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Given the importance of soil for the global carbon cycle, it is essential to understand not only how much carbon soil stores but also how long this carbon persists. Previous studies have shown that the amount and age of soil carbon are strongly affected by the interaction of climate, vegetation, and mineralogy. However, these findings are primarily based on studies from temperate regions and from fine‐scale studies, leaving large knowledge gaps for soils from understudied regions such as sub‐Saharan Africa. In addition, there is a lack of data to validate modeled soil C dynamics at broad scales. Here, we present insights into organic carbon cycling, based on a new broad‐scale radiocarbon and mineral dataset for sub‐Saharan Africa. We found that in moderately weathered soils in seasonal climate zones with poorly crystalline and reactive clay minerals, organic carbon persists longer on average (topsoil: 201 ± 130 years; subsoil: 645 ± 385 years) than in highly weathered soils in humid regions (topsoil: 140 ± 46 years; subsoil: 454 ± 247 years) with less reactive minerals. Soils in arid climate zones (topsoil: 396 ± 339 years; subsoil: 963 ± 669 years) store organic carbon for periods more similar to those in seasonal climate zones, likely reflecting climatic constraints on weathering, carbon inputs and microbial decomposition. These insights into the timescales of organic carbon persistence in soils of sub‐Saharan Africa suggest that a process‐oriented grouping of soils based on pedo‐climatic conditions may be useful to improve predictions of soil responses to climate change at broader scales. [ABSTRACT FROM AUTHOR]

Summary: Growth at increased concentrations of CO2 induces a reduction in seed zinc (Zn) and iron (Fe). Using Arabidopsis thaliana, we investigated whether this could be mitigated by reducing the elevated CO2‐induced decrease in transpiration.We used an infrared imaging‐based screen to isolate mutants in At1g08080 that encodes ALPHA CARBONIC ANHYDRASE 7 (ACA7). aca7 mutant alleles display wild‐type (WT) responses to abscisic acid (ABA) and light but are compromised in their response to elevated CO2.ACA7 is expressed in guard cells. When aca7 mutants are grown at 1000 ppm CO2 they exhibit higher transpiration and higher seed Fe and Zn content than WT grown under the same conditions.Our data show that by increasing transpiration it is possible to partially mitigate the reduction in seed Fe and Zn content when Arabidopsis is grown at elevated CO2. [ABSTRACT FROM AUTHOR]

Maximising resource‐use efficiency, productivity and environmental sustainability are all fundamental requirements to raise global food production by ~70 per cent in order to feed a world population of ~9.7 billion people by 2050. Perhaps the most vital resource within our capacity to achieve this goal is our soil. Broadly, the fundamental question concerns whether or not satisfying this production demand will accelerate soil degradation, climate change, and the loss of soil carbon stocks. This paper builds upon the outputs of the UK Charity 'Food & Farming Futures' (chaired by Lord Curry of Kirkharle) virtual workshop held on 23 March 2021, entitled 'Capturing the Potential of Soil'. The event focussed on the link between soil health, primarily soil organic carbon (SOC), and agricultural productivity. Supported with commentaries by Professor Pete Smith (University of Aberdeen and Science Director of the Scottish Climate Change Centre of Expertise) and Professor Steve McGrath (Head of Sustainable Agricultural Sciences at Rothamsted Research), specific focus will be given to the research challenges within the UK's ability to improve soil health and functionality, the implementation priorities that must be held in order to improve soil management by 2050 and what the potential co‐benefits could be. These co‐benefits were scattered across environmental, economic, social and political issues, yet they may be summarised into six primary co‐benefits: developing natural capital, climate change mitigation, carbon trading, improvements in crop yield, animal performance and human health (nutrition). Additionally, the main barriers to improved soil management practices are centred on knowledge exchange‐regarding agri‐environmental techniques—whilst the most impactful solutions rely on soil monitoring, reporting and verification. [ABSTRACT FROM AUTHOR]

