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This study addresses the effect of using animal excreta on the nutritional content of forages, focusing on macro- and micro-element concentrations (nitrogen; N, phosphorus; P, sulphur; S, copper; Cu, zinc; Zn, manganese; Mn, selenium; Se) from animal feed to excreta, soil, and plants. Data were collected from pot and field trials using separate applications of sheep or cattle urine and faeces. Key findings indicate that soil organic carbon (SOC) and the type of excreta significantly influences nutrient uptake by forages, with varied responses among the seven elements defined above. Although urine contributes fewer micronutrients compared to faeces (as applied at a natural volume/mass basis, respectively), it notably improves forage yield and micronutrient accumulation, thus potentially delivering positive consequences at the farm level regarding economic performance and soil fertility when swards upon clayey soil types receive said urine in temperate agro-climatic regions (i.e., South West England in the current context). In contrast, faeces application in isolation hinders Se and Mn uptake, once again potentially delivering unintended consequences such as micronutrient deficiencies in areas of high faeces deposition. As it is unlikely that (b)ovine grazing fields will receive either urine or faeces in isolation, we also explored combined applications of both excreta types which demonstrates synergistic effects on N, Cu, and Zn uptake, with either synergistic or dilution effects being observed for P and S, depending largely on SOC levels. Additionally, interactions between excreta types can result in dilution or antagonistic effects on Mn and Se uptake. Notably, high SOC combined with faeces reduces Mn and Se in forages, raising concerns for grazed ruminant systems under certain biotic situations, e.g., due to insufficient soil Se levels typically observed in UK pastures for livestock growth. These findings underscore the importance of considering SOC and excreta nutritional composition when designing forage management to optimize nutrient uptake. It should be noted that these findings have potential ramifications for broader studies of sustainable agriculture through system-scale analyses, as the granularity of results reported herein elucidate gaps in knowledge which could affect, both positively and negatively, the interpretation of model-based environmental impact assessments of cattle and sheep production (e.g., in the case of increased yields [beneficial] or the requirement of additional synthetic supplementation [detrimental])., (© 2024. The Author(s).)

Enhanced rock weathering (EW) is an emerging atmospheric carbon dioxide removal (CDR) strategy being scaled up by the commercial sector. Here, we combine multiomics analyses of belowground microbiomes, laboratory-based dissolution studies, and incubation investigations of soils from field EW trials to build the case for manipulating iron chelators in soil to increase EW efficiency and lower costs. Microbial siderophores are high-affinity, highly selective iron (Fe) chelators that enhance the uptake of Fe from soil minerals into cells. Applying RNA-seq metatranscriptomics and shotgun metagenomics to soils and basalt grains from EW field trials revealed that microbial communities on basalt grains significantly upregulate siderophore biosynthesis gene expression relative to microbiomes of the surrounding soil. Separate in vitro laboratory incubation studies showed that micromolar solutions of siderophores and high-affinity synthetic chelator (ethylenediamine- N , N '-bis-2-hydroxyphenylacetic acid, EDDHA) accelerate EW to increase CDR rates. Building on these findings, we develop a potential biotechnology pathway for accelerating EW using the synthetic Fe-chelator EDDHA that is commonly used in agronomy to alleviate the Fe deficiency in high pH soils. Incubation of EW field trial soils with potassium-EDDHA solutions increased potential CDR rates by up to 2.5-fold by promoting the abiotic dissolution of basalt and upregulating microbial siderophore production to further accelerate weathering reactions. Moreover, EDDHA may alleviate potential Fe limitation of crops due to rising soil pH with EW over time. Initial cost-benefit analysis suggests potassium-EDDHA could lower EW-CDR costs by up to U.S. $77 t CO 2 ha -1 to improve EW's competitiveness relative to other CDR strategies.

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., (© 2023 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Background and Aims: The intake of selenium, an essential element for animals and humans, in ruminants is largely determined by selenium concentration in ingested forages, which take up selenium mainly from soil. Ruminant excreta is a common source of organic fertilizer, which provides both nutrients and organic matter. This study aims to unentangle the unclear effect of applying different types of ruminant excreta in soils of different organic matter contents on selenium uptake by forage., Methods: Perennial ryegrass ( Lolium perenne ) was grown in soils of different organic matter contents. Urine and/or feces collected from sheep fed with organic or inorganic mineral supplements, including selenium, were applied to the soils. The selenium in the collected samples were analyzed using ICP-MS. The associated biogeochemical reactions were scrutinized by wet chemistry., Results: The application of urine and/or feces resulted in either the same or lower selenium concentrations in perennial ryegrass. The excreta type did not affect total selenium accumulation in grass grown in low organic matter soil, whereas in high organic matter soil, feces resulted in significantly lower total selenium accumulation than urine, which was attributed to a possible interaction of selenium sorption in soil and microbial reduction of Se., Conclusion: This one-time excreta application did not increase, but further decrease in some treatments, selenium concentration and accumulation in the perennial ryegrass. Consequently, to increase ruminant selenium intake, supplementing selenium directly to animals is more recommended than applying animal manure to soil, which might drive selenium reduction and decrease selenium uptake by grass., Supplementary Information: The online version contains supplementary material available at 10.1007/s11104-023-05898-8., Competing Interests: Competing interestsAlltech Ltd., who provided funding for the lead author (Pei-Tzu Kao)’s PhD, which involves the work included in the current study., (© The Author(s) 2023.)

The use of multispecies swards on livestock farms is growing due to the wide range of benefits they bring, such as improved biomass yield and animal performance. Preferential uptake of micronutrients by some plant species means the inclusion of legumes and forbs in grass-dominated pasture swards could improve micronutrient provision to livestock via careful species selection. However, although soil properties affect plant micronutrient concentrations, it is unknown whether choosing 'best-performing' species, in terms of their micronutrient content, needs to be soil-specific or whether the recommendations can be more generic. To address this question, we carried out an experiment with 15 common grass, forb and legume species grown on four soils for five weeks in a controlled environment. The soils were chosen to have contrasting properties such as texture, organic matter content and micronutrient concentrations. The effect of soil pH was tested on two soils (pH 5.4 and 7.4) chosen to minimise other confounding variables. Yield was significantly affected by soil properties and there was a significant interaction with botanical group but not species within a botanical group (grass, forb or legume). There were differences between botanical groups and between species in both their micronutrient concentrations and total uptake. Micronutrient herbage concentrations often, but not always, reflected soil micronutrient concentrations. There were soil-botanical group interactions for micronutrient concentration and uptake by plants, but the interaction between plant species (within a botanical group) and soil was significant only for forbs, and predominantly occurred when considering micronutrient uptake rather than concentration. Generally, plants had higher yields and micronutrient contents at pH 5.4 than 7.4. Forbs tended to have higher concentrations of micronutrients than other botanical groups and the effect of soil on micronutrient uptake was only significant for forbs., Competing Interests: The authors have declared that no competing interests exist.

