Study of the increase in phytoremediation efficiency in a nickel polluted soil by the usage of native bacteria: Bacillus safensis FO.036b and Micrococcus roseus M2

Motesharezadeh, B.; Savaghebi-Firoozabadi, Gh. R.

Study of the increase in phytoremediation efficiency in a nickel polluted soil by the usage of native bacteria: Bacillus safensis FO.036b and Micrococcus roseus M2

Authors

¹ Dept. of Soil Science Engineering, University College of Agriculture & Natural Resources, University of Tehran, P. O. Box 4111, Karaj, Iran.

² Dept. of Soil Science Engineering, University College of Agriculture & Natural Resources, University of Tehran, P. O. Box 4111, Karaj, Iran. * Corresponding author’s E-mail: moteshare@ut.ac.ir

Abstract

Nickel (Ni) is a heavy metal and soil pollutant but existence of small amount of it as a metallic part of urease enzyme in the plants is necessary. Remediation of spots contaminated with heavy metals is particularly challenging. Phytoremediation, the use of plants for environmental restoration, is a novel clean up technology. In this study, five levels of nickel [control (Ni0), Ni125, Ni250, Ni500 and Ni1000 (mg kg1-)] as nickel chloride (NiCl2.6H2O) and three levels of bacterial inoculants [control (B0), Bacillus safensis FO.036b (B1) and Micrococcus roseus M2 (B2)] were used in sunflower (Helianthus annus), amaranthus (Amaranthus retroflexus) and alfalfa (Medicago sativa) for phytoextraction of nickel. A factorial experiment with a randomized complete block design (RCBD) with three replications was used. Results demonstrated that by increasing the nickel concentration in soil, its absorption by the plants has increased significantly. The highest concentration of nickel was found in shoot of amaranthus (176.83 mg kg-1) and in the root of plants, in alfalfa (462.73 mg kg-1) by usage of inoculant (P<0.05). The highest absorption of nickel occurred with B1 inoculant in amaranthus, which was 459.41 ?gPot-1. Applying this inoculant may also cause an increase in concentration of iron and zinc in the root and shoot of the plants.