Here we describe and evaluate the success of a multi‐institutional Centre for Doctoral Training (CDT), which was established to address a UK skills shortage in Soil Science. The government‐funded 'STARS' (Soils Training And Research Studentships) CDT was established in 2015 across a range of universities and research institutes in the UK. It recruited 41 PhD students equitably split across the institutions under four core research themes identified as being central to the national need, namely, (1) Understanding the soil–root interface, (2) Soils and the delivery of ecosystem services, (3) Resilience and response of functions in soil systems and (4) Modelling the soil ecosystem at different spatial and temporal scales. In addition, the STARS CDT provided a diverse skills programme, including: Holistic training in soils, the promotion of collegiality and joint working, strategies to promote science and generate impact, internships with end users (e.g., policymakers, industry), personal wellbeing, and ways to generate a lasting soils training legacy. Overall, both supervisors and students have reported a positive experience of the CDT in comparison to the conventional doctoral training programmes, which have less discipline focus and little chance for students to scientifically interact with their cohorts or to undertake joint training activities. The STARS CDT also allowed students to freely access research infrastructure across the partner institutions (e.g., long‐term field trials, specialised analytical facilities, high‐performance computing), breaking down traditional institutional barriers and thus maximising the students' potential to undertake high‐quality research. The success and legacy of the STARS CDT can be evidenced in many ways; however, it is exemplified by the large number and diversity of journal papers produced, the lasting collaborations, final career destinations, and creation of a web‐based legacy portal including new and reflective video material. Highlights: Soil science was identified as having a scientific skills shortage in the UK.A dedicated soil science Centre for Doctoral Training (CDT) was established to address this skills gap.The multi‐institutional, discipline‐focused CDT proved more successful than conventional generic PhD training programmes.The CDT model provides critical mass to provide more effective training of soil scientists. [ABSTRACT FROM AUTHOR]

Simple measures of appropriate levels of soil organic matter are needed for soil evaluation, management and monitoring, based on readily measurable soil properties. We test an index of soil organic matter based on the soil organic carbon (SOC) to clay ratio, defined by thresholds of SOC/clay ratio for specified levels of soil structural quality. The thresholds were originally delineated for a small number of Swiss soils. We assess the index using data from the initial sampling (1978–83) of the National Soil Inventory of England and Wales, covering 3,809 sites under arable land, grassland and woodland. Land use, soil type, annual precipitation and soil pH together explained 21% of the variance in SOC/clay ratio in the dataset, with land use the most important variable. Thresholds of SOC/clay ratio of 1/8, 1/10 and 1/13 indicated the boundaries between "very good", "good", "moderate" and "degraded" levels of structural condition. On this scale, 38.2, 6.6 and 5.6% of arable, grassland and woodland sites, respectively, were degraded. The index gives a method to assess and monitor soil organic matter at national, regional or sub‐regional scales based on two routinely measured soil properties. Given the wide range of soils and land uses across England and Wales in the dataset used to test the index, we suggest it should apply to other European soils in similar climate zones. Highlights: We assess the use of SOC/clay ratios as guidelines for soil management in England and Wales.We use data from 3,809 sites to assess thresholds based on work for Polish, French and Swiss soils.SOC/clay threshold values can indicate degraded and good soil structural condition.The thresholds show the effect of land use and provide an index for use in England and Wales. [ABSTRACT FROM AUTHOR]

Optimization of phosphorus (P) fertiliser use is desired to ensure more sustainable use of fertiliser, economic food production and reduction of eutrophication of water bodies. Presently, the Olsen P values on which fertiliser recommendations are based to achieve optimum yield are frequently the same for all soils. The aim of this study was to identify the properties of different soils that affect their critical Olsen P values in order to develop better, soil‐specific P fertiliser recommendations. A pot experiment using 10 soils with low available P with different P additions was carried out to investigate the impact of wide‐ranging soil properties on the relationship between P addition, resultant Olsen P values and yield response of ryegrass to Olsen P values. The relationship between added P and Olsen P varied greatly between the individual soils. These relationships were affected by pH, manganese oxide, crystalline aluminium oxide and amorphous iron oxide contents of the soil. Different soils had widely varying critical Olsen P values for ryegrass. However, these could not be related to the measured soil properties. Fertiliser recommendations and critical values for optimum yield of ryegrass based on the Olsen P test should be soil specific. The complexity and lack of clarity over which combination of soil properties governs critical Olsen P values calls for further investigation with more soil types and additional soil property measurements to elucidate the different factors controlling critical Olsen P values in different soils. Highlights: Soil‐specific P fertiliser recommendations are needed for sustainable fertiliser useWe investigated soil properties affecting critical Olsen P values and added P fertiliser availabilityFertiliser P availability was affected by pH and metal (hydr)oxide contents of the soilCritical Olsen P values varied with soil, but measured soil properties could not explain this variation [ABSTRACT FROM AUTHOR]