Growth at increased concentrations of CO 2 induces a reduction in seed zinc (Zn) and iron (Fe). Using Arabidopsis thaliana, we investigated whether this could be mitigated by reducing the elevated CO 2 -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 CO 2 . ACA7 is expressed in guard cells. When aca7 mutants are grown at 1000 ppm CO 2 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 CO 2 ., (© 2022 The Authors. New Phytologist © 2022 New Phytologist Foundation.)

Realistic targets for soil organic carbon (SOC) concentrations are needed, accounting for differences between soils and land uses. We assess the use of SOC/clay ratio for this purpose by comparing changes over time in (a) the National Soil Inventory of England and Wales, first sampled in 1978-1983 and resampled in 1994-2003, and (b) two long-term experiments under ley-arable rotations on contrasting soils in the East of England. The results showed that normalising for clay concentration provides a more meaningful separation between land uses than changes in SOC alone. Almost half of arable soils in the NSI had degraded SOC/clay ratios (< 1/13), compared with just 5% of permanent grass and woodland soils. Soils with initially large SOC/clay ratios (≥ 1/8) were prone to greater losses of SOC between the two NSI samplings than those with smaller ratios. The results suggest realistic long-term targets for SOC/clay in arable, ley grass, permanent grass and woodland soils are 1/13, 1/10, and > 1/8, respectively. Given the wide range of soils and land uses across England and Wales in the datasets used to test these targets, they should apply across similar temperate regions globally, and at national to sub-regional scales., (© 2022. The Author(s).)

With the increasing popularity of local blending of fertilisers, the fertiliser industry faces issues regarding quality control and fertiliser adulteration. Another problem is the contamination of fertilisers with trace elements that have been shown to subsequently accumulate in the soil and be taken up by plants, posing a danger to the environment and human health. Conventional characterisation methods necessary to ensure the quality of fertilisers and to comply with local regulations are costly, time consuming and sometimes not even accessible. Alternatively, using a wide range of unamended and intentionally amended fertilisers this study developed empirical calibrations for a portable handheld X-ray fluorescence (pXRF) spectrometer, determined the reliability for estimating the macro and micro nutrients and evaluated the use of the pXRF for the high-throughput detection of trace element contaminants in fertilisers. The models developed using pXRF for Mg, P, S, K, Ca, Mn, Fe, Zn and Mo had R2 values greater or equal to 0.97. These models also performed well on validation, with R2 values greater or equal to 0.97 (except for Fe, R2val = 0.55) and slope values ranging from 0.81 to 1.44. A second set of models were developed with a focus on trace elements in amended fertilisers. The R2 values of calibration for Co, Ni, As, Se, Cd and Pb were greater than or equal to 0.80. At concentrations up to 1000 mg kg-1, good validation statistics were also obtained; R2 values ranged from 0.97-0.99, except in one instance. The regression coefficients of the validation also had good prediction in the range of 0-100 mg kg-1 (R2 values were from 0.78-0.99), but not as well at lower concentrations up to 20 mg kg-1 (R2 values ranged from 0.10-0.99), especially for Cd. This study has demonstrated that pXRF can measure several major (P, Ca) and micro (Mn, Fe, Cu) nutrients, as well as trace elements and potential contaminants (Cr, Ni, As) in fertilisers with high accuracy and precision. The results obtained in this study is good, especially considering that loose powders were scanned for a maximum of 90 seconds without the use of a vacuum pump., Competing Interests: The authors have declared that no competing interests exist.

Plastics are ubiquitous contaminants that leak into the environment from multiple pathways including the use of treated sewage sludge (biosolids). Seven common plastics (polymers) were quantified in the solid fraction of archived biosolids samples from Australia and the United Kingdom from between 1950 and 2016. Six plastics were detected, with increasing concentrations observed over time for each plastic. Biosolids plastic concentrations correlated with plastic production estimates, implying a potential link between plastics production, consumption and leakage into the environment. Prior to the 1990s, the leakage of plastics into biosolids was limited except for polystyrene. Increased leakage was observed from the 1990s onwards; potentially driven by increased consumption of polyethylene, polyethylene terephthalate and polyvinyl chloride. We show that looking back in time along specific plastic pollution pathways may help unravel the potential sources of plastics leakage into the environment and provide quantitative evidence to support the development of source control interventions or regulations., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Soil property and class maps for the continent of Africa were so far only available at very generalised scales, with many countries not mapped at all. Thanks to an increasing quantity and availability of soil samples collected at field point locations by various government and/or NGO funded projects, it is now possible to produce detailed pan-African maps of soil nutrients, including micro-nutrients at fine spatial resolutions. In this paper we describe production of a 30 m resolution Soil Information System of the African continent using, to date, the most comprehensive compilation of soil samples ([Formula: see text]) and Earth Observation data. We produced predictions for soil pH, organic carbon (C) and total nitrogen (N), total carbon, effective Cation Exchange Capacity (eCEC), extractable-phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), sodium (Na), iron (Fe), zinc (Zn)-silt, clay and sand, stone content, bulk density and depth to bedrock, at three depths (0, 20 and 50 cm) and using 2-scale 3D Ensemble Machine Learning framework implemented in the mlr (Machine Learning in R) package. As covariate layers we used 250 m resolution (MODIS, PROBA-V and SM2RAIN products), and 30 m resolution (Sentinel-2, Landsat and DTM derivatives) images. Our fivefold spatial Cross-Validation results showed varying accuracy levels ranging from the best performing soil pH (CCC = 0.900) to more poorly predictable extractable phosphorus (CCC = 0.654) and sulphur (CCC = 0.708) and depth to bedrock. Sentinel-2 bands SWIR (B11, B12), NIR (B09, B8A), Landsat SWIR bands, and vertical depth derived from 30 m resolution DTM, were the overall most important 30 m resolution covariates. Climatic data images-SM2RAIN, bioclimatic variables and MODIS Land Surface Temperature-however, remained as the overall most important variables for predicting soil chemical variables at continental scale. This publicly available 30-m Soil Information System of Africa aims at supporting numerous applications, including soil and fertilizer policies and investments, agronomic advice to close yield gaps, environmental programs, or targeting of nutrition interventions.

