Abundance and diversity of ammonia-oxidizing bacteria in rhizosphere and bulk paddy soil under different duration of organic management

Denaturing gradient gel electrophoresis (DGGE) and quantitative real-time PCR (qPCR) approaches were used to assess respectively the quantity and the molecular diversity of the ammonia-oxidizing bacteria (AOB) in rhizosphere and bulk paddy soil under conventional management (2 year) and different duration(2, 3, 5 and 9 years) organic management. Phylogenetic analysis in our study based on bacterial AOB identified thatNitrosospira species were dominated in organic paddy soil. When the quantity of the ammonia monooxygenase gene was determined by qPCR, 3.93×105 to 1.09×106copies/g of soil were detected. Except for organically managed soil (2 year), the copy numbers in all the organically managed soil were significantly higher than in conventionally managed soil. The abundance and diversity of ammonia oxidizing bacteria tended to increase with duration of organic management. And the highest number of ammonia monooxygenase gene copies was observed in the soil under five year organic management. In addition, Analysis of variance and canonical correspondence analysis (CCA) showed that C/N, C and N were important factors influencing the abundance and community of ammonia oxidizing bacterial.   Key words: Ammonia-oxidizing bacteria, molecular diversity, PCR-DGGE analysis, organic and conventional management, paddy soil.