No abstract is provided for this article.
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.
Selenium (Se) speciation in soil affects its bioavailability to crops. An analytical procedure for the determination of inorganic Se species (selenite and selenate) in soil extracts by anion-exchange liquid chromatography (LC) with ICP-MS detection has been developed, with 10-fold higher sensitivity than existing HGAAS-based soil Se measurements. A comparison of phosphate extraction solutions on agricultural soils amended with 20 µg kg–1 selenate or selenite was carried out, and a 0.016 M KH2PO4 extraction solution is recommended. Recovery of selenate was >91%; however, selenite recovery ranged between 18.5% and 46.1%, due to rapid binding to the soil. Soil preparation did not have a significant (p > 0.05) effect on the extractability of the selenate or selenite amendments. The stability of Se species in the phosphate extracts was variable, depending on temperature and storage time. Therefore, immediate (<1 h) analysis of the soil extracts is preferable. The method developed was applied to the determination of extractable Se from six arable soils in the UK. Extractable Se levels in these soils ranged between 6 and 13 µg kg–1 consisting of selenite and some soluble organic Se.
Asparagine is known to accumulate in wheat grain under conditions of sulphur deficiency, leading to increased levels of acrylamide formation during processing. Analyses of milling fractions and of the outer layers of the grain prepared by hand dissection showed that the highest levels of asparagine were present in the bran fractions and in particular the aleurone layer, when grain were grown with sufficient sulphur supply. However, even mild S deficiency resulted in disproportional increases in the asparagine contents of white flour fractions, implying that optimisation of yield in a conventional milling system is not an appropriate strategy for processing grain from sulphur-deficient crops.
The influence of soil characteristics on the phytoremediation potential of Thlaspi caerulescens is not well understood. We investigated the effect of soil pH and Cd concentration on plant Cd uptake on one soil type, and the variation in Cd uptake using a range of field contaminated soils. On soils with total Cd concentrations of 0.6–3.7mg kg−1, T. caerulescens (the Ganges ecotype) produced greater biomass in the pH range 5.1–7.6 than at pH 4.4. The highest plant Cd concentration (236mg kg−1) and Cd uptake (228μg pot−1) were observed at pH 5.1. On soils with total Cd concentrations of 2.6–314.8mg kg−1, shoot Cd concentrations were 10.9–1196mg kg−1. Multiple regression analysis indicated that higher Cd in soil, low pH (within the range of >5) and coarser texture were associated with higher Cd concentration and Cd uptake by T. caerulescens.
No abstract is provided for this article.
Sulphur deficiency has become increasingly widespread in wheat in the U.K. Growth, nutrient content and biochemical responses to S and N supply of a breadm
No abstract is provided for this article.
Thirty six rapeseed samples from a factorial designed nitrogen and sulphur trial were analysed for total glucosinolate content by the X‐ray fluorescence (X‐RF) and HPLC methods and for protein content by the Kjeldahl method. Protein content varied from 16.0 to 22.6%. Correction for seed protein content in the calculation of glucosinolate content by X‐RF significantly improved the agreement between the two methods of glucosinolate analysis. The following equation was used in the correction: Y = 14.99 [ S (mg g −1 )‐protein %/7.5].
No abstract is provided for this article.
With an increased incidence of S deficiency occurring in many crops due to reductions in S deposition from atmospheric sources there is a need to address the questions of optimum quantity and timing for application of S fertilisers. Recent reports have demonstrated...
Arabidopsis halleri is a Cd hyperaccumulator; however, the mechanisms involved in the root to shoot translocation of Cd are not well understood. In this study, we characterized Cd transfer from the root medium to xylem in this species. Arabidopsis halleri accumulated 1,500 mg kg(-1) Cd in the shoot without growth inhibition. A time-course experiment showed that the release of Cd into the xylem was very rapid; by 2 h exposure to Cd, Cd concentration in the xylem sap was 5-fold higher than that in the external solution. The concentration of Cd in the xylem sap increased linearly with increasing Cd concentration in the external solution. Cd transfer to the xylem was completely inhibited by the metabolic inhibitor carbonyl cyanide 3-chlorophenylhydrazone (CCCP). Cd concentration in the xylem sap was decreased by increasing the concentration of external Zn, but enhanced by Fe deficiency treatment. Analysis with 113Cd-nuclear magnetic resonance (NMR) showed that the chemical shift of 113Cd in the xylem sap was the same as that of Cd(NO3)2. Metal speciation with Geochem-PC also showed that Cd occurred mainly in the free ionic form in the xylem sap. These results suggest that Cd transfer from the root medium to the xylem in A. halleri is an energy-dependent process that is partly shared with Zn and/or Fe transport. Furthermore, Cd is translocated from roots to shoots in inorganic forms.
This review focusses on the transfers of metals and metalloids from soil to food and feed, based mostly on UK information. Published information on the behaviour of a number of these contaminants in soil–plant systems is used to evaluate which elements are likely to transfer to food and feed. Data on the concentrations of metals and metalloids in soils and other soil properties in England and Wales are used in models to illustrate the likelihood of transfers exceeding the maximum concentration limits in food and feed in European legislation. Information from crop and herbage quality surveys is used to compare with the output from models. In most cases, the modelled or observed concentrations in food and feed do not reach the maximum allowable concentrations. Of all the contaminants considered, Cd appears to be most likely to exceed limit concentrations under UK conditions, but at present, there is some difficulty predicting Pb uptake and As uptake into the edible parts of crops from soil. However, crops exceeding the food limits are more likely to be grown if those crops are vegetables and if soil limit concentrations and best soil management practices have not been followed (e.g. maintenance of high soil pH in the case of cationic metals). We discuss the gaps and uncertainties for different metals and metalloids and show the need to review the situation if food or feed maximum concentration limits are changed as new information becomes available on toxicology and dietary exposure.