Summary: Understanding the changes in plant–microbe interactions is critically important for predicting ecosystem functioning in response to human‐induced environmental changes such as nitrogen (N) addition. In this study, the effects of a century‐long fertilization treatment (> 150 years) on the networks between plants and soil microbial functional communities, detected by GeoChip, in grassland were determined in the Park Grass Experiment at Rothamsted Research, UK. Our results showed that plants and soil microbes have a consistent response to long‐term fertilization—both richness and diversity of plants and soil microbes are significantly decreased, as well as microbial functional genes involved in soil carbon (C), nitrogen (N) and phosphorus (P) cycling. The network‐based analyses showed that long‐term fertilization decreased the complexity of networks between plant and microbial functional communities in terms of node numbers, connectivity, network density and the clustering coefficient. Similarly, within the soil microbial community, the strength of microbial associations was also weakened in response to long‐term fertilization. Mantel path analysis showed that soil C and N contents were the main factors affecting the network between plants and microbes. Our results indicate that century‐long fertilization weakens the plant–microbe networks, which is important in improving our understanding of grassland ecosystem functions and stability under long‐term agriculture management. [ABSTRACT FROM AUTHOR]

This article is a Commentary on González‐Fontes (226: 1228–1230), Lewis (2020a, 226: 1231), Wimmer et al. (226: 1232–1237), Lewis (2020b, 226: 1238–1239) [ABSTRACT FROM AUTHOR]

The Long-Term Sludge Experiment (LTSE) began in 1994 at nine UK field sites as part of continuing research into the effects of sludge-borne heavy metals on soil fertility. The long-term effects of Zn, Cu, and Cd on the most probable numbers of cells (MPN) of Rhizobium leguminosarum biovar trifolii were monitored for 8 yr in sludge-amended soils. To assess the statutory limits set by the UK Sludge (Use in Agriculture) Regulations, the experimental data were reviewed using statistical methods of meta-analysis. Previous LTSE studies have focused predominantly on statistical significance rather than effect size, whereas meta-analysis focuses on the magnitude and direction of an effect, i.e., the practical significance rather than its statistical significance. Results showed Zn to be the most toxic element causing an overall significant decrease in Rhizobium MPN of -26.6% during the LTSE. The effect of Cu showed no significant effect on Rhizobium MPN at concentrations below the UK limits, although a -5% decrease in Rhizobium MPN was observed in soils where total Cu ranged from 100 to <135 mg kg-1. Overall, there was nothing to indicate that Cd had a significant effect on Rhizobium MPN below the current UK statutory limit. In summary, the UK statutory limit for Zn appears to be insufficient for protecting Rhizobium from Zn toxicity effects. [ABSTRACT FROM AUTHOR]

BACKGROUND Millions of people have Se-deficient diets and Se-biofortified crops could prevent such deficiency. The aim of the present study was to evaluate the potential of chickpea for use in Se fertilization programs in order to increase available Se. Two foliar Se fertilizers (sodium selenate and sodium selenite) at four rates (0, 10, 20, 40 g ha−1) were tested in the 2010/2011 and 2011/2012 growing seasons in a field experiment conducted under semiarid Mediterranean conditions. RESULTS Sodium selenate was much more effectively taken by plants than sodium selenite, and there was a strong and linear relationship between total Se content and Se rate for both. For each gram of Se fertilizer, applied either as sodium selenate or sodium selenite, the increases of total Se concentration in grain were 126 and 87, and 25 and 19 µg Se kg−1 dry weight, in 2010/2011 and 2011/2012, respectively. Se was found to be incorporated into chickpea grains mainly (>70%) as selenomethionine. CONCLUSION Se-enriched chickpeas would be a good candidate for inclusion in biofortification programs under semiarid Mediterranean conditions and for promotion as a 'functional food'. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The cellular and subcellular distributions of trace elements can provide important clues to understanding how the elements are transported and stored in plant cells, but mapping their distributions is a challenging task., The distributions of arsenic, iron, zinc, manganese and copper, as well as physiologically related macro-elements, were mapped in the node, internode and leaf sheath of rice ( Oryza sativa) using synchrotron X-ray fluorescence (S-XRF) and high-resolution secondary ion mass spectrometry (NanoSIMS)., Although copper and silicon generally showed cell wall localization, arsenic, iron and zinc were strongly localized in the vacuoles of specific cell types. Arsenic was highly localized in the companion cell vacuoles of the phloem in all vascular bundles, showing a strong co-localization with sulfur, consistent with As(III)-thiol complexation. Within the node, zinc was localized in the vacuoles of the parenchyma cell bridge bordering the enlarged and diffuse vascular bundles, whereas iron and manganese were localized in the fundamental parenchyma cells, with iron being strongly co-localized with phosphorus in the vacuoles., The highly heterogeneous and contrasting distribution patterns of these elements imply different transport activities and/or storage capacities among different cell types. Sequestration of arsenic in companion cell vacuoles may explain the limited phloem mobility of arsenite. [ABSTRACT FROM AUTHOR]

