No abstract is provided for this article.
No abstract is provided for this article.
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.
No abstract is provided for this article.
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.
No abstract is provided for this article.
Copper (Cu) is an essential micronutrient for plant growth. However, the molecular mechanisms underlying Cu trafficking and distribution to different organs in rice (Oryza sativa) are poorly understood. Here, we report the function and role of Antioxidant Protein1 (OsATX1), a Cu chaperone in rice. Knocking out OsATX1 resulted in increased Cu concentrations in roots, whereas OsATX1 overexpression reduced root Cu concentrations but increased Cu accumulation in the shoots. At the reproductive stage, the concentrations of Cu in developing tissues, including panicles, upper nodes and internodes, younger leaf blades, and leaf sheaths of the main tiller, were increased significantly in OsATX1-overexpressing plants and decreased in osatx1 mutants compared with the wild type. The osatx1 mutants also showed a higher Cu concentration in older leaves. Yeast two-hybrid and bimolecular fluorescence complementation assays showed that OsATX1 interacts with the rice heavy metal P1B-ATPases HMA4, HMA5, HMA6, and HMA9. These results suggest that OsATX1 may function to deliver Cu to heavy metal P1B-ATPases for Cu trafficking and distribution in order to maintain Cu homeostasis in different rice tissues. In addition, heterologous expression of OsATX1 in the yeast (Saccharomyces cerevisiae) cadmium-sensitive mutant Δycf1 increased the tolerance to Cu and cadmium by decreasing their respective concentrations in the transformed yeast cells. Taken together, our results indicate that OsATX1 plays an important role in facilitating root-to-shoot Cu translocation and the redistribution of Cu from old leaves to developing tissues and seeds in rice.
Oxidation of thiosulphate (S2O3 2−) and tetrathionate (S4O6 2−), added at 300mgSkg−1 soil, was studied in four arable soils at 25°C, over incubation periods of 0, 3, 7, 10, 20 and 30d. Thiosulphate was oxidised rapidly to S4O6 2−, with most of the oxidation occurring within 3d. In contrast, S4O6 2− was oxidised to SO4 2− much more slowly. Oxidation of S4O6 2− varied with soil type, being slower in a loamy soil (pH 5.8) than in three other soils (clay loam, silty clay loam and loamy sand, pH 6.2–7.0). An incubation experiment using autoclaved Rothamsted soil indicated a large abiotic component in the oxidation of S2O3 2− to S4O6 2−, whereas the oxidation of S4O6 2− to SO4 2− was of a biological nature. Production of SO4 2− was more rapid from the S2O3 2− amendment than from the S4O6 2− amendment, which suggested that either S2O3 2− primed the S4O6 2− oxidisers, or microorganisms were present that could oxidise S2O3 2− to SO4 2−, but not S4O6 2− to SO4 2−.
No abstract is provided for this article.