REFERENCES
Abou-Shanab, R., A. I., J. S. Angle, A. I., J. S. and Chaney, R. L. (2006) Bacterial inoculants affecting nickel uptake by Alyssum murale from low, moderate and high Ni soils. Soil Biology & Biochemistry 38: 2882–2889.
Abou-Shanab, R., Ghanem, N., Ghanem, K. and Al-Kolaibe, A. (2007) Phytoremediation potential of crop and wild plants for multi-metal contaminated soils. Res. J. Agric. and Boil. Sci. 3: 370-376.
Alexander, D. B. and Zuberer, D. A. (1991) Use of chrome azurol S reagents to evaluate siderophore production by rhizosphere bacteria. Biol. Fertil. Soils 12: 39-45.
Alikhani, H. A. (2004) Potential use of native rhizobacteria strains as Plant Growth-Promoting Rhizobacteria (PGPR) and effects of selected strains on growth characteristics of Wheat, Corn and Alfalfa. Ph D Dissertation in Soil Science (Soil Biology), University of Tehran, Iran.
Allem, A., Isar, J. and Malik, A. (2003) Impact of long-term application of industrial wastewater on the emergence of resistance traits in Azotobacter chroococcum isolated from rhizospheric soil. Bioresource Technol. 86: 7-13.
Alloway, B. J. (1990) Heavy metals in soils. John Wiley & Sons, Inc. New York. USA.
Ansari, M. I. and Malik, A. (2007) Biosorption of nickel and cadmium by metal resistant bacterial isolates from agricultural soil irrigated with industrial wastewater. Bioresource Technol. 98: 3149-3153.
Bar-Ness, E., Chen, Y., Hadar, Y., Marchner, H. and Romheld, V. (1991) Siderophores of Pseudomonas Putida as an iron source for dicot and monocot plants. Plant Soil 130: 231-241.
Bigaliev, A. B., Boguspaev, K. K. and Znanburshin, E. T. (2000) Phytoremediation potential of Amaranthus sp. For heavy metals contaminated soil of oil producing territory. (WWW. Ipec.utulsa.edu).
Bollard, E.G. (1983) Involvement of unusual elements in plant growth and nutrition, in: A. La¨uchli, R.L. Bieleski (Eds.), Encyclopedia of Plant Physiology, New Series, Vol. 15B, Inorganic Plant Nutrition, Springer, pp. 695-744.
Bouyoucos, C. J. (1962) Hydrometer method improved for making particle size analysis of soil. Agron. J. 54: 464- 465. Bremner, J. M. (1996) Nitrogen-total. P. 1085-1122. In Sparks, D.L. et al., Method of soil analysis. Published by: Soil Science Society of America, Inc. American Society of Agronomy, Inc. Madison, Wisconsin, USA.
Brooks, R.R., Lee, J., Reeves, R. D. and Jaffre, T. (1977) Detection of nickeliferous rocks by analysis of herbarium specimens of indicator plants. J. Geochem. Explor. 7: 49–57.
Brooks, R. R. (1998) Plants that hyperaccumulate heavy metals. UK, CABI. Pub. Burd, GL., Dixon, DG. and Glick, BR. (1998) A Plant growth promoting bacterium that decreases nickel toxicity in plant seedling. Appl Environ. Microbial. 64: 3663-3668.
Burd, GL., Dixon, DG. and Glick, BR. (2000) Plant growth-promoting bacteria that decrease heavy metal toxicity in plants. Can. J. Microbiol. 46: 237-245.
Cai, S., Lin, Y., Zhineng, H., Xianzu, Z., Zhalou, Y., Huidong, X., Yuanrong, L., Rongdi, J., enhau, Z. and Fangyuan, Z. (1990) Cadmium exposure and health effects among residents in an irrigation area with ore dressing wastewater. Sci. Total Environ. 90: 67-73.
Erakhrumen, A. and Agbontalor, A. (2007) Phytoremediation: an environmentally sound technology for pollution prevention, control and remediation in developing countries, Educational Research and Reviews, 7: 151-156.
Garbisu, C. and Alkorta, I. (2001) Phytoextraction: a cost effective plant based technology for the removal of metals from the environments. Biores. Technol. 77: 229–236.
Ghosh, M. and Singh, S. P. (2005) A review on phytoremediation of heavy metals and utilization of its byproducts. Appied Ecology and Environmental Research 3: 1-18.
Glick, B. R. (1995) The enhancement of plant growth by free-living bacteria. Can. J. Microbiol. 41: 109-117.
Glick, B. R. (2003) Phytoremediation: Synergistic use of plants and bacteria to clean up the environment. Biotechnology Advances 21: 383-393.
Hemke, P.H. and Sparks, D. L. (1996). Potassium. pp. 551-574. In Sparks, D.L. et al., Method of soil analysis. Published by: Soil Science Society of America, Inc. American Society of Agronomy, Inc. Madison, Wisconsin, USA.
Holt, J. G., Kreig, N. R., Sneath, P. H. A., Staley, J. T. and Williams, S. T. (1994) Bergeys manual of determinative bacteriology. Ninth ed. Baltimore, maryland: Williams and Wilkins.
Hughes, M. N. and Poole, R. K. (1989) Metals and micro-organisms. Chapman and Hall, New York, USA. Jankite, A. and Vasarevicius, S. (2007) Use of poacea f. species to decontaminate soil from heavy metals. Ekologija 53: 84-89.
Karimzadeh, A. R. (1992) Evaluation of type, mineralogy, geochemical and probably genese of lead and zinc Araks Mine. M.S in Pedology, Tarbiat Moallem University, Tehran, Iran.
Kuffner, M. M., Puschenreiter, G. M., Wieshammer, G., Gorfer, M. and Sessitsch, A. (2008) Rhizosphere bacteria affect growth and metal uptake of heavy metal accumulating willows. Plant Soil. 304: 35-44.
Kuo, S. (1996) Phosphorus. pp. 869-920. In Sparks, D.L. et al., Method of soil analysis. Published by: Soil Science Society of America, Inc. American Society of Agronomy, Inc. Madison, Wisconsin, USA.
Lasat, M. M. (2000) The use of plants for the removal of toxic metals from contaminated soil. Grant No. CX 824823.
Lasat, M. M. (2002) Phytoextraction of toxic metal: A review of biological mechanisms. J. Environ. Qual. 31: 109- 120.
Lindsay, W. L. and Norvell, W. A. (1978) Development of DTPA soil test for zinc, iron, manganese and copper. Soil Sci. Soc. Am. J. 42: 421-428.
