fraction was significantly (p < 0.05) higher in wheat leaves than that in organelle fraction and cell walls (46%-66%). Meanwhile, Se⁶⁺ was the main species found in soluble fraction, whereas SeMet and MeSeCys were the species predominantly stored in organelle fraction. In conclusion, wheat cultivar ZM-9023 is the most Se-rich potential cultivar, and the isolation of Se in the soluble fraction plays an important role in Se tolerance and accumulation.

Soil Selenium Concentration and Residents Daily Dietary Intake in a Selenosis Area: A Preliminary Study in Yutangba Village, Enshi City, China

In 1963, selenosis occurred in Yutangba Village, Enshi City, China. Subsequently, local residents migrated to a new area of Yutangba to avoid high selenium (Se) exposure. In this study, 19 soil samples, 43 food samples, 60 hair samples and 58 plasma samples from local residents were randomly collected in New Yutangba Village. The mean total Se concentrations in cultivated soil samples were 1753.6 ± 742.8 µg/kg (n = 14). The estimated daily Se intake in New Yutangba Village decreased to 63.2 ± 39.8 µg/day, slightly higher than the recommended dietary Se intake for adults in China (60 µg/day). The mean Se concentrations in hair and plasma samples were 549.7 ± 165.2 µg/kg (n = 60) and 98.4 ± 32.1 µg/L (n = 58), respectively. The result indicated that appropriate activities, such as relocation, consuming a mixture of local foods and market foods containing low Se concentration, could effectively reduce the risk of high Se exposure.

Understanding boosting selenium accumulation in Wheat (Triticum aestivum L.) following foliar selenium application at different stages, forms, and doses

There are a lack of systematic studies comparing the effects of foliar-applied selenium (Se) with different Se sources at different growth stages in wheat. Herein, we biofortified wheat via the foliar application of selenite and selenate at different rates and different stages under field conditions. Results showed that foliar-applied selenate and selenite had no significant effect either on wheat biomass or grain yield (p < 0.05). Selenium distribution in different parts of wheat plant ranked decrease as leaf > root > grain > glume > stem with selenite treatment, and it appeared in the decline order as leaf > grain > glume > stem > root with selenate treatment. These results suggested that biofortification with selenate caused, relatively to selenite, a higher accumulation of Se in grains. Foliar application of Se of either selenate or selenite at pre-filling stage was superior in improving the Se concentration of wheat grains than application at pre-flowering stage. Meanwhile, organic Se comprised about 72-93% of total Se in wheat grains, which was reduced by 5.8% at high Se rate (100 g ha^-1), irrespective of the forms of Se or stages applied. The organic Se proportion in wheat grains was 9% higher with the selenate treatment than with the selenite treatment. Selenomethionine (SeMet) was the main organic species (67-86%) in wheat grains, followed by selenocysteine (SeCys₂). In summary, our results indicate that Se biofortification of wheat is most effective with 20 g ha^-1 selenate foliar-applied at pre-filling stage.

Accumulation and speciation of selenium in biofortified vegetables grown under high boron and saline field conditions

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Vegetables tolerated high B and saline soils.

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Vegetables accumulated naturally occurring Se and other essential nutrients.

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Monomethylated selenoamino acids were the primary organic forms.

Selenium (Se) biofortification, as an agronomic-based strategy, is utilized to produce Se-enriched food products for increasing Se intake in inhabitants in Se-deficient regions. This strategy can be accomplished by soil and foliar application of Se or by growing crops in soils naturally high in Se. In this study, different cruciferous vegetables were field-grown in high boron (B) and saline soils of central California containing naturally high levels of Se. We investigated whether Se biofortification occurs in salt- and B-tolerant vegetables grown in poor-quality soil. The uptake of Se and other elements occurred in all vegetables. In plant tissues, Se speciation analyses showed greatest percentages of Se-containing compounds were contained in organic Se forms (monomethylated) and as selenate in the inorganic Se forms. Selenium-enriched vegetables produced from saline soils high in B and Se can be a natural source of Se-biofortified food that can be consumed as bioactive food products.

Assessment of speciation and in vitro bioaccessibility of selenium in Se-enriched Pleurotus ostreatus and potential health risks

Due to the two-dimensional effect of selenium (Se) to health, which form of Se is most effective for increasing the bioaccessible Se content in P. ostreatus and whether these products have potential health risks are worth considering. Three Se supplements were applied at different application rates into substrates for cultivating P. ostreatus. The total content and speciation of Se in P. ostreatus fruit bodies were analyzed, and the bioaccessibility of Se was determined via an in vitro physiologically based extraction test (PBET). Results showed that P. ostreatus had the highest utilization efficiency with selenite, followed by Se yeast and selenate. Organic Se (46%-90%) was the major Se speciation in P. ostreatus regardless applied Se species. Although the Se bioaccessibility of the gastrointestinal digestion of P. ostreatus was high (70%-92%), the estimated daily intake and target hazard quotient values are all within the safe ranges. Se-enriched P. ostreatus can be safely used as a dietary source of Se for increasing Se intake.

Fruit nutritional quality under deficit irrigation: the case of table grapes in California

BACKGROUND

Sustainable agricultural practices are needed to face current threats to agricultural production in areas where water scarcity, recurrent droughts, and decreased soil quality are endangering productivity and food security. Deficit irrigation (DI) practices consist of reducing irrigation applied at levels below full crop evapotranspiration losses throughout the growing season or at specific phenological stages of the specific crop. The goal of our study was to evaluate the physiological response of table grapes subjected to DI relative to fruit quality. DI treatments were developed as a percentage of the grower practice (evapotranspiration losses are fully replenished by irrigation) on commercial fields of table grapes in central California. DI practices began in 2011 and were continued throughout 2015. Grape berries were analyzed for mineral elements, berry weight, diameter and firmness, carbon and nitrogen content, pH, soluble solids, and total phenolic compounds.

RESULTS

In this study, DI practices in all treatments did not significantly increase or decrease nutraceutical compounds in grape berry and measured physiological responses to DI were mixed, with significant variation between years.

