Effect of Cr3+ contamination on the population and the denitrification activity of denitrifying bacteria in paddy soils

Effects of heavy metalcontamination on the population and the denitrification activity of denitrifying bacteria were investigated in three type of paddy soil:huangsong paddy soil, developed from shallowsea deposit of intermediate lake deposit,red paddy soil,developed from alluvial deposit and purple paddy soil, developed from parent material of neuter purple sandstone and shale, tested with Cr2(SO4)36H2O at different concentrations for 4 weeks. The results obtained showed that the population of denitrifying bacteria of purple paddy soil,huangsong paddy soil and red paddy soil ranged (59.04-157.59)104、(42.89-108.97)104 and (32.14-75.30104 )cells per gram dried soil, respectively. Cr3+, adding 200mg/kg dried soil, significantly inhabited the population and the denitrification activity of denitrifying bacteria, but that could gradually recover or close to the levels of the control soil in three weeks by paddy soil itself. It was more difficulty recovers the population and the denitrification activity of denitrifying bacteria by paddy soil itself, when adding concentration of Cr3+ was more than 200 mg/kg dried soil. But that could recover by adding some material, which could be increased soil pH. The effectiveness of Cr3+ varied on the population and the denitrification activity of denitrifying bacteria in different paddy soils.