Llamas, A., Ullrich, C. I. and Sanz, A. (2008) Ni2+ toxicity in rice: Effect on membrane functionality and plant Motesharezadeh and Savaghebi-Firoozabadi 141 water content. Plant Physiology and Biochemistry 46: 905-910.
Lombi, E., Zhao, F. J., Dunham, S. J. and McGrath, S. P. (2001) Phytoremediation of heavy metal– contaminated soils, natural hyperaccumulation versus chemically enhanced phytoextraction. J. Environ. Qual. 30: 1919-1926.
McIlveen, W. D. and Negusanti J. J. (1994) Nickel in the terrestrial environment. Sci. Total Environ 148: 109–138.
Madejon, P., Murillo, J. M., Maranon, T., Cabrera, F. and Soriano, M. A. (2003) Trace element and nutrient accumulation in sunflower plants two years after the Aznalcollar mine spill. The Science of the total Environment 307: 239-257.
Madhaiyan, M., Poonguzhali, S. and Tongmin, S. (2007) Metal tolerating methylotrophic bacteria reduces nickel and cadmium toxicity and promotes plant growth of tomato (Lycopersicon esculentum L.). Chemosphere 69: 220– 228.
Marchiol, L., Assolari, S., Sacco, P. and Zerbi, G. (2004) Phytoextraction of heavy metals by canola and radish grown on multicontaminated soil. Environ. Pollut. 132: 21-27.
Marques, A. P. G. C., Moreira, H., Rangel, A. O. S. S. and Castro, P. M. L. (2009) Arsenic, lead and nickel accumulation in Rubus ulmifolius growing in contaminated soil in Portugal. Journal of Hazardous Materials 165: 174–179.
Masalha, J., Kosegrten, H., Elmaci, O. and Mengal, K. (2000) The central role of microbial activity for iron acquisition in maize and sunflower. Biol. Fertil. Soils 30: 433-439.
Moteshare zadeh, B., Savaghebi, Gh. R., Alikhani, H. A. and Hosseini, H. M. (2008) Effect of Sunflower and Amaranthus Culture and Application of Inoculants on Phytoremediation of the Soils Contaminated with Cadmium. American-Eurasian J. Agric. & Environ. Sci. 4: 93-103.
Motesharezadeh, B. and SavaghebiFiroozabadi, Gh. R. (2010) Bioaccumolation and phytotransportation of nickel by medicago sativa in a calcareous soil of Iran. Desert (In Press).
Nelson, R. E. (1982) Carbonate and gypsum, P. 181-196. In A.L. Page (ed), Methods of soil analysis. Part 2. 2^nd edn. Chemical and microbiological properties. Agronomy monograph no.9. SSSA and ASA. Madison, WI.
Nelson, D.W. and Sommers, L. E. (1982) Total carbon, organic carbon, and organic mater, p. 539-580.In A. L. Page (ed), methods of soil analysis. Part 2. 2nd ed. Chemical and microbiological properties. Agronomy monograph no.9. SSSA and ASA, Madison, WI.
Ouzounidou, G., Moustakas, M., Symeonidis, L. and Karataglis, S. (2006) Response of wheat seedlings to Ni stress: Effects of supplemental calcium, Arch. Environ. Contam. Toxicol. 50: 346-352.
Papazoglou, E. G., Serelis, K. G. and Bouranis, D. L. (2007) Impact of high cadmium and nickel soil concentration on selected physiological parameters of Arundo donax L. European Journal of Soil Biology 43: 207-215.
Penroz, D. M. and Glick, B. R. (2001) Levels of ACC and related compounds in exudates and extracts of canola seeds treated with ACC-deaminasecontaining plant growth promoting bacteria. Can. J. Microbiol. 47: 368-372.
Prasad, M.N.V. (2004) Heavy metal stress in plants, Second Ed. Norosa Publishing House. USA.
RAAD, A. (1976) Carbonates in J. A. McKeague, ed. Manual on soil sampling and methods of analysis. Subcommittee (of Canada Soil Survey Committee) on Methods of Analysis Soil Research Inst., Ottawzt.
Rhoades, J. D. (1996) Electrical conductiity and total dissolved solids, P. 417-436. In Sparks, D. L. et al., Method of soil analysis. Published by: Soil Science Society of America, Inc. American Society of Agronomy, Inc. Madison, Wisconsin, USA.
Robinson, B. H., Brooks, R. R. and Clother, B. E. (1999) Soil amendments Affecting Nickel and Cobalt Uptake by Berkheya coddii: Potential Use for Phytomining and Phytoremediation. Annals of Botany 84: 689-694.
Salt, D.E., Blaylock, M., Kumar, P. B. A. N., Dushenkov, V., Ensley, B. D., Chet, L. and Raskin, L. (1995) Phytoreediation: a novel strategy for the removal of toxic metals from the environment using plants. Biotechnology 13: 468–474. S
hing, X.F. and Xia, J. J. (2006) Improvement of rape (Brassica napus) plant growth and cadmium uptake by cadmium-resistant bacteria. Chemosphere 64: 1036–1042.
Smyj, R.P. (1997) A conformational analysis study of a nickel (II) enzyme: urease. Journal of Molecular Structure 391: 207–208.
Sumner, M. E. and Milker, W. P. (1996) Cation exchange capacity and exchange coefficients, P. 1201-1230. In Sparks, D.L. et al., Method of soil analysis. Published by: Soil Science Society of America, Inc. American Society of Agronomy, Inc. Madison, Wisconsin, USA.
Thomas, G. W. (1996) Soil pH and soil acidity, P. 475-490. In Sparks, D.L. et al., Method of soil analysis. Published by: Soil Science Society of America, Inc. American Society of Agronomy, Inc. Madison, Wisconsin, USA.
Wei, W., Jiang, J., Li, X., Wang, L. and Yang, S. S. (2004) Isolation saltsensitive mutants from sinorhizobium meliloti and characterization of genes involved in salt tolerance. Letters in Applied Microbiology 39: 278-283.
Yan-de, J., Zhen-li, H. and Xiao, Y. (2007) Role of soil rhizobacteria in phytoremediation of heavy metal contaminated soils. J. Zhejiang Univ. Sci. 8: 197-207.
Zaidi, S., Usmani, S., Singh, B. R. and Musarrat, J. (2006) Significance of Bacillus subtilis strain SJ-101 as a bioinoculant for concurrent plant growth promotion and nickel accumulation in Brassica juncea. Chemosphere 64: 991–997.