CONCLUSIONS

This study showed that DI practices could be safely used in dry areas for at least four years without affecting the nutritional quality of grape berry in 'Crimson seedless' and 'Sugraone'. © 2018 Society of Chemical Industry.

Spatial variations in soil selenium and residential dietary selenium intake in a selenium-rich county, Shitai, Anhui, China

Shitai, a selenium (Se)-rich county in Anhui, China, has been reported for its resident longevity in the last 20 years. A recent survey by the Anhui Bureau of Geological Survey showed that soil Se contents in the Shitai area ranged from 0.05 to 51.20 mg/kg, with an average of 0.56 mg/kg. To explore the potential relationship between longevity and natural-occurring Se contents in Shitai county, Se concentrations were determined in Shitai's food chain (including soils and foods) and the daily Se intakes and hair Se contents were calculated for the residents. In the present study, 33 soil samples, 66 food samples and 82 hair samples were randomly collected from field sites, local food markets and male and female residents in downtown Shitai and in four nearby villages (Dashan, Xianyu, Yongfu and Yuantou). The total Se contents in all samples and the levels of water soluble, exchangeable, acid soluble, organic bound and residual Se in soil samples were determined with hydride generation - atomic fluorescence spectrometry. The total Se contents in soils ranged from 227 to 2603 μg/kg, with the averages of 1607 ± 242 μg/kg in Dashan, 1149 ± 118 μg/kg in Xianyu, 521 ± 157 μg/kg in Yongfu, and 363 ± 140 μg/kg in Yuantou. The soil bioavailable Se content (soluble and exchangeable Se) in Dashan was highest (14.98%), followed by Xianyu (13.69%), Yongfu (13.18%) and Yuantou (9.38%). For food samples, the highest Se concentration of grains was 468.5 μg/kg in Dashan, while lowest was observed in downtown (41.7 μg/kg). The estimated daily Se intake of residents in Dashan reached 298.4 μg/d/adult, which is about 5 times higher than the recommend nutrient intake in China (60 μg/d/adult), and 6-10 times higher than the levels observed in Xianyu (47.6 μg/d/adult), Yuantou (46.1 μg/d/adult), Yongfu (40.0 μg/d/adult), and downtown (30.0 μg/d/adult). Although hair Se contents in Dashan (male: 709.2 μg/kg; female: 589.2 μg/kg) were significantly higher than those at the other study sites, no significant relationships between daily Se intakes and hair Se contents were observed. The present study demonstrated that Se levels in soils, foods, resident dietary intake and human hairs in Shitai County varied significantly; therefore, the region could be a unique field site to study the direct relationship between Se and human health.

Indications of Selenium Protection against Cadmium and Lead Toxicity in Oilseed Rape (Brassica napus L.)

The present study investigated the beneficial role of selenium (Se) in protecting oilseed rape (Brassica napus L.) plants from cadmium (Cd+2) and lead (Pb+2) toxicity. Exogenous Se markedly reduced Cd and Pb concentration in both roots and shoots. Supplementation of the medium with Se (5, 10, and 15 mg kg-1) alleviated the negative effect of Cd and Pb on growth and led to a decrease in oxidative damages caused by Cd and Pb. Furthermore, Se-enhanced superoxide free radicals ([Formula: see text]), hydrogen peroxide (H2O2), and lipid peroxidation, as indicated by malondialdehyde accumulation, but decreased superoxide dismutase and glutathione peroxidase activities. Meanwhile, the presence of Cd and Pb in the medium affected Se speciation in shoots. The results suggest that Se could alleviate Cd and Pb toxicity by preventing oxidative stress in oilseed rape plant.

Accumulation of Cr, Cd, Pb, Cu, and Zn by plants in tanning sludge storage sites: opportunities for contamination bioindication and phytoremediation

Tanning sludge enriched with high concentrations of Cr and other metals has adverse effects on the environment. Plants growing in the metalliferous soils may have the ability to cope with high metal concentrations. This study focuses on potentials of using native plants for bioindication and/or phytoremediation of Cr-contaminated sites. In the study, we characterized plants and soils from six tanning sludge storage sites. Soil in these sites exhibited toxic levels of Cr (averaged 16,492 mg kg^-1) and other metals (e.g., 48.3 mg Cu kg^-1, 2370 mg Zn kg^-1, 44.9 mg Pb kg^-1, and 0.59 mg Cd kg^-1). Different metal tolerance and accumulation patterns were observed among the sampled plant species. Phragmites australis, Zephyranthes candida, Cynodon dactylon, and Alternanthera philoxeroides accumulated moderate-high concentrations of Cr and other metals, which could make them good bioindicators of heavy metal pollution. High Cr and other metal concentrations (e.g., Cd and Pb) were found in Chenopodium rubrum (372 mg Cr kg^-1), Aster subulatus (310 mg Cr kg^-1), and Brassica chinensis (300 mg Cr kg^-1), being considered as metal accumulators. In addition, Nerium indicum and Z. candida were able to tolerate high concentrations of Cr and other metals, and they may be used as preferable pioneer species to grow or use for restoration in Cr-contaminated sites. This study can be useful for establishing guidelines to select the most suitable plant species to revegetate and remediate metals in tanning sludge-contaminated fields.

