A greenhouse experiment was carried out to compare differences in potential activities of ammonification, nitrification and denitrification in rhizosphere and bulk soil in a heavy-metal-stressed system. Exchangeable f...A greenhouse experiment was carried out to compare differences in potential activities of ammonification, nitrification and denitrification in rhizosphere and bulk soil in a heavy-metal-stressed system. Exchangeable fractions of Cd, Cu and Cr were all higher in the rhizosphere of maize than in bulk soil. Results showed that the mineralization of N in soil was stimulated by low concentration of Cd. Addition of Cd at low levels stimulated the ammonifying and nitrifying activity in soil, while inhibitory influences were shown at high levels. Nitrifying bacteria was proved to be the most sensitive one, whilst the effect on denitrifying bacteria was very limited. Comparing Cd, Cu and Cr(VI) at 20 mg/kg soil, Cd was the most effective inhibitor of ammonification and denitrification, while Cr(VI) had the strongest inhibitory influence on nitrifying activity. Root exudates played important roles on the different exchangeable metal fractions and bacterial activities between rhizosphere and non-rhizosphere. Nitrate was the main form of mineral N in soil, as well as the main form of N absorbed by plants, but the formation and relative absorption of ammonium were promoted in response to high Cd exposure.展开更多
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 ...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.展开更多
基金The National Basic Research and Development Program(No. 2002CB410807) and the Key Project of National Natural Science Foundation of China(40432004)
文摘A greenhouse experiment was carried out to compare differences in potential activities of ammonification, nitrification and denitrification in rhizosphere and bulk soil in a heavy-metal-stressed system. Exchangeable fractions of Cd, Cu and Cr were all higher in the rhizosphere of maize than in bulk soil. Results showed that the mineralization of N in soil was stimulated by low concentration of Cd. Addition of Cd at low levels stimulated the ammonifying and nitrifying activity in soil, while inhibitory influences were shown at high levels. Nitrifying bacteria was proved to be the most sensitive one, whilst the effect on denitrifying bacteria was very limited. Comparing Cd, Cu and Cr(VI) at 20 mg/kg soil, Cd was the most effective inhibitor of ammonification and denitrification, while Cr(VI) had the strongest inhibitory influence on nitrifying activity. Root exudates played important roles on the different exchangeable metal fractions and bacterial activities between rhizosphere and non-rhizosphere. Nitrate was the main form of mineral N in soil, as well as the main form of N absorbed by plants, but the formation and relative absorption of ammonium were promoted in response to high Cd exposure.
基金Project supported by the National Natural Science Foundation of China (No. 2977020) and the NaturalScience Foundation of Zheji
文摘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.