Zinc (Zn) is an important element determining the grain quality of staple food crops and deficient in many Ethiopian soils. However, farming systems are highly variable in Ethiopia due to different soil types and landscape cropping positions. Zinc availability and uptake by plants from soil and fertilizer sources are governed by the retention and release potential of the soil, usually termed as adsorption and desorption, respectively. The aim of this study was to characterize the amount of plant available Zn at different landscape positions. During the 2018/19 cropping season, adsorption-desorption studies were carried out on soil samples collected from on-farm trials conducted at Aba Gerima, Debre Mewi and Markuma in the Amhara Region. In all locations and landscape positions, adsorption and desorption increased with increasing Zn additions. The amount of adsorption and desorption was highly associated with the soil pH, the soil organic carbon concentration and cation exchange capacity, and these factors are linked to landscape positions. The Freundlich isotherm fitted very well to Zn adsorption (r 2 0.87-0.99) and desorption (r 2 0.92-0.99), while the Langmuir isotherm only fitted to Zn desorption (r 2 0.70-0.93). Multiple regression models developed by determining the most influential soil parameters for Zn availability could be used to inform Zn fertilizer management strategies for different locations and landscape positions in this region, and thereby improve plant Zn use efficiency.

Spectroscopic methods for the determination of soil texture are faster and cheaper than the standard methods, but how do the results compare? To address this question, laser diffraction analysis (LDA) and mid-infrared spectroscopy (MIRS) analysis have been compared to conventional sieve-pipette measurements of texture in diverse European and Kenyan soils. To our knowledge this comparison between LDA and MIRS has not been made previously. It has used soils with a broad range of organic carbon (OC) contents to investigate whether, as in other techniques, clay-OC aggregation affects the estimation of clay with MIRS. The MIRS predictions of clay content were much better than the LDA measurements, but both techniques gave good measurements of sand content. The MIRS over-estimated clay at low clay content and under-estimated at high clay content (calibration set R 2  = 0.83). The LDA over-estimated clay by ~ 60% (calibration set R 2  = 0.36), indicating that the widely used clay threshold of < 8 µm was too high, and < 4 µm was found to be more accurate. In samples with < 5% OC content, both the LDA and MIRS gave very good clay predictions (R 2  = 0.88 and 0.81, respectively). But in predictions of clay content in samples with > 5% OC the LDA under-estimated (R 2  =  < 0.1) and MIRS over-estimated (R 2  = 0.34) clay content. In soils with OC removed, the MIRS prediction of clay content improved, indicating interference between over-lapping spectral regions for organic and mineral constituents. Unlike granulometric measurements of texture such as the LDA, MIRS analysis is not subject to the limitations imposed by the shape and density of particles. It was concluded that in typical agricultural soils with < 5% OC and < 60% clay content, both techniques could be used for cheap, fast and reliable estimates of soil texture.

The current study focuses on yield and nutritional quality changes of wheat grain over the last 166 years. It is based on wheat grain quality analyses carried out on samples collected between 1850 and 2016. Samples were obtained from the Broadbalk Continuous Wheat Experiment (UK) and from herbaria from 16 different countries around the world. Our study showed that, together with an increase in carbohydrate content, an impoverishment of mineral composition and protein content occurred. The imbalance in carbohydrate/protein content was specially marked after the 1960's, coinciding with strong increases in ambient [CO 2 ] and temperature and the introduction of progressively shorter straw varieties. The implications of altered crop physiology are discussed.

Portable X-ray fluorescence (pXRF) and Diffuse Reflectance Fourier Transformed Mid-Infrared (DRIFT-MIR) spectroscopy are rapid and cost-effective analytical tools for material characterization. Here, we provide an assessment of these methods for the analysis of total Carbon, Nitrogen and total elemental composition of multiple elements in organic amendments. We developed machine learning methods to rapidly quantify the concentrations of macro- and micronutrient elements present in the samples and propose a novel system for the quality assessment of organic amendments. Two types of machine learning methods, forest regression and extreme gradient boosting, were used with data from both pXRF and DRIFT-MIR spectroscopy. Cross-validation trials were run to evaluate generalizability of models produced on each instrument. Both methods demonstrated similar broad capabilities in estimating nutrients using machine learning, with pXRF being suitable for nutrients and contaminants. The results make portable spectrometry in combination with machine learning a scalable solution to provide comprehensive nutrient analysis for organic amendments., Competing Interests: The authors have declared that no competing interests exist.

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., (© 2019 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.)

The phosphorus (P) supply from soils is crucial to crop production. Given the complexity involved in P-cycling, a model that can simulate the major P-cycling processes and link with other nutrients and environmental factors, e.g., soil temperature and moisture, would be a useful tool. The aim of this study was to describe a process-based P module added to the SPACSYS (Soil Plant and Atmosphere Continuum System) model and to evaluate its predictive capability on the dynamics of P content in crops and the impact of soil P status on crop growth. A P-cycling module was developed and linked to other modules included in the SPACSYS model. We used a winter wheat ( Triticum aestivum, cv Xi-19) field experiment at Rothamsted Research in Harpenden to calibrate and validate the model. Model performance statistics show that the model simulated aboveground dry matter, P accumulation and soil moisture dynamics reasonably well. Simulated dynamics of soil nitrate and ammonium were close to the observed data when P fertiliser was applied. However, there are large discrepancies in fields without P fertiliser. This study demonstrated that the SPACSYS model was able to investigate the interactions between carbon, nitrogen, P and water in a single process-based model after the tested P module was implemented.