Keywords

References

Abou-Shanab, R., A. I., J. S. Angle, A. I., J. S. and Chaney, R. L. (2006) Bacterial inoculants affecting nickel uptake by Alyssum murale from low, moderate and high Ni soils. Soil Biology & Biochemistry38: 2882–2889.

Abou-Shanab, R., Ghanem, N., Ghanem, K. and Al-Kolaibe, A. (2007) Phytoremediation potential of crop and wild plants for multi-metal contaminated soils. Res. J. Agric. and Boil. Sci. 3(5): 370-376.

Alexander, D. B. and Zuberer, D. A. (1991) Use of chrome azurol S reagents to evaluate siderophore production by rhizosphere bacteria. Biol. Fertil. Soils12: 39-45.

Alikhani, H. A. (2004) Potential use of native rhizobacteria strains as Plant Growth-Promoting Rhizobacteria (PGPR) and effects of selected strains on growth characteristics of Wheat, Corn and Alfalfa. Ph. D Thesis in Soil Science (Soil Biology), University of Tehran, Iran.Allem,

A., Isar, J. and Malik, A. (2003) Impact of long-term application of industrial wastewater on the emergence of resistance traits in Azotobacter chroococcum isolated from rhizospheric soil. Bioresource Technol. 86: 7-13.

