Abstract:

Paddy soil is a complex and typical ecosystem. Investigating changes to paddy soil bacterial communities during flooding can provide a theoretical basis for further exploring bacterial effects on and functions in ecosystems, e.g. nutrient transformations, the suppression of methanogenesis and bioremediation of heavy metal pollution. In this study, bacterial genomic DNA was analyzed from 8 paddy soil samples with flooding periods of 1 h, 1 d, 5 d, 10 d, 20 d, 30 d, 40 d and 60 d, respectively. 16S rRNA gene-based real-time PCR and PCR-DGGE (denaturing gradient gel electrophoresis) were used to study abundance and community structure during different flooding periods. The highest bacterial abundance was observed at 1 d with the second highest value at 40 d, indicating that bacterial abundance fluctuated over the flooding period. Succession of bacterial community structure was observed along the entire flooding period: r-strategists were only present in the early flooding stage; k-strategists emerged and were dominant in the late flooding stage; r-k-strategists symbiotic organisms were present in the entire flooding period. The diversity of the bacterial community during the flooding period rose initially and then tended to drop as succession took place. Principal Components Analysis based on digitized DGGE patterns indicated that the changes to bacterial community structure slowed during the mid- to late flooding stages. Sequencing results showed that Firmicutes, Chloroflexi, Bacteroidetes, Proteobacteria and Acidobacteria, which have close phylogenetic relationships with the groups from paddy soils and other soils of different regions, activated sludge systems and lake sediments, were the dominant habitants of the study site.

Key words: flooding paddy soil, bacteria, 16S rRNA, abundance, community structure, r-/k- strategy, succession