Contamination of cadmium (Cd) in paddy soil is a serious environmental problem threatening food safety in some parts of southern China, where rice grain Cd concentration often exceeds the Chinese limit (0.2 mg kg -1 ). We tested the effect of CaCO 3 liming combined with growing low Cd cultivars on Cd accumulation in rice grain in 2-year field trials. A liming model was used to predict the doses of lime required. Lime (2.25-7.5 t ha -1 ) was applied in 2016 only and the effect monitored in both 2016 and 2017. Soil pH was increased from the initial 5.5 to the target value 6.5 by 7.5 t ha -1 CaCO 3 . Liming greatly reduced CaCl 2 -extractable Cd in the rhizospheric soil. Grain Cd concentration in the control exceeded the limit by 2-5 times. Liming at 7.5 t ha -1 decreased grain Cd concentration by 70-80% in both seasons without affecting grain yield. Grain Cd concentration was below the limit in the 7.5 t ha -1 liming treatment in both seasons. Grain Cd concentration correlated closely with CaCl 2 -extractable Cd in rhizospheric soil at the grain maturing stage. Seasonal difference in grain Cd concentration was attributed to the soil water status at the grain maturing stage. Liming had no significant effect on grain arsenic concentration or speciation. A single application of CaCO 3 to raise soil pH to 6.5, combined with low Cd cultivars and delayed drainage of paddy water during late grain filling stage, was highly effective at reducing Cd accumulation in rice grain., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The increasingly widespread usage of silver (Ag) nanoparticles has raised concerns regarding their environmental risk. The behavior of Ag and its transfer risk to the food chain were investigated using a long-term field experiment that commenced in 1942 in which Ag-containing sewage sludge was repeatedly applied to the soil (25 applications during 20 years). The speciation of the Ag in both the sludge and the soils retrieved from the long-term experimental archive was examined using synchrotron-based X-ray absorption spectroscopy, and extractable Ag concentrations from soils were determined using 0.01 M Ca(NO 3 ) 2 and 0.005 M DTPA. The total Ag in the sludge during the time period of 1942-1961 ranged from 155 to 463 mg kg -1 . These values are 1-2 orders of magnitude higher than those in currently produced sludge (ca. 0.5-20 mg kg -1 ). Long-term repeated applications of these sludges resulted in an increase of Ag in soils from 1.9 mg kg -1 in the control to up to 51 mg kg -1 . The majority (>80%) of the Ag in both the sludge and the sludge-treated soils was present as insoluble Ag 2 S, thereby markedly reducing the bioavailability of this Ag. Concentrations of Ag in the archived crop samples were generally <0.70 mg kg -1 in edible tissues, much less than those in diets that may cause an adverse effects in animals and humans (>100 mg kg -1 ). These data indicate that the transfer of Ag (derived from both traditional Ag industry and current nano Ag industry) to the terrestrial food chain is limited.

Previous studies have shown that the Nodulin 26-like intrinsic membrane protein (NIP) Lsi1 (OsNIP2;1) is involved in arsenite [As(III)] uptake in rice (Oryza sativa). However, the role of other rice NIPs in As(III) accumulation in planta remains unknown. In the present study, we investigated the role OsNIP3;2 in As(III) uptake in rice. When expressed in Xenopus laevis oocytes, OsNIP3;2 showed a high transport activity for As(III). Quantitative real-time RT-PCR showed that the expression of OsNIP3;2 was suppressed by 5 µM As(III), but enhanced by 20 and 100 µM As(III). Transgenic rice plants expressing OsNIP3;2pro-GUS showed that the gene was predominantly expressed in the lateral roots and the stele region of the primary roots. Transient expression of OsNIP3;2:GFP fusion protein in rice protoplasts showed that the protein was localized in the plasma membrane. Knockout of OsNIP3;2 significantly decreased As concentration in the roots, but had little effect on shoot As concentration. Synchrotron microfocus X-ray fluorescence showed decreased As accumulation in the stele of the lateral roots in the mutants compared with wild-type. Our results indicate that OsNIP3;2 is involved in As(III) uptake by lateral roots, but its contribution to As accumulation in the shoots is limited., (© The Author 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Mineral binding is a major mechanism for soil carbon (C) stabilization, and mineral availability for C binding critically affects C storage. Yet, the mechanisms regulating mineral availability are poorly understood. Here, we showed that organic amendments in three long-term (23, 154, and 170 yrs, respectively) field experiments significantly increased mineral availability, particularly of short-range-ordered (SRO) phases. Two microcosm studies demonstrated that the presence of roots significantly increased mineral availability and promoted the formation of SRO phases. Mineral transformation experiments and isotopic labeling experiments provided direct evidence that citric acid, a major component of root exudates, promoted the formation of SRO minerals, and that SRO minerals acted as "nuclei" for C retention. Together, these findings indicate that soil organic amendments initialize a positive feedback loop by increasing mineral availability and promoting the formation of SRO minerals for further C binding, thereby possibly serving as a management tool for enhancing carbon storage in soils.

Deficiencies of micronutrients, including essential trace elements, affect up to 3 billion people worldwide. The dietary availability of trace elements is determined largely by their soil concentrations. Until now, the mechanisms governing soil concentrations have been evaluated in small-scale studies, which identify soil physicochemical properties as governing variables. However, global concentrations of trace elements and the factors controlling their distributions are virtually unknown. We used 33,241 soil data points to model recent (1980-1999) global distributions of Selenium (Se), an essential trace element that is required for humans. Worldwide, up to one in seven people have been estimated to have low dietary Se intake. Contrary to small-scale studies, soil Se concentrations were dominated by climate-soil interactions. Using moderate climate-change scenarios for 2080-2099, we predicted that changes in climate and soil organic carbon content will lead to overall decreased soil Se concentrations, particularly in agricultural areas; these decreases could increase the prevalence of Se deficiency. The importance of climate-soil interactions to Se distributions suggests that other trace elements with similar retention mechanisms will be similarly affected by climate change.

Land applications of municipal sewage sludge may pose a risk of introducing antibiotic resistance genes (ARGs) from urban environments into agricultural systems. However, how the sewage sludge recycling and application method influence soil resistome and mobile genetic elements (MGEs) remains unclear. In the present study, high through-put quantitative PCR was conducted on the resistome of soils from a field experiment with past (between 1994 and 1997) and annual (since 1994) applications of five different sewage sludges. Total inputs of organic carbon were similar between the two modes of sludge applications. Intrinsic soil resistome, defined as the ARGs shared by the soils in the control and sludge-amended plots, consisted of genes conferring resistance to multidrug, β-lactam, Macrolide-Lincosamide-Streptogramin B (MLSB), tetracycline, vancomycin, and aminoglycoside, with multidrug resistance genes as the most abundant members. There was a strong correlation between the abundance of ARGs and MGE marker genes in soils. The composition and diversity of ARGs in the five sludges were substantially different from those in soils. Considerable proportions of ARGs and MGE marker genes in the sludges attenuated following the application, especially aminoglycoside and tetracycline resistance genes. Annual applications posed a more significant impact on the soil resistome, through both continued introduction and stimulation of the soil intrinsic ARGs. In addition, direct introduction of sludge-specific ARGs into soil was observed especially from ARG-rich sludge. These results provide a better insight into the characteristics of ARG dissemination from urban environment to the agricultural system through sewage sludge applications.