Alloway, B. J. (1990) Heavy metals in soils. John Wiley & Sons, Inc . New York. USA.Ansari, M. I. and Malik, A. (2007) Biosorption of nickel and cadmium by metal resistant bacterial isolates from agricultural soil irrigated with industrial wastewater. Bioresource Technol. 98: 3149-3153.

Bar-Ness, E., Chen, Y., Hadar, Y., Marchner, H. and Romheld, V. (1991) Siderophores of Pseudomonas Putida as an iron source for dicot and monocot plants. Plant Soil130(1-2): 231-241.

Bigaliev, A. B., Boguspaev, K. K. and Znanburshin, E. T. (2000) Phytoremediation potential of Amaranthus sp. For heavy metals contaminated soil of oil producing territory. (WWW. Ipec.utulsa.edu).

Bollard, E.G. (1983) Involvement of unusual elements in plant growth and nutrition, in: A. La ̈uchli, R.L. Bieleski (Eds.), Encyclopedia of Plant Physiology, New Series, Vol. 15B, Inorganic Plant Nutrition, Springer, pp. 695-744. 140 Study of the increase inphytoremediation efficiency

Bouyoucos, C. J. (1962) Hydrometer method improved for making particle size analysis of soil. Agron. J. 54: 464-465. Bremner, J. M. (1996) Nitrogen-total. P. 1085-1122. In Sparks,

D.L. et al., Method of soil analysis. Published by: Soil Science Society of America, Inc. American Society of Agronomy, Inc. Madison, Wisconsin, USA. Brooks, R.R., Lee, J., Reeves, R.

D. and Jaffre, T. (1977) Detection of nickeliferous rocks by analysis of herbarium specimens of indicator plants. J. Geochem. Explor. 7: 49–57.

Brooks, R. R. (1998) Plants thathyperaccumulate heavy metals. UK, CABI.Pub.

Burd, GL., Dixon, DG. and Glick, BR. (1998) A Plant growth promoting bacterium that decreases nickel toxicity in plant seedling. Appl Environ. Microbial. 64: 3663-3668.

Burd, GL., Dixon, DG. and Glick, BR. (2000) Plant growth-promoting bacteria that decrease heavy metal toxicity in plants. Can. J. Microbiol.46: 237-245.

Cai, S., Lin, Y., Zhineng, H., Xianzu, Z., Zhalou, Y., Huidong, X., Yuanrong, L., Rongdi, J., enhau, Z. and Fangyuan, Z. (1990) Cadmium exposure and health effects among residents in an irrigation area with ore dressing wastewater. Sci. Total Environ. 90: 67-73.

Erakhrumen, A. and Agbontalor, A. (2007) Phytoremediation: an environmentally sound technology for pollution prevention, control and remediation in developing countries, Educational Research and Reviews, 7: 151-156.

Garbisu, C. and Alkorta, I. (2001) Phytoextraction: a cost effective plant based technology for the removal of metals from the environments. Biores. Technol. 77: 229–236.

Ghosh, M. and Singh, S. P. (2005) A review on phytoremediation of heavy metals and utilization of its byproducts. Appied Ecology and Environmental Research3(1): 1-18.

Glick, B. R. (1995) The enhancement of plant growth by free-living bacteria. Can. J. Microbiol. 41: 109-117.

Glick, B. R. (2003) Phytoremediation: Synergistic use of plants and bacteria to clean up the environment. Biotechnology Advances21: 383-393.

Hemke, P.H. and Sparks, D. L. (1996). Potassium. P. 551-574. In Sparks, D.L. et al., Method of soil analysis. Published by: Soil Science Society of America, Inc. American Society of Agronomy, Inc. Madison, Wisconsin, USA.