Continued Selenium Biofortification of Carrots and Broccoli Grown in Soils Once Amended with Se-enriched S. pinnata

Selenium (Se) biofortification has been practiced in Se-deficient regions throughout the world primarily by adding inorganic sources of Se to the soil. Considering the use of adding organic sources of Se could be useful as an alternative Se amendment for the production of Se-biofortified food crops. In this multi-year micro-plot study, we investigate growing carrots and broccoli in soils that had been previously amended with Se-enriched Stanleya pinnata Pursh (Britton) three and 4 years prior to planting one and two, respectively. Results showed that total and extractable Se concentrations in soils (0-30 cm) were 1.65 mg kg(-1) and 88 μg L(-1), and 0.92 mg kg(-1) and 48.6 μg L(-1) at the beginning of the growing season for planting one and two, respectively. After each respective growing season, total Se concentrations in the broccoli florets and carrots ranged from 6.99 to 7.83 mg kg(-1) and 3.15 to 6.25 mg kg(-1) in planting one and two, respectively. In broccoli and carrot plant tissues, SeMet (selenomethionine) was the predominant selenoamino acid identified in Se aqueous extracts. In postharvest soils from planting one, phospholipid fatty acid (PLFA) analyses showed that amending the soil with S. pinnata exerted no effect on the microbial biomass, AMF (arbuscular mycorrhizal fungi), actinomycetes and Gram-positive and bacterial PLFA at both 0-5 and 0-30 cm, respectively, 3 years later. Successfully producing Se-enriched broccoli and carrots 3 and 4 years later after amending soil with Se-enriched S. pinnata clearly demonstrates its potential source as an organic Se enriched fertilizer for Se-deficient regions.

Effect of Selenium on Control of Postharvest Gray Mold of Tomato Fruit and the Possible Mechanisms Involved

Selenium (Se) has important benefits for crop growth and stress tolerance at low concentrations. However, there is very little information on antimicrobial effect of Se against the economically important fungus Botrytis cinerea. In the present study, using sodium selenite as Se source, we investigated the effect of Se salts on spore germination and mycelial growth of the fungal pathogen in vitro and gray mold control in harvested tomato fruit. Se treatment at 24 mg/L significantly inhibited spore germination of the fungal pathogen and effectively controlled gray mold in harvested tomato fruit. Se treatment at 24 mg/L seems to induce the generation of intracellular reactive oxygen species in the fungal spores. The membrane integrity damage was observed with fluorescence microscopy following staining with propidium iodide after treatment of the spores with Se. These results suggest that Se has the potential for controlling gray mold rot of tomato fruits and might be useful in integrated control against gray mold disease of postharvest fruits and vegetables caused by B. cinerea. The mechanisms by which Se decreased gray mold decay of tomato fruit may be directly related to the severe damage to the conidia plasma membrane and loss of cytoplasmic materials from the hyphae.

Selenium cycling across soil-plant-atmosphere interfaces: a critical review

Selenium (Se) is an essential element for humans and animals, which occurs ubiquitously in the environment. It is present in trace amounts in both organic and inorganic forms in marine and freshwater systems, soils, biomass and in the atmosphere. Low Se levels in certain terrestrial environments have resulted in Se deficiency in humans, while elevated Se levels in waters and soils can be toxic and result in the death of aquatic wildlife and other animals. Human dietary Se intake is largely governed by Se concentrations in plants, which are controlled by root uptake of Se as a function of soil Se concentrations, speciation and bioavailability. In addition, plants and microorganisms can biomethylate Se, which can result in a loss of Se to the atmosphere. The mobilization of Se across soil-plant-atmosphere interfaces is thus of crucial importance for human Se status. This review gives an overview of current knowledge on Se cycling with a specific focus on soil-plant-atmosphere interfaces. Sources, speciation and mobility of Se in soils and plants will be discussed as well as Se hyperaccumulation by plants, biofortification and biomethylation. Future research on Se cycling in the environment is essential to minimize the adverse health effects associated with unsafe environmental Se levels.

Biofortification and phytoremediation of selenium in China

Selenium (Se) is an essential trace element for humans and animals but at high concentrations, Se becomes toxic to organisms due to Se replacing sulfur in proteins. Selenium biofortification is an agricultural process that increases the accumulation of Se in crops, through plant breeding, genetic engineering, or use of Se fertilizers. Selenium phytoremediation is a green biotechnology to clean up Se-contaminated environments, primarily through phytoextraction and phytovolatilization. By integrating Se phytoremediation and biofortification technologies, Se-enriched plant materials harvested from Se phytoremediation can be used as Se-enriched green manures or other supplementary sources of Se for producing Se-biofortified agricultural products. Earlier studies primarily aimed at enhancing efficacy of phytoremediation and biofortification of Se based on natural variation in progenitor or identification of unique plant species. In this review, we discuss promising approaches to improve biofortification and phytoremediation of Se using knowledge acquired from model crops. We also explored the feasibility of applying biotechnologies such as inoculation of microbial strains for improving the efficiency of biofortification and phytoremediation of Se. The key research and practical challenges that remain in improving biofortification and phytoremediation of Se have been highlighted, and the future development and uses of Se-biofortified agricultural products in China has also been discussed.

Selenium biofortification of broccoli and carrots grown in soil amended with Se-enriched hyperaccumulator Stanleya pinnata

Amending soils with Se-hyperaccumulator plant derived sources of selenium (Se) may be useful for increasing the Se content in food crops in Se-deficient regions of the world. In this study we evaluated total Se and the different chemical species of Se in broccoli and carrots grown in soils amended with ground shoots of the Se-hyperaccumulator Stanleyapinnata. With increasing application rates of S. pinnata, total plant Se concentrations increased to nutritionally ideal levels inside edible parts. Selenium compounds in aqueous extracts were analyzed by SAX-HPLC-ICPMS and identified as a variety of mainly organic-Se forms. Together with bulk Se K-edge X-ray absorption near-edge structure (XANES) analysis performed on broccoli florets, carrot roots and shoots, dried ground S. pinnata, and the amended soil at post-plant, we demonstrate that Se-enriched S. pinnata is valuable as a soil amendment for enriching broccoli and carrots with healthful forms of organic-Se.