The Long-Term Sludge Experiments (LTSE) began in 1994 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 soil microbial biomass carbon (C mic ) were monitored for 8 years (1997-2005) in sludge amended soils at nine UK field sites. To assess the statutory limits set by the UK Sludge (Use in Agriculture) Regulations the experimental data has been reviewed using the 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. The results presented here show that significant decreases in C mic have occurred in soils where the total concentrations of Zn and Cu fall below the current UK statutory limits. For soils receiving sewage sludge predominantly contaminated with Zn, decreases of approximately 7-11% were observed at concentrations below the UK statutory limit. The effect of Zn appeared to increase over time, with increasingly greater decreases in C mic observed over a period of 8 years. This may be due to an interactive effect between Zn and confounding Cu contamination which has augmented the bioavailability of these metals over time. Similar decreases (7-12%) in C mic were observed in soils receiving sewage sludge predominantly contaminated with Cu; however, C mic appeared to show signs of recovery after a period of 6 years. Application of sewage sludge predominantly contaminated with Cd appeared to have no effect on C mic at concentrations below the current UK statutory limit., (Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.)

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 biovar 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 MPN of -26.6% during the LTSE. The effect of Cu showed no significant effect on MPN at concentrations below the UK limits, although a -5% decrease in MPN was observed in soils where total Cu ranged from 100 to <135 mg kg. Overall, there was nothing to indicate that Cd had a significant effect on MPN below the current UK statutory limit. In summary, the UK statutory limit for Zn appears to be insufficient for protecting from Zn toxicity effects., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

One of the main pathways by which engineered nanoparticles (ENPs) enter the environment is through land application of waste water treatment plant (WWTP) sewage sludges. WWTP sludges, enriched with Ag and ZnO ENPs or their corresponding soluble metal salts during anaerobic digestion and subsequently mixed with soil (targeting a final concentration of 1400 and 140 mg/kg for Zn and Ag, respectively), were subjected to 6 months of ageing and leaching in lysimeter columns outdoors. Amounts of Zn and Ag leached were very low, accounting for <0.3% and <1.4% of the total Zn and Ag, respectively. No differences in total leaching rates were observed between treatments of Zn or Ag originally input to WWTP as ENP or salt forms. Phospholipid fatty acid profiling indicated a reduction in the fungal component of the soil microbial community upon metal exposure. However, overall, the leachate composition and response of the soil microbial community following addition of sewage sludge enriched either with ENPs or metal salts was very similar., (Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.)

We examined the effects of amending soil with biosolids produced from a pilot-scale wastewater treatment plant containing a mixture of metal-based engineered nanomaterials (ENMs) on the growth of Medicago truncatula, its symbiosis with Sinorhizobium meliloti, and on soil microbial community structure. Treatments consisted of soils amended with biosolids generated with (1) Ag, ZnO, and TiO2 ENMs introduced into the influent wastewater (ENM biosolids), (2) AgNO3, Zn(SO4)2, and micron-sized TiO2 (dissolved/bulk metal biosolids) introduced into the influent wastewater stream, or (3) no metal added to influent wastewater (control). Soils were amended with biosolids to simulate 20 years of metal loading, which resulted in nominal metal concentrations of 1450, 100, and 2400 mg kg(-1) of Zn, Ag, and Ti, respectively, in the dissolved/bulk and ENM treatments. Tissue Zn concentrations were significantly higher in the plants grown in the ENM treatment (182 mg kg(-1)) compared to those from the bulk treatment (103 mg kg(-1)). Large reductions in nodulation frequency, plant growth, and significant shifts in soil microbial community composition were found for the ENM treatment compared to the bulk/dissolved metal treatment. These results suggest differences in metal bioavailability and toxicity between ENMs and bulk/dissolved metals at concentrations relevant to regulatory limits.

Knowledge of arsenic (As) accumulation in rice (Oryza sativa L.) is important for minimizing As transfer to the food chain. The aim of this study was to investigate the role of rice nodes in As storage and distribution. Synchrotron μX-ray fluorescence (μ-XRF) was used to map As distribution in the top node and internode of a lsi2 mutant defective in silicon/arsenite efflux carrier and its wild-type (WT) grown in soil. Lsi2 expression in different tissues during grain filling was investigated by quantitative RT-PCR. Arsenite or dimethylarsinic acid (DMA) was supplied to excised panicles to investigate the roles of Lsi2 and phytochelatins (PC) in As distribution. μ-XRF mapping revealed As storage in the phloem of different vascular bundles in the top node and internode. Soil-grown plants of lsi2 had markedly decreased As accumulation in the phloem compared with the WT. Lsi2 was strongly expressed, not only in the roots but also in the nodes. When excised panicles were exposed to As(III), the lsi2 mutant distributed more As to the node and flag leaf but less As to the grain compared with the WT, while there was no significant difference in DMA distribution. Inhibition of PC synthesis by l-buthionine-sulphoximine decreased As(III) deposition in the top node but increased As accumulation in the grain and flag leaf. The results suggest that rice nodes serve as a filter restricting As(III) distribution to the grain. Furthermore, Lsi2 plays a role in As(III) distribution in rice nodes and phytochelatins are important compounds for As(III) storage in the nodes., (© The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

The Park Grass experiment (PGE) in the UK has been ongoing since 1856. Its purpose is to study the response of biological communities to the long-term treatments and associated changes in soil parameters, particularly soil pH. In this study, soil samples were collected across pH gradient (pH 3.6-7) and a range of fertilizers (nitrogen as ammonium sulfate, nitrogen as sodium nitrate, phosphorous) to evaluate the effects nutrients have on soil parameters and microbial community structure. Illumina 16S ribosomal RNA (rRNA) amplicon sequencing was used to determine the relative abundances and diversity of bacterial and archaeal taxa. Relationships between treatments, measured soil parameters, and microbial communities were evaluated. Clostridium, Bacteroides, Bradyrhizobium, Mycobacterium, Ruminococcus, Paenibacillus, and Rhodoplanes were the most abundant genera found at the PGE. The main soil parameter that determined microbial composition, diversity, and biomass in the PGE soil was pH. The most probable mechanism of the pH impact on microbial community may include mediation of nutrient availability in the soil. Addition of nitrogen to the PGE plots as ammonium sulfate decreases soil pH through increased nitrification, which causes buildup of soil carbon, and hence increases C/N ratio. Plant species richness and plant productivity did not reveal significant relationships with microbial diversity; however, plant species richness was positively correlated with soil microbial biomass. Plants responded to the nitrogen treatments with an increase in productivity and a decrease in the species richness.