Holt, J. G., Kreig, N. R., Sneath, P. H. A., Staley, J. T. and Williams, S. T. (1994) Bergeys manual of determinative bacteriology. Ninth ed. Baltimore, maryland: Williams and Wilkins. Hughes, M. N. and Poole, R. K. (1989) Metals and micro-organisms. Chapman and Hall, New York, USA.

Jankite, A. and Vasarevicius, S. (2007) Use of poacea f.species to decontaminate soil from heavy metals. Ekologija 53(4): 84-89.

Karimzadeh, A. R. (1992) Evaluation of type, mineralogy, geochemical and probably genese of lead and zinc Araks Mine. M.S in Pedology, Tarbiat Moallem University, Tehran, Iran.

Kuffner, M. M., Puschenreiter, G. M., Wieshammer, G., Gorfer, M. and Sessitsch, A. (2008) Rhizosphere bacteria affect growth and metal uptake of heavy metal accumulating willows. Plant Soil. 304: 35-44.

Kuo, S. (1996) Phosphorus. P. 869-920. In Sparks, D.L. et al., Method of soil analysis. Published by: Soil Science Society of America, Inc. American Society of Agronomy, Inc. Madison, Wisconsin, USA.

Lasat, M. M. (2000) The use of plants for the removal of toxic metals from contaminated soil. Grant No. CX 824823.

Lasat, M. M. (2002) Phytoextraction of toxic metal: A review of biological mechanisms. J. Environ. Qual. 31: 109-120.

Lindsay, W. L. and Norvell, W. A. (1978) Development of DTPA soil test for zinc, iron, manganese and copper. Soil Sci. Soc. Am. J.42: 421-428.

Llamas, A., Ullrich, C. I. and Sanz, A. (2008) Ni2+ toxicity in rice: Effect on membrane functionality and plant Motesharezadeh and Savaghebi-Firoozabadi 141water content. Plant Physiology and Biochemistry46: 905-910.

Lombi , E., Zhao, F. J., Dunham, S. J. and McGrath, S. P. (2001) Phytoremediationof heavy metal–contaminated soils, natural hyperaccumulation versus chemically enhanced phytoextraction. J. Environ. Qual. 30: 1919-1926.

McIlveen, W. D. and Negusanti J. J. (1994) Nickel in the terrestrial environment. Sci. Total Environ148: 109–138.

Madejon, P., Murillo, J. M., Maranon, T., Cabrera, F. and Soriano, M. A. (2003) Trace element and nutrient accumulation in sunflower plants two years after the Aznalcollar mine spill. The Science of the total Environment307: 239-257.

Madhaiyan, M., Poonguzhali, S. and Tongmin, S. (2007) Metal tolerating methylotrophic bacteria reduces nickel and cadmium toxicity and promotes plant growth of tomato (Lycopersicon esculentum L.). Chemosphere69: 220–228.

Marchiol, L., Assolari, S., Sacco, P. and Zerbi, G. (2004) Phytoextraction of heavy metals by canola and radish grown on multicontaminated soil. Environ. Pollut. 132: 21-27.

Marques, A. P. G. C., Moreira, H., Rangel, A. O. S. S. and Castro, P. M. L. (2009) Arsenic, lead and nickel accumulation in Rubus ulmifolius growing in contaminated soil in Portugal. Journal of Hazardous Materials165: 174–179.

Masalha, J., Kosegrten, H., Elmaci, O. and Mengal, K. (2000) The central role of microbial activity for iron acquisition in maize and sunflower. Biol. Fertil. Soils30(5-6): 433-439.

Moteshare zadeh, B., Savaghebi, Gh. R., Alikhani, H. A. and Hosseini, H. M. (2008) Effect of Sunflower and Amaranthus Culture and Application of Inoculants on Phytoremediation of the Soils Contaminated with Cadmium. American-Eurasian J. Agric. & Environ. Sci. 4 (1): 93-103.