Enhancement of nitrogen and phosphorus removal from eutrophic water by economic plant annual ryegrass (Lolium multiflorum) with ion implantation

Severe eutrophication of surface water has been a major problem of increasing environmental concern worldwide. In the present study, economic plant annual ryegrass (Lolium multiflorum) was grown in floating mats as an economic plant-based treatment system to evaluate its potential after ion implantation for removing nutrients in simulated eutrophic water. The specific weight growth rate of L. multiflorum with ion implantation was significantly greater than that of the control, and the peroxidase, nitrate reductase, and acid phosphatase activities of the irradiated L. multiflorum were found to be greater than those plants without ion implantation. Higher total nitrogen (TN) and total phosphorus (TP) removal efficiencies were obtained for the L. multiflorum irradiated with 25 keV 5.2 × 10(16) N(+) ions/cm(2) and 30 keV 4.16 × 10(16) N(+) ions/cm(2), respectively (p < 0.05). Furthermore, the nitrogen and phosphorus contents in the plant biomass with ion implantation were also greater than those in the control and were positively correlated with TN and TP supplied. L. multiflorum itself was directly responsible for 39-49 and 47-58 % of the overall N and P removal in the experiment, respectively. The research results suggested that ion implantation could become a promising approach for increasing phytoremediation efficiency of nutrients from eutrophic water by L. multiflorum.

Fate and movement of selenium from drainage sediments disposed onto soil with and without vegetation

Disposal options for salty and selenium-laden agricultural drainage sediments are needed to protect the agricultural ecosystem in Central California. Thus, a 7-year pilot-scale field study evaluated the effects of disposing Se-laden drainage sediment onto soil that was planted with either salado grass (Sporobolus airoides 'salado') or cordgrass (Spartina patens 'Flageo'), or on soil left bare with and without irrigation. Significant decreases in salinity and water-extractable and total soil Se concentrations were observed in all treatments to a depth 30 cm, while water extractable Se and salinity increased most significantly between 30 and 60 cm. Total yields increased over time for both species, while plant Se concentrations were ≈10 and 12 mg kg(-1) DM for salado and cordgrass, respectively. The results show that Se and soluble salts disposed of as Se-laden drainage sediment onto light textured soils will significantly migrate to lower depths with or without vegetation.

Selenium biotransformations in an engineered aquatic ecosystem for bioremediation of agricultural wastewater via brine shrimp production

An engineered aquatic ecosystem was specifically designed to bioremediate selenium (Se), occurring as oxidized inorganic selenate from hypersalinized agricultural drainage water while producing brine shrimp enriched in organic Se and omega-3 and omega-6 fatty acids for use in value added nutraceutical food supplements. Selenate was successfully bioremediated by microalgal metabolism into organic Se (seleno-amino acids) and partially removed via gaseous volatile Se formation. Furthermore, filter-feeding brine shrimp that accumulated this organic Se were removed by net harvest. Thriving in this engineered pond system, brine shrimp ( Artemia franciscana Kellogg) and brine fly (Ephydridae sp.) have major ecological relevance as important food sources for large populations of waterfowl, breeding, and migratory shore birds. This aquatic ecosystem was an ideal model for study because it mimics trophic interactions in a Se polluted wetland. Inorganic selenate in drainage water was metabolized differently in microalgae, bacteria, and diatoms where it was accumulated and reduced into various inorganic forms (selenite, selenide, or elemental Se) or partially incorporated into organic Se mainly as selenomethionine. Brine shrimp and brine fly larva then bioaccumulated Se from ingesting aquatic microorganisms and further metabolized Se predominately into organic Se forms. Importantly, adult brine flies, which hatched from aquatic larva, bioaccumulated the highest Se concentrations of all organisms tested.

Daily dietary selenium intake in a high selenium area of Enshi, China

Enshi is a high selenium (Se) region in Hubei, China, where human selenosis was observed between 1958 and 1963. This study investigated the daily dietary Se intake of residents in Shadi, a town located 72 km northeast of Enshi City, to assess the risk of human selenosis in the high Se area. Foods consumed typically by the local residents and their hair samples were analyzed for total Se concentration. Concentrations of Se in different diet categories were as follows: cereals: 0.96 ± 0.90 mg kg(-1) DW in rice and 0.43 ± 0.55 mg kg(-1) DW in corn; tuber: 0.28 ± 0.56 mg kg(-1) in potato and 0.36 ± 0.12 mg kg(-1) in sweet potato; vegetables: ranging from 0.23 ± 1.00 mg kg(-1) in carrot to 1.57 ± 1.06 mg kg(-1) in kidney bean; animal proteins: 1.99 ± 1.11 mg kg(-1) in chicken and egg. Based on the food Se concentrations and the daily per-capita consumption, the estimated daily Se intake in Shadi was 550 ± 307 µg per capita. Moreover, the Se concentrations in the hairs of local adult residents were 3.13 ± 1.91 mg kg(-1) (n = 122) and 2.21 ± 1.14 mg kg(-1) (n = 122) for females and males, respectively, suggesting that females might be exposed to higher levels of Se from daily cooking. Although there was no human selenosis occurrence in recent years, the high level of the daily Se intake suggested that the potential risk of selenosis for local residents, especially females, might be a matter of concern.

Selection of salt and boron tolerant selenium hyperaccumulator Stanleya pinnata genotypes and characterization of Se phytoremediation from agricultural drainage sediments

Genetic variation in salt (Na(2)SO(4), NaCl) and boron (B) tolerance among four ecotypes of the selenium (Se) hyperaccumulator Stanleya pinnata (Pursh) Britton was utilized to select tolerant genotypes capable of phytoremediating Se from salt, B, and Se-laden agricultural drainage sediment. The few individual salt/B tolerant genotypes were successfully selected from among a large population of highly salt/B sensitive seedlings. The distribution, hyperaccumulation, and volatilization of Se were then examined in selected plants capable of tolerating the high salt/B laden drainage sediment. Salt/B tolerant genotypes from each of the four ecotypes had mean Se concentrations ranging from 2510 ± 410 to 1740 ± 620 in leaves and 3180 ± 460 to 2500 ± 1060 in seeds (μg Se g(-1) DW ± SD), while average daily Se volatilization rates ranged from 722 ± 375 to 1182 ± 575 (μg Se m(-2) d(-1) ± SD). After two growing seasons (∼18 months), we estimated that hyperaccumulation and volatilization of Se by tolerant S. pinnata genotypes and their associated microbes can remove approximately 30% of the total soil Se in 0-30 cm sediment. The salt/B tolerant S. pinnata genotypes selected and characterized herein represent promising new tools for the successful phytoremediation of Se from salt/B and Se-laden agricultural drainage sediments.