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•When supplied with arsenate (As(V)), plant roots extrude a substantial amount of arsenite (As(III)) to the external medium through as yet unidentified pathways. The rice ( Oryza sativa) silicon transporter Lsi1 (OsNIP2;1, an aquaporin channel) is the major entry route of arsenite into rice roots. Whether Lsi1 also mediates arsenite efflux was investigated. •Expression of Lsi1 in Xenopus laevis oocytes enhanced arsenite efflux, indicating that Lsi1 facilitates arsenite transport bidirectionally. •Arsenite was the predominant arsenic species in arsenate-exposed rice plants. During 24-h exposure to 5 μm arsenate, rice roots extruded arsenite to the external medium rapidly, accounting for 60–90% of the arsenate uptake. A rice mutant defective in Lsi1 ( lsi1) extruded significantly less arsenite than the wild-type rice and, as a result, accumulated more arsenite in the roots. By contrast, Lsi2 mutation had little effect on arsenite efflux to the external medium. •We conclude that Lsi1 plays a role in arsenite efflux in rice roots exposed to arsenate. However, this pathway accounts for only 15–20% of the total efflux, suggesting the existence of other efflux transporters. [ABSTRACT FROM AUTHOR]

•Cereals are an important source of selenium (Se) to humans and many people have inadequate intakes of this essential trace element. Conversely, arsenic (As) is toxic and may accumulate in rice grain at levels that pose a health risk. Knowledge of the localization of selenium and arsenic within the cereal grain will aid understanding of their deposition patterns and the impact of processes such as milling. •High-resolution secondary ion mass spectrometry (NanoSIMS) was used to determine the localization of Se in wheat ( Triticum aestivum) and As in rice ( Oryza sativa). Combined synchrotron X-ray fluorescence (S-XRF) and NanoSIMS analysis utilized the strengths of both techniques. •Selenium was concentrated in the protein surrounding the starch granules in the starchy endosperm cells and more homogeneously distributed in the aleurone cells but with Se-rich hotspots. Arsenic was concentrated in the subaleurone endosperm cells in association with the protein matrix rather than in the aleurone cells. NanoSIMS indicated that the high intensity of As identified in the S-XRF image was localized in micron-sized hotspots near the ovular vascular trace and nucellar projection. •This is the first study showing subcellular localization in grain samples containing parts per million concentrations of Se and As. There is good quantitative agreement between NanoSIMS and S-XRF. [ABSTRACT FROM AUTHOR]

Total concentrations of metals in soil are poor predictors of toxicity. In the last decade, considerable effort has been made to demonstrate how metal toxicity is affected by the abiotic properties of soil. Here this information is collated and shows how these data have been used in the European Union for defining predicted-no-effect concentrations (PNECs) of Cd, Cu, Co, Ni, Pb, and Zn in soil. Bioavailability models have been calibrated using data from more than 500 new chronic toxicity tests in soils amended with soluble metal salts, in experimentally aged soils, and in field-contaminated soils. In general, soil pH was a good predictor of metal solubility but a poor predictor of metal toxicity across soils. Toxicity thresholds based on the free metal ion activity were generally more variable than those expressed on total soil metal, which can be explained, but not predicted, using the concept of the biotic ligand model. The toxicity thresholds based on total soil metal concentrations rise almost proportionally to the effective cation exchange capacity of soil. Total soil metal concentrations yielding 10% inhibition in freshly amended soils were up to 100-fold smaller (median 3.4-fold, n = 110 comparative tests) than those in corresponding aged soils or field-contaminated soils. The change in isotopically exchangeable metal in soil proved to be a conservative estimate of the change in toxicity upon aging. The PNEC values for specific soil types were calculated using this information. The corrections for aging and for modifying effects of soil properties in metal-salt-amended soils are shown to be the main factors by which PNEC values rise above the natural background range. [ABSTRACT FROM AUTHOR]