China faces great challenges in protecting its soil from contamination caused by rapid industrialization and urbanization over the last three decades. Recent nationwide surveys show that 16% of the soil samples, 19% for the agricultural soils, are contaminated based on China’s soil environmental quality limits, mainly with heavy metals and metalloids. Comparisons with other regions of the world show that the current status of soil contamination, based on the total contaminant concentrations, is not worse in China. However, the concentrations of some heavy metals in Chinese soils appear to be increasing at much greater rates. Exceedance of the contaminant limits in food crops is widespread in some areas, especially southern China, due to elevated inputs of contaminants, acidic nature of the soil and crop species or cultivars prone to heavy metal accumulation. Minimizing the transfer of contaminants from soil to the food chain is a top priority. A number of options are proposed, including identification of the sources of contaminants to agricultural systems, minimization of contaminant inputs, reduction of heavy metal phytoavailability in soil with liming or other immobilizing materials, selection and breeding of low accumulating crop cultivars, adoption of appropriate water and fertilizer management, bioremediation, and change of land use to grow nonfood crops. Implementation of these strategies requires not only technological advances, but also social-economic evaluation and effective enforcement of environmental protection law.

Selenium (Se) biofortification of barley is a suitable strategy to increase the Se concentration in grain. In the present paper, the suitability of this Se-biofortified grain for making Se-enriched beer is analyzed. The aim of the present study was to evaluate the effect of different Se fertilizer doses (0, 10, and 20 g of Se ha(-1)) and forms (sodium selenate or sodium selenite) on the Se loss during the malting and brewing processes and Se speciation in grain, malt, wort, and beer. Samples were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS) and high-performance liquid chromatography (HPLC)-ICP-MS for total Se and speciation. Mashing-lautering was the process with the greatest Se loss (83.8%). After malting and brewing, only 7.3% of the initial Se was retained in beer, mainly in selenite form. Even so, the fertilizer application of sodium selenate at 20 g ha(-1) increased the total Se concentration almost 6-fold in the final beer in comparison to the use of grain derived from unfertilized barley. The present paper provides evidence that the use of Se-biofortified barley grain as a raw material to produce Se-enriched beer is possible, and the results are comparable to other methods in terms of efficiency.

Increasing nitrogen supply can increase Fe and Zn concentrations in wheat grain, but the underlying mechanisms remain unclear. Size-exclusion chromatography coupled with inductively coupled plasma mass spectrometry was used to determine Fe and Zn speciation in the soluble extracts of grain pearling fractions of two wheat cultivars grown at two N rates (100 and 350 kg of N ha(-1)). Increasing N supply increased the concentrations of total Fe and Zn and the portions of Fe and Zn unextractable with a Tris-HCl buffer and decreased the concentrations of Tris-HCl-extractable (soluble) Fe and Zn. Within the soluble fraction, Fe and Zn bound to low molecular weight compounds, likely to be Fe-nicotianamine and Fe-deoxymugineic acid or Zn-nicotianamine, were decreased by 5-12% and 4-37%, respectively, by the high N treatment, whereas Fe and Zn bound to soluble high molecular weight or soluble phytate fractions were less affected. The positive effect of N on grain Fe and Zn concentrations was attributed to an increased sink in the grain, probably in the form of water-insoluble proteins.

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.)

The mineral concentrations in cereals are important for human health, especially for individuals who consume a cereal subsistence diet. A number of elements, such as zinc, are required within the diet, while some elements are toxic to humans, for example arsenic. In this study we carry out genome-wide association (GWA) mapping of grain concentrations of arsenic, copper, molybdenum and zinc in brown rice using an established rice diversity panel of ∼ 300 accessions and 36.9 k single nucleotide polymorphisms (SNPs). The study was performed across five environments: one field site in Bangladesh, one in China and two in the US, with one of the US sites repeated over two years. GWA mapping on the whole dataset and on separate subpopulations of rice revealed a large number of loci significantly associated with variation in grain arsenic, copper, molybdenum and zinc. Seventeen of these loci were detected in data obtained from grain cultivated in more than one field location, and six co-localise with previously identified quantitative trait loci. Additionally, a number of candidate genes for the uptake or transport of these elements were located near significantly associated SNPs (within 200 kb, the estimated global linkage disequilibrium previously employed in this rice panel). This analysis highlights a number of genomic regions and candidate genes for further analysis as well as the challenges faced when mapping environmentally-variable traits in a highly genetically structured diversity panel.

This study aimed to determine differences among wheat cultivars in the distribution and speciation of Fe and Zn in grain milling fractions. Cultivars with higher Fe and Zn concentrations in the wholemeal flour were found to contain higher concentrations in the white flour. Soluble Fe and Zn were extracted and analyzed by size exclusion-inductively coupled plasma mass spectrometry. Fe speciation varied between milling fractions with a low molecular weight (LMW) complex likely to be Fe-deoxymugenic acid/nicotianamine being the predominant extractable Fe species in white flour, accounting for approximately 85% of the extractable Fe. Bran fractions had a lower amount of LMW-Fe form but more as soluble Fe-phytate and an unidentified high molecular weight peak. In the white flour fraction soluble Zn was found to be present mainly as a LMW peak likely to be Zn-nicotianamine complex. Soluble Fe-phytate was found in the white flour fraction of a high-Fe cultivar but not in a low-Fe cultivar.

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., (© 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.)

Archived samples from the Park Grass Experiment, established in 1856, were analysed to determine the impacts of long-term phosphate fertiliser applications on arsenic concentrations in soil and herbage. In plots receiving 35 kg P ha(-1) annually (+P), topsoil As concentrations almost doubled from an initial value of ∼10 mg kg(-1) during 1888-1947 and remained stable thereafter. The phosphate fertilisers used before 1948 contained 401-1575 mg As kg(-1), compared to 1.6-20.3 mg As kg(-1) in the later samples. Herbage samples from the +P plots collected during 1888-1947 contained significantly more As than those from the -P plots, but later samples did not differ significantly. Mass-balance calculations show that the increase in soil As can be explained by the As input from P fertiliser applications before 1948. The results demonstrate that the P fertilisers used on the Park Grass Experiment before 1948 caused substantial As contamination of the soil., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Methylation of arsenic in soil influences its environmental behavior and accumulation by plants, but little is known about the factors affecting As methylation. As speciation was determined in the pore waters of six soils from diverse geographical locations over 54 days of incubation under flooded conditions. The concentration of methylated As (monomethylarsonic acid, MMA, and dimethylarsinic acid, DMA) varied from 0 to 85 μg L(-1) (0 - 69% of the total As in pore water). Two Bangladeshi paddy soils contaminated by irrigation of As-laden groundwater produced large concentrations of inorganic As but relatively little methylated As. Two contaminated paddy soils from China produced a transient peak of DMA during the early phase of incubation. Methylated As represented considerable proportions of the total soluble As in the two uncontaminated soils from the UK and U.S. The copy number of the microbial arsenite methyltransferase gene (arsM) correlated positively with soil pH. However, pore-water methylated As correlated negatively with pH or arsM copy number, and positively with dissolved organic C. GeoChip assay revealed considerable arsM diversity among the six soils, with 27-35 out of 66 sequences in the microarray being detected. As speciation in rice plants grown in the soils generally mirrored that in the pore water. The results suggest that methylated As species in plants originated from the soil and As methylation in soil was influenced strongly by the soil conditions.

