Effects Of Engineered Bacteria And Plant Ash On Soil Cd Fractions And Wheat Growth In Contaminated Soils

Remediation of heavy metal-contaminated soil received great attention in the recent decades due to the high toxicity and increasing discharge of these pollutants. In contaminated soils, these toxic metals could be absorbed by crops and then enter into the food chains.Brown-red soil collected nearby Shizi mountain, Wuhan, and treated with various levels of Cd (0,1,2,4 mg kg-1 soil) was used in this study, to evaluate the effect of plant ash and genetically engineered bacteria (Pseudomonas putida) on the immobilization and biotoxicity of Cd in wheat(Triticum aestivum L.) potted soils.The main results are outlined as follows:1.No significant changes were observed in soil pH and activity of soil enzymes after application of genetically engineered bacteria. However, soil pH increased by 0.83～1.01 units after application of plant ash with a concentration of 10 g kg-1 soil. Moreover, the activities of sucrose, urease, catalase were promoted with the highest increase by 4.13 times, but that of phosphatase was depressed by 8.18～49.94%.2.In Cd-contaminated soils, the species of Cd were redistributed after application of plant ash and engineered bacteria. The introduction of plant ash caused soluble/exchangeable Cd to convert to inorganic-bound form. In all treated soils, soluble/exchangeable and inorganic-bound Cd accounted for 86.1% of total Cd. Soluble/exchangeable Cd took up 51.6～59.6% of total Cd in contaminated soils without the introduction of plant ash, while 14.68～21.14% of Cd were observed as soluble/exchangeable species and 69.9～82.4% as inorganic-bound species after adding plant ash.3.The content of Cd in the wheat seed was decreased by 8.92～26.72% in engineered bacteria treatment. Cd content in wheat straw, seed and root were reduced by 3.95～67.17% after applying plant ash. The content of Cd in the seed were decreased by 14.70～26.70% due to application of plant ash and engineered bacteria.4.The height of wheat was increased by 5.50～11.88 cm and the dry yield was increased by 0.48～1.42 g per pot with inoculation of engineered bacteria, no effects was observed in the content of crude protein in wheat seeds.The addition of plant ash decreased the height of wheat slightly while increased the dry yield of wheat by 1.62-2.53 g per pot.5.In this experiment, the immobilization of Cd can be strengthened in soil with elevation of soil pH by applying plant ash, which translate bioavailability Cd into inert state, and the accumulation of Cd in wheat seed was reduced; engineered bacteria can also reduce the Cd uptake in wheat seed, a better effect could result from combining with plant ash. However, Cd accumulation of wheat seed in all treatment exceed the national food safety and hygiene standards of GB 2762-2005(Cd<0.1 mg kg-1).Appropriate application of plant ash and construction genetically engineered bacteria of stronger heavy metals adsorption can be considered in future trials to control heavy metal pollution.