Selenium accumulation in flowers and its effects on pollination

• Selenium (Se) hyperaccumulation has a profound effect on plant-arthropod interactions. Here, we investigated floral Se distribution and speciation in flowers and the effects of floral Se on pollen quality and plant-pollinator interactions. • Floral Se distribution and speciation were compared in Stanleya pinnata, an Se hyperaccumulator, and Brassica juncea, a comparable nonhyperaccumulator. Pollen germination was measured from plants grown with varying concentrations of Se and floral visitation was compared between plants with high and low Se. • Stanleya pinnata preferentially allocated Se to flowers, as nontoxic methyl-selenocysteine (MeSeCys). Brassica juncea had higher Se concentrations in leaves than flowers, and a lower fraction of MeSeCys. For B. juncea, high floral Se concentration impaired pollen germination; in S. pinnata Se had no effect on pollen germination. Floral visitors collected from Se-rich S. pinnata contained up to 270 μg g(-1), concentrations toxic to many herbivores. Indeed, floral visitors showed no visitation preference between high- and low-Se plants. Honey from seleniferous areas contained 0.4-1 μg Se g(-1), concentrations that could provide human health benefits. • This study is the first to shed light on the possible evolutionary cost, through decreased pollen germination in B. juncea, of Se accumulation and has implications for the management of seleniferous areas.

Selenium accumulation, distribution, and speciation in spineless prickly pear cactus: a drought- and salt-tolerant, selenium-enriched nutraceutical fruit crop for biofortified foods

The organ-specific accumulation, spatial distribution, and chemical speciation of selenium (Se) were previously unknown for any species of cactus. We investigated Se in Opuntia ficus-indica using inductively coupled plasma mass spectrometry, microfocused x-ray fluorescence elemental and chemical mapping (μXRF), Se K-edge x-ray absorption near-edge structure (XANES) spectroscopy, and liquid chromatography-mass spectrometry (LC-MS). μXRF showed Se concentrated inside small conic, vestigial leaves (cladode tips), the cladode vasculature, and the seed embryos. Se K-edge XANES demonstrated that approximately 96% of total Se in cladode, fruit juice, fruit pulp, and seed is carbon-Se-carbon (C-Se-C). Micro and bulk XANES analysis showed that cladode tips contained both selenate and C-Se-C forms. Inductively coupled plasma mass spectrometry quantification of Se in high-performance liquid chromatography fractions followed by LC-MS structural identification showed selenocystathionine-to-selenomethionine (SeMet) ratios of 75:25, 71:29, and 32:68, respectively in cladode, fruit, and seed. Enzymatic digestions and subsequent analysis confirmed that Se was mainly present in a "free" nonproteinaceous form inside cladode and fruit, while in the seed, Se was incorporated into proteins associated with lipids. μXRF chemical mapping illuminated the specific location of Se reduction and assimilation from selenate accumulated in the cladode tips into the two LC-MS-identified C-Se-C forms before they were transported into the cladode mesophyll. We conclude that Opuntia is a secondary Se-accumulating plant whose fruit and cladode contain mostly free selenocystathionine and SeMet, while seeds contain mainly SeMet in protein. When eaten, the organic Se forms in Opuntia fruit, cladode, and seed may improve health, increase Se mineral nutrition, and help prevent multiple human cancers.

Developing a sustainable phytomanagement strategy for excessive selenium in western United States and India

Phytomanagement technology is recognized as an inexpensive and environmental friendly strategy for managing natural-occurring selenium (Se) in soils and in poor quality waters. Multi-year field and greenhouse studies were conducted with different plant species in California, USA and Punjab, India under high Se growing conditions. Some of the plant species included; canola (Brassica napus), mustard (B. juncea), broccoli (B. oleracea), spearmint (Mentha viridis), sugarcane (Saccharum officcinarum), guar (Cyamopsis tetragonoloba), wheat (Triticum aestivum), and poplar (Populus deltoides). California soils had a sodium-sulfate-dominated salinity between 6-10 dS m(-1), while Indian soils had a calcium carbonate salinity less than 1 dS m(-1). Results demonstrated that high sulfate conditions reduced plant Se accumulation more than 100 x in Californian grown plants compared to Se accumulation in Indian grown plants. Tissue concentrations generally did not exceed 10 and 200 mg kg DM(-1) in leaves of plants grown in California and India, respectively. At these plant concentrations, Se phytomanagement is more effective in Indian soils than in California soils. Successful management of Se by plants requires selecting crops or crop rotations that are tolerant of the soil condition and identifying and creating new viable Se-enriched products.

Evaluating the tolerance of young hybrid poplar trees to recycled waters high in salinity and boron

The successful adoption of water recycling strategies in many arid regions will require crops able to tolerate poor-quality waters. We evaluated different clones for salt and boron (B) tolerance within each of seven genetically distinct genomic groups (e.g., deltoides, deltoides x nigra, trichocarpa x deltoides, trichocarpa x deltoides x maximowizcii, trichocarpa x deltoides x nigra, trichocarpa x nigra, trichocarpa x maximowizcii). During each evaluation period, different clones within each of the groups were irrigated with high sodium chloride (NaCl) salinity (i.e., 10-30 dS m(-1)) and B (i.e., 10 mg L(-1)) water up to a maximum of 150 days, for a 4-year testing period under micro-field plot conditions. Excessive accumulation (up to 6%) of chloride (Cl) likely caused toxicity symptoms (necrosis of the leaves) observed in the less tolerant clones, while leaf B concentrations rarely exceeded 300 mg kg(-1) DM in any clone. Increased soil salinity likely hindered the uptake of B by the clones. Our results show that a wide range of selected Populus clones, of parentage trichocarpa x nigra, followed by deltoides x nigra show potential salt and B tolerance as young trees to recycled waters high in salinity and B.