The free ion approach has been previously used to calculate critical limit concentrations for soil metals based on point estimates of toxicity. Here, the approach was applied to dose-response data for copper effects on seven biological endpoints in each of 19 European soils. The approach was applied using the concept of an effective dose, comprising a function of the concentrations of free copper and 'protective' major cations, including H(+). A significant influence of H(+) on the toxicity of Cu(2+) was found, while the effects of other cations were inconsistent. The model could be generalised by forcing the effect of H(+) and the slope of the dose-response relationship to be equal for all endpoints. This suggests the possibility of a general bioavailability model for copper effects on organisms. Furthermore, the possibility of such a model could be explored for other cationic metals such as nickel, zinc, cadmium and lead., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Agricultural land management, such as fertilization, liming, and tillage affects soil properties, including pH, organic matter content, nitrification rates, and the microbial community. Three different study sites were used to identify microorganisms that correlate with agricultural land use and to determine which factors regulate the relative abundance of the microbial signatures of the agricultural land-use. The three sites included in this study are the Broadbalk Experiment at Rothamsted Research, UK, the Everglades Agricultural Area, Florida, USA, and the Kellogg Biological Station, Michigan, USA. The effects of agricultural management on the abundance and diversity of bacteria and archaea were determined using high throughput, barcoded 16S rRNA sequencing. In addition, the relative abundance of these organisms was correlated with soil features. Two groups of microorganisms involved in nitrogen cycle were highly correlated with land use at all three sites. The ammonia oxidizing-archaea, dominated by Ca. Nitrososphaera, were positively correlated with agriculture while a ubiquitous group of soil bacteria closely related to the diazotrophic symbiont, Bradyrhizobium, was negatively correlated with agricultural management. Analysis of successional plots showed that the abundance of ammonia oxidizing-archaea declined and the abundance of bradyrhizobia increased with time away from agriculture. This observation suggests that the effect of agriculture on the relative abundance of these genera is reversible. Soil pH and NH3 concentrations were positively correlated with archaeal abundance but negatively correlated with the abundance of Bradyrhizobium. The high correlations of Ca. Nitrososphaera and Bradyrhizobium abundances with agricultural management at three long-term experiments with different edaphoclimatic conditions allowed us to suggest these two genera as signature microorganisms for agricultural land use.

The rootless duckweed Wolffia globosa can accumulate and tolerate relatively large amounts of arsenic (As); however, the underlying mechanisms were unknown. W. globosa was exposed to different concentrations of arsenate with or without l-buthionine sulphoximine (BSO), a specific inhibitor of γ-glutamylcysteine synthetase. Free thiol compounds and As(III)-thiol complexes were identified and quantified using HPLC - high resolution ICP-MS - accurate mass ESI-MS. Without BSO, 74% of the As accumulated in the duckweed was complexed with phytochelatins (PCs), with As(III)-PC(4) and As(III)-PC(3) being the main species. BSO was taken up by the duckweed and partly deaminated. The BSO treatment completely suppressed the synthesis of PCs and the formation of As(III)-PC complexes, and also inhibited the reduction of arsenate to arsenite. BSO markedly decreased both As accumulation and As tolerance in W. globosa. The results demonstrate an important role of PCs in detoxifying As and enabling As accumulation in W. globosa., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

To determine if long-term equilibration may alleviate molybdenum toxicity, earthworms, enchytraeids, collembolans and four plant species were exposed to three soils freshly spiked with Na(2)MoO(4).2H(2)O and equilibrated for 6 or 11 months in the field with free drainage. Total Mo concentrations in soil decreased by leaching, most (up to 98%) in sandy soil and less (54-62%) in silty and clayey soils. Changes in residual Mo toxicity with time were inconclusive in sandy soil. In the other two soils, toxicity of residual total Mo was significantly reduced after 11 months equilibration with a median 5.5-fold increase in ED50s. Mo fixation in soil, i.e. the decrease of soil solution Mo concentrations at equivalent residual total soil Mo, was maximally a factor of 2.1 only. This experiment shows natural attenuation of molybdate ecotoxicity under field conditions is related to leaching of excess Mo and other ions as well as to slow ageing reactions., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

• Inorganic arsenic (As(i) ) in rice (Oryza sativa) grains is a possible threat to human health, with risk being strongly linked to total dietary rice consumption and consumed rice As(i) content. This study aimed to identify the range and stability of genetic variation in grain arsenic (As) in rice. • Six field trials were conducted (one each in Bangladesh and China, two in Arkansas, USA over 2 yr, and two in Texas, USA comparing flooded and nonflood treatments) on a large number of common rice cultivars (c. 300) representing genetic diversity among international rice cultivars. • Within each field there was a 3-34 fold range in grain As concentration which varied between rice subpopulations. Importantly, As(i) correlated strongly with total As among a subset of 40 cultivars harvested in Bangladesh and China. • Genetic variation at all field sites was a large determining factor for grain As concentration, indicating that cultivars low in grain As could be developed through breeding. The temperate japonicas exhibited lower grain As compared with other subpopulations. Effects for year, location and flooding management were also statistically significant, suggesting that breeding strategies must take into account environmental factors., (© 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.)

