Biochemical mechanisms of rhizospheric Bacillus subtilis-facilitated phytoextraction by alfalfa under cadmium stress - Microbial diversity and metabolomics analyses.

The effects of Bacillus subtilis inoculation on the growth and Cd uptake of alfalfa were evaluated in this research using pot experiments, and the relevant biochemical mechanisms were first investigated by combined microbial diversity and nontarget metabolomics analyses. The results indicated that inoculation with alfalfa significantly decreased the amount of plant malondialdehyde (MDA) and improved the activities of plant antioxidant enzymes and soil nutrient cycling-involved enzymes, thereby promoting biomass by 29.4%. Inoculation also increased Cd bioavailability in rhizosphere soil by 12.0% and Cd removal efficiency by 139.3%. The biochemical mechanisms included enhanced bacterial diversity, transformed microbial community composition, regulated amounts of amino acids, fatty acids, carbohydrates, flavonoids and phenols in rhizosphere soil metabolites, and modulations of the corresponding Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. These responses were beneficial to microbial activity, nutrient cycling, and Cd mobilization, detoxification, and decontamination by alfalfa in soil. This study, especially the newly identified differential metabolites and metabolic pathways, provides new insights into mechanism revelation and strategy development in microbe-assisted phytomanagement of heavy metal-contaminated soils.

The effects of cement on some physical and chemical behavior for surface paste disposal method.

Environmental impacts resulting from conventional tailings disposal such as tailings dam accidents are a common problem for base metal mines around the world. In this context, laboratory-scale studies have been carried out on the Surface Paste Disposal (SPD) method, which is one of the alternative surface storage methods. In this study, three different SPD designs were tested; and volumetric water content, oxygen consumption, and matric suction sensors in first, fifth and 10th paste layers plus pH- electric conductivity (EC) values were all measured. Specifically, it was determined that the amount of oxygen in the environment required for the oxidation of sulfur minerals is reduced in the cemented layers in Design 3. In addition, the cement additive keeps the pH values of the seepage in an alkaline environment (over 7) so that it minimizes the risks of Acid Mine Drainage (AMD) and heavy metals mobilization at low pH values. Also, the EC values started a downward trend and ion dissolution decreased in designs with cemented layers. As a result, it was understood from the sensor measurements that the cemented layers act like a barrier.

EDTA application on agricultural soils affects microelement uptake of plants.

Chelates such as ethylenediaminetetraacetic acid (EDTA) enter soils via various sources but their effect on agricultural crops is mostly unknown. Sources of EDTA include industry, households, sewage water and agricultural practices. In a field experiment EDTA was applied in its free form at different rates (0, 150, 550, 1050kgha-1) to study its translocation in the soil profile and to evaluate its effect on yield and mineral composition of the cultivated crop, both in the year of application (oilseed rape) and in the following year (winter wheat). The results indicate that EDTA was translocated from the soil surface to deeper soil layers in the time-frame of the experiment. EDTA was still detectable in the rooting zone 19months after application, indicating its persistence in the soil. Only the highest EDTA rate (1050kgha-1) reduced vegetative growth of oilseed rape until stem elongation, but seed yield was not affected by EDTA application. EDTA application changed the mineral composition of plants. Higher phosphorus (P), sulphur (S), iron (Fe) and manganese (Mn) and lower cadmium (Cd) concentrations were determined in the seeds of oilseed rape. No yield effects of residual EDTA were observed for the following crop, winter wheat, but the Cd content in seeds was still lower in plots where EDTA had been applied in the previous year. Data show that EDTA application affects the mineral uptake of cultivated crops under field conditions.