Developing selenium-enriched animal feed and biofuel from canola planted for managing Se-laden drainage waters in the westside of central California

We studied the reuse of selenium (Se)-laden effluent for producing canola (Brassica napus) and subsequent bioproducts in central California. Canola was irrigated with poor quality waters [electrical conductivity (EC) of approximately 5 dS m(-1) sulfate-salinity, 5 mg B L(-1), and 0.25 mg Se L(-1)]. Typical seed yields were 2.2 metric tons ha(-1). Seeds were processed for their oil, and transesterified to produce ASTM-quality biodiesel (BD) blends. The resulting Se-enriched seed cake meal (containing approximately 2 mg Se kg(-1) DM) was used in a dairy feed trial. Seventy-two Jersey and Holstein cows, 36 respectively, were fed Se-enriched canola meal as 6.2% of their daily feed ration for five weeks. Blood and milk samples were collected weekly and analyzed for total Se. This study showed that Se-enriched canola meal did not significantly increase total blood Se content in either cow breed. Milk Se concentrations did, however, significantly increase to safe levels of 59 microg Se L(-1) and 52 microg Se L(-1) in Jersey and Holstein cows, respectively. The production of BD 20 biofuels and Se-enriched feed meal from canola irrigated with poor quality waters may help sustain similar phytomanagement strategies under Se-rich conditions.

Acceleration of selenium volatilization in seleniferous agricultural drainage sediments amended with methionine and casein

Phytoremediation is potentially effective for managing excessive selenium (Se) in drainage sediment residing in the San Luis Drain in central California. This 2-year field study examined the feasibility of amending drainage sediment (containing 4.78microgSeg(-1)) with methionine and casein to enhance volatilization without or with vegetation of Sporobolus airoides. Results show that without organic amendments, rates of Se volatilization were less than 25microgm(-2)d(-1) in all plots. After amending the sediment with 71.4mgmethioninekg(-1) soil, Se volatilization rates were 434+/-107microgm(-2)d(-1) in vegetated plots and 289+/-117microgm(-2)d(-1) in irrigated bare plots. With the amendment of 572mgcaseinkg(-1) soil, rates increased to 346+/-103microgm(-2)d(-1) in irrigated bare plots and to 114+/-55microgm(-2)d(-1) in vegetated plots. Both methionine and casein promoted biological remediation of Se via volatilization most effectively during the warmest months.

Phytoremediation management of selenium-laden drainage sediments in the San Luis Drain: a greenhouse feasibility study

An estimated 100,000m(3) selenium (Se)-laden drainage sediment resides in the San Luis Drain (SLD) of Central California. This greenhouse study was undertaken to evaluate the feasibility of growing salt- and boron-tolerant plant species in sediment for reduction of Se content by plant extraction. Drainage sediment was collected from the SLD and mixed with control soil (i.e., uncontaminated soil) to the following ratios (sediment:control soil) by volume: 0:3 (i.e., control soil only), 1:2 (i.e., 1/3 sediment and 2/3 control soil), 2:1 (i.e., 2/3 sediment and 1/3 control soil), and 3:0 (i.e., sediment only). Salt-tolerant plant species consisted of canola (Brassica napus var. Hyola 420), tall fescue (Festuca arundinacea var. Au Triumph), salado grass (Sporobulus airoides), and cordgrass (Spartina patens var. Flageo). Increased ratios of sediment:soil resulted in decreased dry matter production for all tested plant species; especially at ratios of sediment:soil greater than 1:2. Plant Se concentrations (mgkg(-1) DM) ranged as follows for plant species at all ratios of sediment:soil: canola (51-72), tall fescue (16-36), and cordgrass and salado grass (9-14). Total Se concentrations in the soil were at least 20% lower at postharvest compared to preplant concentrations for all plant species at each ratio of sediment:soil. In contrast, water-extractable Se concentrations in the soil were at least three times higher at postharvest than at preplant for all plant species, irrespective of the ratio of sediment:soil. Leaching of Se occurred in irrigated bare pots from each respective ratio of sediment:soil over a duration of 60 days. Based upon the downward movement of Se in bare pots of sediment:soil, it may be more prudent to leave the drainage sediment in the SLD, incorporate clean soil, and then grow low maintenance salt-tolerant plants (e.g., cordgrass, salado grass) in the concrete-lined canal. By this means, possible contamination of groundwater with soluble Se will be eliminated, while phytoremediation slowly reduces Se content in the drainage sediment.

Selenium volatilization in vegetated agricultural drainage sediment from the San Luis Drain, Central California

The presence of large amounts of Se-laden agricultural drainage sediment in the San Luis Drain, Central California, poses a serious toxic threat to wildlife in the surrounding environment. Effective management of the drainage sediment becomes a practical challenge because the sediment is polluted with high levels of Se, B, and salts. This two-year field study was conducted to identify the best plant species that are salt and B tolerant and that have a superior ability of volatilizing Se from drainage sediment. The drainage sediment was mixed with clean soil, and vegetated with salado alfalfa (Medicago sativa 'salado'), salado grass (Sporobulus airoides 'salado'), saltgrass-turf (Distichlis spp. 'NYPA Turf'), saltgrass-forage (Distichlis spicata (L.) Greene), cordgrass (Spartina patens 'Flageo'), Leucaenia (Leucaena leucocephola), elephant grass (Pennistum purpureum), or wild type-Brassica (Brassica spp.). Results show that elephant grass produced the greatest amount of biomass and accumulated highest concentrations of B. Highest concentrations of Se, S, and Cl were observed in wild-type Brassica. Biogenic volatilization of Se by plants and soil microbes was greater in summer. Among the treatments, the mean daily rates of Se volatilization (microg Se m(-2)d(-1)) were wild-type Brassica (39) > saltgrass-turf (31) > cordgrass (27) > saltgrass forage (24) > elephant grass (22) > salado grass (21) > leucaenia (19) > salado alfalfa (14) > irrigated bare soil (11) > non-irrigated bare soil (6). Overall, rates of Se volatilization in drainage sediment were relatively low due to high levels of sulfate. To manage Se in drainage sediment by phytoremediation, the biological volatilization process needs to be enhanced substantially under field conditions.