• Inorganic arsenic (iAs) is a ubiquitous human carcinogen, and rice (Oryza sativa) is the main contributor to iAs in the diet. Methylated pentavalent As species are less toxic and are routinely found in plants; however, it is currently unknown whether plants are able to methylate As. • Rice, tomato (Solanum lycopersicum) and red clover (Trifolium pratense) were exposed to iAs, monomethylarsonic acid (MMA(V)), or dimethylarsinic acid (DMA(V)), under axenic conditions. Rice seedlings were also grown in two soils under nonsterile flooded conditions, and rice plants exposed to arsenite or DMA(V) were grown to maturity in nonsterile hydroponic culture. Arsenic speciation in samples was determined by HPLC-ICP-MS. • Methylated arsenicals were not found in the three plant species exposed to iAs under axenic conditions. Axenically grown rice was able to take up MMA(V) or DMA(V), and reduce MMA(V) to MMA(III) but not convert it to DMA(V). Methylated As was detected in the shoots of soil-grown rice, and in rice grain from nonsterile hydroponic culture. GeoChip analysis of microbial genes in a Bangladeshi paddy soil showed the presence of the microbial As methyltransferase gene arsM. • Our results suggest that plants are unable to methylate iAs, and instead take up methylated As produced by microorganisms., (© 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.)

Selenium (Se) hyperaccumulator plants can concentrate the toxic element Se up to 1% of shoot (DW) which is known to protect hyperaccumulator plants from generalist herbivores. There is evidence for Se-resistant insect herbivores capable of feeding upon hyperaccumulators. In this study, resistance to Se was investigated in seed chalcids and seed beetles found consuming seeds inside pods of Se-hyperaccumulator species Astragalus bisulcatus and Stanleya pinnata. Selenium accumulation, localization and speciation were determined in seeds collected from hyperaccumulators in a seleniferous habitat and in seed herbivores. Astragalus bisulcatus seeds were consumed by seed beetle larvae (Acanthoscelides fraterculus Horn, Coleoptera: Bruchidae) and seed chalcid larvae (Bruchophagus mexicanus, Hymenoptera: Eurytomidae). Stanleya pinnata seeds were consumed by an unidentified seed chalcid larva. Micro X-ray absorption near-edge structure (µXANES) and micro-X-Ray Fluorescence mapping (µXRF) demonstrated Se was mostly organic C-Se-C forms in seeds of both hyperaccumulators, and S. pinnata seeds contained ∼24% elemental Se. Liquid chromatography-mass spectrometry of Se-compounds in S. pinnata seeds detected the C-Se-C compound seleno-cystathionine while previous studies of A. bisulcatus seeds detected the C-Se-C compounds methyl-selenocysteine and γ-glutamyl-methyl-selenocysteine. Micro-XRF and µXANES revealed Se ingested from hyperaccumulator seeds redistributed throughout seed herbivore tissues, and portions of seed C-Se-C were biotransformed into selenocysteine, selenocystine, selenodiglutathione, selenate and selenite. Astragalus bisulcatus seeds contained on average 5,750 µg Se g(-1), however adult beetles and adult chalcid wasps emerging from A. bisulcatus seed pods contained 4-6 µg Se g(-1). Stanleya pinnata seeds contained 1,329 µg Se g(-1) on average; however chalcid wasp larvae and adults emerging from S. pinnata seed pods contained 9 and 47 µg Se g(-1). The results suggest Se resistant seed herbivores exclude Se, greatly reducing tissue accumulation; this explains their ability to consume high-Se seeds without suffering toxicity, allowing them to occupy the unique niche offered by Se hyperaccumulator plants.

Many plant species are able to reduce arsenate to arsenite efficiently, which is an important step allowing detoxification of As through either efflux of arsenite or complexation with thiol compounds. It has been suggested that this reduction is catalyzed by ACR2, a plant homologue of the yeast arsenate reductase ScACR2. Silencing of AtACR2 was reported to result in As hyperaccumulation in the shoots of Arabidopsis thaliana. However, no information of the in vivo As speciation has been reported. Here, we investigated the effect of AtACR2 knockout or overexpression on As speciation, arsenite efflux from roots and As accumulation in shoots. T-DNA insertion lines, overexpression lines and wild-type (WT) plants were exposed to different concentrations of arsenate for different periods, and As speciation in plants and arsenite efflux were determined using HPLC-ICP-MS. There were no significant differences in As speciation between different lines, with arsenite accounting for >90% of the total extractable As in both roots and shoots. Arsenite efflux to the external medium represented on average 77% of the arsenate taken up during 6 h exposure, but there were no significant differences between WT and mutants or overexpression lines. Accumulation of As in the shoots was also unaffected by AtACR2 knockout or overexpression. Additionally, after exposure to arsenate, the yeast (Saccharomyces cerevisiae) strain with ScACR2 deleted showed similar As speciation as the WT with arsenite-thiol complexes being the predominant species. Our results suggest the existence of multiple pathways of arsenate reduction in plants and yeast.

Arsenic (As) accumulation in food crops such as rice is of major concern. To investigate whether phytoremediation can reduce As uptake by rice, the As hyperaccumulator Pteris vittata was grown in five contaminated paddy soils in a pot experiment. Over a 9-month period P. vittata removed 3.5-11.4% of the total soil As, and decreased phosphate-extractable As and soil pore water As by 11-38% and 18-77%, respectively. Rice grown following P. vittata had significantly lower As concentrations in straw and grain, being 17-82% and 22-58% of those in the control, respectively. Phytoremediation also resulted in significant changes in As speciation in rice grain by greatly decreasing the concentration of dimethylarsinic acid (DMA). In two soils the concentration of inorganic As in rice grain was decreased by 50-58%. The results demonstrate an effective stripping of bioavailable As from contaminated paddy soils thus reducing As uptake by rice., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Assessing environmental risks of metal contamination in soils is a complex task because the biologically effective concentrations of metals in soils vary widely with soil properties. The factors influencing the toxic effect of nickel (Ni) on root growth of barley (Hordeum vulgare) were re-evaluated using published data from both soil and hydroponic cultures. The electrical potential (ψ(0) (o) ) and ion activities ({I(z) }(0) (o) ) at the outer surfaces of root-cell plasma membranes (PMs) were computed as the basis of the re-evaluation. The reanalyses demonstrated that root growth was related to: the Ni(2+) activity at the PM surface, ({Ni(2+) }(0) (o) ); calcium (Ca) deficiency (related to {Ca(2+) }(0) (o) ); osmotic effects; and modification of intrinsic Ni(2+) toxicity by magnesium (Mg(2+) ; this appeared to exert an intrinsic (specific) ameliorating effect on intrinsic Ni(2+) toxicity). Electrostatic toxicity models (ETM) were developed to relate root growth to these factors (R(2)  > 0.751). Based on the ETM developed in soil culture and a Ni(2+) solid-solution partitioning model, critical metal concentrations in soils linked to a biological effect were well predicted for 16 European soils with a wide range of properties, indicating the potential utility of ETM in risk assessment of metals in terrestrial ecosystems., (© 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.)