Motesharezadeh, B. and Savaghebi-Firoozabadi, Gh. R. (2010) Bioaccumolation and phyto-transportation of nickel by medicago sativa in a calcareous soil of Iran. Desert(In Press). Nelson, R. E. (1982) Carbonate and gypsum, P. 181-196. In A.L. Page (ed),

Methods of soil analysis. Part 2. 2nd ed. Chemical and microbiological properties. Agronomy monograph no.9. SSSA and ASA. Madison, WI. Nelson, D.W. and Sommers, L. E. (1982) Total carbon, organic carbon, and organic mater, p. 539-580.In A. L. Page (ed), methods of soil analysis. Part 2. 2nd ed. Chemical and microbiological properties. Agronomy monograph no.9. SSSA and ASA,

Madison,WI. Ouzounidou, G., Moustakas, M., Symeonidis, L. and Karataglis, S. (2006) Response of wheat seedlings to Ni stress: Effects of supplemental calcium, Arch. Environ. Contam. Toxicol. 50: 346-352.

Papazoglou, E. G., Serelis, K. G. and Bouranis, D. L. (2007) Impact of high cadmium and nickel soil concentration on selected physiological parameters of Arundo donax L. European Journal of Soil Biology43: 207-215.

Penroz, D. M. and Glick, B. R. (2001) Levels of ACC and related compounds in exudates and extracts of canola seeds treated with ACC-deaminase- containing plant growth promoting bacteria. Can. J. Microbiol. 47: 368-372.

Prasad, M.N.V. (2004) Heavy metal stress in plants, Second Ed. Norosa Publishing House. USA. RAAD, A. (1976) Carbonates in J. A. McKeague, ed. Manual on soil sampling and methods of analysis. Subcommittee (of Canada Soil Survey Committee) on Methods of Analysis Soil Research Inst., Ottawzt.

Rhoades, J. D. (1996) Electrical conductiity and total dissolved solids, P. 417-436. In Sparks, D. L. et al., Method of soil analysis. Published by: Soil Science Society of America, Inc. American Society of Agronomy, Inc. Madison, Wisconsin, USA.

Robinson, B. H., Brooks, R. R. and Clother, B. E. (1999) Soil amendments Affecting Nickel and Cobalt Uptake by Berkheya coddii: Potential Use for Phytomining and Phytoremediation. Annals of Botany 84: 689-694.

Salt, D.E., Blaylock, M., Kumar, P. B. A. N., Dushenkov, V., Ensley, B. D., Chet, L. and Raskin, L. (1995) Phytoreediation: 142 Study of the increase inphytoremediation efficiencya novel strategy for the removal of toxic metals from the environment using plants. Biotechnology13: 468–474.

Shing, X.F. and Xia, J. J. (2006) Improvement of rape (Brassica napus) plant growth and cadmium uptake by cadmium-resistant bacteria. Chemosphere64: 1036–1042.

Smyj, R.P. (1997) A conformational analysis study of a nickel (II) enzyme: urease. Journal of Molecular Structure391: 207–208.

Sumner, M. E. and Milker, W. P. (1996) Cation exchange capacity and exchange coefficients, P. 1201-1230. In Sparks, D.L. et al.,

Method of soil analysis. Published by: Soil Science Society of America, Inc. American Society of Agronomy, Inc. Madison, Wisconsin, USA. Thomas, G. W. (1996) Soil pH and soil acidity, P. 475-490. In Sparks, D.L. et al.,

Method of soil analysis. Published by: Soil Science Society of America, Inc. American Society of Agronomy, Inc.

Madison, Wisconsin, USA. Wei, W., Jiang, J., Li, X., Wang, L. and Yang, S. S. (2004) Isolation salt-sensitive mutants from sinorhizobium meliloti and characterization of genes involved in salt tolerance. Letters in Applied Microbiology39: 278-283.

Yan-de, J., Zhen-li, H. and Xiao, Y. (2007) Role of soil rhizobacteria in phytoremediation of heavy metal contaminated soils. J. Zhejiang Univ. Sci. 8(3): 197-207.

Zaidi, S., Usmani, S., Singh, B. R. and Musarrat, J. (2006) Significance of Bacillus subtilis strain SJ-101 as a bioinoculant for concurrent plant growth promotion and nickel accumulation in Brassica juncea. Chemosphere 64: 991–997.