• Selenite can be a dominant form of selenium (Se) in aerobic soils; however, unlike selenate, the mechanism of selenite uptake by plants remains unclear. • Uptake, translocation and Se speciation in wheat ( Triticum aestivum) supplied with selenate or selenite, or both, were investigated in hydroponic experiments. The kinetics of selenite influx was determined in short-term (30 min) experiments. Selenium speciation in the water-extractable fraction of roots and shoots was determined by HPLC-ICPMS. • Plants absorbed similar amounts of Se within 1 d when supplied with selenite or selenate. Selenate and selenite uptake were enhanced in sulphur-starved and phosphorus-starved plants, respectively. Phosphate markedly increased Km of the selenite influx. Selenate and selenite uptake were both metabolically dependent. Selenite was rapidly converted to organic forms in roots, with limited translocation to shoots. Selenomethionine, selenomethionine Se-oxide, Se-methyl-selenocysteine and several other unidentified Se species were detected in the root extracts and xylem sap from selenite-treated plants. Selenate was highly mobile in xylem transport, but little was assimilated to organic forms in 1 d. The presence of selenite decreased selenate uptake and xylem transport. • Selenite uptake is an active process likely mediated, at least partly, by phosphate transporters. Selenite and selenate differ greatly in the ease of assimilation and xylem transport. [ABSTRACT FROM AUTHOR]

Bioavailability of As varies among soils, and this needs to be taken into account during environmental risk assessment. Using a standardized barley root elongation assay, we investigated the phytotoxicity of arsenate added to 16 European soils that varied widely in their physicochemical properties. The effective concentrations of As causing 10% (EC10) and 50% (EC50) inhibition were estimated based on the concentrations of total added As or As extracted with 0.05 M (NH4)2SO4 or 0.05 M NH4H2PO4. In addition, four soils were used to evaluate changes in arsenate phytotoxicity over a three-month period. The EC10s and EC50s of added As varied from 4.2 to 206.7 mg/kg and from 26.6 to 458.2 mg/kg, respectively. Multiple-regression analysis showed that the variability in the EC10 and EC50 was largely (>89%) explained by the contents of amorphous Mn oxide and clay and, to a lesser extent, Fe oxide, indicating that arsenate adsorption was a key factor controlling its bioavailability. Neither (NH4)2SO4 nor NH4H2PO4 extraction could explain arsenate phytotoxicity independently of soil properties. Furthermore, arsenate phytotoxicity decreased significantly after aging for three months, although the extent of aging differed among soils. This aging effect should be taken into account during the risk assessment. [ABSTRACT FROM AUTHOR]

The long-term accumulation of Zn in soils provides the microbial community time to adapt to this heavy metal. To assess the effects of long-term exposure to Zn on the metabolic diversity and tolerance to Zn of soil microbial community, the pollution-induced community tolerance (PICT) method, based on the Biolog microtitre plate system, was used. It especially is useful to study gradients of pollutants for detecting PICT. Such a Zn gradient was found by selecting soils at increasing distances from galvanized electricity pylons at two sites where Zn accumulation had occurred over a period of decades. Soil metabolic profiles showed a humpbacked response to increasing soil Zn concentrations, indicating that accumulation of Zn up to 2,000 mg/kg did not decrease the metabolic biodiversity in the culturable fraction of the microbial community. This fraction of the microbial community showed significant PICT, because the effective concentration that reduces the metabolic biodiversity by 50% (EC50), values for Zn added to the Biolog wells increased by up to two orders of magnitude with increasing soil-Zn concentration along the transects. Significant PICT was detectable at soil Zn concentrations above approximately 300 mg/kg. The EC50 values correlated more closely with soil total Zn than with soil pore water Zn. The results suggest that, although long-term exposure to Zn imposes stress on soil microbes, resulting in an increased tolerance, detectable PICT does not necessarily lead to a decrease in metabolic diversity. [ABSTRACT FROM AUTHOR]

Assesses the use of industrial by-products to remediate a copper- and arsenic-contaminated soil. Increase of soil hydrogen-ion concentration; Determination of changes in the growth of ryegrass and lettuce; Significance of treatment effects on soil fertility.

