Pedosphere 11(2): 115--122, 2001
ISSN 1002-0160/CN 32-1315/P
©2001 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Effects of heavy metals on ammonification, nitrification and denitrification in maize rhizosphere
CHEN Ying-Xu1, YANG Ye2, WANG Kai-Xiong1, LIN Qi1 and TIAN Guang-Ming1
1 Department of Environmental Engineering, Zhejiang University, Hangzhou 310029 (China)
2 Department of Environntentad Engineering, Zhejiang University of Technology, Hangzhou 310032 (China)
      The ammonification, nitrification and denitrification in maize rhizosphere of alluvial soils were compared with those in the bulk soil after exposure to different kinds of heavy metals. The addition of cadmium at low levels (2 mg kg-1 and 5 mg kg-1) could stimulate the ammonification and nitrification in the soils, while inhibition influences were found at high levels of Cd addition (10 mg kg-1 and 20 mg kg-1). The relationship between microbial activity and cadmium concentration varied with the kind of microorganisms. The nitrifying bacteria were more sensitive to cadmium pollution than the ammonifying bacteria. When Cd(Ⅱ), Cu(Ⅱ) and Cr(Ⅵ) were compared at the same addition concentration of 20 mg kg-1 soil, Cd(Ⅱ) was the most effective inhibitor of ammonification and denitrification among the three investigated heavy metals, and Cr(Ⅵ) had the most strong inhibitory influence on the nitrifying bacteria. The microbial activities in rhizosphere were higher than those in the bulk soil for most of the treatments. Cr(Ⅵ) proved to be the most effective in enhancing the microbial activities in rhizosphere, and this could be caused by the positive reduction of Cr(VI) to Cr(Ⅲ) in rhizosphere, and the relatively sufficient existence of organic matter which intensified the adsorption of the metal. It seemed that the rhizosphere had some mitigation effect on heavy metal toxicity.
Key Words:  ammonification, denitrification, heavy metal pollution, nitrification, rhizosphere
Citation: Chen, Y. X., Yang, Y., Wang, K. X., Lin, Q. and Tian, G. M. 2001. Effects of heavy metals on ammonification, nitrification and denitrification in maize rhizosphere. Pedosphere. 11(2): 115-122.
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