Soil bacterial communities in three rice-based cropping systems differing in productivity

Soil microorganisms play an important role in determining productivity of agro-ecosystems. This study was conducted to compare diversity, richness, and structure (relative abundance at the phylum level) of soil bacterial communities among three rice-based cropping systems, namely, a winter fallow-rice-rice (FRR), green manure (Chinese milk vetch)-rice-rice (MRR), and oilseed rape-rice-rice (ORR), in which MRR and ORR had significantly higher productivity than FRR. A 16S rRNA gene sequence analysis showed that no significant differences were observed in diversity and richness indices (observed species, Shannon, Simpson, Chao1, abundance-based coverage estimators, and phylogeny-based metrics) of soil bacterial communities among the three cropping systems. However, relative abundances of dominant phyla in soil bacterial communities, including Proteobacteria, Acidobacteria, Nitrospirae, Gemmatimonadetes, and Verrucomicrobia, were significantly different among the three cropping systems. In particular, a significant reduction in the relative abundance of Nitrospirae was observed in both MRR and ORR compared with FRR. These results indicate that bacterial community structure was affected by cropping systems in the tested paddy soils. Based on the results of our studies and existing knowledge bases, we speculate that benefits to rice yield may be obtained by reducing the relative abundance of Nitrospirae and increasing the ratio of abundances of Proteobacteria/Acidobacteria in paddy soils.