Soil microbial processes are readily disturbed by added zinc (Zn) in laboratory ecotoxicity tests. This study compares Zn toxicity between freshly spiked soils and soils that have been contaminated with Zn in the field. Soils were sampled in three transects (<80 m) toward galvanized electricity transmission towers (pylons). The soil total Zn concentrations gradually increased in each transect from background values (25-82 mg Zn/kg) to elevated Zn concentrations near the pylon (226-595 mg Zn/kg). Soil samples taken at the furthest distance from the Zn source were spiked with ZnCl2 to a range of total Zn concentrations similar to those in the transect. Nitrification, respiration, and N-mineralization rates were significantly reduced by added Zn in laboratory-spiked soils and were 9 to 95% (mean 32%) of the control values at largest doses depending on soil type and the microbial process. In contrast, these processes were either unaffected by soil Zn (p> 0.05) or increased significantly with soil Zn concentrations in the transect soils. These increases could not be explained by soil pH or %soil organic carbon. Leaching soils after spiking significantly lowered the toxic effects of Zn on nitrification or on substrate-induced respiration. The soil solution Zn concentrations of field soils were always smaller than in spiked soils at equivalent total Zn. Highest soil solution Zn concentrations were always lower than the soil-solution EC50s of spiked soils. It is concluded that there is a large discrepancy in microbial responses to elevated Zn between spiked soils (unleached) and field-contaminated soils and there is a need to explain this discrepancy in terms of Zn availability, adaptation processes, and additional soil factors controlling the microbial processes. [ABSTRACT FROM AUTHOR]

Summary • Pteris vittata is the first plant reported to be a hyperaccumulator of arsenic (As), and little is known about the mechanisms of As hyperaccumulation in this plant. • Arsenic distribution at the whole plant (fronds) and cellular level was investigated using chemical analyses and energy dispersive X-ray microanalyses (EDXA). Speciation of As in the fronds was determined using X-ray absorption near edge spectroscopy (XANES) analyses. • The majority of As was found in the pinnae (96% of total As). The concentration of As in pinnae decreased from the base to the apex of the fronds. Arsenic concentrations in spores and midribs were much lower than in the pinnae. EDXA analyses revealed that As was compartmentalized mainly in the upper and lower epidermal cells, probably in the vacuoles. The distribution pattern of potassium was similar to As, whereas other elements (Ca, Cl, K, Mg, P and S) were distributed differently. • XANES analyses showed that approximately 75% of the As in fronds was present in the As(III) oxidation state and the remaining as As(V). [ABSTRACT FROM AUTHOR]

Grain Cd concentrations were determined in the wheat (Triticum aestivum L.) cultivars Soissons, Brigadier, and Hereward grown in 1994, 1996, and 1999, respectively, in soils of a long‐term field experiment to which sewage sludges contaminated with Zn, Cu, Ni, or Cr had previously been added. Soil pore water soluble Cd and free Cd2+ increased linearly with increasing total soil Cd (R2 = 0.82 and 0.84, respectively; P < 0.001). Similarly, soil pore water free Cd2+ increased linearly with increasing soil pore water soluble Cd (R2 = 0.98; P < 0.001). There was no evidence of a plateau in soil pore water Cd concentrations with increasing soil Cd concentrations. Grain Cd concentrations were significantly correlated with total soil Cd (P < 0.001), soil pore water Cd (P < 0.001), and free Cd2+ (P < 0.001). A slight curvilinear relationship between grain Cd and soil Cd was apparent, but there was no plateau, even at the maximum soil Cd concentration of about 2.7 mg kg−1 The relationship between soil pore water Cd and grain Cd was linear for all three cultivars. The slopes were in the order 1994 > 1996 > 1999, with more Cd being taken up into the grain by Soissons grown in 1994, and least by Hereward grown in 1999. For Soissons, Cd concentration in the grain greater than the EU limit (0.24 mg kg−1 dry wt.) occurred at soil Cd less than the current UK limit of 3 mg kg−1 for soils receiving sewage sludge. In contrast, for Brigadier and Hereward, grain Cd concentrations were near to and less than the EU limit, respectively, at soil Cd concentrations of 3 mg kg−1 [ABSTRACT FROM AUTHOR]