Selenium and sulfur accumulation and soil selenium dissipation in planting of four herbaceous plant species in soil contaminated with drainage sediment rich in both selenium and sulfur

Four selenium (Se) nonaccumulator plant species, including a forage grass species, Tall Fescue (Festuca arundinacea Schreb.), a forage legume species, Alfalfa (Medicago sativa L.), a wetland species, Rush (Juncus tenuis Wild.), and a dry-land alkaline soil species, Saltgrass (Distichlis spicata L.), were grown in soil contaminated by agricultural drainage sediment having elevated levels of Se and sulfur (S). The above-ground plant tissues were consecutively harvested five times and examined for Se and S accumulation. Plant tissue Se concentrations ranged from 23.0 mg kg-1 to 8.3 mg kg-1. Tissue S concentrations ranged from 3239 mg kg-1 to 7034 mg kg-1. Both tissue Se and S concentrations were significantly different between harvests, species, and species/harvest interactions. Total Se accumulation by the plant biomass harvested ranged from 0.3 to 1.3 mg per soil column and total S accumulations ranged from 87.5 to 321.1 mg per soil column. The reduction in the percentage of total soil Se after 24 weeks growth of the plant species ranged from 12.0% in the Tall Fescue planting to 17.3% in the Rush planting. Over 90% of the soil Se losses were unidentified losses and leaching of Se was prevented. The accumulations of Se and S in the plant biomass were very small compared with the total soil Se and S losses, but substantial amounts of total soil Se (12.0 to 15.0%) and S (28.0 to 50.9%) inventories were dissipated by the growing and harvesting of the plants. The soil S concentration was several hundred times higher than the soil Se concentration, but Se accumulation by the plants and Se dissipation from the soil were not impaired by the high level of soil sulfur. For natural grassland habitat restoration, such as at the Kesterson Wildlife Refuge in the Central Valley of California, or for restoration of large-scale Se contaminated agricultural lands, Se nonaccumulator plant species are favorable candidates, because the possibility of introducing Se toxicity into the food chain can be minimized.

Irrigation of broccoli and canola with boron- and selenium-laden effluent

Selenium (Se), boron (B), and salinity contamination of agricultural drainage water is potentially hazardous for water reuse strategies in central California. To demonstrate the feasibility of using plants to extract Se from drainage water, Se accumulation was determined in canola (Brassica napus L.) and broccoli (Brassica oleracea L.) irrigated with drainage effluent in the San Joaquin Valley, California. In the 2-yr field study, both crops were irrigated with a typical drainage water containing Se (150 microg L(-1)), B (5 mg L(-1)), and a sulfate dominated salinity (EC of 7 dS m(-1)). Total dry matter yields were at least 11 Mg ha(-1) for both canola and broccoli, and plant tissue Se concentrations did not exceed 7 mg kg(-1) DM for either crop. Based on the amount of soluble Se applied to crops with drainage water and the estimated amount of soluble Se remaining in soil to a depth of 90 cm at harvest, both canola and broccoli accumulated at least 40% of the estimated soluble Se lost from the soil for both years. Applied Se not accounted for in plant tissue or as soluble Se in the soil was presumably lost by biological volatilization. This study suggests that irrigating two high value crops such as canola and broccoli with Se-laden effluent helps manage Se-laden effluent requiring treatment, and also produces economically viable Se-enriched crops. Future research should focus on managing residual salt and B in the soil for sustaining long time water reuse strategies.

Phytoremediation of selenium-contaminated soils and waters: fundamentals and future prospects

Interest in selenium pollution and remediation technology has escalated during the past two decades. Although not known to be essential for plants, selenium is an essential micronutrient for humans and animals, having important benefits for their nutrition. At high concentrations, however, selenium becomes toxic to animals and humans. A major selenium controversy in the 1980s emerged in California at the Kesterson National Wildlife Refuge; hence, scientists, environmental regulators, politicians, and the general public in the United States became aware of selenium's potential as an environmental contaminant. Consequently, extensive research has been conducted in the western United States, and a vast amount of financial resources have been allocated to develop management strategies and remediation technologies for reducing the impact of naturally occurring selenium on the biological environment. A plant-based technology, defined as 'phytoremediation', has received increasing recognition as a low-cost, environmentally friendly approach for managing the toxic effects of selenium. Plants have the ability to absorb and sequester selenium and to convert inorganic selenium to volatile forms of organic compounds that are released harmlessly into the atmosphere. The present review summarizes recent research findings and information about strategies on using phytoremediation systems to detoxify selenium-contaminated soils and waters in natural and agricultural ecosystems.

Evaluation of Atriplex lines for selenium accumulation, salt tolerance and suitability for a key agricultural insect pest

Thirty Atriplex lines were examined for potential habitat improvement and phytoremediation of selenium (Se) contaminated sites. Studies were conducted to determine the biomass production, Se accumulation, and resistance of each line to the beet armyworm, Spodoptera exigua, an agriculturally important insect. Plants were tested using three salinity treatments: (1) control, no Se; (2) NaCl and CaCl2 salts and 1 mg l(-1) Se (12.7 microM) added as sodium selenate; and (3) iso-osmotic to treatment 2 containing high concentrations of sulfate and I mg l(-1) Se added as sodium selenate. Insect bioassays measured survival, growth, and development. Atriplex patula. A. spongiosa 415862, A. hortensis, A. hortensis 379088 and A. hortensis 379092 were among the top biomass producers and Se accumulators, yet they exhibited significantly reduced insect growth, development, and survival. High background sulfate strongly reduced Se accumulation, suggesting that phytoremediation potential is greatest in saline areas having low to moderate sulfate levels. However, these lines grew well in high salinity soils, indicating possible use as a self-seeding cover crop to improve habitat. All plant lines grown in control and high sulfate salinity treatments are acceptable oviposition sites for S. exigua, indicating that these plants would help reduce populations of this key agricultural pest.

