Document Type : Research Paper
Authors
1
Former M.Sc.Student, Tarbiat Modares University of Tehran. College of Agriculture. Soil Science Department
2
Associate Professor, Soil and Water Research Institute of Karaj. Biology Department
3
Professor, Tarbiat Modares University of Tehran. College of Agriculture. Soil Science Department
Abstract
Cadmium (Cd) is one of the most toxic pollutants whose concentration in soil has been rising due to the increasing application of phosphorus fertilizers in agricultural fields. Phytoremediation, an emerging low-cost and ecologically benign technology for decontamination of soils, is defined as the process of utilizing plants to absorb, accumulate and detoxify contaminants in soil through physical, chemical and biological processes. One of the problems of this method is slow growth rate of the selected plant. Use of plant growth promoting Rhizobacteria (PGPR), especially those containing ACC deaminase, stimulates growth of plants and, thereby, improves bioremediation of Cd in contaminated soil. Therefore, to investigate the bacteria effect on the efficiency of Cd bioremediation by kale (Brassica oleraceae var. viridis), a pot-culture experiment was conducted in a completely randomized block design in the green house of agricultural college, Tarbiat Modares University, in 2009-2010. In this experiment, inoculants including:1) control (un-inoculated), 2) Pseudomonas fluorescens strain 169, 3) P. putida strain 108, 4) P. putida strain 11, 5) P. putida strain 159 , 6) P. putida strain 4, and seven Cd concentration levels, i.e. 0, 5, 10, 15, 30, 50 and 100 mg kg-1, were studied. Inoculated and un-inoculated seeds of kale were planted. Plants grew in green house for seven months. Afterwards, kale shoots and roots were harvested separately. In all treatments, Cd concentration was measured using flame Atomic Absorption spectrophotometer. The results were analyzed using SAS software and revealed that the inoculants and Cd concentration levels had significant effects on kale growth and Cd concentration in both shoots and roots (α=1%). By increasing Cd concentration, shoots and roots growth decreased, but inoculants, especially inoculant (5), decreased this effect. Maximum Cd concentrations were 136 and 58 mg kg-1 in roots and shoots, respectively, in 100 mg kg-1 Cd concentration treatment accompanied by inoculant (6). Maximum root dry weight was 1.96 gr for inoculant (4) in 15 mg kg-1 Cd concentration treatment and maximum shoot dry weight was 12.53 gr for inoculant (3) in 30 mg kg-1Cd concentration treatment. According to the noticeable amount of Cd uptake in case of the combination of the plant and the inoculants, kale accompanied by the bacteria can be considered as a reliable option for the remediation of low to moderate Cd-polluted soils (< 50 mg kg-1). In high Cd-polluted soils, however, due to severe decrease in Cd translocation, kale is not a suitable plant for phytoremediation in highly Cd contaminated soils, even if inoculated with bacteria.
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