We assessed the ability of several populations of the metal‐hyperaccumulator species, Thlaspi caerulescens, to mobilize non‐labile cadmium in soils historically contaminated by Pb/Zn mine spoil or sewage sludge. Radio‐ labile Cd was determined chemically as an ‘E‐value’, [CdE], and biologically as an ‘L‐value’, [CdL]. For comparison, chloride‐extractable Cd, [Cdchlor], was also determined using 1 M CaCl2 as a single‐step soil extractant. Values of [CdL] were measured for six populations of T. caerulescens that varied substantially in their ability to assimilate soil Cd, and a non‐accumulator species with a similar growth habit, Lepidium heterophyllum. Seeds were sown in soil spiked with 109Cd and grown for 9–12 wk in a controlled environment room. Values of [CdL] were determined from the specific activity of 109Cd and concentration of Cd in the plant leaves. For the six soils studied, [CdE] ranged from 4.9 to 49% of total soil Cd [CdT]. Values of [CdL] were, in general, in close agreement with both [CdE] and [Cdchlor] and substantially less than [CdT]. However, [CdL] showed no correlation with the concentration of Cd in plant tissue, [Cdshoot]. This suggests that, in the soils studied, T. caerulescens did not mobilize non‐labile soil Cd by producing root exudates or altering rhizosphere pH. The results imply that there may be significant restrictions to metal bioavailability, even to hyperaccumulator species, in heavily contaminated soils in which a large proportion of the metal may be present in ‘non‐labile’ forms. [ABSTRACT FROM AUTHOR]

The effects of localized zinc (ZnO) and cadmium (CdS) enrichment on the allocation of root biomass, root length and partitioning of current assimilate within root systems of the Zn hyperaccumulator Thlaspi carrulescens were investigated using a rhizobox system. The rhizoboxes contained either homogeneous soil or juxtaposed control and metal-enriched soil. In the heterogeneous treatments the Zn-enriched soil contained 250, 500 and 1000 mg Zn kg. The plants consistently allocated c. 70% of their total root biomass and length into the metal-enriched soil. Moreover, 70% of the current assimilate (11C) allocated to the roots was localized in the Zn-enriched soil of the heterogeneous treatments. The concentration of Zn (250-1000 mg kg 1) in the enriched soil had no effect on these patterns of root allocation, nor were three significant effects of the Zn treatments on the total root or shoot biomass of the plants. The positive responses to the localized metal treatments were therefore, characterized by a concomitant reduction in root allocation into the control soil. In contrast to T caerulescens, when grown with juxtaposed control and Zn-enriched soil the non-accumulator Thlaspi arvense showed reduced root allocation into a patch enriched with 500 mg kg 1Zn. In a further experiments, two populations of T. caerulescens that differ in their abilities to accumulate Cd were grown with juxtaposed control and Cd-enriched soil. The plants from a population that accumulated Cd also showed increased root biomass and root length allocation into the Cd-enrichment soil. Plants from the population that did not accumulate Cd showed no such increase. The possibilit that T. caerulescens forages for metals, and the precision of its root allocation with respect to localized metal enrichment is highlighted. The significance of these findings for the selection of hyperaccumulator plants for use in the phytoextraction of Zn and Cd from mine from mine spoils (phytomining) and the phytoremediation of heterogeneous contaminated soils are discussed. [ABSTRACT FROM AUTHOR]

The relationship between Zn and P in the Zn hyperaccumulator Thlaspi caerulescens J. & C. Presl was investigated using hydroponic culture. Total concentrations of Zn in the shoots increased from 0·2 to 27 g kg–1 dry mass when solution Zn increased from 1 to 1000 mmol m–3. Water-soluble Zn accounted for > 80% of the total Zn in the shoots containing > 5 g Zn kg–1 dry mass. Total P was maintained at about 3 g kg–1 dry mass in the shoots containing < 20 g Zn kg–1 dry mass, but significantly decreased with higher Zn concentrations. Linear regression between insoluble P and insoluble Zn in the shoots produced a small slope, suggesting that co-precipitation of Zn and P was not an important detoxification mechanism in the shoots. In contrast, there was a strong correlation between insoluble P and insoluble Zn in the roots, with a linear slope of 0·3 — close to the P:Zn ratio in Zn3(PO4)2. Foliar sprays of phosphate did not affect shoot dry mass significantly, but decreased root length and root dry mass significantly at Zn concentrations in solution from 10 to 3000 mmol m–3. Foliar P was translocated to roots to enhance co-precipitation of Zn and P, although this did not enhance Zn tolerance. The results suggest that T.caerulescens possesses mechanisms which allow it to accumulate and sequester huge amounts of Zn in the shoots without causing P deficiency. [ABSTRACT FROM AUTHOR]