The green technology of selenium phytoremediation

Selenium toxicity is encountered in arid and semi-arid regions of the world with alkaline, seleniferous soils derived from marine sediments. Once present in soils and waters at high concentrations, Se is very complicated and highly expensive to remove with conventional physical and chemical techniques. Phytoremediation is a plant-based technology that is being considered for managing Se in central California soils. The technology involves the use of plants in conjunction with microbial activity associated with the plants to extract, accumulate, and volatilize Se. Once absorbed by plant roots, Se is translocated to the shoot where it may be harvested and removed from the site. Therefore, plant species used for phytoremediation of Se-laden soils may by plant uptake and volatilization minimize the Se load eventually entering agricultural effluent and the harvested crop can be carefully blended with animal forage and fed to animals in Se-deficient areas.

Absorption and distribution of selenium in animals consuming canola grown for selenium phytoremediation

Canola (Brassica napus) grown as a selected plant species for field phytoremediation of selenium (Se) may be harvested and utilized as Se-enriched forage for marginally Se-deficient lambs and cows. Two field studies were conducted under controlled conditions to evaluate the accumulation of Se into different animal tissues, including blood, excreta, and milk. In Study 1, treatments consisted of feeding lambs freshly cut Se-enriched canola (containing approximately 4 mg Se kg(-1) DM) or control canola (containing <0.1 mg Se kg(-1) DM), respectively, for 64 days. In Study 2, treatments consisted of feeding cows dried Se-enriched canola (containing approximately 3.5 mg Se kg(-1) DM) as part of their daily ration for 20 days. In Study 1 at postmortem, Se concentrations were significantly greater in all tested tissues and in excreta from lambs fed Se-enriched canola. In Study 2, Se values were slightly higher in blood and excreta, but not significantly higher in milk from cows sampled throughout the study. Significant differences in total live animal weight were not observed between treatments in either study. Based on these results, canola plants (not including seeds) used for field phytoremediation of Se may be harvested and safely fed to lambs and cows to help meet normal Se intake requirements.

Germination responses and boron accumulation in germplasm from Chile and the United States grown with boron-enriched water

Boron (B) is toxic to most plant species when accumulated in high concentrations. Differences in a plant's ability to adapt to high concentrations of B may depend on the origin of the germplasm. Chilean and domestic (U.S.) germplasm, corn (Zea mays L.), carrots (Daucus carotas), tomato (Lycopersicum esculentum L.), and alfalfa (Medicago sativa L.) were evaluated for germination, emergence of cotyledonary leaves, and tissue B accumulation under high-B conditions in both an environmental growth chamber and a greenhouse. Increasing B levels (20-40 mg B liter-1) inhibited the percentage germination for both the Chilean and domestic germplasm. Chilean germplasm exhibited generally a greater percentage of healthy cotyledonary leaves at the 20 mg B liter-1 treatment than the domestic germplasm. Comparing B concentrations between both germplasm grown and irrigated with B-enriched water (10-20 mg B liter-1) under greenhouse conditions, leaves from domestic germplasm contained more B. Moreover, B troxicity symptoms were more severe for the tested plant species from the domestic germplasm. Apparent B tolerance by germplasm of different origin should be further tested under field conditions.

Selenium-induced growth reduction in Brassica land races considered for phytoremediation

Brassica species considered for use in selenium (Se) phytoremediation need to accumulate large amounts of Se to be successful. Retarded plant growth and impaired protein synthesis are common symptoms for plants grown under seleniferous soils. Selenium accumulation by different land races of Brassica juncea (L.) Czern and Coss and one land race of Brassica carinata was investigated in Se-enriched water and soil cultures containing 2 mg Se kg-1. Effects of Se concentration in the root environment on the assimilation of Se, leaf surface area, dry matter yield, total leaf protein concentration, and free seleno-amino acid concentrations were analyzed for plants grown in Se-laden media. In water culture, shoot Se concentrations among the land races ranged from 501 to 1017 mg Se kg-1 dry matter (DM), and in plants grown in Se-laden soil, concentrations ranged from 407 to 769 mg Se kg-1 DM. Land races grown with Se exhibited decreases in dry matter yields from 12 to 23% and in leaf surface area from 5 to 26% compared to the same land races grown without Se. Protein content was significantly correlated both with shoot Se concentrations (r = 0.746, P < 0.001) and with leaf surface area (r = 0.446, P < 0.01) for all land races grown in Se-enriched water culture. There was also a significant correlation (r = 0.767, P < 0.001) between total Se assimilation and shoot protein for all land races. Free selenomethionine was detected for plants grown with Se and ranged from 92 to 958 ng g-1 DM. Other seleno-amino acids, Se-methyl-selenocysteine and selenocysteine, were not consistently detected as free amino acids in the different land races. Although visual symptoms of Se toxicity were not observed in the Brassica species, dry matter yield, leaf surface, and total shoot protein decreased, depending on the land races tested.

Bioextraction of soil boron by tall fescue

High concentrations of soil B are detrimental to crop productivity in certain arid and semiarid regions of the western United States. Production of tall fescue on B-affected soils may be a viable strategy to reduce and maintain soil B concentrations at nontoxic levels for most agronomic crops. A 2-year field experiment was conducted to study B uptake in tall fescue (Festuca arundinacea) Schreb. cv. Au Triumph grown in soil containing potentially toxic levels of native soil B. The soil B concentrations (water-extractable B greater than 5 mg B liter-1) did not affect the dry matter (DM) yield of tall fescue. Boron concentrations in shoot tissue for both years ranged from 88 to 121 mg B kg-1 DM. whereas in root tissue, concentrations ranged from 50 to 60 mg B kg-1 DM. For both years of the study, soil samples were taken at depth of 0-45 and 45-90 cm at the beginning and end of the designated growing season and analyzed for water-extractable B. Summary data from all cropped plots at the two soil depths indicated that the mean water-extractable B concentrations were reduced by 35% after 2 years in the tall fescue plots, whereas losses of extractable B from bare plots did not exceed 13% for both years. Tall fescue apparently can be used as a component in an overall strategy to lower extractable soil native B levels in irrigated agriculture soils and potentially reduce leaching of B into shallow ground water.