Abundance, composition and activity of denitrifier communities in metal polluted paddy soils

Denitrification is one of the most important soil microbial processes leading to the production of nitrous oxide (N(2)O). The potential changes with metal pollution in soil microbial community for N(2)O production and reduction are not well addressed. In this study, topsoil samples were collected both from polluted and non-polluted rice paddy fields and denitrifier communities were characterized with molecular fingerprinting procedures. All the retrieved nirK sequences could be grouped into neither α- nor β- proteobacteria, while most of the nosZ sequences were affiliated with α-proteobacteria. The abundances of the nirK and nosZ genes were reduced significantly in the two polluted soils. Thus, metal pollution markedly affected composition of both nirK and nosZ denitrifiers. While the total denitrifying activity and N(2)O production rate were both reduced under heavy metal pollution of the two sites, the N(2)O reduction rate showed no significant change. These findings suggest that N(2)O production activity could be sensitive to heavy metal pollution, which could potentially lead to a decrease in N(2)O emission in polluted paddies. Therefore, metal pollution could have potential impacts on soil N transformation and thus on N(2)O emission from paddy soils.