Determining the distribution of trace elements in biological materials with subcellular resolution is very challenging but vitally important in order to understand their mechanisms of uptake. Rice grain is efficient in the accumulation of arsenic (As) in the grain, potentially posing a severe health risk to millions of people in South-East Asia. The NanoSIMS is a state-of-the-art microscope capable of high resolution chemical imaging (down to 50 nm) and detecting very low elemental concentrations (parts-per-million levels). This makes it ideally suited for trace element localisation in biological materials. This paper shows how the NanoSIMS can be used to investigate the localisation of As in rice grain at high resolution and how different treatments result in different distributions in the grain. The precise location of parts-per-million As concentrations and its localisation with other elements at the subcellular scale in rice roots are also shown. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Focuses on the comparative plant physiology of hyperaccumulate cadium in different ecotypes. Examination on the different ecotypes of T. caerulescens; Study on the techniques of plant molecular biology and biochemistry; identification of hyperaccumulate cadium.

The impact of soil properties on metal bioavailability to plants is well recognized. However, the effect of soil bioavailability parameters on toxicity threshold values for Cu in plants needs quantification. Eighteen European soils varying widely in soil properties were amended with CuCl2 to obtain a range of seven concentrations including an unamended control. Two plant toxicity assays, barley root elongation (4 d) and tomato shoot growth (21 d after emergence), were performed on each soil under controlled environment conditions. The effective concentration of added Cu causing 50% inhibition (EC50) ranged from 36 to 536 mg/kg soil and from 22 to 851 mg/kg soil for barley root elongation and tomato shoot growth, respectively, representing variation in EC50 among soils of 15- and 39-fold. Single regressions carried out between Cu toxicity threshold values and various soil properties showed that exchangeable calcium and soil cation exchange capacity (CEC; measured at soil pH) were the best single predictors for toxicity values from both plant tests. The inclusion of other soil properties, such as iron oxide concentration, soil pH, clay, or organic carbon content, further improved predictions. For risk assessment, we suggest that Cu toxicity threshold values (EC50) be normalized on the key soil property of CEC. If available, soil exchangeable calcium and iron oxide concentration would improve the normalization. [ABSTRACT FROM AUTHOR]

The bioavailability of metal contaminants in soils varies widely, depending on soil characteristics and the source of the contaminant. As a consequence, site-specific risk assessment requires accurate prediction of the bioavailable (or labile) fraction of soil metal. Moreover, metals in soil are subject to time-dependent processes, which affect their bioavailability and thereby complicate the prediction of future risk. The aim of the present study was to describe the development of simple, readily applicable models for the time-dependent changes in lability of Cd and Zn in soils. We present data showing the time-dependent behavior of radiolabile and soil solution concentrations of Cd and Zn during an incubation study over a period of 813 d in 23 diverse soils. The data are used to parameterize candidate models of metal fixation in soils designed to be readily applicable and therefore relevant to risk assessment. We conclude that the final extent of metal fixation increases with pH and generally is greater for Zn than for Cd; however, the rate of fixation is independent of pH and equivalent to a half-time to equilibrium of 29 and 89 d for Cd and Zn, respectively. It is possible that longer-term processes occur, especially for Zn, but these could not be detected in the present study. [ABSTRACT FROM AUTHOR]

The toxicity effect concentrations (10% effective concentration [EC10] and 50% effective concentration [EC50]) of total added Cu derived from barley root elongation and tomato growth assays varied widely among 18 European soils. We investigated whether this variation could be explained by the solubility or speciation of Cu in soil solutions or the diffusive gradients in thin-films (DGT) measurement. Solubility and Cu speciation varied greatly among the soils tested. However, the EC10 and EC50 of soil solution Cu or free Cu2+ activity varied even more widely than those based on the total added Cu, indicating that solubility or soil solution speciation alone could not explain intersoil variation in Cu toxicity. Estimated EC10 and EC50 of free Cu2+ activity correlated closely and negatively with soil pH, indicating a protective effect of H+, which is consistent with the biotic ligand model concept. The DGT measurement was found to narrow the intersoil variation in EC50 considerably and to be a better predictor of plant Cu concentrations than either soil solution Cu or free Cu2+ activity. We conclude that plant bioavailability of Cu in soil depends on Cu speciation, interactions with protective ions (particularly H+), and the resupply from the solid phase, and we conclude that the DGT measurement provides a useful indicator of Cu bioavailability in soil. [ABSTRACT FROM AUTHOR]